IMPROVEMENTS IN OR RELATING TO CAPSULES

Abstract: A controlled release capsule comprises a female body (10) having a charge receiving portion (15) for holding a charge (20) of an agent to be released. A water-swellable male plug member (25) is engaged within a neck portion (30) of the female body. Buoyancy means (45) are provided to keep the closed end of the female body uppermost, so that when the male member is released from the female body the buoyancy means cause the female body to orientate to facilitate release of the charge under gravity from the female body. The construction promotes rapid emptying of the charge from the capsule after swelling and disengagement of the male plug member.

Description: IMPROVEMENTS IN OR RELATING TO CAPSULES TECHNICAL FIELD This invention relates to an improved capsule and in particular to an improved controlled release capsule for use, for example, in in-vitro tests. The invention further relates to an improved test kit including such a capsule and to an improved test method employing such a capsule. BACKGROUND Controlled release devices are known. For example, WO 90/09168 (National Research Development Corp.) discloses a device of this type which comprises a water swellable male hydrogel plug engaged within a female body. A pharmaceutically active material is contained within the device. When the capsule is exposed to water, the male hydrogel plug swells and eventually disengages itself from the female body, thereby allowing the pharmaceutically active material contained within the device to be released. It has been found that the time taken to release the pharmaceutical material is predictable and reproducible, so that the device may be used to release pharmaceutically active materials within the body of a patient after a predetermined time interval (e.g. 0.5 to 12 hours). This may, for example, be useful in the treatment of medical conditions where it is desirable to administer a pharmaceutically active material to the patient sometime through the night, while the patient is asleep, so as to provide a desired level of the drug in the patient in accordance with the patient's needs, for example, during the night or when the patient awakes. It may also be useful to allow dosing of materials at a predetermined point as the capsule passes through the gastro-intestinal tract, for example, in the colon. A further improved controlled release capsule is known from WO 94/09745 (R.P. Scherer Corporation) . This type of capsule is known as the "PULSINCAP" (Trade Mark) . As well as a requirement for controlled release capsules for the administration of pharmaceuticals to human or animal patients, there has also been found to be a need for controlled release capsules in in-vitro test procedures. It has, however, been found that known controlled release capsules suffer from a number of disadvantages, particularly when used in in-vitro tests. For example, it has been found with known capsules that, in use, when the hydrogel plug disengages from the female body the active material contained within the female body may not be completely released therefrom. It is an object of the present invention to obviate or at least mitigate one or more of the aforementioned problems in the prior art. SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided a controlled release capsule comprising a female body having a charge receiving portion for holding a charge of an agent to be released, a male member engaged within a neck portion of the female body, and buoyant means, wherein, in use, when the capsule is placed in a liquid and at least when the male member is released from the female body the buoyant means cause the female body to orientate such that the charge receiving portion is above the neck portion thereby facilitating release of the charge from the female body. Advantageously the female body comprises a substantially tubular body having a first end providing the neck portion and a second end providing the buoyancy means. The ratio of length to width of the female body is usually 3:1 to 1.5:1. Advantageously the charge receiving portion is provided between the first and second ends. The charge may be provided in any convenient form, and preferably in the form of a slug. However, it should be appreciated that the charge may alternatively be provided in any suitable form, for example, in the form of tablets, granules, pellet or other dosage units. The buoyancy means formed at the second end of the female body may comprise a cavity formed within the female body. Alternatively, the buoyancy means could be any other way of entrapping air or other gas, such as a sealed enclosure or enclosures, or a foam material. The sealed enclosure could be a hollow sphere of suitable volume (e.g. a hollow soft gelatin capsule) . A plurality of small hollow spheres could also be used. The volume of entrapped gas should be sufficient to invert the capsule, and will be related to the weight of the female body and the weight of the charge. Generally, the overall density of the capsule will be greater than the density of the liquid (e.g. 1 g/ml for water) so that the capsule does not float prior to ejection of the male member. It is advantageous if the density of the female body containing the charge is less than the liquid so that the body tends to rise upwards after ejection of the male member, facilitating release of the charge therefrom. Generally, the female body itself will have a density less than that of the liquid, so that the empty body floats upwards, and so assists release of the charge and its distribution through the liquid. Preferably, the centre of buoyancy of the capsule is spaced away from the (usually heavier) male member so as to provide a maximum turning moment to orient the capsule with the male member (and the first open end of the female body) downwards. The charge receiving portion may communicate with the cavity. The cavity may be of a lesser internal bore than the charge receiving portion at least at an area where the cavity and portion meet, the cavity and portion preferably being joined by a step portion. However, other ways of spacing a solid charge from the closed second end of the female body so as to maintain a cavity are possible, such as a rod, a series of circumferentially spaced detents, a grid or other way of creating a restriction in cross- section. The slug may be so dimensioned such that it may be inserted into the charge receiving portion but not into the cavity. That is to say an outer dimension of the slug may advantageously be greater than the internal bore of the cavity, such that, upon insertion of the slug a portion of the slug may be caused to abut the step portion. Generally, the charge occupies more than 20% of the internal volume of the female body (including any buoyancy cavity) . The female body may be of substantially cylindrical shape, and the second end may further be of substantially hemi-spherical form. The charge receiving portion may be substantially cylindrical . Further, the slug may be substantially cylindrical. The neck portion may provide a tapered portion which tapers outwardly towards the first end. The neck portion may be substantially circular in cross-section. Walls of the female body may be formed from a wide variety of materials. They may be of homogenous constructions or they may be laminated. Examples of materials suitable for use in the construction of the body include particularly polyethylene, (e.g. low density polyethylene), polypropylene (e.g. grade BK130, T50, or R50) , poly (methylmethacrylate) , polyvinyl chloride, polystyrene, polyurethanes, polytetrafluoroethylene, a nylon, a polyformaldehyde, a polyester, cellulose acetate, a nitro cellulose and gelatin. Generally, the body will be liquid-impermeable and insoluble in the liquid. However, one construction may use an ' impermeable coating to cover the exterior of a body which has been formed from a water soluble material. The coating may conveniently be formed by dipping the body in a solution of a material which forms a layer which is impermeable to water. Alternatively, the body might be spray-coated. A preferred class of capsule bodies are conventional hard gelatin or starch capsule bodies coated with a solution of polyvinyl chloride or a polyvinyl acetate copolymer or an ethyl cellulose solution. The male member may comprise a plug, usually of cylindrical configuration. The plug may be of a water swellable material, which is preferably a hydrogel. As it absorbs water, the hydrogel plug swells and becomes disengaged from the female body. The hydrogel is preferably a water swellable material as disclosed in WO90/09168. In its unswollen state, the male member usually occupies 10-30% of the volume of the female body (including any buoyancy cavity) . Usually the neck portion is substantially cylindrical, so as to form a tight fit with the cylindrical male plug. In one embodiment of the present invention, the female body comprises a flared mouth portion adjacent the neck portion, the mouth portion having an entrance which is wider than the neck portion and wider than the male member so as to facilitate insertion of the male member into the neck portion. The flared mouth portion may provide a ramped lead-in, so that the male member may be inserted readily into the neck of the female body. The mouth portion may be flared at an angle of 10° to 60°, preferably 15° - 45°, and most preferably approximately 19° to the line of the capsule. The capsule may be made by known capsule manufacturing techniques, such as injection moulding of thermoplastic materials. Alternatively, the female body may be prepared by conventional capsule forming techniques, which involve dipping a mould pin in a solution of the material from which the capsule is to be formed. Spraying could be used instead of dipping. The material is then dried and stripped from the pin. The capsule body may then be trimmed as necessary. According to a second aspect of the present invention there is provided a controlled release capsule which comprises a male member engaged within a neck portion of a female body, the male member being a plug formed of a water swellable material; the female body being adapted to receive a charge of an agent to be released, and to provide a free volume at an end of the body remote from the neck portion, such that when the capsule is placed in a liquid the free volume exerts a buoyancy effect which raises the free volume end of the body above the neck portion of the body and facilitates release of the agent from the body. According to a third aspect of the present invention there is provided an in-vitro test kit including a controlled release capsule, the capsule comprising a female body having a charge receiving portion holding a charge of an agent to be released, a male body engaged within a neck portion of the female body, and buoyancy means, wherein, in use, when the capsule is placed in a liquid and at least when the male body is released from the female body the buoyant means cause the female body to orientate such that the charge receiving portion is above the neck portion thereby facilitating release of the charge from the female body. According to a fourth aspect of the present invention there is provided an in-vitro test method comprising the steps of: providing a liquid container containing a select liquid; providing at least one controlled release capsule, the capsule (s) comprising a female body having a charge receiving portion holding a charge of an agent to be released, a male body engaged within a neck portion of the female body, and buoyancy means, wherein, in use, when the capsule is placed in a liquid and at least when the male body is released from the female body the buoyancy means cause the female body to orientate such that the charge receiving portion is above the neck portion thereby facilitating release of the charge from the female body, placing the capsule (s) in the liquid so as to allow the male body to release from the female body, and the female body to orientate such that the charge receiving portion is above the neck portion so as to facilitate release of the agent from the female body into the liquid. The method may be particularly adapted for the cultivation and detection of micro organisms, such as salmonellae. BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings, which are: Figure 1 is a sectional side view of a controlled release capsule according to an embodiment of the present invention; Figure 2 is a sectional side view to a reduced scale of a female body of the capsule of Fig. 1 ; Figure 3 is an end view of the female body of Fig. 2; Figures 4 (a) -(e) are a series of schematic diagrams illustrating the capsule of Figure 1, in use. DETAILED DESCRIPTION OF AN EMBODIMENT Referring to the drawings, there is illustrated a controlled release capsule, generally designated 5, according to an embodiment of the present invention. The capsule 5 comprises a female body 10 having a charge receiving portion 15 holding a charge 20 of an agent to be released, a male member 25 engaged within a neck portion 30 of the female body 10, and buoyancy means hereinafter described. In use, when the capsule 5 is placed in a liquid and at least when the male member 25 is released from the female body 10 the buoyancy means cause the female body 10 to orientate such that the charge receiving portion 15 is above the neck portion 30 thereby facilitating release of the charge 20 from the female body 10. The female body 10 comprises a substantially tubular body having a first end 35 providing the neck portion 30 and a second end 40 providing the buoyancy means. The charge receiving portion 15 is provided between the first and second ends 35,40. In the illustrated embodiment the charge 20 is in the form of a slug. However, it should be appreciated that the charge may alternatively be provided in any suitable form, for example, in the form of tablets, granules, pellet or other dosage units. The buoyancy means formed at the second end 40 of the female body 10 comprise a domed air filled cavity 45 formed with the female body 10. The charge receiving portion 15 communicates with the cavity 45. The cavity 45 is of a lesser internal bore than the charge receiving portion 15 at an area where the cavity 45 and portion 15 meet, the cavity 45 and portion 15 being joined by a step portion 50. The charge slug 20 is dimensioned such that it can be inserted into the charge receiving portion 15 but not into the cavity 45. That is to say an outer dimension of the charge slug 20 is greater than the internal bore of the cavity 45, such that upon insertion of the charge slug 20 into the portion 15 the charge slug 20 may be caused to abut the step portion 50. In this embodiment the female body 10 is of substantially cylindrical shape, the second end further being substantially of hemi-spherical form. Further the charge receiving portion 15 is substantially cylindrical, as is the charge slug 20. The neck portion 30 is provided with an outmost cylindrical portion 55 and a tapered portion 60 of frusto-conical form which tapers outwardly towards the first end 35. The tapered portion 60 is flared at an angle of approximately 19° to either side of a centre line of the capsule 5. Walls of the female body 10 may be formed from a wide variety of materials. They may be of homogenous constructions or they may be laminated. Examples of materials suitable for use in the construction of the body include particularly polyethylene (e.g. low density polyethylene) , polypropylene (e.g. BK 130, T50, R50) , or alternatively poly (methylmethacrylate) , polyvinyl chloride, polystyrene, polyurethanes, polytetrafluoroethylene, nylons, polyformaldehydes, polyesters, cellulose acetate and nitro cellulose. The male member 25 is in the form of a plug of part cylindrical configuration. The male member 25 formed of a water swellable material, which is preferably a hydrogel. As it absorbs water, the hydrogel plug swells and becomes disengaged from the female body 10. The hydrogel is preferably a water swellable material as disclosed in WO90/09168. The neck portion 30 is substantially cylindrical, so as to form a tight fit with the cylindrical part of male member 25. In this embodiment the outermost cylindrical portion 55 is 0.25mm long and 7.00mm in internal diameter to allow the male body 25 to sit square in the neck portion 30 of the capsule 5. Further the tapered portion 60 is 0.55mm long, over which the internal diameter is reduced from 7.00mm to 6.62mm. When fitted flush the majority of the male member 25 sits in the neck portion 30 of the capsule 5 with an internal diameter of 6.62mm, 5mm long. Using this capsule 5 it is possible to use a range of male member 25 plug lengths between 3.00mm and 5.8mm. With a charge 20 length of between 10mm and 11.5mm this ensures that the centre of gravity of the capsule 5 is always towards the first end 35 of the capsule 5. For a thermoplastic material, the capsule body is generally produced by injection moulding in a mould cavity provided with a retractable mould pin. Ridge 47 engages a corresponding groove on the mould pin and retains the body as it is withdrawn from the mould cavity. Polypropylene is a preferred material and the finished body has a flexural modulus of elasticity (ASTM D790) of 1700 MPa. Alternatively, the capsule body may be prepared by conventional capsule forming techniques, which involve dipping a mould pin in a solution of the material from which the capsule 5 is to be formed. Spraying could be used instead of dipping. The material is then dried and stripped from the pin. The female body 10 may then be trimmed as necessary. The capsule 5 may be employed as part of a test kit such as an in-vitro test kit, for example, for the cultivation and detection of salmonellae. In such application the capsules 5 can be used to deliver a selected bacteride after a selected time delay/ incubation period of, for example, 4 to 6 hours. Referring now to Figures 4(a) to (e) , in use, a person wishing to undertake an in-vitro test will follow the steps of: providing a suitable liquid container containing a selected aqueous liquid as is known in the art; provide at least one capsule 5; placing the/each capsule 5 in the liquid such that hydration of the male body(ies) 25 after a predetermined time(s) causes the/each capsule 5 to orientate with the neck portion (s) 30 below the charge receiving portion (s) 15 and thence the male body(ies) 25 to eject from the female body(ies) 10 causing the charge slug(s) 20 to exit the female body(ies) 10 into the liquid. EXAMPLE The following tests have been undertaken with capsules of the invention. 225ml of purified water or other aqueous medium is placed into each of a series of dissolution pots at 20°C(±2°C) . The test is started by placing six capsules 5 into each pot, switching on a heater, with the thermostat set at 35°C and starting stirring paddles at 50rpm. After 2 hours the thermostat temperature is increased to 42°C. At this point in the test the majority, if not all, of the capsules 5 should be orientated with the male body 25 end down. Prior to ejection, as the male member 25 begins to extract itself from the female body 10, the capsule 5 will begin to float with the male body 25 end down. When the male member 25 finally separates from the capsule 5 the charge slug 20 will fall to the bottom of the dissolution pot. During all of the tests carried out to date, with a charge slug 20 weight of 570mg and length approximately 10.5mm, all of the capsules 5 have behaved as described above. Emptying of the capsule closely follows ejection of the plug. Finally, it should be appreciated that the embodiment of the invention hereinbefore described is given by way of example only and is not meant to limit the scope of the invention in any way. It should particularly be understood that a capsule according to the present invention is in essence of a self-emptying nature in that the capsule orientates itself with the plug end downmost to allow the charge to fall out.

Claims: CLAIMS 1. A controlled release capsule which comprises a female body having a charge-receiving portion for holding a charge of an agent to be released, a male member engaged within a neck portion of the female body, and buoyancy means; wherein in use when the capsule is placed in a liquid and at least when the male member is released from the female body the buoyancy means cause the female body to orientate such that the charge receiving portion is above the neck portion thereby facilitating release of the charge from the female body. 2. A capsule according to the preceding claim, wherein the female body has a first end providing the neck portion and a closed second end where the buoyancy means are located. 3. A capsule according to claim 2 wherein the buoyancy means comprises a cavity formed at the second end of the female body. 4. A capsule according to claim 3 wherein the female body is substantially tubular and has an internal bore, and the cavity has a lesser internal bore than said charge- receiving portion. 5. A capsule according to claim 4 wherein the internal bore of the charge-receiving portion and the internal bore of the cavity are joined by a step portion. 6. A capsule according to claim 3 wherein the cavity is provided by spacing means adapted to space a charge in solid form from the closed end of the female body. 7. A capsule according to claim 6 wherein the spacing means comprises restriction means for creating a restriction in cross-section of the female body. 8. A capsule according to any preceding claim wherein the restriction means comprises a rod, a series of circumferentially spaced detents, or a grid. 9. A capsule according to claim 2 wherein the buoyancy means comprises gas entrapping means. 10. A capsule according to claim 9 wherein the gas entrapping means comprises a sealed enclosure or enclosures . 11. A capsule according to claim 10 wherein the gas entrapping means comprises a plurality of hollow spheres. 12. A capsule according to claim 9 wherein the gas entrapping means comprises a foam material. 13. A capsule according to any preceding claim which contains said charge of agent to be released. 14. A capsule according to claim 13 wherein the overall density of the capsule is greater than lg/ml so that the capsule does not float in water prior to ejection of the male member. 15. A capsule according to claim 13 or 14 wherein after release of the male member the density of the female body containing said charge of agent is less than lg/ml. 16. A capsule according to claim 13, 14 or 15 wherein the density of the female body is less than lg/ml. 17. A capsule according to any of claims 13 to 16 wherein the centre of buoyancy of the capsule is spaced away from the male member such that when the capsule is under liquid the capsule orients with the male member downwards. 18. A capsule according to any preceding claim wherein the male member is a plug formed of a water swellable material. 19. A test kit for cultivation and detection of microorganisms which comprises a capsule according to any preceding claim.

Inventors: ATKINS GERARD, HEGARTY MARK, MCFARLANE STEPHEN DONALD, ATKINS, GERARD, HEGARTY, MARK, MCFARLANE, STEPHEN, DONALD
Applicants: ATKINS GERARD, HEGARTY MARK, MCFARLANE STEPHEN DONALD, SCHERER CORP R P, ATKINS, GERARD, HEGARTY, MARK, MCFARLANE, STEPHEN, DONALD, R.P. SCHERER CORPORATION
Application year: 1998
Main classification: A61K9
IPC codes: A61K9, A61M31