in describing the preferred embodiment , certain terminology will be utilized for the sake of clarity . such terminology is intended to encompass the recited embodiment , as well as all technical equivalents which operate in a similar manner for a similar purpose to achieve a similar result . the present invention relates to an injection implant comprising two separate delivery vehicles of the same biologically active ingredient . the first vehicle is capable of providing an immediate - release of the ingredient to the animal system whereas the second vehicle is capable of providing a sustained or extended release of the same active . by the term “ implant ” is meant any physical device containing the biologically active material in multiple delivery vehicles such that the vehicles are delivered to the animal &# 39 ; s system via an injection . in most embodiments the implant contains the immediate - release and sustained - release vehicles such that they both be administered in a single injection , but embodiments where multiple injections of either the immediate - release and / or sustained - release vehicles occurring at different points in time is expressly covered . the concept of injectable implants is well known to those skilled in the art and it is submitted that one could envision any of a number of embodiments designed to simultaneously deliver the multiple vehicles via a single injection . for example , an injectable implant system is described in u . s . pat . no . 5 , 874 , 098 . to the extent necessary for completion , this reference is expressly incorporated by reference . the term “ immediate - release ” defines a vehicle that , within a finite period of time , for example 24 hours , releases in vivo enough of the biologically active material to begin to achieve a desired effect in the patient . for example , an implant which releases at least 30 % percent of its active material within 24 hours as defined by the methodology of example 1 could qualify as such a vehicle . the term “ sustained - release ” defines a vehicle that releases the same active material at a slower rate as compared to the “ immediate - release ” vehicle . for example , an implant which retains at least 30 % percent of its active material within 24 hours as defined by the methodology of example 1 , provided that its release rate is slower than that of the immediate - release vehicle could qualify as such a vehicle . the concept of immediate - release and sustained - release compositions are known in the art . however , the use of an implant containing multiple delivery vehicles which can deliver the same active both immediately and over a sustained period of time is novel . furthermore , the time period defined by “ immediate - release ” or “ sustained - release ” is often determined by the disease or disorder being treated . for example , for some diseases or disorders , an immediate - release will produce a desired effect in minutes or hours , whereas for other diseases or disorders , an immediate - release will produce a desired effect in a matter of days or weeks . the first delivery vehicle comprises a delivery system capable of immediately releasing enough active material to generate a desired effect in a patient shortly after administration . there are many ways to design a vehicle capable of this and such vehicles are considered as being within the skill of the artisan . examples of immediate - release vehicles include , but are not limited to the following : coated solids or liquids where the coating wall material is very thin , coated solids or liquids where the coating wall material is very soluble in body fluids , porous or freeze - dried solids having an increased surface area contact , a solid tablet or pellet containing a disintegrating agent which causes the solid tablet to rapidly break down when in body fluids , a solid or pellet containing a relatively small or micronized active particle size , an osmotic delivery system where the osmotic system is such that a substantial amount of the active is released upon implantation , and mixtures thereof . the above listing is considered merely representative and one skilled in the art could envision other immediate - release mechanisms / embodiments . the second delivery vehicle comprises a sustained release delivery system . as a practical matter , the skilled artisan may select any of the following non - limiting sustained release delivery vehicles to contain the actives of the implant of the claimed invention : encapsulated solutions or suspensions , biodegradable solid substances , conventional tablet / pellet formulations optionally utilizing either disintegrating agents and / or active particle size to modulate release , conventional tablet / pellet formulations coated with a polymeric membrane to control release ( e . g ., ethylcellulose ), matrix - tablets based on gel - forming excipients ( e . g ., hydroxypropyl methyl cellulose ), matrix - type systems based on non - biodegradable polymers ( e . g ., medical grade silastics ), membrane - type systems based on non - biodegradable polymers ( e . g ., medical grade silastics ), matrix - type systems based on biodegradable polymers ( e . g ., polylactic acid and polyglycolic acid homo and copolymers of various compositions ), matrix - type systems based on lipidic excipients ( e . g ., cholesterol , waxes ), mass transfer systems based on osmotic pressure pumping through a hole in an impermeable coating and mixtures thereof . the above listing is considered merely representative and one skilled in the art could envision other sustained release mechanisms / embodiments . in particularly preferred embodiments , the implant comprises a magazine containing solid biodegradable pellets containing the same actives and having differential release characteristics it is still further contemplated that a magazine containing greater than two pellets could be used in accordance with the present invention . selection of the specific implant embodiment is largely determined by the specific end result desired . in a preferred embodiment , the biologically active ingredient can be provided in the form of a immediate - release component containing a disintegrating agent and a sustained - release component that does not contain a disintegrating agent . the immediate - release component can be provided in the form of granules or pellets containing the biologically active ingredient and can be formed by conventional granulation practices or through direct compression processes . the pellets typically contain from about 1 to 99 wt . % of the biologically active ingredient with the remainder being conventional tableting ingredients such as magnesium stearate , stearic acid , colloidal silicon dioxide , talc , titanium dioxide , magnesium , calcium and aluminum salts , lactose , povidone , high molecular weight polyethylene glycols and derivatives thereof , bioerodible polymers such as poly ( orthoesters ) and polyanhydrides and anhydride co - polymers , polyoxystearates , carboxymethylcellulose , cellulose esters such as acetate phthalate , acetate succinate and cellulose acetate , n , n - diethylamino acetate , polyvinyl alcohol , hydroxypropyl methyl cellulose , and the like . in the immediate - release vehicle , a disintegrating agent is also preferably present in order to enable the immediate - release of the pharmacologically active ingredient once it is implanted into the subject . conventional disintegrating agents used in tableting processes can be used in the present invention with sodium crosscaramellose , sodium carboxymethylcellulose , microcrystalline cellulose , powdered cellulose , colloidal silicon dioxide , crospovidone , guar gum , magnesium aluminum silicate , methyl cellulose , alginic acid , calcium carboxymethylcellulose , potassium polacrilin ( and other cation exchange resins such as amberlite resins ), starch , pregelatinized starch , sodium starch glycolate , and sodium alginate being especially preferred . the disintegrating agent typically is contained in the pellet in an amount of 0 . 1 - 50 % by weight , based on the total weight of the pellet , with 0 . 5 - 15 % by weight being preferred and 1 - 6 % by weight being especially preferred . the pellets are formed according to conventional methods that involve the mixing of the ingredients , wet , dry , or fluid - bed granulation , or extrusion / spheronization , followed by screening , drying , screening / sizing , lubrication and compression . these steps are well known in the art . as discussed above , the implant dose is comprised of a combination of the two types of pellets . the time release properties of the implant composition can be controlled by varying the number of pellets containing the disintegrating agent with respect to the pellets not containing a disintegrating agent . the number of pellets containing a disintegrating agent and the number of pellets which do not contain a disintegrating agent in the implant composition can be readily determined depending on the drug being administered , the subject to whom the drug is being administered and the desired duration of treatment . alternatively , differential active loadings can also be utilized to achieve desired results . the method of choice is considered as falling within the skill of the artisan . in the present invention , the biologically active ingredient contained in the implant composition is not critical and can be any substance such as enzymes or other organic catalysts , ribozymes , organometalics , proteins and glycoproteins , peptides , poly ( amino acids ), antibodies , nucleic acids , steroids , antibiotics , antimycotics , anti - narcotics , cytostatics , cytotoxics , cytokines , carbohydrates , oleophobics , lipids , antihistamines , laxatives , vitamins , decongestants , gastrointestinal sedatives , anti - inflammatory substances , antimanics , anti - infectives , coronary vasodilators , peripheral vasodilators , cerebral vasodilators , psychotropics , stimulants , anti - diarrheal preparations , anti - anginal drugs , vasoconstrictors , anticoagulants , antithrombotic drugs , analgesics , antipyretics , hypnotics , sedatives , antiemetics , antinauseants , anticonvulsants , neuromuscular drugs , hyperglycemic and hypoglycemic agents , antivirals , antineoplastics antidepressants , anticholinergics , antiallergic agents , antidiabetic agents , antiarrythmics , antihormones , antihistamines , β - blockers , cardiac glycosides , contraceptives , contrast materials , radiopharmaceuticals , dopaminergic agents , lipid - regulating agents , uricoscurics , tranquilizers , thyroid and antithyroid preparations , diuretics , antispasmodics , uterine relaxants , mineral and nutritional additives , antiobesity drugs , hormones , antihelmentics , pharmaceuticals and other therapeutic agents . the invention may also be employed for the delivery of microorganisms , either living , attenuated or dead such as bacteria , and viruses such as indigenous vira , enterovira , bacteriophages . the present invention is especially suited for the immediate and sustained delivery of hormones and steroids such as androgens , such as testosterone , trenbolone acetate ( tba ), dihydroepiandroterone , and other androgenic steroids , estrogens , such as estradiol - 17 - β , estradiol benzoate , zeralanone , and other estrogenic steroids , progestins , such as progesterone , melengestrol acetate ( mga ), megestrol acetate , medroxyprogesterone acetate , norgestemet , norethidrone , and other progestin compounds , releasing factors , such as leutinizing hormone releasing hormone and analogs , growth hormone releasing hormone and analogs , thyroid releasing hormone and analogs , and other releasing factors and analogs , growth hormones / somatotropin , such as natural and recombinant somatotropins and analogs from various species , growth factors , such as insulin - like growth factor , epidermal growth factor and other such factors . it is also especially suited for delivery of antihelmintics , such as invermectins , and antigens . an especially preferred use of the present invention is in the suppression of estrus , inhibition of pregnancy and increased body weight of cattle through the implantation of the implant composition of the present invention in the body of the cattle containing mga , a combination of mga and tba or a combination of mga , tba and estradiol as the biologically active ingredient . a preferred embodiment for this use comprises an implant containing one to four , more preferably one to two immediate - release pellets and four to six , more preferably three to five sustained - release pellets . an even more preferred embodiment for this use comprises an implant containing one immediate - release pellet and five sustained - release pellets . in practice , the active ingredients are contained in the delivery vehicle , for example pellets , preferably in an amount of from 1 to 99 % and preferably from 50 to 90 wt . %. in particularly preferred embodiments , when used to administer mga and / or tba , the present invention can provide beneficial and advantageous results in the hormonal control of the reproductive cycle in animals , for example , by reducing the post - partum anestrual period in cattle ; by synchronization of the estrual period in a group of cattle ; by preventing estrual activity in fattening meat animals ; by controlling the estrual period in individual animals ; and by providing compositions and methods to further weight gain with lessened side effects in beef cattle . when mga or tba are the biologically active compositions , each delivery vehicle contains between about 5 to about 200 mg of mga or tba . in addition , the carcass composition of the animal may be improved ; for example , a carcass having increased lean and less fat may result . in addition to the active ingredients , each of the delivery vehicles of the implant may independently contain standard granulating aids such as lubricants , diluents , binders and glidants , magnesium stearate , stearic acid , colloidal silicon dioxide , talc , titanium dioxide , magnesium , calcium and aluminum salts , lactose , cyclodextrins and derivatives thereof , starches , povidone , high molecular weight polyethylene glycols and derivatives thereof , bioerodible polymers such as poly ( orthoesters ) and polyanhydride and anhydride co - polymers , polystearates , carboxymethyl cellulose , cellulose esters such as acetate phthalate , acetate succinate and cellulose acetate , n , n - diethylamine acetate , polyvinyl alcohol , hydroxypropyl methyl cellulose , other biologically active or inactive substances , other pharmaceutically active or inactive substances , and the like . the implant composition of the present invention can be administered subcutaneously , intramuscularly , intraperitoneally , intracranially , etc ., depending on the most desirable site of administration for the biologically active ingredient . in a particularly preferred embodiment , the implant is injected via needle subcutaneously in the posterior of the ear of the animal . the implanter used to inject the needle may be any of those commonly used in the art , with an implanter equipped with a hypodermic needle being particularly preferred . the implant composition of the present invention can be used to deliver the active ingredient on an immediate and a sustained release basis to the following types of animals : cows , horses , sheep , swine , dogs , cats or any other suitable animal , including humans . in particularly preferred embodiments the implant containing differentially releasing mga and / or tba is injected into a heifer . to use the implant of the present invention , the implant composition containing the immediate and sustained release vehicles is first prepared and then packaged for injectable use , typically as a magazine . thereafter , the magazine is inserted into the implanter housing and the operator activates the implanter to puncture the skin of the animal . this is typically accomplished by a hypodermic needle . the implant composition thereafter traverses through the bore of the needle and into the puncture site . the operator thereafter withdraws the needle , leaving the implant device in the animal . because of the physical or chemical nature of the immediate - release vehicle , the active is immediately released to the body and once distributed into the body is able to achieve an immediate and desired result . for example in a heifer , an immediate - release of substantial amount of mga ( e . g ., in one pellet ) can immediately inhibit pregnancy of the heifer . because of the physical or chemical nature of the sustained release vehicle , the same active is distributed to the animal over a desired period of time ( e . g ., in five pellets ). using the above example , the sustained release of mga can inhibit pregnancy for an extended period of time . in the preferred embodiment where mga ( either alone or in combination with other actives ) is contained in differential releasing pellets , the composition is capable of providing immediate and sustained release properties so that one injection will yield desired results in the animal first , immediately , and then for between about 60 to about 365 days with a more preferred range of from about 150 to about 200 days and a most preferred range of from about 180 to about 200 days . by utilizing the implant composition and method as claimed herein , the following advantages are provided to the operator : dual effect by using the same biologically active material , modification of release rate providing for both immediate and sustained duration of effectiveness , potential reduction of residues that would occur if only one type of vehicle were used and treatment dosage only for the desired duration since a larger - than - optimal dose is not needed in order to achieve a rapid - onset of action , and possible carcass improvement in the case where the animal subject to treatment is a food animal . two sets of biologically active pellets are formulated by conventional tableting technology , such as wet granulation with water as a granulation liquid or dry granulation , followed by screening , sizing and tablet compression . mg per component pellet immediate - release pellets : melengestrol acetate micronized 24 mg lactose monohydrate nf bolted 5 . 0 mg crosscaramellose sodium nf type a 1 . 5 mg pregelatinized starch nf 6 . 0 mg colloidal silicon dioxide nf 0 . 2 mg magnesium stearate nf powder food grade 1 . 0 mg sustained - release pellets : melengestrol acetate micronized 24 mg lactose monohydrate nf bolted 8 . 235 mg sorbitol nf crystalline 0 . 355 mg sucrose nf granular 0 . 2755 pregelatinized starch nf 2 . 0 mg colloidal silicon dioxide nf 0 . 2 mg magnesium stearate nf powder food grade 1 . 0 mg in - vitro release characteristics of the rapid - release and slow - release pellets of example 1 are shown in fig1 for dissolution testing carried out in a usp dissolution apparatus no . ii ( paddle ) at 37 ° c ., in a dissolution medium composed of 0 . 3 % sds ( sodium dodecyl sulfate ), at 25 rpm . referring to fig1 the combining of the immediate - release and sustained - release pellets in different proportions in the same implant dose will allow for a wide range of in - vitro release profiles to be created , and thereby giving a range of in - vivo release rates . for the same total dose of active agent , an implant comprising of a larger number of rapid - releasing pellets , when compared to another comprising fewer of the rapid - releasing pellets , will provide a more rapid onset of action and also a shorter total duration of effect . one or more of each of the immediate - release and sustained - release pellets of example 1 are inserted into the magazine of an implanter device containing a hypodermic needle . for example , the implant may contain one immediate - release pellet and five sustained - release pellets . the operator activates the implanter to first puncture the skin , then deliver the implant composition through the needle and into the animal . in the case where the animal is a heifer , it is preferred that the puncture occurs at the posterior portion of the ear . the immediate - release pellet of the implant delivers the mga in an amount of and rate sufficient to immediately inhibit pregnancy . the sustained - release pellets of the implant delivers the mga in an amount of and rate sufficient to deliver to the heifer on a sustained release basis in order to exhibit growth increase , estrus suppression and inhibit pregnancy for an additional time period of from 150 to 200 days . various modifications of the present invention can be made without departing from the spirit or scope thereof and it should be understood that the invention is intended to be limited only as defined in the appended claims .
a pharmaceutical implant for administering a biologically active substance is made up of an immediate - release component , preferably containing a disintegrating agent , and a sustained - release component . the implant of the present invention provides flexibility in adjusting the release of the medicament and a faster onset of release can be provided along with a long - term sustained - release . the release rate of the biologically active substance can be adjusted by controlling the relative quantities of the immediate - release component and the sustained - release component .