Patent Publication Number: US-7896841-B2

Title: Injection device for administering a vaccine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the National Stage of International Application PCT/US2005/004996, with an international filing date of Feb. 17, 2005, which claimed the benefit of U.S. Provisional Application No. 60/521,076, filed Feb. 17, 2004. 
    
    
     BACKGROUND 
     The present invention relates to the injection of vaccines and other medication and, more particularly, to an improved injection device that can be used in a method for administering vaccine injections painlessly for a patient. 
     Conventional medical injection devices for injecting medication into the muscle or tissue of a patient typically comprise some form of a manual hypodermic syringe. Generally speaking, a hypodermic syringe consists of a cylindrical barrel having a chamber that provides a reservoir for a liquid medication, a distal end adapted to be connected to a hollow hypodermic needle and for placing one end of the needle into flow communication with the medication contained within the chamber, and a proximal end adapted for receiving a stopper and plunger assembly. The stopper and plunger assembly includes a stopper effective for moving along the barrel chamber and an elongated plunger effective for causing movement of the stopper. The needle of the hypodermic syringe is manually inserted into the patient through the skin. The stopper is moved along the barrel chamber by applying axial force to the plunger, thereby forcing the liquid medication out of the barrel chamber, through the hypodermic needle and into the muscle or tissue of the patient. 
     Receiving an injection by such a conventional device can be a very traumatic experience, particularly for a child. The child&#39;s fears, and that of the child&#39;s parent, can become a significant medical problem if it leads to the child not receiving a required vaccination. These fears are predominately caused by pain that is associated with injections given by conventional injection devices and methods. 
     We have found that the pain associated with an injection is related to the size of the needle and the flow rate at which the medication is injected. It has been found that the amount of pain or discomfort experienced by a patient increases as the outside diameter of the needle increases. It is believed that high flow rates of medication injection (e.g., about 0.5-2 ml per second) into the patient can tear internal tissue and cause pain. The tearing of tissue is caused by the build-up of excessive pressure within the tissue when the surrounding tissue is unable to quickly absorb the injected medication. 
     While the injection of a medication at a relatively slow flow rate is more comfortable for the patient, the increased amount of time the syringe remains in the hand of the medical personnel can make the technique tiring for such personnel as well as the patient. In addition, small vibrations or disturbances of the needle caused by movement of the medical personnel or the patient can result in pain to the patient. It is known that the fluctuation of flow rate of the injection of medication being delivered by a hand-held syringe can vary greatly. It is extremely difficult, if not impossible, to deliver a steady, very slow flow of medication from a hand-operated syringe (the human thumb depressing the syringe plunger) over an extended amount of time. 
     It has also been found that the sight of the hypodermic needle by itself is often enough to cause many patients to become anxious and tense. This reaction in turn may cause the patient&#39;s muscles to become tight and hard, making needle penetration even more difficult and painful. 
     A number of methods and devices have been developed for reducing or eliminating the pain and discomfort associated with medical injections. One such method includes the application of a topical anesthetic to the injection site on the patient&#39;s skin prior to the injection, which itself can be painful. While this method has reduced some of the discomfort associated with injections, the topical anesthetic does not substantially penetrate the skin into the deeper skin and muscle tissue, and can take significant time (up to 45 minutes) to show effects. Substantial pain and discomfort with intramuscular injections can remain. 
     Another technique for reducing the pain and discomfort associated with medical injections includes the step of injecting an anesthetic at the site of the injection using a fine gauge needle, then inserting the larger medication hypodermic needle through the anesthetized skin to inject the medication at a constant and slow flow rate intramuscularly at the desired depth. Unfortunately, injecting an anesthetic into a patient is not always desirable and the technique is relatively expensive and impractical for many routine injection procedures. 
     In addition to reducing pain or discomfort to the patient, safety has also become a principal concern to medical personnel. Special precautions must be taken to avoid accidental needle sticks that could place a user at serious risk because of the danger from fluid borne pathogens. Despite the taking of special precautions, there still remains the possibility of an accidental needle contact and attendant injury. Accordingly, medical injection devices should operate to minimize the possibility of injury caused by accidental needle sticks. 
     In recent years, increased emphasis has been placed on establishing treatment protocols aimed at providing a patient as well as medical personnel with greater freedom of movement. To this end, there is a great deal of interest in the development of light weight and easy-to-use portable injection devices. 
     Accordingly, a need exists for substantially painless method and an apparatus for performing the method of injecting medication into a patient that does not require the use of an anesthetic, that does not require the medical personnel to spend a substantial amount of time performing a particular procedure, that is relatively simple, portable and inexpensive to perform and operate, that permits the patient a relatively high degree of movement during the injection, and that provides a relatively high degree of safety for both the medical personnel and for the patient. 
     SUMMARY OF INVENTION 
     The present invention relates to improvements in an injection device configured for self-administering painlessly an injectable liquid composition, such as a vaccine or medicament. The device can be used in a method for providing a substantially painless injection of the injectable liquid composition to a patient that does not require the use of an anesthetic, that does not require the medical personnel to spend a substantial amount of time performing the injection procedure, that is relatively simple and inexpensive to prepare and operate, and that provides a relatively high degree of safety for both the medical personnel and for the patient. The device can be manually powered, or can have self-contained power for at least inserting the injection needle into the patient. 
     The present invention also relates to an improved injection device for self-administering painlessly inter-muscular injections of an injectable liquid composition to a patient, comprising: a housing having a base portion; a needle positioned within the housing, the needle having an injection end having an outside diameter greater than 0.20 mm and less than about 0.38 mm, and being configured for extension to a position wherein the injection end extends through and beyond the base portion; a reservoir for the vaccine; and a means for liquid communication between the reservoir and the injection needle; a separable base associated with the base portion, comprising an adhesive on a skin-facing surface thereof and an opposed surface, and a means for separably affixing the separable base with the base portion. 
     The invention also relates to an improved device for injecting painlessly at least two injectable liquid compositions to a patient, comprising: a housing having a base for semi-permanent attachment to the skin of a patient, at least two injection needles disposed substantially perpendicular to the base and within the housing, each needle having an injection end and having an outside diameter greater than 0.20 mm and less than about 0.38 mm, and being configured for axial movement between a first position wherein the injection end is within the housing and a second position wherein the injection end extends outwardly from the base, and at least two reservoirs configured for liquid communication with the injection needles, a means for inserting each injection needle to its second position, a means for injecting the liquid composition from the reservoir to the injection end of the needle, and optionally a means for retracting each needle. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIG. 1  shows a cross-sectioned elevation view of a housing of a manually-powered painless injection device of the present invention in an extracted position, taken through line  1 - 1  of the housing shown in  FIG. 4 . 
         FIG. 2  shows the cross-sectioned elevation view of  FIG. 1  of the housing in an inserted position. 
         FIG. 3  shows a cross-sectioned elevation view of the housing shown in  FIG. 4 , taken through line  3 - 3  of  FIG. 4 . 
         FIG. 3A  shows a detailed cross-sectional view of the housing of  FIG. 3 . 
         FIG. 4  shows a top plan view of the housing of the manually-powered painless injection device. 
         FIG. 5  shows a cross-sectioned elevation view of the housing of  FIG. 4 , taken through line  5 - 5 . 
         FIG. 6  shows a cross-sectioned elevation view of the housing of  FIG. 4  taken through line  6 - 6 . 
         FIG. 7  shows a cross-sectioned plan view of the housing of  FIG. 1 , taken through line  7 - 7 . 
         FIG. 8  shows a cross-sectioned plan view of the housing of  FIG. 1 , taken through line  8 - 8 . 
         FIG. 9  shows an exploded cross-sectioned elevation view of the elements of the housing of  FIG. 1 . 
         FIG. 10  shows a cross-sectioned elevation view of a syringe cartridge of a manually-powered painless injection device of the present invention in an extended position, taken through line  10 - 10  of the syringe cartridge shown in  FIG. 12 . 
         FIG. 11  shows a cross-sectioned elevation view of the syringe cartridge in an extended position, taken through line  11 - 11  of  FIG. 12 . 
         FIG. 12  shows a plan view of the syringe cartridge of  FIG. 10 . 
         FIG. 13  shows a detailed cross-sectional elevation view of the syringe cartridge of  FIG. 10 . 
         FIG. 14  shows another detailed cross-sectional elevation view of the syringe cartridge of  FIG. 10 . 
         FIG. 15  shows a plan view of the syringe cartridge shown in  FIG. 14 . 
         FIG. 16  shows a cross-sectioned plan view of the syringe cartridge of  FIG. 11 . 
         FIG. 17  shows a bottom plan view of the syringe cartridge of  FIG. 11 . 
         FIG. 18  shows an exploded cross-sectioned elevation view of the elements of the syringe cartridge of  FIG. 10 . 
         FIG. 19  shows a cross-sectioned elevation view of the syringe cartridge of  FIG. 10  containing an injectable liquid composition in a pressurized position. 
         FIG. 20  shows a cross-sectioned elevation view of the housing and a separable base assembly prior to its attachment to the housing, and of a syringe cartridge prior to its installation into the housing. 
         FIG. 21  shows the housing and syringe cartridge of  FIG. 20 , with the housing being affixed to a patient&#39;s skin. 
         FIG. 22  shows the syringe cartridge being installed into the housing of  FIG. 21 . 
         FIG. 23  shows the syringe cartridge being force into an inserted position within the housing. 
         FIG. 24  shows the syringe cartridge in the inserted position within the housing, injecting the liquid composition. 
         FIG. 25  shows the syringe cartridge in the inserted position within the housing, at the completion of the liquid composition injection. 
         FIG. 26  shows the syringe cartridge in the inserted position within the housing of  FIG. 25 , being manipulated to retract the needle. 
         FIG. 27  shows the syringe cartridge and housing of  FIG. 26 , with the needle retracted. 
         FIG. 28  shows the housing and the syringe cartridge of  FIG. 27  being removed from the separable base that remains attached to the patient. 
         FIG. 29  shows a top plan view of another embodiment of the invention, of a device having a housing that can accommodate two syringe cartridges. 
         FIG. 30  shows an elevation view of the device of  FIG. 29 . 
         FIG. 31  shows a cross-sectioned elevation view of the dual-syringe device of  FIG. 29  taken through line  31 - 31 . 
         FIG. 32  shows a separable base assembly having an adhesive flap for use in attaching the device of the present invention to the skin of a patient. 
         FIG. 33  shows a cross-sectioned elevation view of the separable base assembly of  FIG. 32  through lines  33 - 33 . 
         FIG. 34  shows a detailed cross-sectioned elevation view of the separable base assembly of  FIG. 33 . 
         FIG. 35  shows another detailed cross-sectioned elevation view of the separable base assembly of  FIG. 33 . 
         FIG. 36  shows a cross-sectional plan view of a base shown in  FIG. 22  through lines  36 - 36 , which has been modified to provide blocking plate that is in a deployment position to allow needle deployment. 
         FIG. 37  shows a cross-sectional elevation view of the base of  FIG. 36 . 
         FIG. 38  shows a cross-sectional plan view of the base of  FIG. 36 , which is in a blocking position to prevent needle deployment. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Definitions 
     As used herein, “patient” means a mammal, including a person, including a child or infant, or an animal, typically a mammal, on which the device is attached, and into whom the device injects an injectable liquid composition. 
     As used herein, unless specified otherwise, the phrase “manually powered” means that the power provided to the device of the present invention to at least insert the injection needle into the patient&#39;s body is provided manually by a person, including a medical technician (a nurse, doctor, or other person who can administer the injection) or a patient, by manipulating the injection device with the hands or fingers, or by manipulating an appropriate implement that interacts with the device. 
     As used herein, unless specified otherwise, the term “self-administering” describes the ability of the device of the present invention to be held or to hold itself in a position attached to the skin of a patient by a securement means, without requiring a medical technician, the patient, or other person, to hold the device, during the time that an injectable liquid composition contained within the device is injected into the patient through the injection needle. 
     As used herein, unless specified otherwise, the term “upward” means in a direction or oriented away from the patient&#39;s skin or the base of the device; the term “downward” means in a direction or oriented toward the patient&#39;s skin or the base of the device; the term “inward” means in a direction or oriented toward the centerline of the device, typically the needle; and the term “outward” means in a direction or oriented away from the centerline of the device. 
     The self-administering injection device of the present invention typically comprises a housing, an injection needle, a reservoir for containing an injectable liquid composition, such as a vaccine or a medicament, and a plurality of elements associated with and at least semi-permanently attached to the housing. The other associated elements can also include the various means of providing power or energy for the functional operations of the device, such as the insertion and retraction of the injection needle, and the pumping or injecting of vaccine to the injection needle. A self-contained, self-powered device embodiment will also have means for inserting the injection needle that is powered by an on-board element of the device. Typically, these associated elements are contained within the confines of the housing, although these elements can also partially confront or penetrate through the outer surface of the housing. 
     In the course of administering most injections of vaccines and other medicaments, the injection can be advantageously administered intramuscularly, that is, into the muscle. The injection is made with an injection needle that is configured for insertion through the outer layer of the patient&#39;s skin, and more typically into the muscle tissue of the patient. Typically, the depth of insertion is at least about 5 mm, and typically up to about 35 mm or more, more typically from about 10 mm to about 25 mm, and even more typically from about 15 mm to about 20 mm. For a young child or infant, the depth of insertion is typically from about 10 mm to about 25 mm, more typically from about 12 mm to about 15 mm. Alternatively, some injections can be administered intradermally, or into other internal organs or the general body cavity of the patient. 
     Painless injections can be achieved when the size or diameter of the injection needle is minimized, typically by using a needle of gauge size 28 or small (typically up to gauge size 33), and when the injectable liquid composition, such as a vaccine or other medicament, is injected at a volumetric flow rate significantly lower than that of a conventional injection made by hand, typically less than about 50 microliter per second (μL/s) and more typically about 1-4 μL/s. To achieve such low flow rates when administering a typical injection dose of between 0.5 ml to about 1.0 ml, an injection time of about 3 to 5 minutes may be needed. Typically, the human hand, using a conventional syringe, can not accurately or reproducibly control the flow rate within a range that ensures a painless injection. Furthermore, the desired slower injection rate of the medicament would require that the medical technician (or the patient) hold the conventional syringe carefully in place against the skin of the patient, and that the patient not move the limb or body part that is the site of the injection while the injection is being administered. The present invention overcomes these problems by providing a self-administering device that remains in position on the skin of the patient at the injection site, and administers the injection of the injectable liquid composition, without requiring a medical technician or patient to hold the injecting device in its place by hand, and without requiring that the patient remain still and not move while the injection is being administered. These problems are particularly troublesome when the patient is an infant or young child. 
     The self-administering device of the invention is intended to be attached semi-permanently to the skin of the patient before, during or after the injection. The device is typically configured to be attached to the upper arm or to the thigh area, providing access to the larger skeletal muscles (the deltoids and the quadriceps) for intramuscular injection. The attachment is preferably semi-permanent, whereby the device can be removed reasonably easily from the skin. The device is configured to attach to the body of the patient so that it does not move or migrate along the surface of the skin after attachment. In many situations, an adhesive attachment is sufficient. Alternative attachment means can include strapping, such as with a buckle strap or with a “hook and loop” attachment means commonly referred to as “Velcro”, or cuffing, as with a sphygmomanometer cuff. In another alternative embodiment, a portion of the device, such as a bandage associated with the device or a portion of the base of the housing, can be configured to remain affixed to the patient&#39;s skin after the housing of the device has been removed. 
     A typical adhesive for securing the device directly to the skin is a pressure sensitive adhesive (PSA). The direct-attaching PSA and the base where the PSA is affixed are typically configured whereby the PSA adheres to the device more strongly than the PSA adheres to the skin. The PSA is typically permanently affixed to the device, such that no PSA will remain adhered to the skin of the patient when the device, or at least the housing portion of the device, is removed from the skin. The PSA is also selected for a secure though releasable affixment to the skin. These criteria ensure that the device, or at least the bandage or base portion of the device, can be securely affixed to the skin for the vaccination procedure, and can be safely and efficiently removed from the skin thereafter. 
     Typically, the manually-powered device having a skin-attaching PSA will also include a release member, such as a release paper or film, which overlies the adhesive on its skin-contacting side. After the release member is peeled from the PSA, the exposed adhesive layer can be placed against the patient&#39;s skin to attach the device thereto. 
     A main objective for initiating the development of the present injection was effecting a painless injection of injectable liquid compositions. While pain can be a relative experience, typically the painless device of the present invention will, after having been secured to the skin of the patient, effect the insertion of the injection needle and injection of the injectable liquid composition into the body without a sensation or feeling of pain, and more typically without any sensation or feeling whatsoever. In other words, the patient in most circumstances will have no sensation that the device has inserted a needle into the body, or that the injectable liquid composition is or has been injected into the body, except perhaps visually observing the device or touching the device with a hand, or feeling the attachment of the device to the outside of the skin. 
     Typically the manually-powered device is configured to complete the vaccination or injection of medicament into the patient utilizing a source of power or energy that is external to the device itself. The source of power can be provided by a person, such as a medical technician (a nurse, doctor, or other person who can administer the injection) or the patient, typically by manually (or bodily) manipulating the injection device with the hands or fingers, or by using an appropriate implement, as hereinafter described. The self-administering feature of the device and method of the invention enables injection of injectable liquid compositions without requiring medical personnel to hold the device against the skin of the patient during the time that the injectable liquid composition is in liquid communication with the needle, and is being pumped from the device into the patient. The use of the device that self-administers an injection allows medical personnel to perform other tasks while the injection proceeds. The device also allows the patient to have freedom of movement for the minutes of time that the injection proceeds. Typically, the source of power for arming the manually-powered device from its unarmed configuration comprises a manual power. This can be the use of the hands or fingers of a technician or an adult patient to manipulate the device or elements thereof with force. The manipulating force can also be applied using an implement, such as a key, push rod, or other inanimate object. The manually-applied kinetic force is stored by a power means within the device as potential energy, which can, upon subsequent activation, power one or more of the functions of the device. Typically, the external force used for the needle insertion function can also be used to store potential energy within the device, such as in a compressed spring or other biased resilient member. The external force can also be stored as electrical power or pneumatic power. 
     Typically, the self-contained device is intended to be self-powered, wherein the device comprises a power means to provide the energy necessary for one or more of the functions of the device, such as inserting the injection needle, pumping the medicament to the injection needle, and withdrawing the injection needle from the skin. The power means can include one or more such power means, each of which can employ one or more different forms of power. Typically, the power means include electrical power, supplied from a battery or electrical condenser. The power means can also include a pneumatic power means, such as a source of compressed gas or air. The power means can also include a fluidic power means, which includes both pneumatic and hydraulic power, such as a source of compressed air or gas, or hydraulic fluid. The power means can also include a mechanical power means, such as a compressed, stretched or torsioned spring, or a physical member that is biased into a strained or stressed position. The power means can also include a chemical power means, an electronic power means, such as an energized piezoelectric material, or an electrical power means such as an energized coil. The power means can also include an electro-chemical power means, where an electric charge or current can be converted into a chemical source of power, such as gas pressure from a gas generator. Non-limiting examples of self-powered, self-administering devices that can employ the improvements described herein are disclosed in US Patent Publication 20040116847, incorporated herein by reference. 
     The device can also be at least partially self-controlled, wherein at least one of the elements of the device can function automatically in response to the operation of another element. In some embodiments, all of the functioning elements of the device are actuating in response to the operation of one other element, or in response to some outside parameter, or automatically by time. 
     Typically, the device is manufactured and shipped to a use center, such as a clinic or hospital, with the needle insertion function in a first unarmed configuration. The unarmed configuration provides that the injection needle, which in its first position has its injection tip wholly within the housing, can not be intentionally or accidentally extended to a second position wherein the injection tip extends through the base of the device and outside of the device. In the unarmed configuration, there is typically no potential energy source, such as a compressed wire spring, available to the needle insertion means for spontaneous insertion of the needle. The unarmed condition can also be termed a fail-safe position, since, in this configuration, even a malfunction of the device will no allow the needle to extend from the housing. By contrast, if the needle insertion means is armed, then the device has potential energy stored on board, such as in a compressed, extended or torsioned spring, or other power means for insertion of the needle. If this armed device is activated, such as when an actuation button is depressed, the potential energy of the power means is released as kinetic energy that can move the needle insertion means from its first position to its second, extended position. If the device is shipped, stored, or handled in an armed configuration, there is a risk of an inadvertent, or even an intentional, activation of the needle insertion means. Consequently, the shipment and handling of the manually-powered device of the present invention in an unarmed configuration can avoid both an intentional and accidental needle sticks prior to its use in administering an injectable liquid composition. This improves the safety and security of the device during, storage, and pre-injection handling. In this configuration, at least the needle extension function (also called the insertion function when the needle tip extends into the skin of the patient) is unarmed. 
     Other functions, such as the pumping or injection means (for passing the injectable liquid composition through the injection needle) and the needle retraction means (to withdraw the needle from its second position in the body back toward its first position in the housing) can be configured for shipment and storage as either armed or unarmed. Preferably, the power means for the pumping means has an unarmed configuration, to avoid an accidental activation of the pumping of injectable liquid composition from the reservoir, which could prematurely empty the reservoir and render the device useless. Likewise, any needle retraction means is preferably shipped and stored in an unarmed configuration, to avoid the possibility of an unintentional or accidental activation, which in some embodiments may make the opposing needle insertion function inoperable, where the needle retraction is irreversible. 
     The power means can be used to provide energy to one or more of the elements of the device, such as insertion and retraction of the injection needle, or pumping of the medicament. Two or more power means can be used to provide energy for different elements, such as where the injection needle is moved from one position to another by a first power means, and an injectable liquid composition is pumped from a reservoir to the injection needle by a different, second power means. 
     The device can be at least partially self-controlled, wherein at least one of the elements of the device can initiate operation automatically in response to the operation of another element. 
     The typical device of the present invention has a housing comprising a base for placement against the skin of a patient for attachment of the device. The base can have a contoured surface that generally conforms to the shape of the body (typically, the arm or leg), to maintain the base surface in optimum confronting relationship with the skin. For example, the base of the device can have a slightly concave surface, which arches inwardly toward the interior of the housing. 
     The housing is typically made of a thermoplastic material that is light and inexpensive to manufacture, such as by molding, and yet is durable and resilient to gross deformation or breakage. A typical plastic material can include polyethylene, polypropylene, and polycarbonate. The housing can be designed with a shape that is both aesthetically pleasing and functional, for example, to allow insertion of the reservoir, to allow activation of one or more of the elements, such as the injection needle and liquid communication means, and other elements of the device. The housing can be made as a single part or as a plurality of parts configured to associate and secure together in both either static or moving relation to one another. 
     The housing also provides a visual enclosure for the injection needle that keeps the needle out of sight of the patient at all times during the injection procedure. This can reduce or eliminate the patient&#39;s apprehension or fear caused by the sight of a needle, thereby reducing the tendency of the patient&#39;s muscles to tighten and harden, which can make needle penetration more difficult and painful for the patient. 
     The housing also provides a physical enclosure for the injection needle that helps to avoid accidental needle stick, particularly after an injection, which could place a user at serious risk from fluid-borne pathogens. The device can be configured for use only once (unless completely disassembled and retrofitted), thereby minimizing the likelihood of reuse of a contaminated hypodermic needle. The device can also advantageously be configured wherein some parts or assemblies, such as the housing and it associated elements, can be reused. 
     The housing can also be configured to receive and secure the needle and optionally the reservoir of injectable liquid composition as a modular insert into the housing body. The housing can include two or more parts, at least one of which is movable relative to another, which can be configured into an open position wherein either the needle or the reservoir, or both, can be inserted into the body of the housing, or a closed position wherein the needle and/or reservoir are not accessible or retrievable from within the housing. The movable part can be a door or a panel that is movable to provide an access port into the housing. The door or panel can be hinged or removably affixed to the housing, or can be slidable away from the access port. 
     The injection needle of the device provides for liquid communication of the injectable liquid composition passing from the reservoir and through other liquid communication means of the device into the body tissue of the patient, from where the injectable liquid composition can dissipate into the surrounding tissue and throughout the body. The injection needle should be shaped and configured to provide painless insertion and painless injection of the injectable liquid composition. Generally an injection needle having a smooth circular outer surface and an outer diameter D of about 0.36 mm (28 gauge needle) and less can be inserted painlessly through the skin of a patient. For small children, infants and patients having more sensitive skin, an outer diameter D of about 0.30 mm (30 gauge needle) and less (31 gauge to 33 gauge), will typically ensure painless needle insertion. 
     Typically the injection needle is configured to be substantially linear or straight, from its tip toward the opposed inlet opening. The needle can be configured to be linear completely to its inlet end, or can be configured with a bent or curved portion near the inlet opening. 
     The needle size should be sufficiently large to allow passage of the required volume of liquid medicament into the body within a period of time that is suitable to avoid causing pain. For a typical medicament volume of about 0.5 ml to about 1.0 ml, a substantially painless to completely painless injection can be achieved over an injection period of from about 1 minute to about 10 minutes, more typically from about 3 minutes to about 5 minutes. The volumetric flow rate is at least about 0.05 microliter per second μL/s, and up to about 50 μL/s. Typically, the volumetric flow rate is about 0.5 μL/s to about 20 μL/s, and more typically about 1 μL/s to about 4 μL/s. The injection needle should be sufficiently durable and axially rigid to avoid bending or breaking when inserted into the skin and muscle. Typically, a needle having an outer diameter of from 0.20 mm (33 gauge), more typically of from 0.23 mm (32 gauge), to 0.36 mm (28 gauge), is sufficiently painless, durable, and liquid conductive. 
     It is also within the practice of the device and method of the present invention to inject medicament volumes of greater than about 1.0 ml, and to deliver the injection over time periods greater than 10 minutes. 
     Typically, the injection needle is pre-installed into the injection device during its manufacture, prior to its distribution to at the facility or site where the injection shall occur. Although the device can be configured for installation of the injection needle at the use facility, the small, fine size of the injection needle may make it difficult for a medical technician or patient to manipulate it into position within the device. Likewise, after a vaccination, the injection needle and the housing or assembly thereof into which the needle is secured can be disposed of in accordance with health and safety regulations and guidelines. 
     The liquid composition is typically contained within the cavity of the reservoir, and flows from the reservoir to the injection needle during injection. The reservoir is typically positioned within the housing although the structure of the reservoir can also form a portion of the outer surface of the housing. The reservoir can have a rigid structure having a fixed volume with a moveable member, such as a plunger that defines a variable volume cavity. The reservoir can also have a flexible structure where its volume can decrease as its content of medical technician or patient is removed there from. Typical materials for use in making the reservoir include natural and synthetic rubber, polyolefin, and other elastomeric plastics. The selection of the structure and material of construction of the reservoir will depend in part on the specific means of pumping the medicament from the reservoir to the injection needle. Selection of the material of the reservoir should also be chemically stable with the medical technician or patient. In another typical embodiment, the reservoir can be affixed to the injection needle as part of a liquid composition product, for assembly into the device. A reservoir will generally have a volume sufficient to contain about 0.1 ml to about 10 ml, typically about 0.1 ml to about 3 ml, of medicament. In a more typical embodiment, the reservoir would hold about 0.5 ml to about 1.0 ml of medicament. 
     The reservoir comprises an outlet port, typically comprising a penetrable membrane that can provide an air-tight and leak-proof seal over the outlet opening of the reservoir during manufacture, shipment and storage of the filled reservoir, and that can provide a self-sealing, leak-proof joint when pierced by the inlet end of the needle or a separate piercing conduit at the time of the injection. A typical reservoir membrane comprises natural or synthetic rubber or a thermoplastic material. Alternatively, a wall of the reservoir can be adapted to allow penetration thereof by the piercing conduit, such as the inlet end of a needle. 
     A typical embodiment of a reservoir comprises a reservoir body having a cavity that has been pre-filled with the injectable liquid composition and sealed. The pre-filled reservoir can be assembled into the device during manufacture. In this case, the device is labeled to identify the particular injectable liquid composition that is contained therein. 
     More typically, pre-filled reservoir will be configured for installation or insertion into the housing of the injection device at the facility or site where the injection will occur. The technician would typically remove the reservoir from a storage area, such as a refrigerator, and insert it into position within the housing of the device. An identity label associated with the reservoir can be provided that is conveniently transferred to the patient&#39;s records. 
     Alternatively, a device comprising an empty reservoir can be filled by medical personnel with the appropriate quantity and type of medicament, prior to injection. Typically, this embodiment of the reservoir comprises a liquid composition flow valve that has a self-closing, self-sealing opening to the cavity of the reservoir. The liquid composition flow valve is typically an elastomeric or rubber material. The opening is typically a cylindrical member having a slit opening formed axially there through. The liquid composition flow value can be inserted into a bore formed in the sidewall of the reservoir that is slightly smaller in diameter than the flow valve. A hypodermic needle of a syringe can be inserted through the slit opening to inject a desired dose of the liquid composition into the cavity of the reservoir. When withdrawn, the slit opening closes and seals. When the device is used by medical personnel as supplied from a manufacturer with the reservoir securely inserted within the housing, the device can have a companion flow valve disposed in the surface of the housing, or otherwise accessible to the medial personnel. If the reservoir is configured so that a portion of the reservoir is integral with the housing, then a single flow valve can be used, with an inlet accessible to the medical technician and an outlet into the cavity of the reservoir. Alternatively, the device can be configured with a second liquid composition flow valve positioned in the housing, disposed adjacent to and aligned with the first flow valve disposed in the reservoir. 
     An important requirement of the liquid communication means is to ensure that the liquid composition can flow from the reservoir to the injection needle regardless of the specific orientation of the device. Typically, the attachment of the device to the skin of the patient can position the reservoir and the injection needle into a variety of relative spatial orientations that can sometimes require the liquid composition to flow upward against gravity, or that can position the outlet of the reservoir in an upward position, opposite the pool of liquid composition disposed in the reservoir. 
     Consequently, a preferred configuration of the reservoir and liquid communication means provides that the outlet of the reservoir is maintained in communication with the remaining liquid composition in the reservoir. A typical configuration comprises a collapsible reservoir comprising an outlet that maintains liquid communication with any residual liquid composition present in the reservoir. This reservoir has an upper flexible wall that can be conformed to the volume of the liquid remaining therein. The reservoir typically contains little or no air or gas when filled with the supply of liquid composition and during its displacement and injection operation. Thus, the reservoir collapses to become essentially empty, terminating delivery. In like manner, when a non-flexible material is used for a reservoir such as a conventional tube-with-plunger syringe, the displacement of the plunger empties the reservoir, which terminates delivery. 
     The housing can also comprise an outer support structure that confines and protects the reservoir from outside elements that might puncture it, and which can define the initial shape of the reservoir. 
     The reservoir can also be constructed of an elastomeric material that can be expanded in volume when filled with the liquid composition, and holds the liquid composition under pressure. After puncture by a piercing conduit, such as the inlet end of the injection needle or an intermediate member that is in liquid communication, such as via tube, with the injection needle, the expanded reservoir can contract to reduce the effective volume of the reservoir as liquid composition is pumped there from. One or more of the walls of the reservoir can be made of an elastomeric material, while other walls or surfaces are made of other elastic or inelastic rubber or plastic material. 
     The reservoir can also comprise an adaptable structure having a means of varying its effective volume, such as a piston-plunger construction or an accordion construction, as in a bellows. In the embodiments described herein, a self-contained reservoir can be replaced with a more conventional syringe and plunger for storing and injecting the liquid composition to the injection needle. 
     Non-limiting examples of a reservoir of the present invention are those described in U.S. Pat. No. 5,527,288 (element 10), U.S. Pat. No. 5,704,520 (element 12), and U.S. Pat. No. 5,858,001 (elements 16 and 17), all such publications incorporated herein by reference. 
     A first embodiment of the invention is shown in  FIGS. 1-3 ,  3 A, and  4 - 28 . The device includes a housing, shown in  FIGS. 1-3 ,  3 A, and  4 - 9 , and a cylindrical syringe cartridge shown in  FIGS. 10-19 . The use and operation of the device for manually self-administering a painless injection is illustrated in  FIGS. 20-28 . A device having a housing for retaining a plurality of cylindrical syringe cartridges is shown in  FIGS. 29-31 .  FIGS. 32-25  show a separable base and means for attaching the device to a patient&#39;s skin. 
       FIGS. 1-8  show an assembled housing  10  in various views and aspects.  FIG. 1  shows the housing  10  having an outer body  11 , a needle carriage  70 , a means for retaining a reservoir for an injectable liquid composition, and a base  12  for placement of the device against the skin of a patient. The carriage  70  is configured for movement along an axial centerline  100  in a direction perpendicular to the base  12 . The cylindrical carriage has a cylindrical recess  71  having a tapered bottom  78 , that opens to a connector portion  73  having internal female threads, which provide the at least a portion of the retaining means for the reservoir, described below. A needle  40  lies along the centerline  100  and is disposed through the axial center of a needle hub  72  that is secured to the connector  73 . The inlet  42  end of the needle  40  extends within the connector portion  73  sufficiently below the opening in the tapered bottom  78  to prevent the sticking of a finger that may probe the recess. A retraction spring  76  is positioned about the centerline  100 , having one end disposed within an annular groove  74  in the underside of carriage  70 , and the other end disposed around an annular flange  94  projecting up from the base  12 . The needle  40  extends downward from the lower end of the needle hub  72  toward the base  12 . The needle is completely within the housing when the carriage  70  when in the first retracted position shown in  FIG. 1 . 
     In a second inserted position, shown in  FIG. 2 , the carriage  70  has moved axially toward a position proximate to the base  12  of the device, and the needle  40  extends downwardly and out through the opening  13  in the base. The guide wall  14  comprises an inwardly-projecting, axially-oriented elongated rib  19  that registers along its length with an axially-oriented peripheral groove  77  in the outer wall  75  of the carriage  70 , shown in  FIG. 3 , to prevent the carriage  70  from rotating within the guide wall  14 . A retainer heel  86  is biased inward from an opening in the cylindrical guide wall  14 . As the carriage  70  passes down the guide wall  14 , the heel  86  is temporarily biased outward, allowing the carriage to pass. The retraction spring  76  is compressed between the underside of the carriage  70  and the base  12 . When the carriage arrives at the fully inserted position shown in  FIG. 2 , the lower end flange  79  of the carriage has cleared past the heel  86 , which returns to its inwardly-biased position, where it can secure the carriage  70  and the needle  40  in the inserted position, and secures the retraction spring  76  in a compressed state. The heel  86  is part of a release arm  80 , described herein after. 
       FIG. 4  shows a plan view of the housing  10  in its first retracted position, with selected cross-sectional views taken as  FIGS. 1 ,  3 ,  5 , and  6  to illustrate certain elements of the housing.  FIGS. 7 and 8  are sectional views of the housing in  FIG. 1 . An exploded view of the elements of the housing  10  is shown in  FIG. 9 . 
       FIGS. 10 and 11  are sectional views of the syringe cartridge  18  taken through perpendicular section lines  10 - 10  and  11 - 11  of  FIG. 12 .  FIGS. 13-17  provide additional detailed views of the syringe cartridge  18  shown in  FIGS. 10 and 11 .  FIG. 18  shows an exploded view of the elements of the syringe cartridge  18 . 
     The syringe cartridge  18  shown in  FIGS. 10 and 11  comprises a syringe assembly  20  and a telescoping pressurizing assembly  30 , configured as a reservoir having liquid cavity  66  for the injectable liquid composition. The syringe cartridge  18  is configured to be associated with and retained within the housing  10  of the device. In the illustrated embodiment, the cylindrical recess  71  of the needle carriage  70  provides the means for retaining the reservoir of injectable liquid composition, embodied by the syringe cartridge  18 . The syringe assembly  20  comprises a syringe body comprising a cylindrical wall  21  that has an open upper end  25  and a tapering base  22  that has, at the lower end, an externally-threaded syringe hub  64  having an aperture  23 . A cylindrical plunger  24  can be inserted through the opening in the upper end  25  for engagement with the inner surface of the wall  21 . The space between the plunger  24  and the syringe body in  FIG. 10  defines the reservoir cavity  66 . The respective threads of the syringe hub  64  of the syringe cartridge and of connector portion  73  of the needle carriage cooperate and engage when the syringe cartridge is placed into the needle carriage and rotated, which secures or locks the syringe cartridge into its retained position within the needle carriage. The cooperating threads also provide liquid communication between the injection needle and the reservoir of the syringe cartridge, as the inlet  41  end of the needle advances and penetrates a membrane  65  of the membrane plug  67  disposed in the opening of the syringe hub  64  (see  FIG. 14 ). 
     The plunger  24  is typically a flexible, resilient rubber material that can form an effective liquid seal about its periphery with the sidewall  21  of the syringe. The plunger  24  is secured around a rigid plunger plug  26  to maintain its cylindrical shape. As can be seen in greater detail in called-out  FIG. 13 , the inner surface of the syringe wall  21  has, at its upper end, a slight inwardly-extending rim  38  that can engage the upper end of the outer wall  43  of the plunger  24 , which can prevent the plunger  24  from incidentally withdrawing from and falling out of the upper opening of the syringe wall  21 . Nevertheless, the plunger wall  43  is sufficiently flexible to be inserted into or extracted out of the syringe opening by force. The threaded bore in the plunger plug  26  is provided for attachment of a stem (not shown) having a mating thread so that the plug  26  and the plunger  24  secured thereto can be manipulated into and out of the syringe opening, and along the length of the syringe. 
     The telescoping pressurizing assembly  30  comprises a cylindrical body  31  that is closed at an upper end  34  and has an opening  32  at the opposed lower end. The lower edge of the cylindrical body  31  has a pair of opposed mechanical engaging means shown as inwardly-extending ribs  36  that can engage an outwardly-extending rim  28  disposed on the upper end  25  of the syringe wall  21 , to secure the pressurizing assembly  30  to the upper end  25  of the syringe assembly  20  in a first extended position, as shown in  FIGS. 10 and 13 . A pressurizing spring  33  is restrained within the body  31  between an annular groove  35  at the closed end  34 , and an annular groove  27  in the plunger plug  26 . When the pressurizing assembly  30  is in the extended position shown in  FIG. 10 , the pressurizing spring  33  is typically under minimal compression.  FIG. 11  shows the same syringe cartridge as in  FIG. 10 , but with the plunger  24  and the pressurizing spring  33  extended to the bottom of the syringe body  21 . In this configuration, a medical technician can fill the syringe assembly. The upper pressurizing assembly  30  and the membrane plug  67  are first removed. Then, using a threaded stem (not shown), the plunger can be pulled upward to draw injectable liquid composition through the aperture  23 . The membrane plug  67  and the upper assembly  30  then can be reinstalled. 
     The wall  31  of the pressurizing assembly  30  is configure to telescope axially over the outside of the syringe wall  21  to a second pressurizing position (shown in  FIG. 19 ), where the ribs  36  can engage a second set of outwardly-extending rims  29  disposed near the lower end of the syringe wall  21 , also shown in  FIG. 10 . This causes the closed upper end  34  of the pressurizing body  31  to compress fully the pressurizing spring  33  against the plunger plug  26 , which causes the plunger  24  to move to the bottom  22  of the syringe  21  when no liquid is contained in the cavity  66  of the syringe. The engagement of the ribs  36  with the lower rims  29  retains cylindrical body  31  in the fully pressurized configuration. When the cavity  66  of syringe  21  contains a volume of injectable liquid composition, such as vaccine V as shown in  FIG. 19  the manual depressing of the syringe cartridge causes the compression of the pressurizing spring  33 . The engagement of ribs  36  with rims  29  restrains the compressed pressurizing spring  33 , and retains the potential energy within the compressed spring  33  as a means for injecting the liquid composition from the cavity. The manually-powered, compressed spring  33  exerts a downward force upon the plunger  24 , which exerts pressure upon the liquid composition in the cavity  66 . When the cavity  66  is put into liquid communication with the needle, the pressurized liquid vaccine can flow out of the cavity  66  under pressure. The pressurizing spring  33  is configured and designed to maintain a relatively constant force, resulting in a relatively constant pressure and liquid composition flow rate through the needle throughout the injection process. 
     The device  1  of the present invention comprises a separable base  92 , from which the housing  10  can be removed at any time, particularly and advantageously after completion of the injection. The separable base  92  is typically configured for separable securement to the base  12  of the housing by a base securement means, and typically provides the skin-contacting surface of the device  1 . A base separating means provides selective separation of the separable base  92  from the device.  FIGS. 2 ,  27  and  28  illustrate an embodiment of a separable base  92 , as embodied in a separable attachment assembly  93  that removably associates with the base  12  of the housing  10 . 
     The base securement means can comprise a mechanical engagement, such as a catch  89  formed on a distal end of a release finger  88  that depends downward from a portion of the housing body  11 . The distal end of the finger  88  extends through an opening  95  in an inner base member  91  shown in  FIG. 2 . The finger  88  further extends through an opening  98  in the removable base  92  when the removable base  92  is positioned against the base  12  of the housing. The finger  88  is configured to bias the catch  89  toward and into engagement with a latch  96  formed in the separable base  92 , shown in  FIG. 27 . The separable base  92  remains affixed to the housing of the device provided that the catch  89  remains engaged with the latch  96 . 
     The base separating means for separating the separable base  92  from the permanent housing base  12  can comprise a mechanically-biased member associated with the housing  10  that is configured for manipulation that forces to disengage the base securement means, specifically in the illustrated embodiment by moving the catch  89  out of engagement with the latch  96 . In  FIG. 27 , after the needle  40  and carriage  70  have been retracted, the person can depress the release button  81  even further, thereby causing a toe  87  on a release arm  80  to pivot into engagement with the release finger  88 , and to bias the catch  89  out of engagement with latch  96 . With the catch  89  disengaged from latch  96 , and with the needle  40  fully retracted, the housing can be safely and easily separated from the separable base  92  for post-injection inspection, and for disposal. 
     The separable base further comprises a means for attachment to the skin of the patient. Typically, the means for attachment comprises an adhesive means adhered to the skin-contacting surface of the separable base. 
     While the figures and associated description describe the separation of the separable base from the housing while the device is attached to the skin of a patient, it can be understood that the separable base can also be removed from the housing while the device is free from attachment to the body. 
     In a method of using the device of the invention, a device  1  is provided as shown in  FIG. 20  comprising a housing  10  having a separable attachment assembly  93  comprising a separable base assembly  92 , and a syringe cartridge  18 . The three members are shown separated to illustrate, that prior to use as an assembled product, the components can be separated and visually inspected. 
     The separable attachment assembly  93  can be attached manually to the base  12  of the housing  10  as previously described. Prior to attachment of the device to a person, a release paper  111  that covers the separable base  92  and adhesive flaps  112 , is peeled away and disposed of. 
     As shown in  FIG. 21 , the separable attachment assembly  93  of the housing  10  can be attached to an area of the patient&#39;s skin on the upper arm or leg of the patient P, designated as the injection site, secured by the adhesive on the underside of the adhesive flap  112  that extends outward from the periphery of the separable base  92 . 
     After attachment of the device to the skin, a seal  105  is removed that covers the opening to the carriage recess  71  to protect the inlet end  41  of the needle  40  from contamination, as shown in  FIGS. 21 and 22 . The syringe cartridge  18  is then inserted into the recess  71  of the carriage  70 . The threaded syringe hub  64  engages the threaded connector  73 , so that manual axial rotation of the syringe cartridge  18  mates the respective threads and secures the syringe cartridge  18  to the carriage  70 . As that occurs, a membrane  65  disposed in the opening of the syringe hub  64  (see  FIG. 14 ), is penetrated by the inlet  41  end of the needle, which establishes liquid communication with the syringe cavity  66 . A pair of tabs  45  extending out from the top of the pressurizing body  31  provides a grip for manually rotating the syringe cartridge  18  into the carriage  70 . Relative axial rotation between the syringe assembly  20  and the pressurizing assembly  30  is prevented by disposing the outwardly-extending rims  28  of the syringe wall  21  into longitudinal grooves  37  formed in the inner surface of the pressurizing body  31 . 
     In an alternative method, the syringe cartridge  18  can be provided in its pressurized configuration, as shown in  FIG. 19 , just after the technician has compressed the telescoping pressurizing assembly  30  down onto the syringe assembly  20 , and just prior to insertion of the cartridge  18  into the carriage  70 , shown in  FIG. 22 . When the technician inserts the pressurized cartridge  18  into the recess  17  of the carriage  70 , and rotates or twists the cartridge  18  to establish liquid communication between the reservoir cavity  66  and the needle  40 , liquid composition may begin to flow from the syringe cavity and into and through the needle  40 . 
     The device can also be configured to prevent rotation and removal of the modular syringe from its position in fluid communication with the needle, once the carriage  70  has been moved to and secured in the injection position. The tabs  45  extending from the closed end  34  of the pressurizing assembly  30  nest within the oblong recess  17  in the top of the housing  10  to inhibit finger access to the assembly, and to prevent manual rotation and removal of the syringe cartridge  18  in the injection position. This prevents an unwanted exposure of a needle that is penetrating the skin from being open at its inlet  42  end to the atmosphere. 
     As shown in  FIG. 23 , the needle  40  is then inserted into the patient by manual force downward on the syringe cartridge  18  to move it into the housing  10  and toward the base  12 , thereby inserting the injection needle  40  into the body and initiating the injection. The pressing downward of the syringe cartridge  18  has also compressed the retraction spring  76 . Fully manually pressing the syringe cartridge  18  downward causes the carriage  70  to be retained in a second position associated with the second injection position of the injection needle. A needle insertion securement, such as the retainer heel  86  shown in  FIG. 24 , is configured to retain the needle carriage, and the injection needle, in the second, inserted position while the liquid composition is injected. Under the relatively constant force of the pressurizing spring  33 , the vaccine V is slowly though constantly expressed out of the syringe cavity  66  and into the targeted body tissue  150 . The size of the needle and the force factor of the pressurizing spring  33  can be configured and designed to cause the liquid composition to flow under pressure through the needle within a target volumetric flow rate, to complete the injection within a prescribed period of time. 
     At the end of the injection term, shown in  FIG. 25 , the plunger  24  has moved under the force of spring  33  to the bottom  22  of the syringe, and has collapsed the reservoir cavity  66  and driven substantially all of the vaccine out of the syringe cartridge  18 . 
     An alternative method of inserting the needle  40  can employ the syringe cartridge  18  itself as an “implement or plunger” for depressing the needle cartridge to its inserted position, without having the needle inlet  41  penetrate the membrane  65  to the syringe cavity and placing the needle into liquid communication with the cavity. The syringe hub  64  of syringe cartridge  18  can be rested against the bottom of the carriage  70 , as shown by the left-side syringe in  FIG. 31 , and pressed downward with having engaged the threads, or having only partially engaged the threads, of needle hub  72  and connector  73 . Alternatively, the syringe hub  64  and the connector  73  can be configured to provide a first position wherein the threads partial engage without establishing liquid communication between the needle and the cavity (that is, without rupturing the membrane  65 ), and a second position wherein the threads further engage and establish liquid communication by penetration of the membrane by the inlet end of the needle. 
     Once the injection has been completed, or at any time during the vaccination, the needle can be retracted from its second or inserted position by activating a needle retraction means. The needle retraction means can comprise a disengagement means that is configured to disengage the needle insertion securement, and a power means configured to bias the needle, and the needle carriage, to respective third positions where the injection end of the needle is disposed within the housing. In the illustrated embodiment of  FIG. 26 , the disengagement means comprises one or more release arms  80  and one or more release buttons  81 . The release arm  80  comprises an upper end  82  shown as a ball having an inward flat surface that is secured within a socket  15  formed in the main body  11 . The release arm  80  also comprises a pivot  83  that resides in a detent in the outside of the guide wall  14 , and a resilient, flexible elbow portion  84  intermediate the ball end  82  and the pivot  83 . A lateral bar  85  on the inside of the release button  81  is disposed proximate the elbow  84 . In response to an inwardly-directed force on the button  81  that moves the button inward, as shown in  FIG. 26 , bar  85  causes the release arm  80  to flex inwardly at the elbow  84 , causing heel  86  to pivot outwardly and out of engagement with the carriage lower flange  79 . As shown in  FIG. 27 , the power means comprises a compressed retraction spring  76  that had been manually disposed into a compressed configuration when the needle was manually inserted, and biases the needle toward a third position. With the needle carriage  70  unsecured by the needle insertion securement, retainer heel  86 , the compressed retraction spring  76  can drive the carriage  70  upward from the base  12 , and retract the needle tip  41  completely out of the body of the patient P and into the third position where the needle tip is within the housing  10 . 
     The needle insertion securement and the disengagement means can function through or comprise the same element of the device (like the release arm  80  which functions to both secure the carriage and to disengage the securement), or can employ distinct elements. 
     After retraction of the needle  40 , the syringe cartridge  18  can be grasped and removed by oppositely rotating the cartridge to disengage the threaded connection of the cartridge with the carriage. The cartridge assembly  18  can be inspected to confirm that all the liquid composition from the syringe cavity  66  had been injected, and then is disposed. If for any reason a significant amount of the liquid composition remained in the syringe, the syringe cartridge  18  can be reinserted into the carriage  70  and again rotated into liquid communication with the inlet of the needle  40 , and the carriage and needle reinserted into the patient to complete the injection. 
     The illustrated embodiment shown in  FIGS. 5 ,  25  and  27  shows that the release button  81  can have a generally cylindrical shape. The button can have a main inner wall  104  and an annular outer wall  101  having an annular periphery that is slightly larger than the annular opening  102  in the housing body  11  in which the button is disposed. The flared outer wall  101  resist movement of the button  81  into the opening  102  until a manual force is applied that is sufficient to bias inward the outer wall  101 . As the button  81  is depressed, it biases elbow  84  of the release arm  80 . When the force on the button  81  is released, the resilient elbow  84  will spring back against, and move, button  80  outward to its original position. The button  81  can also provided with a small aperture in its face, through which a small hooked implement can be inserted to pull out the button if it should become lodged inwardly. 
     To assist in installing the separable attachment assembly  93  to the housing of the device, the lower surface of the housing base  12  can optionally be provided with a wide indent  97  surrounding the opening  95  in the inner base  91 , and the separable base  92  can be provided with a raised flange  94  that registers with the indent  97 , as shown in  FIG. 20 . Pressing upward on this area assists engaging the catch  89  onto the latch  96  of the separable base  92 . 
     A top plan view of a typical separable base assembly  93  is shown in  FIG. 32 , with a sectional view  FIG. 33  taken through line  33 - 33 , and detailed sectional views shown in  FIGS. 34-35 . The adhesive flap  112  extends outwardly from the periphery of the separable base  92 , and is covered on its slower surface with the release paper  111 . The adhesive flap  112  comprises a first film layer  114  that is affixed on its upper surface to cover the skin-facing surface of the separable base  92 , and extends outward from the peripheral circumference of the base  92 . The flap  112  has a PSA on its lower surface (not shown) for attachment to the skin. Flap  112  also comprises a second film layer  115  that is shaped as a ring with an inner circular edge  116  and an outer edge  117 . The inner edge  116  extends inwardly and is affixed, typically with PSA, to the upper surface of the separable base  92  inboard of its circumferential edge. The second film layer  115  extends outwardly from the separable base  92 , to overlap the first film layer  114  to its periphery, and there beyond to its outer edge  117 . Typically, the adhesive flap layers  114  and  115  can be made of a flexible plastic film, and can be optionally vapor permeable or breathable. 
     Alternatively, the second film layer  114  can be eliminated, and the underside of the separable base  92  can have a coating of PSA for direct-contact adhesion to the skin. Optionally a gauze bandage  113  can be secured to the underside of the separable base  92  over the opening  13 , as shown in  FIG. 35 . 
     In an alternative embodiment, the base securing means and the base separating means can comprise other mechanical securements, an adhesive securement, and a magnetic securement of the separable base to the housing of the device. The other mechanical securements could include a mechanical “hook-and-loop” device that can include Velcro®, a hasp, a frangible joint, and a threaded joint). The magnetic securement can comprise a first magnetic member proximate the upwardly-facing surface of the separable base; and a second magnetic member proximate to the base portion and inside of the housing; wherein first magnet member and the second magnetic member have a magnetic attraction that secures the removable base to the housing, and wherein the removable base can be manually separated from the base portion of the housing by a manually-applied force that overcomes the force of the magnetic attraction. 
     The separable base provides a means for obtaining a secure attachment of the housing of the device to the patient&#39;s skin, by providing for outwardly-extending adhesive flaps that are securely affixed to the relatively rigid structure of the separable base. In most circumstances, the separable base that remains behind on the skin of the patient is well tolerated by the patient, and can be removed at any time, since most vaccinations, particularly with very small needle diameters, leave little wounding of the skin 
     The separable base  92  can also be removed for pre-injection inspection of the device, by fully depressing the release button  81 , prior to installing the reservoir or the initiating needle insertion. The inner base  91 , or a portion thereof, can be made of a transparent thermoplastic material to allow a visual inspection of the needle and the internal assembly prior to use. The separable base  92  can then be easily reaffixed. 
     As shown in  FIG. 28 , after completing the injection, the syringe cartridge  18  can first be removed from the attached housing  10 , before the housing is removed from the separable base  92 ; or, the housing  10  with the syringe cartridge  18  attached can be removed from the separable base  92  as a unit, and then the syringe cartridge can be removed. 
     The device can also comprise a means for preventing deployment of the needle through the opening in the base of the housing, particularly after the needle has been inside the skin and body of a person. A typical deployment prevention means for preventing needle deployment comprises a sliding or rotating plate disposed in the base that can moved between a first position where the needle opening in the base is not covered by the plate, and a second position wherein the plate covers the opening. In the embodiment illustrated in  FIGS. 36-38 , a rotating plate  131  is disposed in an annular recess  130  on the annular flange  94  of the inner base  91 . The recess  130  and plate  131  have a center that is positioned off the centerline  100  passing through the needle, though they overlap the needle opening  13  in the base  12 . The plate  131  has an opening  136  disposed between the center of the plate  131  and its periphery. The plate  131  can rotate between a first deployment position shown in  FIGS. 36  and  37  wherein the plate opening  136  registers with and leaves exposed the opening  13 , and a second blocking position shown in  FIG. 38  wherein the plate  131  covers the opening  13 , and prevents deployment of the needle  40 . The plate is movable between the first and second positions by a knob  132  that is attached to the plate by a stem  133 . The stem is disposed within arc-shaped stem slot  134 . The knob  132  moves along a knob recess  135  formed in the inner surface of the removable base  92 , and that lies below the knob slot  134 . The knob retains the plate in position, and can be manipulated by finger to move the plate between its first and second positions. Prior to injection, the technician can remove the removable base plate and manipulate the knob  132  to move the plate  131  to its deployment position. After the device is removed from the skin following the injection, and the device has been removed from the separable base  92 , the exposed knob  132  can be manipulated to move the plate  131  to its blocking position. This physically closes the opening  13  to ensure that the needle  40  can not be redeployed accidentally and cause an undesired stick. 
     In a second embodiment of the present invention, the device employing a separable base  92  can comprise a device that comprises an on-board power means, as described above, for inserting the injection needle, and optionally, injecting the medication and retracting the needle. As shown in  FIG. 19 , and referring to  FIG. 11 , the syringe cavity can comprise a self-contained power source in the form of the compressed pressurizing spring  33 . In the illustrated embodiment, the compressed spring is exerting its force upon the vaccine contained in the cavity  66 , placing it under pressure. Optionally, in this alternative embodiment, the cylindrical body  31  can be configured with a retainer pin that withholds the pressurizing spring  33  (and therefore pressure upon the vaccine) from contact with the plunger  24 , or withholds the plunger  24  itself, until released by a releasing means, such as an annular retaining ring having a tab extending through the cylinder wall  31 . 
     In a third embodiment of the present invention, a device can have a plurality of injection needles and reservoirs disposed within the housing. The device can provide for injecting at least two injectable liquid compositions to a patient.  FIGS. 29 and 30  show a top plan view and an elevation view of a device  1  for injecting at least two liquid compositions from separate reservoirs contained in the housing. As shown in  FIG. 31 , the device  1  can comprise a housing  10  and base  12  for two needle carriages  70   a  and  70   b  and two injection needles  40   a  and  40   b , which can be configured to be separately and independently manipulated for insertion, injection and retraction, as described herein above. 
     Alternatively, the two needle carriages and needles can be configured for simultaneous insertion, injection, and retraction using shared elements, including a shared, dual-recess needle carriage, and a dual unitary pressurizing assembly. 
     If only one injectable liquid composition will be administered, there is a potential for the patient, during the injection procedure, to pick at and possibly poke a finger though the seal  105  that is initially positioned over the cavity recess  71 . To prevent this, the seal  105  can be affixed to a cylindrical member  106  that partly supports the underside of the seal  105  layer, as shown in  FIG. 3A . Alternatively, the seal can be removed and replaced with a “dummy” plunger that has the upper appearance of the active syringe cartridge, but which fits securely in the opening in the housing above the carriage to block any attempt to depress the carriage. 
     A further embodiment of the invention can comprise a means of indicating the extent of liquid composition dispensed from the reservoir. The indication means can comprise a visual means that allows personnel to actually view the remaining contents of the reservoir. An embodiment of a visual indication means can comprise a transparent section positioned in a portion of the housing adjacent the reservoir, to view the reservoir. Alternatively, the housing can comprise a door or panel that can be opened to permit inspection. Further, the reservoir can be provided with a corresponding transparent portion to permit the medical personnel to see the medication contained within the reservoir. The transparent portion can include a portion of the base or a portion of the housing, or both. The transparent portion can be a small area relative to the total surface area of the housing body, or can be a significant portion of the housing body surface. In a typical embodiment, the transparent portion is positioned on one side of the housing body that, when applied to the patient&#39;s arm, can face away for the patient&#39;s line of sight. This allows the medical technician to see through the transparent portion, but provides no indication to the patient, typically a small child, that the inside of the device contains something interesting that might arouse the patient&#39;s curiosity. 
     The indication means can also comprise a signal means that signals the end or the approaching end of medicament dispensing. A signal means can comprise a mechanical or electrical switch that is activated by the plunger member as the last remaining contents of the reservoir is dispensed. The signal can be a flag, a pop-out tab, an illuminated light, or any other well known signal. 
     Another embodiment of the invention can comprise a covering or disguise configured for attachment or placement over the injection device either to provide the device with a pleasurable impression, or to direct the patient&#39;s attention away from the device. The covering can be formed as a cartoon character, a zoo animal, or the like. In this way, much of the patient&#39;s fear that might be caused by the sight of the device can be alleviated. 
     In another embodiment of the invention, the housing of the device can be colored coded or have a colored indicator or marking that identifies the particular type or quantity of medication contained within the reservoir. For example, for one certain medication the outer casing may be blue in color. The device can also display various warnings, such as a precaution to avoid needle stick and possible side effects to the medication. The device can also comprise a removable label comprising information about the liquid composition to be administered (such as the type of vaccine or medicament, the manufacturer and lot number, and volume), which can be placed into a medical record or patient chart. 
     Another embodiment of the invention, shown in the figures, is an improved injection device for self-administering an injection that does not provide the patient with any convenient fingerhold to grasp the device for jostling or removing the device from the skin during the injection procedure. A preferred design of the device will include an outer surface that has not sharp edges or deep groove with which the patient can get a fingerhold. Preferably, the housing and the base are constructed of a thermoplastic material that has a non-grip or non-sticky surface, and is preferably a resilient material that can flex but not deform in shape. A matte finish on the outside surface can make the housing difficult to grasp, except when properly grasped by a medical technician by its release buttons. Typically, the indentures and grooves in the housing, and including the base, have a breadth not greater than 3 mm, more typically not greater than 1 mm. Typically, external edges can be rounded, maintaining an edge radius of about at least 1 mm, more typically of about at least 3 mm. 
     While specific embodiments of the apparatus and method of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the present invention as defined in the appended claims.