FORM 2THE PATENT ACT 1970(39 of 1970)&The Patents Rules, 2003COMPLETE SPECIFICATION(See section 10 and rule 13)
1. TITLE OF THE INVENTION:
2. APPLICANT (S)(a) NAME: WOCKHARDT LIMITED(b)NATIONALITY:(d) ADDRESS: Wockhardt Towers,Bandra-Kurla Complex, Bandra East, Mumbai -400051.
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.ATTACHED HEREWITH.

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5 PHARMACEUTICAL COMPOSITIONS FOR ANALGESIA AND PYREXIA.
Field of the Invention
[0001] The present invention relates to a combination composition for treatment of in
10 body temperature leading to fever. The combination composition comprises of three drugs one belonging to a centrally acting analgesic class, an antipyretic agent and an antiinflammatory agent exerting peripheral analgesia with a different mechanism of action. The combination composition has been found to provide superior analgesia as evidenced from animal studies conducted to evaluate the better efficacy of the combination
15 composition. Preferred active ingredients include tramadol as the centrally acting analgesic agent, acetaminophen as the antipyretic agent and ibuprofen / diclofenac as the peripheral anti-inflammatory agent.
Background of the Invention
20
[0002] U.S. Pat. No. 3,652,589 discloses a class of analgesic cycloalkanol-substituted phenol esters having a basic amine group in the cycloalkyl ring. The compound (1R, 2R or IS, 2S)-2-[(dimethylamino) methyl]-l-(3-methoxyphenyi)-cyclohexenyl, commonly known as tramadol, is specifically disclosed therein. A series of articles pertaining to the
25 pharmacology, toxicology and clinical studies of tramadol are found in Arzneim, Forsch. (Drug Res.), 28(1), 114 (1978). Driessen et al., Arch. Pharmacol., 341, R104 (1990) discl ose that tramadol produces its analgesic effect through a mechanism that is neither fully opioid-like nor non-opioid-like. The Abstracts of the Vlth World Congress on Pain, Apr. 1-6 (1990), disclose that tramadol hydrochloride is an orally active pure agonist opioid
30 analgesic. However, clinical experience indicates that tramadol lacks many of the typical side effects of opioid agonists, e.g., respiratory depression (W. Vogel et al., Arzneim Forsch. (Drug Res.), 28(1), 183 (1978)), constipation (I. Arend et al., Arzneim. Forsch. ( Drug Res.), 28(1), 199 (1978)), tolerance (L. Flohe et, al., Arzneim. Forsch. (Drug Res.), 28(1), 213 (1978)), and abuse liability ( T. Yanagita, Arzneim. Forsch. (Drug Res.), 28(1),
35 158 (1978)). When given at a dose of 50 mg by rapid i.v. injection, tramadol may produce certain side effects unique to tramadol including hot flushes and sweating. Despite these side effects, tramadol's combination of non-opioid and opioid activity
1

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5 makes tramadol a very unique drug. Tramadol is currently being marketed by Grunenthal GMBH as an analgesic.
[0003] Opioids have for many years been used as analgesics to treat severe pain. They, however, produce undesirable side effects and as a result cannot always be given repeatedly or at high doses. The side effect problems are well documented in the
10 literature. See, for example, J. Jaffe in "Goodman and Gilman's, The Pharmacological Basis of Therapeutics", 8th edition; Gilman et al.; Pergamon Press, New York, 1990; Chapter 22; pages 522-573 wherein it is disclosed that morphine and its congeners, e.g., codeine, hydrocodone and oxycodone, are opioid agonist analgesics that exhibit side effects such as respiratory depression, constipation, tolerance and abuse liability.
15 [0004] As alternatives to using opioids, non-opioids such as aspirin and ibuprofen are used as analgesics. Ibuprofen, like aspirin, is not subject to the tolerance, addiction and toxicity of the opioid analgesics. However, ibuprofen, aspirin and other nonsteroidal antiinflammatory drugs (commonly referred to as NSAIDs) are only useful in relieving pain of moderate intensity, whereas the opioid analgesics are useful in relieving more intense
20 pain; See Woodbury, D. and Fingl, E. in "The Pharmacological Basis of Therapeutics", 5th Ed.; Goodman, L. and Gilman, A., Chapter 15, (1975).
[0005] To reduce the side effect problems of opioids, opioids have been combined with other drugs including non-opioid analgesic agents, which lower the amount of opioid needed to produce an equivalent degree of analgesia. It has been claimed that some of
25 these combination products also have the advantage of producing a synergistic analgesic effect. For example, A. Takemori, Annals New York Acad. Sci., 281,262 (1976) discloses that compositions including combinations of opioid analgesics with drugs other than analgesics exhibit a variety of effects, i.e., sub additive (inhibitory), additive or super additive. R. Taber et al., J. Pharm. Expt. Thera., 169(1), 29 (1969) disclose that the
30 combination of morphine and methadone, another opioid analgesic, exhibits an additive effect. U.S. Pat. No. 4,571,400 discloses that the combination of dihydrocodeine, an opioid analgesic, and ibuprofen, a non-opioid analgesic, provides super additive effects when the components are within certain ratios. See also U.S. Pat. Nos. 4,587,252 and 4,569,937, which disclose other ibuprofen opioid combinations. A. Pircio et al., Arch. Int.
2

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5 Pharmacodyn., 235, 116 (1978) report super additive analgesia with a 1:125 mixture of butorphanol, another opioid analgesic, and acetaminophen, a non-opioid analgesic, whereas a 1:10 mixture did not show any statistically significant super additive analgesia. Combinations of non-opioid analgesics have also been prepared to avoid the side effects associated with opioids, and the combinations are noted to have the benefit of requiring
10 less of each ingredient and producing super additive effects. G. Stacher et. al., Int. J. Clin. Pharmacol. Biopharmacy, 17, 250 (1979) report that the combination of non-opioid analgesics, i.e., tolmetin (another NSAID) and acetaminophen, allows for a marked reduction in the amount of tolmetin required to produce analgesia. In addition, U.S. Pat. No. 4,260,629 discloses that an orally administered composition of acetaminophen and
15 zomepirac, a non-opioid analgesic, in a particular weight ratio range produces a superadditive relief of pain in mammals. Furthermore, U.S. Pat. No. 4,132,788 discloses that 5-aroyl-l-(lower)alkylpyrrole-2-acetic acid derivatives, non-opioid analgesics, when combined with acetaminophen or aspirin exhibit superadditive antiarthritic activity. However, there have been warnings against the daily consumption of non-opioid
20 analgesic mixtures and of the consumption of a single non-opioid analgesic in large amounts or over long periods (see, D. Woodbury and E. Fingl at page 349). In addition, ibuprofen, aspirin and some other NSAIDs may cause gastrointestinal side effects especially if used repeatedly. See, for example, M. J. S. Langman, Am. J. Med. 84 (Suppl. 2A): 15-19, 1988; P. A. Insel in "The Pharmacological Basis of Therapeutics" 8th
25 Ed.; Gilman, A.G. et al., Chapter 26, pp. 664-668, 1990.
[0006] Acetaminophen, 4'-hydroxyacetanilide, is a non-opiate, non-salicylate analgesic and antipyretic drug. It is a peripherally acting analgesic and is well absorbed orally. It produces analgesia by elevation of the pain threshold and antipyretic through action on
30 the hypothalamic heat-regulating center. Acetaminophen is chemically JV-(4-Hydroxyphenyl)acetamide. It is commercially available under the trade name of TYLENOL®. Acetaminophen provides temporary relief of minor aches and pains with heartburn or acid indigestion and upset stomach associated with these symptoms.

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5 [0007] Ibuprofen, a nonsteroidal anti-inflammatory drug, possesses analgesic and antipyretic activities. Its mode of action is related to prostaglandin synthetase inhibition. Ibuprofen is chemically (±) - 2 - (p - isobutylphenyl) propionic acid represented by Formula III. It is commercially available under the trade name of Motrin®, Ibu and Ibu-Tab. It is indicated in the treatment for relief of the signs and symptoms of rheumatoid
10 arthritis and osteoarthritis, mild to moderate pain and treatment of primary dysmenorrhea.
[0008] Tramadol is a centrally acting synthetic opioid analgesic. It is chemically (±) cis-2-[(dimethylamino)methyl]-l-(3-methoxyphenyl) cyclo-hexanol hydrochloride. It is commercially available in form of its hydrochloride salt (Formula I) as Ultram tablets.
15 Tramadol is indicated in the treatment of the management of moderate to moderately severe pain in adults.
[0009] Combinations of tramadol with acetaminophen and tramadol with Ibuprofen are the disclosures made in US 5,336,691 and US 5,516,803 respectively.
[0010] US 6284274 assigned to Alza corporation discloses compositions comprising an
20 opiate or non-opiate analgesic using an osmotic release technology.
[0011] US 6221377 discloses a method of enhancing the analgesic, anti-inflammatory and anti-pyretic responses by administering the medicament with a pharmaceutically acceptable solution containing nitrous oxide. The presence of nitrous oxide enhances the efficacy of the medicament.
25 [0012] US 6007841 assigned to Algos discloses the potentiation of analgesic effectiveness of a narcotic agonist antagonist analgesic by co-administration of it with at least one non-toxic N-methyl D aspartate receptor antagonist. The N-methyl D aspartate receptor antagonist may comprise of drugs, which include tramadol, ibuprofen and acetaminophen. However an essential feature of the invention is the use of N-methyl D
30 aspartate receptor antagonist to potentiate the effect of a narcotic agonist antagonist.
[0013] US 5945416 and US 5998434 both assigned to Lilly relate to combination compositions of olanzapine with analgesic drugs like ibuprofen, naproxen and others for treatment of pain. 4

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5 [0014] US 5914129 (Alexander et al) discloses magnesium containing analgesic compositions, which comprise a magnesium salt, a stimulant and an analgesic agent.
[0015] US 2003203028 assigned to Impax Pharmaceuticals is the subject of a multiplex drug delivery system comprising at least two immediate release components substantially enveloped by a second extended release component.
10 [0016] WO0029022A1 assigned to Algos Pharmaceuticals claims a combination
composition of a COX-2 inhibitor with a centrally acting narcotic analgesic or an agonist antagonist analgesic and tramadol.
[0017] WO 06053012 published and assigned to Azaya Therapeutics discloses a pharmaceutical composition comprising an analgesic combination comprising a) an
15 NMDA antagonist or a pharmaceutically acceptable salt thereof, b) a methylxanthine or a pharmaceutically acceptable salt thereof and c) an opiate agonist, partial agonist or agonist/antagonist, or a pharmaceutically acceptable salt thereof.
[0018] WO 09850075 assigned to Algos Pharmaceuticals claims a combination composition of a COX-2 inhibitor with a N-methyl D aspartate receptor antagonist and/or
20 a nontoxic substance that block at least one major intracellular consequence of NMDA receptor activation.
[0019] EP 08459989B1 assigned to Virginia Commonwealth University disclose a triple composition comprising an analgesic, a skeletal muscle relaxant / sedative and a N-methyl D aspartate receptor antagonist.
25 [0020] WO 05107467 assigned to Descartes Therapeutics claims a combination of an opioid, NSAID and a dopaminergic agent for treating pain or nociception.
[0021] The prior art, however, does not disclose that a combination composition comprising an centrally acting opioid analgesic like tramadol, an antipyretic agent like acetaminophen and a peripherally acting non-opioid analgesic like ibuprofen / diclofenac.
30 Such a triple combination comprising three active therapeutic ingredients differing in their pharmacological basis of action would certainly alleviate symptoms, wherein inflammation leading to pain is accompanied by pyrexia. The addition of acetaminophen serves to control the pyrexia as the cause of pyrexia is many times of unknown origin and is inherent in many of the diseased conditions. In addition, the triple combination may
5

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5 offer better analgesic control than the dual combinations currently available in terms of exhibiting a super additive effect and thus achieving an analgesic level at a lower dose of the individual agents. This is advantageous as there will be a decreased dosing of the active ingredient to the patient coupled with the decrease in frequency of dosing over a dual combination and thus promote better patient compliance.
10
Summary of the Invention
[0022] The present invention relates to a combination composition comprising
a centrally acting opioid analgesic, an antipyretic and a peripherally acting non-opioid analgesic. It has now been found that the combination composition of the present
15 invention shows better analgesia when compared to the individual agents alone or dual combination compositions described in prior art. The combination employs lesser amounts of all the ingredients than would be necessary to produce the same amount of analgesia if either was used alone or the ingredients used as a dual combination. By using lesser amounts of the active drugs the side effects associated with each are reduced in
20 number and degree. Surprisingly the combination compositions comprising tramadol, acetaminophen and ibuprofen have been found to exhibit synergistic analgesic activity at certain ratios. In addition these combination compositions have been found to be particularly useful in conditions to treat inflammation accompanied by pyrexia.
25 Detailed Description of the Invention
[0023] The present invention is directed to compositions comprising tramadol,
acetaminophen and ibuprofen / diclofenac. The tramadol material is any one of (1R, 2R or IS, 2S)-(dimethylaminomethyl)-l-(3-methoxyphenyl)-cyclohexanol (tramadol), its N-oxide derivative ("tramadol N-oxide"), and its O-desmethyl derivative ("O-desmethyl
30 tramadol") or mixtures thereof. It also includes the individual stereoisomers, mixtures of stereoisomers, including the racemates, pharmaceutically acceptable salts of the amines, such as the hydrochloride salt, solvates and polymorphs of the tramadol material. Tramadol is commercially available from Grunenthal or may be made by the process described in U.S. Pat. No. 3,652,589, which is herein incorporated by reference.
6

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5 [0024] The pharmacology of acetaminophen is reviewed by B. Ameer et al.,
Ann. Int. Med., 87, 202 (1977), and the preparation of acetaminophen is disclosed in U.S. Pat. No. 2,998,450, which is incorporated herein by reference.
[0025] NSAIDs according to the present invention are non-opioid analgesics
10 characterized in that they are nonsteroidal drugs, which act as anti-inflammatory, analgesic and anti-pyretic agents. This class of drugs is well known in the art. See for example, Goodman, L. and Gilman, A., supra, in Chapter 26 (1990). These drugs share certain therapeutic actions and side effects. Within this broad class of drugs are salicylates, such as aspirin; pyrazolone derivatives such as phenylbutazone,
15 oxyphenbutazone, antipyrine, aminopyrine, dipyrone and apazone; indomethacin; sulindac; fenamates such as mefenamic, meclofenamic, flufenamic, tolfenamic and etofenamice acids; aryl acetic acid and propionic acid compounds such as 2-(p-isobutylphenyl)propionic acid (generic name ibuprofen); alphamethyl-4-(2-thienylcarbonyl) benzene acetic acid (generic name suprofen); 4,5-diphenyl-2-oxazole
20 propionic acid (generic name oxprozin); rac-6-chloro-alphamethyl-carbazole-2-acetic acid (generic name carprofen); 2-(3-phenyloxyphenyl)-propionic acid, particularly the calcium salt dihydrate thereof (these compounds being referred to generically as fenoprofen and fenoprofen calcium); 2-(6-methoxy-2-naphthyl) propionic acid (generic name naproxen; the generic name of the sodium salt is naproxen sodium); 4-(l,3-
25 dihydro- l-oxo-2H-isoindol-2-yl)-.alpha.-methylbenzene acetic acid (generic name indoprofen); 2-(3-benzoylphenyl)propionic acid (generic name ketoprofen); and 2-(2-fluoro-4-biphenylyl) propionic acid (generic name flurbiprofen) and l-5-(4-methylbenzoyl)-lH-pyrrole-2-acetic acid (generic name tolmetin). Also included within NSAIDs are compounds within the class including sodium 5-(4-chlorobenzoyl)-l,4-
30 dimethyl-lH-pyrrole-2-acetate dihydrate (generically referred to as zomepirac sodium); 4-hydroxy-2-methyl-N-(2-pyridyl-2H-1,2-benzothiazine-3-carboxamide-1,1 -dioxide (generic name piroxicam); 2', 4'-difluoro-4-hydroxy-3-biphenylcarboxylic acid (generic name diflunisal) or l-isopropyl-7-methyl-4-phenyl-2(lH)-quinozolinone (generic name proquazone), phenylacetic acid derivatives such as diclofenac; etodolac and nabumetone.
35 For the purposes of this invention, para-aminophenol derivatives such as acetaminophen
7

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5 are not considered NSAIDs because of their general lack of anti-inflammatory activity. All of the NSAIDs are commercially available materials. A particularly preferred class of NSAIDs for use in the composition of the present invention is the propionic acid derivatives. Within this class of compounds ibuprofen is the most preferred.
[0026] The doses of tramadol, acetaminophen and Ibuprofen as used in the present day
10 regimen when given individually as a single ingredient or as a dual combination are between 37.5 to 300mg, 200-750 mg and 200 to 800mg.
[0027] The preferred ratios of tramadol : acetaminophen: ibuprofen is from about 1:20:50, and more preferably from 1:15:30. The most preferred ratios are from about 1:10:25 to about 1:15:30. Combination compositions with the above weight ratios have
15 been demonstrated to exhibit synergistic analgesic effect coupled with superior efficacy in decreasing pyrexia accompanying anti-inflammatory conditions.
[0028] The following experimental examples describe the invention in greater particulars and are intended to be a way of illustrating but not limiting the invention
Example 1:

S.No. Ingredients mg/tab
Part 1
Intragranular
1 Tramadol 37.5
2 Acetaminophen 325
3 Starch 17.5
4 Sodium Starch Glycolate 5
5 Povidone - K 30 7.5
6 Sodium Lauryl Sulfate 5
Extragranular
7 Sodium Starch Glycolate 2.5
8 Microcrystalline cellulose 11
9 Talc 5
10 Colloidal Silicon Dioxide 4
11 Magnesium stearate 5
Part 2
Intragranular
12 Ibuprofen 200
13 Lactose Monohydrate 10
14 Microcrystalline cellulose 17.5
15 Croscarmellose sodium 5
8

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16 Povidone - K 30 5
Extragranular
17 Croscarmellose sodium 7.5
18 Colloidal Silicon Dioxide 2.5
19 Magnesium stearate 2.5
Wt. of core tablets 675
20 Opadry * 13.5
Total wt of coated tablet 688.5
5
Procedure:
[0029] Part 1: Tramadol, acetaminophen, starch and sodium starch glycolate are mixed in a Rapid Mixer Granulator (RMG). This blend is then subjected to wet granulation using an aqueous solution of povidone containing sodium lauryl sulphate. The resultant
10 granules are dried , milled and sized. The extragranular material comprising sodium starch glycolate, microcrystalline cellulose, talc, magnesium stearate and colloidal silicon dioxide are sifted and blended with the granules obtained from the intragranular stage.
[0030] Part 2: Ibuprofen, lactose, microcrystalline cellulose and crosscarmellose
15 sodium are mixed in a Rapid Mixer Granulator (RMG). This blend is then subjected to
wet granulation using an alcoholic solution of povidone. The resultant granules are dried
, milled and sized. The extragranular material comprising crosscarmellose sodium
glycolate, magnesium stearate and colloidal silicon dioxide are sifted and blended with
the granules obtained from the intragranular stage.
20
[0031] Compression and Coating: Granules of Part 1 and Part 2 are mixed together
and compressed as a single unit tablet or may be compressed separately to form s
bilayered tablet. The tablets are coated with Opadry to obtain a weight gain of
approximately 2%.
25
Example 2

S.No. Ingredients mg/tab
Part 1
Intragranular
1 Tramadol 37.5
2 Acetaminophen 325
9

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3 Starch 17.5
4 Sodium Starch Glycolate 5
5 Povidone - K 30 7.5
6 Sodium Lauryl Sulfate 5
Extragranular
7 Sodium Starch Glycolate 2.5
8 Microcrystalline cellulose 11
9 Talc 5
10 Colloidal Silicon Dioxide 4
11 Magnesium stearate 5
Part 2
Intragranular
12 Ibuprofen 400
13 Lactose Monohydrate 20
14 Microcrystalline cellulose 35
15 Croscarmellose sodium 10
16 Povidone - K 30 10
Extragranular
17 Croscarmellose sodium 15
18 Colloidal Silicon Dioxide 5
19 Magnesium stearate 5
Wt. of core tablets 925
20 Opadry 18.5
Total wt of coated tablet 943.5
5
[0032] The ingredients for Part 1 and Part 2 were blended according to the procedure described in Example 1. The excipients used were similar to those used in Example 1, except the final doses of tramadol, acetaminophen, and ibuprofen were 37.5 mg, 325 mg, and 400 mg, respectively.
10 [0033] The granules prepared in Part 1 and Part 2 are mixed together and compressed as a single layered tablets. Alternatively, the granules may be compressed separately to form bilayered tablets. The tablets (both types) are coated with Opadry to obtain a weight gain of approximately 2%.
Example 3

S.No. Ingredients mg/tab
Part 1
Intragranular
1 Tramadol 37.5
2 Acetaminophen 325
10

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3 Starch 17.5
4 Sodium Starch Glycolate 5
5 Povidone - K 30 7.5
6 Sodium Lauryl Sulfate 5
Extragranular
7 Sodium Starch Glycolate 2.5
8 Microcrystalline cellulose 11
9 Talc 5
10 Colloidal Silicon Dioxide 4
11 Magnesium stearate 5
Part 2
Intragranular
12 Ibuprofen 600
13 Lactose Monohydrate 30
14 Microcrystalline cellulose 52.5
15 Croscarmellose sodium 15
16 Povidone - K 30 15
Extragranular 0
17 Croscarmellose sodium 22.5
18 Colloidal Silicon Dioxide 7.5
19 Magnesium stearate 7.5
Wt. of core tablets 1175
20 Opadry 23.5
Total wt of coated tablet 1198.5
5
[0034] The ingredients for Part 1 and Part 2 were blended according to the procedure described in Example 1. The excipients used were similar to those used in Example 1, except the final doses of tramadol, acetaminophen, and ibuprofen were 37.5 mg, 325 mg, and 600 mg, respectively.
10 [0035] The granules prepared in Part 1 and Part 2 are mixed together and compressed as a single layered tablets. Alternatively, the granules may be compressed separately to form bilayered tablets. The tablets (both types) are coated with Opadry to obtain a weight gain of approximately 2%.
Example 4

15

S.No. Ingredients mg/tab
Part 1
Intragranular
1 Tramadol 37.5
2 Acetaminophen 325

11

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3 Starch 17.5
4 Sodium Starch Glycolate 5
5 Povidone - K 30 7.5
6 Sodium Lauryl Sulfate 5
Extragranular
7 Sodium Starch Glycolate 2.5
8 Microcrystalline cellulose 11
9 Talc 5
10 Colloidal Silicon Dioxide 4
11 Magnesium stearate 5
Part 2
Intragranular
12 Ibuprofen 800
13 Lactose Monohydrate 40
14 Microcrystalline cellulose 70
15 Croscarmellose sodium 20
16 Povidone - K 30 20
Extragranular 0
17 Croscarmellose sodium 30
18 Colloidal Silicon Dioxide 10
19 Magnesium stearate 10
Wt. of core tablets 1425
20 Opadry 28.5
Total wt of coated tablet 1453.5
5
[0036] The ingredients for Part 1 and Part 2 were blended according to the procedure described in Example 1. The excipients used were similar to those used in Example 1, except the final doses of tramadol, acetaminophen, and ibuprofen were 37.5 mg, 325 mg, and 800 mg, respectively.
10
[0037] The granules prepared in Part 1 and Part 2 are mixed together and compressed as a single layered tablets. Alternatively, the granules may be compressed separately to form bilayered tablets. The tablets (both types) are coated with Opadry to obtain a weight gain of approximately 2%.
15 Example 1: Analgesic Activity
[0038] Male mice (preferably of CD1 strain) were utilized in determining the analgesic effects associated with the compositions of the invention. The mice were all dosed orally with (a) a mixture of tramadol hydrochloride and acetaminophen (calculated individually
12

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5 in the base form), which is completely dissolved in distilled water, and (b) a mixture of tramadol hydrochloride and ibuprofen (calculated individually in the base form), which is completely dissolved in distilled water, or in distilled water containing 2% by volume of Tween 80 containing 100% polysorbate 80. An appropriate dosing volume is used.
[0039] The procedure used in detecting and comparing the analgesic activity of
10 different classes of analgesic drugs for which there is a good correlation with human efficacy is the prevention of acetylcholine-induced abdominal constriction in mice (H. Collier et al., Br. J. Pharmacol., 32, 295 (1968)).
[0040] Mice, are intubated with test doses containing (a) tramadol hydrochloride with ibuprofen (b) tramadol hydrochloride with acetaminophen and (c) tramadol
15 hydrochloride with acetaminophen with ibuprofen, or (d) a vehicle such as distilled water, or distilled water containing approximately about 2% by volume of Tween 80, were injected intraperitoneally with a challenge dose of acetylcholine bromide. The acetylcholine was completely dissolved in distilled water at a preferred concentration of about 5.0 to 10 mg/kg and injected at a preferred rate of about 0.20 mL/20 g. For scoring
20 purposes an "abdominal constriction" was defined as a contraction of the abdominal musculature accompanied by arching of the back and extension of the limbs. The mice were observed 10 minutes for the presence or absence of the abdominal constriction response beginning immediately after receiving the acetylcholine dose, which is about 30 minutes after receiving the oral administration of tramadol hydrochloride and ibuprofen,
25 tramadol hydrochloride and acetaminophen, combined doses of tramadol hydrochloride, acetaminophen and ibuprofen, or vehicle. Each mouse was used only once.
[0041] The analysis of possible superadditivity for the compositions at each fixed ratio was determined as disclosed by R. J. Tallarida et al., Life Sci., 45, 947 (1989). This procedure involved the determination of the total amount in the mixture that is required to
30 produce a specified level of effect, such as 50% (ED5o mix), and the corresponding total amount that would be expected under simple additivity (ED50add)- Where it was established that ED50mix