Patent Publication Number: US-2022218968-A1

Title: Metered dose topical applicator

Description:
This application claims priority to U.S. Provisional Application No. 62/845,789 filed May 9, 2019. Said application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The disclosed invention relates to devices and methods for preparing and dispensing pharmaceutical preparations, such as creams, liquids, and gels that are applied to the skin or other body surface. In particular, the disclosed invention relates to a metered dose topical applicator device suitable for filling with a flowable pharmaceutical compound, and that can be used to accurately dispense that compound and apply it to the body. 
     BACKGROUND OF THE INVENTION 
     One modality for administering therapeutic medicaments is by dermal application with subsequent transdermal absorption. This is quite common for hormone therapy, but is also used for pain medications and corticosteroids, among others. The therapeutic agent is typically blended into a carrier cream that is then rubbed onto the skin. Often, the formulation must be individualized for each consumer based on prescribed medicaments and dosages. These formulations are often prepared in compounding pharmacies, who then also prepare a container filled with the formulation and give it to the consumer. These containers are dispensers of various kinds, for example syringes or pump dispensers. Moreover, this modality is not limited to human adults, but can also be suitable for children, babies, and even pets such as cats and dogs. 
     Dispensing devices called propel/repel containers are common commercially available items used for cosmetics such as lip balm, lipstick, deodorants, antiperspirants, and moisturizers, and also for household and industrial products such as glue and lubricants. These have been adapted for topical application of therapeutic agents. 
     One of the most common configurations of propel/repel container features a hollow cylinder with a movable floor, female threads formed in the floor, a male-threaded rod passing through the female threads, and a screw knob, integral with the male-threaded rod, captured on one end of the cylinder. The product to be dispensed resides in the cylinder above the elevator. Turning the screw knob one direction forces the elevator upward, propelling the product from the cylinder, with the other direction repelling it. U.S. Pat. No. 1,499,784 to Becker discloses an example propel/repel container of this configuration, in this case for solid or semi-solid products like lipstick. 
     U.S. Pat. No. 3,616,970 to Baumann adds a closed exit end with an exit hole or holes, making it suitable for liquids and gels. U.S. Pat. No. 4,139,127 adds a ratchet mechanism to prevent repel motion, making it a propel dispenser only. U.S. Pat. No. 1,568,178 to Noble shows a configuration in which the drive screw is disposed entirely outside of the product reservoir, making the reservoir a simple, empty cylinder. U.S. Pat. No. 5,851,079 discloses a one-way ratchet mechanism as well as audible and tactile signals that are tied to metered incremental doses, called clicks, related to the volume of product dispensed. 
     The prior art also contains dispensers with drive systems that are engageable and disengageable, and that, further, feature the ability to be filled or refilled when the drive is disengaged. An early example is the grease gun shown in U.S. Pat. No. 9,49,163 to Stapley. This device is, essentially, a screw thread driven syringe with a barrel with an outlet and a moveable plunger. It employs a lever that toggles on and off the engagement of a set of female threads to a threaded screw. Turning the screw expels grease from the outlet of the gun when the drive system is toggled on. When toggled off, the gun may be filled through the outlet because the plunger is not restrained by the thread engagement. Similar devices are disclosed in U.S. Pat. No. 2,283,915 to Cole, U.S. Pat. No. 3,353,718 to McLay, and U.S. Pat. No. 4,810,249 to Haber, et al, all of which could be used for, or are intended for, delivering medicaments. 
     U.S. Pat. No. 4,865,591 employs an engageable/disengageable drive combined with a metering system that is used to accurately dispense medicament from an attached medicament cartridge. It features a drive plunger with ratchet-style teeth that is engaged by mating toothed blocks to advance a plunger in the cartridge a distance preselected by the metering system. Disengagement of the drive plunger allows it to be quickly reset to a start position when replacing an empty cartridge with a new one. 
     Topical applicators for pharmaceutical formulations of liquids, creams, and gels with dose metering features also exist in the prior art. Examples of these devices are disclosed in U.S. Pat. Nos. 7,213,994 and 7,303,348 to Phipps, et al, and U.S. Pat. No. 8,544,684 to Perez. These are propel/repel containers of conventional construction with the additions of an indexed dose metering capability, ratchet mechanisms to prevent repel, and audible and tactile dose indicators. These are commercially available as the Topi-CLICK® from DoseLogix and the Ticker™ Transdermal Applicator from BIOSRX, respectively. 
     Another prior art metered dose topical applicator is disclosed in U.S. Pat. Pub. 2018/0207413 to Skakoon et al, titled “Metered Dose Topical Applicator,” which is commercially available as the UnoDose™ metered dose topical applicator from Reflex Medical. 
     All three of the commercially available applicators mentioned immediately above are best suited for adult patients to apply topical creams to large body surfaces such as a forearm. Even if they dispense small enough volumes per actuation (such as, for example, 50 microliters) their physical size is unsuitable for many applications, an example of which is applying a dispensed cream to the inside of pets&#39; ears. 
     Thus, “micro-sized” metered dose topical applicators have been developed. Two example devices are the MD™ Pen and MD™ Syringe available from Medisca, Inc. of Montreal, Quebec, Canada. These devices feature an open medicament chamber that is filled with a therapeutic cream by a compounding pharmacy. After filling, a pump assembly with an outlet port is attached to the open end of the chamber. The pump is then actuated by pushing a pushbutton, on the opposite end of the chamber, in a motion similar to a clicking ball point pen. Each push of the pushbutton dispenses a metered dose of the cream out of the outlet port for dermal application. In this case, the dose size is 0.1 or 0.15 milliliters, depending on the model. 
     Two more examples of micro-sized metered dose topical applicators are the Topical TWIST Pen and the Topical CLICK pen available in the United States through RxCoop of Goldenrod, Fla. These devices again feature an open medicament chamber that is filled with a therapeutic cream by a compounding pharmacy. After filling, an applicator tip assembly is attached to the open end of the medicament chamber. Both devices have a screw thread drive system the advances an elevator to expel the cream through a hole or holes in the applicator tip. In the Topical TWIST Pen version, rotating a knob on the opposite end of the medicament chamber advances the elevator. There are also a metering and anti-rotation functions included in the drive mechanism, which also include sensory feedback for the user. In the case of the Topical CLICK pen, pushing a pushbutton on the opposite end of the medicament chamber advances the elevator. This is similar to the action of a clicking ball point pen. Each click dispenses a metered dose and provides sensory feedback to the user. These devices dispense 0.01, 0.025, or 0.05 milliliters per metered dose, depending on the model. 
     The examples immediately above suffer drawbacks, the most obvious of which is inconvenient and ineffective filling. Because the medicament chambers are long and slender, the cream can only be added by using a long nozzle inserted into the chamber. Even then, filling the chamber without pockets of air is challenging. Moreover, removing any entrapped air bubbles can be almost impossible in some cases. This is especially detrimental to the overall performance and the accuracy of these micro-sized applicators because the metered-dose volumes are so small, and any bubbles can have a large negative effect. 
     Another example of a micro-sized metered dose applicator is disclosed in U.S. Pat. Application No. 2018/0178968 to Phipps, et al. A device based on this disclosure is commercially available as the Topi-Click MICRO™. This device may be filled with a compounded cream, the volume of which is discretionary between about 1 and 10 milliliters, and dispensed in 50 microliter increments (0.05 milliliters). 
     Fillable metered dose dispensers of the form disclosed in U.S. Pat. Application No. 2018/0178968 to Phipps, et al include: 1) a free-floating sealing plunger that moves during filling, and 2) a drive system that moves a plunger driver via a user action. The user action that moves the plunger driver first takes up the space, if any, between the plunger and plunger driver then moves the plunger as intended for dose dispensing. This arrangement, however, has disadvantages. In particular, if dispensers of this type are only filled partially, which is often the case, the distance between the plunger driver and the plunger can be large. This means that the dosing means (e.g. a rotating knob) must be actuated numerous times to take up that distance. Motorized tools (i.e. a battery-operated drill) can be employed, but that means having one available. Furthermore, stopping a motorized tool while never overshooting is difficult. Moreover, for the plunger driver to mechanically capture the plunger might be difficult or impossible, meaning that the plunger could possibly move forward during use independent of the plunger driver. 
     In light of the drawbacks of the prior art, there exists a need for an improved metered dose applicator that can be loaded with a flowable compound to any desired fraction of a full fill, and that can dispense the contents with a minimum of additional user handling steps. 
     SUMMARY OF THE INVENTION 
     Embodiments of the disclosed invention feature a device for incrementally metering discrete volumes of a compounded pharmaceutical liquid, cream, or gel formulations, and for topically applying the formulation for dermal absorption. The device is configured to allow any fraction of its maximum fill volume to be loaded when the drive mechanism is not engaged, yet allow the drive to be fully engaged immediately when desired by triggering an actuating element. 
     Embodiments can also include additional advantageous features as described in the following: Embodiments can include a connection port through which compounded formulations may be introduced into an expandable and collapsible storage reservoir. 
     Embodiments can include a means of collapsing a storage reservoir, thus propelling the formulations out of the storage reservoir. 
     Embodiments can include an accurate means of propelling the formulation out of the device through the tip, such as an elevator driven by a drive mechanism comprising a screw thread and drive nut, which, in turn, may be actuated by user action such as rotating a knob. 
     Embodiments can include an actuating means that engages a drive mechanism upon demand. 
     Embodiments can include an attachable tip for the device with a plurality of openings to allow outflow of the formulation, and to provide a means of hands-free topical application of the formulation. 
     In embodiments, the nut can have flexible fingers with threaded portions at one end, a tubular end portion with cooperating ratchet portion at an opposing end. The cooperating ratchet portion may comprise a plurality of detent portions that engage recesses or openings in a surface of the container housing. In embodiments, the recesses or openings may be positioned on a plate unitary with a barrel portion or sub-assembly of the container housing and may provide audible and/or tactile indication of incremental rotations corresponding to indexed metered doses. 
     In embodiments, the nut can have flexible fingers with threaded portions that are initially not engaged with screw threads of a drive mechanism, but that can be flexed via an operator actuation to become engaged. 
     Embodiments can include an indexing means that partitions the propelled formulation into metered doses. 
     Embodiments can include audible and tactile indications corresponding to the indexed metered doses. 
     Embodiments can include a one-way, or ratcheting, mechanism to prevent reversing of the propel action (repel). 
     Embodiments can include other useful features such as volumetric or other measurement scales, protective covers, and ergonomic geometric elements. 
     A further feature and advantage of the invention is that of a container housing configured as a barrel and elevator defining a reservoir that is conducive of holding a wide range of volumes of a compounded pharmaceutical liquid, cream, or gel formulation without needing a time consuming rotation of a knob to move the elevator forward, thereby bringing the liquid, cream, or gel formulation to the dispensing tip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of the metered dose topical applicator. 
         FIG. 2  is another perspective view of an embodiment of the metered dose topical applicator of  FIG. 1  showing another configuration. 
         FIG. 3  is another perspective view of an embodiment of the metered dose topical applicator of  FIG. 1  and  FIG. 2  showing another configuration. 
         FIG. 4  is an exploded orthogonal view showing the components of the applicator individually. 
         FIG. 5  is a perspective, partially cut-away view showing the applicator in one configuration. 
         FIG. 6  is a detailed perspective view of one end of the applicator. 
         FIG. 7  is detailed perspective view, partially cut away, showing a middle portion of the applicator. 
         FIG. 8  is detailed perspective view, partially cut away, showing the other end of the applicator. 
         FIG. 9  detailed perspective view, partially cut away, showing the same end of the applicator as shown in  FIG. 8 , but viewed from a different angle. 
         FIG. 10  is a detailed perspective cross-section view showing components of the end of the applicator shown in  FIG. 8  and  FIG. 9 . 
         FIG. 11  is a detailed perspective view, partially cut away, showing a middle portion of the applicator similar to  FIG. 7 , but in another configuration and from a different direction. 
         FIG. 12  is detailed perspective view, partially cut away, showing a middle portion of the applicator similar to  FIG. 7 , but in another configuration and with a component or components hidden. 
         FIG. 13  is a perspective view of one end of the applicator and with a filling syringe aligned to be attached to the applicator. 
         FIG. 14  is a perspective, partial cut-away view of a partially filled applicator that has dispensed a dose. 
         FIG. 15  is a perspective view of the applicator after filling. 
         FIGS. 16A and 16B  are perspective views showing an alternate embodiment of a metered dose applicator. 
         FIGS. 17A and 17B  are perspective views showing another alternate embodiment of a metered dose applicator. 
         FIG. 18  is a perspective view showing another alternate embodiment of a metered dose applicator. 
         FIGS. 19A and 19B  are perspective views showing an alternate embodiment of a metered dose applicator. 
         FIG. 20  is a perspective view of an embodiment of a metered dose applicator with a pushbutton. 
         FIG. 21  is a cross-sectional view of the applicator of  FIG. 20 . 
         FIG. 22  is a detailed cross-sectional view of the applicator of  FIGS. 20 and 21   
         FIG. 23  is a perspective view of the applicator of  FIGS. 20 to 22 , with portions removed for clarity. 
         FIG. 24  is a detailed perspective view of the applicator of  FIG. 23 , with portions removed. 
         FIG. 25  is a detailed cross-sectional view of a components of the applicator of  FIG. 24 . 
         FIG. 26A to 26C  are diagrammatic cross-sectional views of components of the applicator of  FIGS. 20 to 25 . 
         FIGS. 27 and 28  is cross-sectional views of the applicator of  FIGS. 20 to 26C . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an embodiment of a metered dose topical applicator  10  in accordance with the present invention is shown. The applicator  10  includes a barrel  100 , which has two regions, a medicament reservoir  102  and a mechanism housing  104 . The applicator  10  also includes a cover  1000 , a drive actuator  800 , and a dosing knob  600 , the functions of which are explained in detail below. 
       FIG. 2  shows the applicator  10  with cover  1000  removed to show an applicator tip  900 , which is used to topically apply cream that has been metered from the applicator  10 . The applicator tip  900  has an exit hole  902  through which the cream is dispensed from the applicator  10 . 
       FIG. 3  shows the applicator  10  in a configuration suitable for filling with a compounded cream. The applicator tip  900  has not yet been assembled, and the drive actuator has not been actuated, as shown by the notated gap shown in  FIG. 3 . This configuration represents how applicator  10  may be provided to the user for preparation. 
     Referring now to  FIG. 4 , internal components of one embodiment of applicator  10  are shown in an exploded view. Barrel  100  (with housing  104  and medicament reservoir  102 ), applicator tip  900 , and cover  1000  have been exploded sideways for clarity, although in the actual assembly are coaxial with the other components. An elevator  200  sealingly and slidably rides in barrel  100  defining a volume in medicament reservoir  102 . Elevator  200  attaches to drive screw  300 . Drive nut  400  includes nut threads  404 , which are configured initially as disengaged to drive screw  300 , yet are engageable upon demand. Dosing knob  600  attaches to drive nut  400  via, for example, snap fit features. Retainer  500  assembles into housing  104  and provides capturing features that retain and position the rotatable subassembly of dosing knob  600  and drive nut  400 . An important function included in applicator  10  is its drive mechanism  12 , which comprises dosing knob  600  connected to drive nut  400 , which threadably and electively couples to drive screw  300  by way of the action of locking ring  700 . Briefly, rotating dosing knob  600  (as shown on  FIG. 1 ) turns drive nut  400 , which axially advances drive screw  300 . Drive screw  300  likewise pushes on elevator  200 , meaning that drive mechanism  12  expels cream out of applicator tip  900  of applicator  10 . 
     Referring now to  FIG. 5 , elevator  200  is shown in the empty position within medicament reservoir  102  of barrel  100 , meaning that the compounded cream capacity of applicator  10  is substantially zero. As shown in  FIG. 6 , elevator  200  includes a seal lip  202  that sealingly and slidably engages with the internal wall  112  of medicament reservoir  102 . In this embodiment, elevator  200  is separate from, but attaches to drive screw  300 , for example by a press or snap fit. Nevertheless, elevator  200  and drive screw  300  can be a single component without affecting the essence of the disclosed invention. Moreover, elevator  200  can be made from an elastomer, or can include an elastomer seal such as an O-ring, or can include a plurality of sealing lips, any of which could improve the seal integrity as required. 
     Referring to  FIG. 5  and detail  FIG. 7 , drive screw  300  includes screw threads  302 , which can engage with nut threads  404  of drive nut  400 , which arrangement is shown here. Nut threads  404  are not yet engaged with screw threads  302  in  FIG. 7 , but become engaged during use of applicator  10 , as is further explained below. 
     Referring back to  FIG. 5 , nut threads  404  are integral with nut leg(s)  402 , which extends back to nut body  416 . Nut body  416  includes pawl(s)  412  and snapfit slot(s)  410 , which are also shown in detail  FIG. 8 . Retainer  500  is shown in its assembled position within housing  104  of barrel  100 . Retainer  500  may be affixed to housing  104  in various ways including a press or snap fit, adhesives, or welding. Retainer  500  includes retainer flange  506 . 
     Referring now to  FIG. 9 , dosing knob  600  is shown in its assembled position, in which snapfit leg(s)  602  have snapped into snapfit slot(s)  410  of nut body  416  in a typical snap-fit arrangement. Dosing knob  600  may be connected to drive nut  400  in various ways, the only functional criteria being that once the connection is made between drive nut  400  and dosing knob  600 , those two parts, once affixed together, are accurately and stably positioned within barrel  100 , yet are free to rotate about the main axis of applicator  10 . 
     Referring now to  FIG. 10 , retainer  500  includes ratchet tooth  502  and detent nest  504 , both of which work together with pawl  412  and detent bump  414 , which is integral with pawl  412 . Ratchet tooth  502  and pawl  412  allow rotation of drive nut  400  (and dosing knob  600 ) in one direction, as shown by the arrow, yet check rotation in the opposite direction. Moreover, pawl  412  and ratchet tooth  502  can create an audible indicator of the passing of pawl  412  past ratchet tooth  502 , as is typical for ratchet and pawl mechanisms. Detent bump  414  and detent nest  504  work together to provide a stable detent position or positions at various rotational locations. This keeps the dosing knob  600  (and drive nut  400 ) from rotating inadvertently while applicator  10  is not actively being used. 
     Referring back now to  FIG. 5  and detail  FIG. 7 , nut leg  402  includes lock ramp  406  and lock nest  408 , whose purpose is to work together with locking ring  700  to effect engagement of nut threads  404  with screw threads  302 , as explained below. Drive actuator  800  is concentrically retained on the outer diameter of medicament reservoir  102 , yet is axially slidable between predefined stop positions. Drive actuator  800  includes actuator leg(s)  802  that contact locking ring face  704 . Thus pushing drive actuator  800  (to the right as shown in  FIG. 7 ), will simultaneously push locking ring  700  to the right. Referring momentarily back to  FIG. 1 , barrel  100  includes a step feature, barrel stop  114 , between medicament reservoir  102  and housing  104 , which includes barrel slots  110  of barrel  100  through which actuator leg(s)  802  of drive actuator  800  fit. This combination acts to align and retain drive actuator  800  in its position. 
     Referring back to  FIG. 7 , as drive actuator  800  pushes locking ring  700  to the right, lock ramp  406  of nut leg  402  works together with guide slot  702  (see  FIG. 12 ) of locking ring  700  to deform nut leg(s)  402  inward, which deformation engages nut threads  404  with screw threads  302 . Once locking ring  700  reaches its final position, it will be captured in lock nest  408  of nut leg  402 , and will rotate together with nut when dosing knob  600  ( FIG. 5 ) is rotated. 
     Referring now to  FIG. 11 , drive actuator  800  has been pushed inward, or to the right, until it contacts barrel stop  114 , which action has also pushed locking ring  700  in the same direction, which has engaged nut threads  404  with screw threads  302 , and which has positioned locking ring  700  into a secure position in lock nest  408 . Nut leg  402  is essentially a cantilever spring, and has been deformed inward by locking ring  700 . 
     Referring to  FIG. 12 , locking ring  700  is shown in the locked position to where it has moved past lock ramp  406  into lock nest  408  (see  FIG. 7 ). (Drive actuator  800  has been hidden in  FIG. 12  for a clearer view.) Guide slot  702  of locking ring  700  aligns and guides locking ring  700  along nut leg  402 . Because of the inward deflection of nut leg  402 , nut threads  404  are engaged with screw threads  302 , as shown. As previously noted, locking ring  700  rotates with drive nut  400  and dosing knob  600  (not shown in  FIG. 12 ). 
       FIG. 13  shows access port  106  of barrel  100 . Access port  106  includes port connector  108 , which can be, for example, a Luer style connector, in this case a male Luer lock. Any suitable connector style may be used, but a Luer configuration allows port connector  108  to attach directly to a Luer-tipped syringe (syringe  14  as shown). Syringe  14 , when connected, allows drug carriers such as liquids, creams, or gels to be added to medicament reservoir  102  of applicator  10  by pushing syringe plunger  16  forward. 
     We now turn to an explanation of the physical functionality of the present invention during use by referring to  FIG. 5 . Applicator  10  may be supplied to a pharmacy for preparation in an empty state with elevator  200  substantially seated against end face  116  of barrel  100 . Thus, the volume held by medicament reservoir  102 , which is defined by the inside diameter of medicament reservoir  102  and the distance between end face  116  and elevator  200 , is substantially zero. Because nut threads  404  are not engaged with screw threads  302 , elevator  200  (and drive screw  300 ) are free to move along the central axis of applicator  10 . Thus, for example, if syringe  14  has been used to inject a cream through access port  106  as shown in  FIG. 13 , elevator  200  (and drive screw  300 ) will move to accommodate a carrier cream  22  (not shown) by increasing the volume of medicament reservoir  102 . 
     Once the desired volume of a medicament and carrier cream  22  has been added to applicator  10 , drive actuator  800  is pushed in until it butts against barrel stop  114 , which, as explained above, engages nut threads  404  with screw threads  302 , which means the drive mechanism  12  (see  FIG. 4 ) of applicator  10  is likewise engaged. 
     Because the drive mechanism  12  is not engaged, i.e. nut threads  404  not meshed with screw threads  302 , during filling of applicator  10 , any desired percentage of fill volume, from 0 to 100% of medicament reservoir  102 , may be introduced. Engaging the drive mechanism  12  after filling, regardless of the fill volume, means the drive mechanism  12  is engaged only when desired, but immediately engaged when desired, with the single action of pushing drive actuator  800  to the position shown in  FIG. 2 . Thus there is no need for a priming or take-up operation to accommodate medicament reservoir  102  fill volumes of less than 100%. 
     Actual dosing is shown in  FIG. 14  wherein applicator  10  contains a quantity of carrier cream  22 , which can hold a suitable medicament. Drive actuator  800  has been pushed in, engaging nut threads  404  with screw threads  302  as described above. Doing knob  600  has been turned in the direction shown so that a dose  24  of carrier cream  22  has been expelled out exit hole  902  of applicator tip  900 , and dose  24  is ready of application to the intended site. 
     Numerous other construction arrangements are possible that embody the functional characteristics of the present invention. For example, in  FIG. 15 , a metered dose topical applicator  10  is shown in which its drive mechanism is also not engaged during filling, as described above. Applicator  10  also includes barrel  100 , dosing knob  600  and applicator tip  900 . In this alternative embodiment, however, the drive mechanism is engaged by rotating drive actuator  800  as shown, which engages nut threads and screw threads, which have been arranged internally to engage by this alternate action. 
     Likewise,  FIG. 16A  shows an embodiment wherein metered dose topical applicator  10  includes side pushbutton  18 . After filling, side pushbutton  18  is pushed as shown by the arrow, which engages the drive mechanism in a fashion similar to what is described above. Side pushbutton  18  can latch, for example, in the pushed position to present a smooth outer surface to barrel  100  as shown in  FIG. 16B . 
     An alternative embodiment is shown in  FIG. 17A , wherein applicator  10  has a drive mechanism that, as before, is not engaged to accommodate filling. Applicator  10  includes end pushbutton  20  that can be positioned proud of dosing knob  600  during filling, but when pushed as shown can trigger engagement of nut threads with screw threads as before. End pushbutton  20  can latch in a position flush with dosing knob  600  to present a smooth appearance, and to visually indicate engagement status as shown in  FIG. 17B . 
     Another alternative embodiment is shown in  FIG. 18 . In this embodiment, the drive system is also initially not engaged to accommodate filling. Applicator  10  includes a dosing knob  26 , much like before, but in this embodiment, dosing knob  26  serves the dual function of also being the drive actuator. Thus, after the applicator has been filled with cream, dosing knob  26  is rotated as shown. This first causes the drive system&#39;s nut threads to engage with the screw threads, analogous to the internal action previously disclosed. Thereafter, rotating dosing knob  26  meters doses with sensory feedback and anti-rotation features as with other embodiments. 
     Another alternative embodiment is shown in  FIG. 19A . In this embodiment, the drive system is also initially not engaged to accommodate filling. In this embodiment, however, rather than a rotating knob, a pushbutton  28  is used to activate the metered doses. Moreover, pushbutton  28  can serve the dual function of also being the drive actuator. Thus, after the applicator has been filled with cream, pushing pushbutton  28  first causes the drive system&#39;s nut threads to engage with the screw threads, analogous to the internal action previously disclosed. That could, for example, put pushbutton  28  in the location shown in  FIG. 19B . Pushing further on pushbutton  28 , until it stops, then meters a dose by way of an internal drive mechanism similar to previously disclosed embodiments. In other words, pushing pushbutton  28  can rotate a drive nut, which then translates a screw, advances an elevator, and expels cream from the medicament reservoir. Releasing pushbutton  28  allows it to return to the position shown in  FIG. 19B  by way of a return spring for example, which readies the applicator for another dose activation. 
     The embodiment shown in  FIGS. 19A and 19B  can be realized with various arrangements of functional internal components. One such arrangement is metered dose topical applicator  50  shown in  FIG. 20 . Applicator  50  includes a barrel  52  and an applicator tip  54 . Drive housing  66  is assembled and affixed to barrel  52 . Pushbutton  74  is concentrically captured within drive housing  66 , but is free to move axially, within limits. 
       FIG. 21  shows the internal components of applicator  50 , starting with an elevator  56  and a screw  58 . In  FIG. 21 , applicator  50  is shown in the configuration as supplied to the preparing agency (e.g. compounding pharmacy) in a state ready to be filled with medicament-containing cream. Elevator  56  and screw  58  can be a single component or an assembly of two affixed components, the preferred configuration defined only by manufacturing considerations. Disposed within barrel  52  is nut  62 , which will become engaged with screw  58  to drive elevator  56 , as will be explained below. Disposed within drive housing  66  is locking wedge  64  that, when repositioned, will effect the engagement of nut  62  with screw  58 . Also disposed within drive housing  66  is drive guide  68 , which is concentrically and axially affixed to barrel  52 . Disposed within drive guide  68  is drive actuator  70 , which is free to rotate and to translate axially, within limits. Pusher  72  is also disposed within drive guide  68 , and is free to translate axially, within limits. Pushbutton  74  is affixed to pusher  72 , and is the external link accessible to the user to initiate the internal drive system functioning of applicator  50 . Return spring  76  is disposed within drive housing  66 , and serves to bias drive actuator  70  to a start position, which bias can be overcome by the operator pushing on pushbutton  74 . 
     Referring now to  FIG. 22 , nut  62  is shown within barrel  52  in the as-supplied configuration, i.e. ready to be filled. As with other embodiments of the present invention, nut  62  is not engaged with screw  58 , which allows screw  58  (and elevator  56 ) to move axially during filling. Nut  62  includes two opposing flexible legs  78 , on which threaded portions  80  are disposed. As shown threaded portions  80  are spaced away from screw  58 . Screw  58  includes screw threads  60 , but, because of the spacing, are not engaged with screw threads  60  in this configuration. Locking wedge  64 , shown here not in contact with nut  62  and legs  78 , serves to engage and lock the drive components, i.e. nut  62  with screw  58 , together for dispensing doses, as described below. Drive actuator  70  contacts locking wedge  64  in this configuration, as shown, and will urge locking wedge  64  to the left when applicator  50  is operated via pushbutton  74 . 
     Referring now to  FIG. 23 , the assembled components of applicator  50  are shown in the same configuration as in the previous figure. Nut  62  is constrained axially, but is free to rotate about the axis, which rotation is accomplished with rotation of drive actuator  70 . Drive actuator  70  includes guide slots  82  that cooperate with drive lugs  84  of nut  62 , so that nut  62  rotates with drive actuator  70 . Nonetheless, drive actuator  70  is allowed to translate along the axis, within limits. Pusher  72  contacts drive actuator  70  as shown, and axial translation of pusher  72  to the left will translate drive actuator  70  as well. As previously described, pushbutton  74  is affixed to pusher  72 . 
     Referring now to  FIG. 24  and  FIG. 25 , the physical relationship between pusher  72  and drive guide  68  is shown. Pusher  72  includes guide lugs  86 . Drive guide  68  includes guide ribs  88 , which form guide rib slots  90  ( FIG. 25 ). Guide lugs  86  ride in guide rib slots  90  preventing pusher  72  from rotating during its allowed translation. Guide lugs  86 , guide ribs  88 , and pilot lugs  92  all include inclined planes  94 , which function as cams translating linear to rotary motion as will be explained further below. 
     Another important feature of applicator  50  is best described now by referring back to  FIG. 23 . Just as guide lugs  86  of pusher  72  ride in guide rib slots  90  ( FIG. 25 ) of drive housing  66 , so, too, do pilot lugs  92  of drive actuator  70 , preventing drive actuator  70  from rotating, but in this case for only a portion of the allowable translation. Once pilot lugs  92  are no longer constrained by guide rib slots  90 , drive actuator  70  is free to rotate. 
     Having now defined the components of applicator  50 , the function of the drive system will be explained. Generally, pushing pushbutton  74  translates pusher  72 , which moves drive actuator  70  until it is no longer rotationally constrained. At that point, drive actuator  70  rotates by action of a spring force on inclined surfaces. This rotates nut  62 . Once pusher  72  reaches its travel limit, pushbutton  74  is released, and drive actuator  70  rotates again by additional action of the spring force supplied by return spring  76  on a different pair of inclined surfaces. This again rotates nut  62 . Rotation of nut  62  causes axial advancement of screw  58 , and elevator  56 , which do not rotate, to expel a dose. 
     This type of push-to-rotate mechanism is analogous, in part, to ordinary click-style ballpoint pens. In that case, the rotating member simply returns to either of two alternating positions, in or out, as the pushbutton is cycled. Adding female threads to the rotating member and a male-threaded screw, and eliminating the alternating return positions, are what make it into a dispensing mechanism rather than an alternating position mechanism. The aforementioned prior art device, the Topical CLICK pen available through RxCoop, uses a mechanism of this form. 
     Referring to  FIGS. 26A, 26B, and 26C  shed additional light on the function of the drive mechanism of applicator  50 . For easier visualization, these figures show, conceptually, the key components “unwrapped” from their round configuration. Entities shown are block diagram analogs of those as described above, but with their entity numbers denoted by a prime (′). In the start position shown in  FIG. 26A , guide lug  86 ′ and pilot lug  92 ′ ride in guide rib slots  90 ′. As previously explained pushing pushbutton  74  translates pusher  72 , and thus guide lug  86 , and, in turn, pilot lug  92 . Once pilot lug  92  moves beyond guide rib slot  90 , it rotates as shown in  FIG. 26B  by action of the spring force on the mating inclined planes  94 . When pushbutton  74  is released, all components return toward the start position, rotated, however, to the next indexed location, as shown in  FIG. 26C . 
     Referring again to  FIG. 22 , how the drive system of applicator  50  is changed from unengaged to engaged will be explained. Threaded portion  80  of nut  62  is not engaged with screw threads  60  of screw  58  in the as-supplied, ready-to-fill configuration. As previously explained, this allows applicator  50  to by filled with any desired volume of a flowable compound. Once filled, the operator pushes the pushbutton  74  to dispense metered doses as previously described. However, the first actuation of pushbutton  74  is what causes threaded portion  80  to engage with screw threads  60 . This is shown in  FIG. 27 , and in detail in  FIG. 28 . Drive actuator  70 , when moved via pushbutton  74 , translates locking wedge  64  into a gap in nut  62  formed in legs  78 , which flexes legs  78  in such a way to force engagement of threaded portion  80  with screw threads  60 . Once in this position, locking wedge  64  remains there to keep the drive system engaged.  FIG. 28  shows the now-engaged drive system in detail. Drive actuator  70  will be forced to return to its start position by return spring  76  once the operator releases pushbutton  74 . 
     So to summarize, applicator  50  has a drive system that is initially unengaged, which allows any desired amount of cream to be filled. Once filled, the first push of the dosing pushbutton permanently engages the drive system. Thereafter, each push dispenses a metered dose. 
     Additional permutations of actuating the drive system after filling, and dispensing metered doses after that, are possible. For example, one variation of the embodiment shown in  FIGS. 19A and 19B  is to separate the drive actuation and dose activation functions into two different physical elements. Thus, this embodiment could include a side button as shown on  FIG. 16A  to actuate the drive, leaving pushbutton  28  with the sole function of activating metered doses. 
     Other embodiments in accordance to the present invention may be constructed that present a drive actuation feature in any location and with any motion, being restrained only by whatever action is most convenient for the user, and which internal arrangement of components yields best to manufacturability. For example, no strict adherence to the elevator-to-drive screw-to-drive nut-to-dosing knob configuration is required to practice the present invention. The drive nut could be attached to, or integral with, the elevator, with the drive screw then attached to the knob. In other words, component locations and relationships can be inverted or otherwise changed and still function in the manner herein disclosed. 
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     The above disclosure is related to the detailed technical contents and inventive futures thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered by the spirit and technical theory of the subject invention. 
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and described in detail. It is understood, however, that the intention is not to limit the application to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims. 
     Persons of ordinary skill in the relevant arts will recognize that various embodiments can comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the claims can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. 
     References to “embodiment(s)”, “disclosure”, “present disclosure”, “embodiment(s) of the disclosure”, “disclosed embodiment(s)”, and the like contained herein refer to the specification (text, including the claims, and figures) of this patent application that are not admitted prior art. “Portion” when used herein may refer to a portion of a discrete component, all of a component, or a portion of an assembly, that is, for example, two components of an assembly of 5 components may be a “portion”, the terminology is not intended to be limiting. 
     For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. 112(f) are not to be invoked unless the specific terms “means for” or “step for” are recited in the respective claim.