Patent Publication Number: US-2012046615-A1

Title: Syringe needle assembly and medicament injection device

Description:
TECHNICAL FIELD 
     The present invention relates to a syringe needle assembly (injection needle assembly) and a medicament injection device (drug injection device) that are used to inject a drug into a skin upper layer part by sticking a needle tip from the skin surface. 
     BACKGROUND ART 
     Recently, human infection of bird flu has been reported, and heavy damage by human pandemic of bird flu is worried about. So, pre-pandemic vaccine that has a high possibility of being effective against bird flu is being stockpiled worldwide. Also, to administer pre-pandemic vaccine to many people, a study is being carried out on expanding the production quantity of vaccine. 
     Skin is composed of three parts, an epidermis, a dermis, and a subcutaneous tissue. The epidermis is a layer of about 50-200 μm from the skin surface, and the dermis is a layer of about 1.5-3.5 mm continuing from the epidermis. Because flu vaccine is generally subcutaneously or intramuscularly administered, it is administered to a lower layer part of skin or a portion deeper than that. 
     On the other hand, it has been reported that by administering flu vaccine to an upper layer part of skin as a target site where many immunocompetent cells are present, even if the dosage is reduced, the same immunity acquisition ability as in subcutaneous administration or intramuscular administration can be obtained (Non-patent Document 1). Thus, by administering pre-pandemic vaccine to the skin upper layer part, the dosage can be reduced, so that it will result in that pre-pandemic vaccine can be administered to more people. Note that the skin upper layer part refers to the epidermis and dermis of skin. 
     As the method of administering a drug to the skin upper layer part, methods using a single-needle, a multi-needle, a patch, gas, etc. have been reported. And, if stability and reliability of administration and production cost are considered, as the method of administering a drug to the skin upper layer part, the method using a single needle is regarded most suitable. As the method of administering vaccine to the skin upper layer part using a single needle, a Mantoux method has been known from a long time ago. The Mantoux method is a method in which a needle, generally 26-27 G in size and having a short bevel needle tip, is inserted into skin about 2-5 mm, from an oblique direction of about 10-15° relative to the skin, to administer a drug of about 100 μl. 
     However, the Mantoux method is difficult in manipulation, and the rate of success is left in the skill of the doctor giving an injection. In particular, a child has a possibility of moving at the time of administration, so that it is difficult to administer flu vaccine with the Mantoux method. Accordingly, it is desired that a device is developed that can administer vaccine to the skin upper layer part in a simple and convenient manner. 
     Patent Document 1 describes an injection device for the skin upper layer part in which a limiter having a skin contacting surface is connected with a needle hub. The limiter described in Patent Document 1 is provided around a needle tube, and has a gap with the needle tube. By regulating the length (protrusion length) of the needle tube protruding from the surface of the limiter contacting the skin to 0.5-3.0 mm, the drug is administered in the skin. 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-137343 
     Non-patent Document 1: R. T. Kenney et al. New England Journal of Medicine, 351, 2295-2301 (2004) 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the injection device described in Patent Document 1, because the needle tip of the needle tube protrudes from the surface of the limiter contacting the skin, there has been a problem that after the drug has been administered or when discarding the injection device, the needle tip of the needle tube might be accidentally stuck into the user. 
     The present invention aims in view of the above-described problems to provide an injection needle assembly and a drug injection device that prevent the needle tip of the needle tube from being accidentally stuck into the user after the drug has been administered or when discarding the drug injection device. 
     Means for Solving the Problems 
     To solve the above-described problems and achieve the object of the present invention, an injection needle assembly of the present invention includes a needle tube having a needle tip capable of being stuck into a living body, and a hub holding the needle tube. The injection needle assembly further includes a stabilization unit arranged so as to cover the circumference of the needle tube in a condition that the needle tip of the needle tube protrudes. The stabilization unit has an end face that contacts a skin when causing the needle tube to be stuck into the living body. The injection needle assembly unit further includes a housing unit movable along an axial direction of the needle tube from a first position where the needle tip of the needle tube is exposed to a second position where the needle tip of the needle tube is housed. 
     A drug injection device of the present invention includes a needle tube having a needle tip capable of being stuck into a living body; a hub configured to hold the needle tube; and a syringe configured to be connected with the hub. The drug injection device further includes a stabilization unit arranged so as to cover the circumference of the needle tube in a condition that the needle tip of the needle tube protrudes, the stabilization unit having an end face that contacts a skin when causing the needle tube to be stuck into the living body; and a housing unit movable along an axial direction of the needle tube from a first position where the needle tip of the needle tube is exposed to a second position where the needle tip of the needle tube is housed. 
     Effects of the Invention 
     According to the injection needle assembly and the drug injection device of the present invention, a housing unit for housing the needle tip of the used needle tube is provided. As a result, it is possible to hold the injection needle assembly and the drug injection device after use in a safe condition, and it can be prevented that the needle tip of the needle tube is caused to be stuck in the user contrary to the user&#39;s intentions after administering the drug. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a first embodiment of an injection needle assembly of the present invention. 
         FIG. 2  is a cross-sectional view illustrating the first embodiment of the injection needle assembly of the present invention. 
         FIG. 3  is a perspective view illustrating the first embodiment of the injection needle assembly with a housing unit thereof removed. 
         FIG. 4  is a perspective view illustrating the housing unit of the injection needle assembly according to the first embodiment of the present invention. 
         FIG. 5  is a perspective view illustrating an outer housing unit of the injection needle assembly according to the first embodiment of the present invention, when viewed from the opposite side. 
         FIG. 6  is a perspective view illustrating the first embodiment of the injection needle assembly with the outer housing unit and the inner housing unit moved to a second position. 
         FIG. 7  is a cross-sectional view illustrating the first embodiment of the injection needle assembly with the outer housing unit and the inner housing unit moved to the second position. 
         FIG. 8  is a perspective view illustrating a second embodiment of the injection needle assembly of the present invention. 
         FIG. 9  is a perspective view illustrating the second embodiment of the injection needle assembly of the present invention with the outer housing unit moved to the second position. 
         FIG. 10  is a perspective view illustrating a third embodiment of the injection needle assembly of the present invention. 
         FIG. 11  is a cross-sectional view illustrating a third embodiment of the injection needle assembly of the present invention assembly before being used. 
         FIG. 12  is a perspective view illustrating the third embodiment of the injection needle assembly of the present invention with the inner housing unit moved to the second position. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Below, description will be made, referring to  FIG. 1  through  FIG. 12 , with respect to embodiments of an injection needle assembly and a drug injection device of the present invention. Note that the common parts in respective drawings are denoted by the same references numerals. The present invention is not limited to the following embodiments. The description will be made in the following order. 
     1. First embodiment 
     1.1. Exemplary constitutions of an injection needle assembly and a drug injection device 
     1.2. Method of using a drug injection device 
     2. Second embodiment 
     3. Third embodiment 
     1. First Embodiment 
     1.1. Exemplary Constitutions of an Injection Needle Assembly and a Drug Injection Device 
     First, referring to  FIG. 1  through  FIG. 5 , description is made with respect to an injection needle assembly and a drug injection device according to the first embodiment of the present invention. 
       FIG. 1  is a perspective view illustrating the injection needle assembly of the present embodiment,  FIG. 2  is a cross-sectional view illustrating the injection needle assembly of the present embodiment,  FIG. 3  is a perspective view illustrating the injection needle assembly of the present embodiment with an outer housing unit thereof removed, and  FIG. 4  and  FIG. 5  are perspective views illustrating the outer housing unit of the present embodiment. 
     As illustrated in  FIG. 1  and  FIG. 2 , an injection needle assembly  1  includes a hollow needle tube  2 , a hub  3  that holds the needle tube  2 , an adjustment unit  4  fixed to the needle tube  2 , a stabilization unit  6 , an outer housing unit  7  and an inner housing unit  8  that are movable along an axial direction of the needle tube  2 , and an a guide unit  9 . By connecting a syringe  11  to the hub  3 , the injection needle assembly  1  is constituted as a drug injection device of the present invention (see  FIG. 2 ). 
     [Needle Tube] 
     For the needle tube  2 , a needle tube with the size of 26-33 G (outer diameter: 0.2-0.45 mm) by ISO standard for medical needle tubes (ISO9626: 1991/Amd.1:2001(E)), preferably the one with the size of 30-33 G, is used. At the tip end part of the needle tube  2 , a blade face  2   a  for making the needle tip acute-angled is formed. The blade face  2   a  may be of any length in the direction that the needle tube  2  extends (hereinafter, called “bevel length B”, shown in  FIG. 2 ) so long as it is 1.4 mm or below, which is the thinnest thickness of the later-described skin upper layer part in adults, and about 0.5 mm or above, which is the bevel length when a short bevel has been formed in the needle tube of 33 G. That is, the bevel length B is preferably set in the range of 0.5-1.4 mm. 
     Further, the bevel length B is more preferably 0.9 mm or below, which is the thinnest thickness of the skin upper layer part in children, that is, in the range of 0.5-0.9 mm. Note that the short bevel refers to a blade face forming 18-25° with respect to the longitudinal direction of the needle, which is generally used in injection needles. 
     As the materials of the needle tube  2 , for example, stainless steel can be given, but the materials are not limited to this, and aluminum, aluminum alloy, titanium, titanium alloy, and other metals may be used. Also, for the needle tube  2 , a straight needle, and a tapered needle in which at least a portion thereof is tapered may be applied. 
     The tapered needle may be configured such that the base end portion that is fixed to the hub has a larger outer diameter compared with the tip end portion including the needle tip, and the middle portion thereof is tapered. Further, by providing the adjustment unit in the tapered portion, because of the existence of the slope of the tapered portion, the adjustment unit is prevented from being moved toward the base end. Thereby, even if the needle-protruding surface is strongly pressed against the skin, the length that the needle tip protrudes from the needle-protruding surface will never change, and the needle can be surely stuck to a predetermined depth of the skin. 
     The tube hole of the needle tube  2  is communicated with the hub  3 . The hub  3  includes a hub body  3   a  that holds the needle tube  2 , and a flange  3   b  that continues from the hub body  3   a.  The hub body  3   a  is tapered so as to be made smaller toward the tip end. At the tip end part of the hub body  3   a,  the base end part of the needle tube  2  is fixed. The flange  3   b  is provided at the base end part of the hub body  3   a.  The stabilization unit  6  is fixed to the flange  3   b.  The hub  3  may be in any form so long as it can be connected with the syringe  11 . 
     The syringe  11  may be such a syringe that is to be filled with a drug when using the drug injection device, or a pre-filled syringe filled with a drug in advance. Also, as the drug that is filled in the syringe  11 , vaccine may be cited, however, the drug may be those using macromolecular substances such as cytokine, etc., or hormones. 
     [Adjustment Unit] 
     The adjustment unit  4  is formed in a cylindrical shape. The needle tube  2  penetrates through the adjustment unit  4 , and the shaft center of the needle tube  2  and the shaft center of the adjustment unit  4  coincide with each other. The adjustment unit  4  is fixed in close contact with the circumferential surface of the needle tube  2 . One end surface of the adjustment unit  4  forms a hub-opposing surface  4   a  opposing the hub  3  and the other end surface of the adjustment unit  4  forms a flat needle-protruding surface  4   b  from which the needle tip of the needle tube  2  protrudes. 
     In the hub-opposing surface  4   a  of the adjustment unit  4 , a concave part  4   c  for adhesive agent is provided so as to surround the circumference of the needle tube  2 . The adjustment unit  4  is fixed in close contact with the circumferential surface of the needle tube  2  by coating an adhesive agent  5  in the concave part  4   c  for adhesive agent in the state that the needle tube has penetrated through. As the adhesive agent  5 , cyanoacrylate, epoxy resin, light curing resin, etc. may be cited, however, the adhesive agent  5  may be those made of other resin. 
     The needle-protruding surface  4   b  of the adjustment unit  4  contacts the surface of skin and defines the depth the needle tube  2  is stuck, when the needle tube  2  is stuck into the skin upper layer part. That is, the depth that the needle tube  2  is stuck into the skin is determined by the protrusion length of the needle tube  2  from the needle-protruding surface  4   b.  Hereinafter, this length is called a protrusion length L. 
     The thickness of the skin upper layer part corresponds to the depth of the epidermis layer and the dermis layer from the skin surface, which is generally in the range of 0.5-3.0 mm. Therefore, the protrusion length L of the needle tube  2  can be set in the range of 0.5-3.0 mm. 
     Further, the thickness of the skin upper layer part of a deltoid muscle, which is a flu vaccine administration cite, was measured with respect to  19  children and  31  adults. Using an ultrasonic measurement device (NP60R-UBM high-resolution echo for small animals, NEPA GENE, CO., LTD.), the skin upper layer part having high ultrasonic reflectivity was imaged and the thickness thereof was measured. Here, because the measured values showed log-normal distribution, the range of MEAN±2SD was obtained by geometrical mean. The result showed 0.9-1.6 mm with respect to children, and with respect to adults, the results were 1.4-2.6 mm in the far part, 1.4-2.5 mm in the middle part, and 1.5-2.5 mm in the near part. From the above, the thickness of the skin upper layer part of the deltoid muscle was confirmed as 0.9 mm or above in the case of children and 1.4 mm or above in the case of adults. Consequently, in injection in the skin upper layer part of the deltoid muscle, the preferable protrusion length L of the needle tube  2  can be set in the range of 0.9-1.4 mm. 
     Further, by setting the protrusion length L of the needle tube  2  in this manner, it becomes possible to securely position the blade face  2   a  in the skin upper layer part. As a result, the medicinal solution discharging outlet opened in the blade face  2   a  can be positioned in the skin upper layer part, regardless of its position in the blade face  2   a.  Note that even when the medicinal solution discharging outlet is located in the skin upper layer part, if the needle tip is stuck deeper than the skin upper layer part, the medicinal solution escapes to the outside of the skin upper layer part (e.g., to the subcutaneous tissue) from between the side face of the needle tip end part and the incised skin. For this reason, it is important that the needle tip of the needle tube  2  and the blade face are securely located in the skin upper layer part. 
     Note that in the case of a needle tube larger than 26 G, it is difficult to make the bevel length B 1.0 mm or smaller. Accordingly, to set the protrusion length L of the needle tube  2  in the preferable range (0.9-1.4 mm), it is desirable to use a needle tube that is smaller than 26 G. 
     The needle-protruding surface  4   b  of the adjustment unit  4  is formed such that the distance S from the circumferential edge to the circumferential surface of the needle tube  2  is 1.4 mm or below, preferably in the range of 0.3-1.4 mm. This distance S from the circumferential edge of the needle-protruding surface  4   b  to the circumferential surface of the needle tube  2  is set considering that the needle protruding surface  4   b  depresses the skin around the needle tube  2  and pressure is given to a blister formed in the skin upper layer part. Thereby, when the needle-protruding surface  4   b  depresses the skin around the needle tube  2 , it can be prevented that the administered drug leaks to the outside of the skin. 
     As the material of the adjustment unit  4 , synthetic resin (plastic), such as polycarbonate, polypropylene, polyethylene, etc., maybe used, or metals such as stainless, aluminum, etc. may be used. 
     In the present embodiment, the adjustment unit  4  has been fixed to the needle tube  2  using the adhesive agent  5 , however, as the injection needle assembly of the present invention, the adjustment unit  4  may be fixed to the needle tube  2  by another method. For example, such methods are conceivable that the adjustment unit  4  is formed of metal and is fixed to the needle tube  2  by caulking, welding, etc., and that the adjustment unit  4  is formed of synthetic resin and is fixed to the needle tube  2  by welding and integral molding (especially, insert molding). Note that the adjustment unit  4  is not essential for solving the problems to be solved by the present invention, and the problems to be solved by the present invention can be solved without providing the adjustment unit  4  to the needle tube  2 . 
     [Stabilization Unit] 
     As illustrated in  FIG. 3 , the stabilization unit  6  has a shape that two circular cylinders that are different in diameter axially continue in series. The needle tube  2 , the hub  3 , and the adjustment unit  4  are arranged in the cylindrical hole of the stabilization unit  6 . The stabilization unit  6  includes a fixing part  6   a  that is fixed to the hub  3  and a contact part  6   b  that covers the circumference of the needle tube  2  and the adjustment unit  4 . One end portion of the fixing part  6   a  is fixed to the flange  3   b  of the hub  3  by a fixing method, such as an adhesive, etc. The hub body  3   a  of the hub  3  is housed in the cylindrical hole of the fixing part  6   a.  The contact part  6   b  is provided on the other end side of the fixing part  6   a  continuing circumferentially. 
     The contact part  6   b  is arranged so as to surround the circumference of the needle tube  2  and the adjustment unit  4  by fixing the fixing unit  6   a  to the hub  3 . The inner diameter of the contact part  6   b  is set so as to be larger than the internal diameter of the fixing unit  6   a.  Returning to  FIG. 2 , an end face  6   c  on the one end side in the axial direction of the contact part  6   b  is located substantially on the same plane as the needle protruding surface  4   b  of the adjustment unit  4 . And, the needle tube  2  is perpendicular to the plane formed by the end face  6   c  of the stabilization unit  6  and the needle protruding surface  4   b  of the adjustment unit  4 . 
     Accordingly, when the needle tube  2  has been stuck into a living body, the needle protruding surface  4   b  of the adjustment unit  4  contacts the surface of skin, and the end face  6   c  of the stabilization unit  6  also contacts the surface of skin. Thereby, it is possible to support the needle tube  2  substantially perpendicular to the skin by the stabilization unit  6 . As a result, it can be prevented that the needle tube  2  deviates, and it is enabled to cause the needle tube  2  to be stuck straight to the skin. 
     Note that the needle protruding surface  4   b  of the adjustment unit  4  does not need to be located on the same plane as the end face  6   c  of the stabilization unit  6 . That is, even if the needle protruding surface  4   b  of the adjustment unit  4  is located on the other end side (on the fixing part  6   a  side) in the axial direction of the contact part  6   b  relative to the end face  6   c,  the object of the present invention can be attained. If a bulge of skin when the stabilization unit  6  is depressed to the skin is considered, it is preferable to set the distance in the axial direction of the contact part  6   b  between the planes formed by the needle protruding surface  4   b  of the adjustment unit  4  and the end face  6   c,  respectively, to 1.3 mm or below. 
     The inner diameter d of the contact part  6   b  of the stabilization unit  6  is set at a value equivalent to the diameter of a blister which is formed in the skin or larger than that. Specifically, the inner diameter d is set such that the distance T from the internal wall surface of the contact part  6   b  to the outer circumferential surface of the adjustment unit  4  is in the range of 4-15 mm. Thereby, it is possible to prevent that pressure is applied from the internal wall of the stabilization unit  6  to a blister and formation of the blister is thereby disturbed by the stabilization unit  6 . 
     There is no upper limit for the distance T from the internal wall surface of the stabilization unit  6  to the outer circumferential surface of the adjustment unit  4  so long as it is 4 mm or above. However, if the distance T is increased, the outer diameter of the stabilization unit  6  and the outer diameter of the contact part  6   b  increase. If the outer diameter of the contact part  6   b  is increased, when sticking the needle tube  2  to a thin arm as in a child, it becomes difficult to cause the end face  6   c  of the contact unit  6   b  to contact the skin. Accordingly, when the thinness of children&#39;s arms is considered, it is preferable to specify the distance T from the internal wall surface of the stabilization unit  6  (contact part  6   b ) to the outer circumferential surface of the adjustment unit  4  to 15 mm at the maximum. 
     Also, if the distance S from the circumferential edge of the needle protruding surface  4   b  of the adjustment unit  4  to the circumferential surface of the needle tube  2  is 0.3 mm or above, the needle tube  2  will never penetrate the skin. Accordingly, if the distance T (4 mm or above) from the internal wall surface of the contact part  6   b  to the outer circumferential surface of the adjustment unit  4  and the diameter (about 0.3 mm) of the needle tube  2  are considered, the internal diameter d of the contact part  6   b  can be set to 9 mm or above. 
     Further, in the contact part  6   b,  four sliding grooves  6   d  are formed by making cuts in the axial direction from the end face  6   c.  The four sliding grooves  6   d  are arranged in the contact part  6   b  substantially at equal intervals. Also, an engaging groove  6   e  is provided in the outer circumferential surface on the other end side of the contact part  6   b.  The engaging groove  6   e  is formed continuing along the circumferential direction of the contact part  6   b.  Also, the outer housing unit  7  is arranged so as to cover the circumference of the stabilization unit  7 . 
     [Outer Housing Unit and Inner Housing Unit] 
     As illustrated in  FIG. 4  and  FIG. 5 , the outer housing unit  7  includes a covering part  7   a  to house the needle tube  2  after use, and four leg parts  7   b.  The covering part  7   a  is formed substantially in a cylindrical shape, and the internal diameter thereof is set slightly larger than the outer diameter of the contact part  6   b  of the stabilization unit  6 . The four leg parts  7   b  are arranged at substantially equiangular intervals at the other end in the axial direction of the covering part  7   a  and protrude in the axial direction of the covering part  7   a.  At end parts of the four leg parts  7   b,  engaging claws  7   c  to be fixed to the engaging groove  6   e  of the stabilization unit  6  (see  FIG. 3 ) are provided, respectively. That is, a fixing mechanism is constituted by the engaging groove  6   e  of the stabilization unit  6  and the engaging claws  7   c  of the outer housing unit  7 . 
     Further, the inner housing unit  8  is arranged in the tube hole of the covering part  7   a  of the outer housing unit  7 . As illustrated in  FIG. 2 , the inner housing unit  8  is arranged to cover the circumference of the needle tube  2  between the contact part  6   b  of the stabilization unit  6  and the needle tube  2 . The inner housing unit  8  is formed in a substantially cylindrical shape, and includes one end face  8   a  in a substantially circular shape at one end in the axial direction thereof, and other end face  8   b  that opposes the one end face  8   a.  An insertion hole  8   c  connecting substantially centers of the one end face  8   a  and the other end face  8   b  is formed. The needle tube  2  and the adjustment unit  4  are inserted in the insertion hole  8   c.  Further, the inner housing unit  8  is formed integrally with the outer housing unit  7  through four connection pins  12 . 
     The four connection pins  12  are arranged at substantially equal intervals at the internal wall of the outer housing unit  7 , and are inserted in the four sliding grooves  6   d  of the stabilization unit  6 . The four connection pins  12  are slidable along the four sliding grooves  6   d  of the stabilization unit  6 . The four connection pins  12  slide along the four sliding grooves  6   d,  and thereby the outer housing unit  7  and the inner housing unit  8  are made to be slidable along the axial direction of the needle tube  2  and the stabilization unit  6 . 
     Returning to  FIG. 1  and  FIG. 2 , in a state before the drug is administered in the human body, the outer housing unit  7  and the inner housing unit  8  are arranged in positions where the other end face  8   b  of the inner housing unit  8  and the internal wall surface  6 f of the stabilization unit  6  contact each other. Herein below, this position is referred to as “a first position”. When the outer housing unit  7  and the inner housing unit  8  are arranged in the first position, the needle tip of the needle tube  2  protrudes from the outer housing unit  7  and the inner housing unit  8  and is exposed. Therefore, when the outer housing unit  7  and the inner housing unit  8  are arranged in the first position, the needle tip of the needle tube  2  can be stuck to the living body. 
     Further, a guide part  9  is integrally formed in the outer circumferential surface of the covering part  7   a  of the outer housing unit  7 . The guide part  9  is provided at the one end side in the axial direction of the covering part  7   a  continuously along the circumferential direction of the outer circumferential surface of the covering part  7   a.  The guide part  9  is formed as a ring-like flange protruding from the outer circumferential surface of the outer housing unit  7  in the outward radial direction, substantially perpendicularly. The guide part  9  includes a contact surface  9   a  that contacts the skin. The contact surface  9   a  is a flat surface that is substantially parallel to the end face  6   c  of the stabilization unit  6 . 
     By causing the stabilization unit  6  to be pressed to skin until the contact surface  9   a  of the guide part  9  contacts the skin, it is possible to ensure that the force the stabilization unit  6  and the needle tube  2  press the skin is always at a predetermined value or above. Thereby, the part of the needle tube  2  protruding from the needle protruding surface  4   b  (corresponding to the protrusion length L) is surely stuck in the skin. And, the distance from the contact surface  9   a  of the guide part  9  to the end face  6   c  of the stabilization unit  6  in a state that the outer housing unit  7  is arranged in the first position is set such that the needle tube  2  and the stabilization unit  6  are pressed to skin with an appropriate pressing force and thereby the part of the needle tube  2  protruding from the needle protruding surface  4   b  can be surely stuck in the skin. Hereinafter, the length of this distance is referred to as “a guide part height y”. 
     Note that the appropriate pressing force of the needle tube  2  and the stabilization unit  6  for causing the part of the needle tube  2  protruding from the needle protruding surface  4   b  to be surely stuck in the skin is, for example, 0.5-20 N. As a result, effects are obtained that the guide part  9  can ensure that the pressing force applied by the needle tube  2  and the stabilization unit  6  to the skin is always at a predetermined value or above by being caused to contact the skin and the needle tip and blade face  2   a  of the needle tube  2  can be securely positioned in the skin upper layer part, thereby giving the user a sense of safety. 
     As shown in  FIG. 2 , specifically, when the internal diameter d of the stabilization unit  6  is within the range of 12-14 mm, the guide part height y is in the range calculated according to the following expression 1 based on a length x from the protruding end face of the guide part  9  to the outer circumferential surface of the stabilization unit  6  (below, called a guide part length x). 
       1.0  Ln ( x )+1.2&lt; y &lt;3.1  Ln ( x )+3.2 
     Note that when the internal diameter d of the stabilization unit  6  is 11 mm, the guide part height y is set, for example when the guide part length x is 0.5 mm, in the range of 0.75-2.6 mm. 
     As the material for the stabilization unit  6 , the outer housing unit  7 , and the inner housing unit  8 , as in the adjustment unit  4 , synthetic resin (plastic), such as polycarbonate, polypropylene, polyethylene, etc., may be used, or metals such as stainless steel, aluminum, etc. may be used. 
     The shape of the stabilization unit  6  is not limited to the circular cylinder, and the stabilization unit  6  may be formed, for example, in a rectangular cylinder, such as a square cylinder, a hexagonal cylinder, etc., having a cylindrical hole in the center. Also, the shapes of the outer housing unit  7  and the inner housing unit  8  are set correspondingly to the shape of the stabilization unit  6 . Further, description has been made with respect to the case that four pieces of the sliding grooves  6   d  and the connection pins  12  are formed, respectively, however, the numbers of the sliding grooves  6   d  and the connection pins  12  may be three or below, or five or more, respectively. Also, description has been made for the case that the outer housing unit  7  and the inner housing unit  8  are integrally formed, however, the outer housing unit  7  and the inner housing unit  8  may be separate members. In addition, description has been made with respect to the case that the engaging groove  6   e  that constitutes the fixing mechanism is continuously formed along the circumferential direction of the contact part  6   b,  however, a plurality of concave parts to be engaged with the engaging claws  7   c,  respectively, may be formed in the outer circumferential surface of the contact part  6   b.    
     Further, description has been made with respect to the case that the stabilization unit  6  is fixed to the hub  3 , however, the stabilization unit  6  may be fixed to the syringe  11  constituting a drug injection device. Also, in the present example, the stabilization unit  6  is fixed to the hub  3  using an adhesive agent, however, the stabilization unit  6  may be fixed to the hub  3  by another method. For example, as the method for forming the stabilization unit  6  with metal and fixing the stabilization unit  6  to the hub  3 , caulking, etc. may be cited. Also, as the method for forming the stabilization unit  6  with synthetic resin and fixing the stabilization unit  6  to the hub  3 , welding and integral molding (in particular, insert molding including the needle tube  2 ) may be cited. 
     1.2. Method of Using a Drug Injection Device 
     Next, description will be made with respect to a method of using a drug injection device to which the injection needle assembly  1  has been applied, referring to  FIG. 1 ,  FIG. 2 ,  FIG. 6 , and  FIG. 7 . 
     First, the end face  6   c  of the stabilization unit  6  is caused to face the skin. Thereby, the needle tip of the needle tube  2  faces the skin to which the needle tip is stuck. Note that as illustrated in  FIG. 1  and  FIG. 2 , the outer housing unit  7  and the inner housing unit  8  are arranged in the first position, respectively, and the needle tip of the needle tube  2  is exposed. Next, the injection needle assembly  1  is moved substantially perpendicularly to the skin, the needle tube  2  is stuck into the skin, and the end face  6   c  of the stabilization unit  6  is pressed to the skin. Here, the needle protruding surface  4   b  of the adjustment unit  4  and the end face  6   c  of the stabilization unit  6  are on the same plane. Thereby, the needle protruding surface  4   b  of the adjustment unit  4  can contact the skin and deform the skin so as to be flat, and the needle tube  2  can be stuck into the skin by the protrusion length L. 
     Next, the stabilization unit  6  is pressed to skin until the contact surface  9   a  of the guide part  9  contacts the skin. Here, the guide part height y is set such that the needle tube  2  and the stabilization unit  6  are pressed to skin with an appropriate pressing force and the part of the needle tube  2  protruding from the needle protruding surface  4   b  is surely stuck into the skin. Therefore, the force to press the skin with the stabilization unit  6  becomes a predetermined value. Accordingly, it is possible to ensure that the pressing force of the stabilization unit  6  to the skin is at a predetermined value by causing the guide part  9  to contact the skin and press the stabilization unit  6  to the skin with a suitable pressing force, and the needle tip and the blade face  2   a  of the needle tube  2  can be surely positioned in the skin upper layer part. Thus, since the guide part  9  serves as a mark for ensuring that the pressing force of the stabilization unit  6  is at a predetermined value by being caused to contact the skin, it is possible to reliably position the needle tip of the needle tube  2  in the skin upper layer part, administer the drug in the skin upper layer part, and improve the sense of safety of the user. 
     Also, by causing the stabilization unit  6  to contact the skin, the needle tube  2  is stabilized, and the needle tube  2  can be stuck straight to the skin. Accordingly, deviation caused in the needle tube  2  can be prevented, and stable administration of drug can be carried out. Also, with the needle having a very short protrusion length of about 0.5 mm for example, even if the needle tip is caused to contact the skin, there is a case that the needle tip is not stuck into the skin. However, if the stabilization unit  6  is pressed to the skin and the skin is depressed in a perpendicular direction, the skin on the inner side of the stabilization unit  6  is pulled and put in a condition that a tensional force has been applied to the skin. Therefore, the skin becomes hard to flee from the needle tip of the needle tube  2 , so that the stabilization unit  6  has an effect that it becomes easier for the needle tip to be stuck into the skin. 
     Further, the protrusion length L being set in the range of 0.5-3.0 mm, the needle tip and the blade face  2   a  of the needle tube  2  are reliably positioned in the skin upper layer part. Thereafter, a drug is injected into the skin upper layer part with the syringe  11  connected with the hub  3 . 
     The adjustment unit  4  of the injection needle assembly  1  is fixed in close contact with the circumference of the needle tube  2 , and there is no gap between the adjustment part  4  and the part of the needle tube  2  penetrating the adjustment part  4 . Therefore, if the needle protruding surface  4   b  of the adjustment unit  4  is caused to contact the skin, the skin around the needle tube  2  can be deformed to be flattened. As a result, the needle tube  2  can be stuck in the skin by the protrusion length L, and the needle tip of the needle tube  2  can be reliably positioned in the skin upper layer part. 
     Further, because the needle protruding surface  4   b  of the adjustment unit  4  and the internal diameter d of the stabilization unit  6  are set in suitable sizes, it becomes possible to cause the injected drug not to leak to the outside of the body, and the drug can be reliably administered in the skin upper layer part. 
     Next, as illustrated in  FIG. 6  and  FIG. 7 , the outer housing unit  7  and the inner housing unit  8  of the injection needle assembly  1  after administering the drug are caused to slide along the axial direction of the needle tube  2 , and the engaging claws  7   c  are fixed in the engaging groove  6   e.  Below, the position of the outer housing unit  7  and the inner housing unit  8  at this time is referred to as “a second position”. Note that because a clicking feeling and a clicking sound are generated when fixing the engaging claws  7   c  in the engaging groove  6   e,  the user can confirm that the outer housing unit  7  and the inner housing unit  8  have been surely moved to the second position. Here, the end part of the covering part  7   a  and the one end face  8   a  of the inner housing unit  8  are located on the distal end side beyond the needle tip of the needle tube  2 . That is, the needle tube  2  is housed in the covering part  7   a  of the outer housing unit  7  and the insertion hole  8   c  of the inner housing unit  8 . As a result, it becomes possible to prevent that the needle tip of the needle tube  2  is stuck in the living body contrary to user&#39;s intents. 
     Here, the inner housing unit  8  moves integrally with the outer housing unit  7 , and is arranged so as to close an opening of the covering part  7   a  of the outer housing unit  7 . That is, the inner housing unit  8  is arranged so as to fill the space between the outer housing unit  7  and the needle tube  2 , and thereby it is possible to prevent that the finger tip, etc. of the user enters into the cylinder hole of the stabilization unit  6  from the opening of the covering part  7   a.  Thereby, the needle tube  2  of the injection needle assembly  1  after use can be housed in a safer condition. 
     Also, by fixing the engaging claws  7   c  in the engaging groove  6   e,  it is prevented that the outer housing unit  7  and the inner housing unit  8  move from the second position to the first position. Therefore, there is no fear that the needle tube  2  housed in the outer housing unit  7  and the inner housing unit  8  protrudes from the outer housing unit  7  and the inner housing unit  8  again and is exposed. Thereby, it is possible to keep the injection needle assembly  1  after use always in a safe condition, and the user can carry out disposal, etc. of the used injection needle assembly  1  at ease. 
     2. Second Embodiment 
     Next, referring to  FIG. 8  and  FIG. 9 , description will be made with respect to an injection needle assembly according to the second embodiment of the present invention. 
       FIG. 8  and  FIG. 9  are perspective views showing the injection needle assembly according to the second embodiment of the present invention. 
     An injection needle assembly  20  according to the second embodiment is constituted by removing the inner housing unit  8  of the injection needle assembly  1  according to the first embodiment and providing a guide part on a stabilization unit. Therefore, here, description will be made with respect to a stabilization unit, a guide part, and an outer housing unit, and the common parts with the injection needle assembly  1  are denoted with the same reference numerals and overlapped part of description will be omitted. 
     Note that the injection needle assembly  20  according to the second embodiment constitutes a drug injection device of the present invention by connecting a syringe to the hub  3  as in the above-described first embodiment. 
     As illustrated in  FIG. 8 , a stabilization unit  21  has a shape that two circular cylinders different in diameter continue in series in the axial direction. The needle tube  2 , the hub  3 , and the adjustment unit  4  are arranged in the cylindrical hole of the stabilization unit  21 . The stabilization unit  21  includes a fixing part  21   a,  which is fixed to the hub  3 , and a contact part  21   b  covering the circumference of the needle tube  2  and the adjustment unit  4 . Further, although not shown in figure, an engaging groove or engaging concave part which constitutes a fixing mechanism is provided in the stabilization unit  21 . 
     A guide part  22  is integrally molded in the outer circumferential surface of the contact part  21   b  of the stabilization unit  21 . The guide part  22  is provided continuing along the circumferential direction of the outer circumferential surface of the contact part  21   b  of the stabilization unit  21 . The guide part  22  is formed as a flange in a ring-like shape protruding from the outer circumferential surface of the stabilization unit  21  substantially perpendicularly in the outward radial direction. The guide part  22  includes a contact surface  22   a  which contacts the skin. 
     Further, three opening parts  22   b  are provided in the guide part  22  at substantially equiangular intervals. The three opening parts  22   b  are opened in the outward radial direction from the outer circumferential surface of the contact part  21   b.  An outer housing unit  23  is slidably arranged so as to cover the outer circumference of the stabilization unit  21 . 
     The outer housing unit  23  is formed in a substantially circular cylinder shape, and the internal diameter thereof is set slightly larger than the outer diameter of the contact part  21   b  of the stabilization unit  21 . The outer housing unit  23  is cutout in three places at substantially equal intervals in the axial direction, and thereby three covering parts  23   a  are formed. These three covering parts  23   a  are slidably inserted in the three opening parts  22   b  of the guide part  22 . Thereby, the outer housing unit  23  is supported slidably along the axial direction of the stabilization unit  21  and the needle tube  2 . 
     Also, although not shown in figure, protrusions that constitute a fixing mechanism are provided in the internal wall of the outer housing unit  23 . The protrusions are engaged with the engaging groove or engaging concave part provided in the stabilization unit  21 . By causing the protrusions and the engaging groove or engaging concave part to be engaged with each other, it is prevented that the outer housing unit  23  moves from the second position where the needle tube  2  is housed to the first position where the needle tube  2  is exposed. 
     As illustrated in  FIG. 8 , before use, the outer housing unit  23  is arranged in the position, which is the first position, where end faces of the three covering part  23   a  are substantially in the same plane with the contact surface  22   a  of the guide part  22 . Then, as illustrated in  FIG. 9 , after administering the drug, the outer housing unit  23  is slid to the second position to cover the outer circumference of the needle tube  2  with the covering parts  23   a.  Thereby, the needle tube  2  can be housed in the outer housing unit  23 , and the injection needle assembly  20  after use can be put in a safe condition. 
     Note that in the injection needle assembly  20  according to the second embodiment also, as in the injection needle assembly  1  according to the above-described first embodiment, an inner housing unit, which is slidably supported between the stabilization unit  21  and the needle tube  2 , may be provided. 
     The constitution of other parts of the injection needle assembly  20  is similar to that of the injection needle assembly  1  according to the first embodiment, so that description thereof is omitted. With the injection needle assembly  20  having such constitution also, it is possible to obtain functions and effects similar to those of the injection needle assembly  1  according to the above-described first embodiment. 
     3. Third Embodiment 
     Next, referring to  FIG. 10 ,  FIG. 11 , and  FIG. 12 , description will be made with respect to an injection needle assembly according to the third embodiment of the present invention. 
       FIG. 10  is a perspective view illustrating the injection needle assembly according to the third embodiment of the present invention, and  FIG. 11  and  FIG. 12  are cross-sectional views illustrating the injection needle assembly according to the third embodiment of the present invention. 
     As illustrated in  FIG. 10  and  FIG. 11 , an injection needle assembly  30  according to the third embodiment is constituted by removing the outer housing unit from the injection needle assembly  1 . Therefore, here, description will be made with respect to a stabilization unit, a guide part, and an inner housing unit, and the common parts with the injection needle assembly  1  are denoted with the same reference numerals and overlapped part of description will be omitted. 
     Note that the injection needle assembly  30  according to the third embodiment constitutes a drug injection device of the present invention by connecting a syringe to the hub  3  as in the above-described first embodiment. 
     As illustrated in  FIG. 10 , a stabilization unit  31  has a shape that two circular cylinders different in diameter continue in series in the axial direction. The needle tube  2 , the hub  3 , and the adjustment unit  4  are arranged in the cylindrical hole of the stabilization unit  31 . The stabilization unit  31  includes a fixing part  31   a,  which is fixed to the hub  3 , and a contact part  31   b  covering the circumference of the needle tube  2  and the adjustment unit  4 . 
     Further, a first engaging groove  31   c  and a second engaging groove  31   d  are provided in the outer circumferential surface of the fixing part  31   a.  The second engaging groove  31   d  is arranged closer to the contact part  31   b  of the fixing part  31   a  than the first engaging groove  31   c.    
     A guide part  32  is integrally formed in the outer circumferential surface of the contact part  31   b  of the stabilization unit  31 . The guide part  32  is continuously provided along the circumferential direction of the outer circumferential surface of the contact part  31   b  of the stabilization unit  31 . The guide part  32  is formed as a flange in a ring-like shape protruding from the outer circumferential surface of the stabilization unit  31  substantially perpendicularly in the outward radial direction. The guide part  32  includes a contact surface  32   a  which contacts the skin. 
     Further, opening portions  33  are provided at substantially equiangular intervals at places where the contact part  31   b  and the fixing part  31   a  connect with each other. Leg parts  38   b  of an inner housing unit  38  described later movably penetrate through the opening portions  33 . 
     The inner housing unit  38  includes a covering part  38   a  which houses the needle tube  2  after use, and a plurality of leg parts  38   b  provided continuously from the covering part  38   a.  The covering part  38   a  is formed in a substantially circular cylinder shape. The diameter of the covering part  38   a  is set smaller than the internal diameter of the contact part  31   b.  A connection part  38   d  is provided from one end in the axial direction of the covering part  38   a.  The connection part  38   d  protrudes from the outer circumferential surface of the covering part  38   a  substantially perpendicularly in the outward radial direction. The plurality of leg parts  38   b  are arranged at substantially equiangular intervals from the circumferential edge of the connection part  38   d,  and protrude in the opposite direction of the covering part  38   a.  Engaging claws  38   c,  which engage with the first engaging groove  31   c  and the second engaging groove  31   d  of the stabilization unit  31 , are provided in end portions of the leg parts  38   b,  respectively. 
     As illustrated in  FIG. 11 , in a condition before use, the inner housing unit  38  is arranged such that the end face of the covering part  38   a  is positioned on the side of the fixing part  31   a  of the stabilization unit  31  than the needle tip of the needle tube  2 . That is, the inner housing unit  38  is arranged in the first position where the needle tip of the needle tube  2  is exposed. At this time, the engaging claws of the leg parts  38   b  are engaged with the first engaging groove  31   c  of the stabilization unit  31 . 
     Then, as illustrated in  FIG. 12 , after administering the drug, the inner housing unit  38  is moved to the second position by holding the leg parts  38   b  of the inner housing unit  38  to thereby cover the circumference of the needle tube  2  with the covering part  38   a.  Thereby, the needle tube  2  can be housed in the inner housing unit  38 , and the injection needle assembly  30  after use can be put in a safe condition. At this time, the engaging claws  38   c  of the leg part  38   b  are fixed in the second engaging groove  31   d  of the stabilization unit  31 . The second engaging groove  31   d  of the stabilization unit  31  and the engaging claws  38   c  of the inner housing unit  38  constitute a fixing mechanism. 
     The constitution of other parts of the injection needle assembly  30  is similar to that of the injection needle assembly  1  according to the first embodiment, so that description thereof is omitted. With the injection needle assembly  30  having the constitution as described above also, it is possible to obtain functions and effects similar to those of the injection needle assembly  1  according to the above-described first embodiment. 
     Note that the present invention is not limited to the embodiments described above and illustrated in figures, and various modifications can be possible within the scope not departing from the gist of the invention described in claims. For example, the outer housing unit maybe configured to slide so as to cover the outside in the radial direction of the guide part. 
     EXPLANATION OF REFERENCE NUMERALS 
       1 ,  20 ,  30 : injection needle assembly,  2 : needle tube,  2   a:  blade face,  3 : hub,  4 : adjustment unit,  4   b:  needle protruding surface,  5 : adhesive agent,  6 ,  21 ,  31 : stabilization unit,  6   a,    21   a,    31   a:  fixing part,  6   b,    21   b,    31   b:  contact part,  6   c:  end face,  6   d:  sliding groove,  6   e,    31   c,    31   d:  engaging groove,  7 ,  23 : outer housing unit (housing unit),  7   a,    23   a,    38   a:  covering part,  7   b,   38   b:  leg part,  7   c,    38   c:  engaging claw,  8 ,  38 : internal housing unit (housing unit),  8   c:  insertion hole,  9 ,  22 ,  32 : guide part,  9   a,    22   a,    32   a:  contact surface,  11 : syringe,  12 : connection pin,  22   b:  opening part, B: bevel length, L: protrusion length, S: distance from the circumferential edge of the needle protruding surface to the circumferential surface of the needle tube, T: distance from the internal wall surface of the stabilization unit to the outer circumferential surface of the adjustment unit, x: guide part length, y: guide part height, d: internal diameter