Combination of a centrally-acting analgesic and a selective cyclooxygenase-2 inhibitor anti-inflammatory agent for the treatment of inflammation and pain in the veterinary field

Abstract

The present invention relates to veterinary pharmaceutical compositions for the treatment of pain and inflammation, containing a combination of Tramadol and Firocoxib, for oral administration.

Claims

1. Method of treating inflammation in animals in need thereof comprising preparing a medicament comprising a combination of Tramadol and Firocoxib; administering an effective dose of said combination to said animals, said Firocoxib being administered below a minimum effective anti-inflammatory dose; and treating said inflammation in said animals.

2. Method of claim 1, in which the animals are pets, caged birds, rodents, lagomorphs, mustelids, ruminants and swine.

3. Method of claim 2, in which the pets are dogs, cats and horses.

4. Method of claim 1, wherein said effective amounts comprises 2 to 8 mg/Kg of Tramadol and approximately 0.5 to 4 mg/Kg of Firocoxib.

5. Method of claim 1, wherein said effective amounts comprises 2 to 8 mg/Kg of Tramadol and approximately 2 to 3 mg/kg of Firocoxib.

Description

BRIEF DESCRIPTION OF FIGURE

(1) The annexed FIGURE shows the anti-inflammatory activity of Tramadol and Firocoxib alone or combined. The intensity of the oedema, measured with a plethysmometer, is shown as the algebraic difference between the inflamed paw and the normal paw (ml).

PHARMACOLOGICAL TESTS

(2) A study has been conducted to evaluate the effect of combining a very low dose of Firocoxib, with no anti-inflammatory efficacy, and an analgesic dose of Tramadol.

(3) An inflammation model extensively used and validated in the rat was used for the study.

Experimental Protocol

Animals

(4) Sprague-Dawley rats weighing 200-250 grams were used. The animals were housed in groups of 4 to a cage, at the temperature of 22° C.±2° C., with a light-dark cycle of 12/12-hour and unlimited access to food and water. The animals were used after a week's acclimatisation in the housing facility. Each test group consisted of 8 rats.

(5) Inducement of Inflammation

(6) Inflammation was induced in one limb of the rat by administering a suspension of complete Freund adjuvant (CFA) containing 0.1 mg/0.1 ml of inactivated mycobacterium tuberculosis (H37Ra, ATCC 25177), in paraffin oil and mannide monooleate. The CFA was injected into the plantar surface of the left hind paw of the rat. This method induces reproducible inflammation characterised by oedema and pain.

(7) Medicaments

(8) All the medicaments were administered 3 days after the inflammation was induced with CFA. The Firocoxib was resuspended in a carrier consisting of 0.5% methocel, and administered orally in the volume of 1 ml at the doses of 2.5 and 5 mg/Kg.

(9) The dose of 2.5 mg/Kg was combined with Tramadol at the dose of 4 mg/Kg. Tramadol dissolved in saline was administered by the intraperitoneal route (i.p., 0.2 ml/100 grams of weight) 30 minutes before the Firocoxib. Inflammatory oedema was evaluated 1 hour after the Tramadol, corresponding to 90 minutes after the Firocoxib. This period was selected on the basis of earlier studies which demonstrated that the analgesic effect of Tramadol and the anti-inflammatory effect of Firocoxib were greatest at the full dose. The control animals were treated per os with the carrier, and i.p. with the same volume of saline.

(10) Evaluation of Anti-Inflammatory Effect

(11) The intensity of the oedema was measured on day 3 after intraplantar administration of CFA, 90 minutes after Firocoxib, corresponding to 1 hour after i.p. administration of Tramadol. We chose to evaluate the oedema 3 days after it was induced, because it is largest at this time. The paw swelling (oedema) was evaluated by measuring the volume of both hind paws using a specific instrument, the plethysmometer (7150 plethysmometer, Basile, Comerio, Italy). The results are expressed as the algebraic difference between the volume in ml of the inflamed paw (injected with CFA) and the normal uninflamed paw: the greater the difference, the larger the oedema present.

(12) Statistical Analysis

(13) The values are the mean±SD of 8/10 rats.

(14) The significance of the anti-inflammatory activity was evaluated with the Analysis of Variance (ANOVA) test, followed by the Bonferroni multiple comparison test. ANOVA test is the most suitable statistical test when more than 2 treatment groups are present. It is a restrictive test because it takes account of the variability of all the trial groups.

(15) Results

(16) The table and FIGURE show the intensity of the inflammatory oedema after treatment with Tramadol (4 mg/kg) alone, Firocoxib alone at the dose of 5.0 and 2.5 mg/Kg, and the combination of Tramadol 4 mg/kg+Firocoxib 2.5 mg/Kg.

(17) TABLE-US-00001 TABLE Treatment 90 min. after Firocoxib p.o. ml (inflamed paw/ and 60 min. after Tramadol normal paw) Saline 0.84 ± 0.06 Tramadol 0.80 ± 0.06 4 mg/kg Firocoxib 0.42 ± 0.08* 5 mg/Kg Firocoxib 0.83 ± 0.05 2.5 mg/kg Firocoxib 2.5 mg/kg + Tramadol 4 mg/kg 0.50 ± 0.06*# Mean ± SD (6-8 animals) *= p < 0.01 vs saline #= p < 0.01 vs Firocoxib 2.5 mg/Kg

(18) ANOVA+Bonferroni's t-Test for Multiple Comparisons

(19) As was to be expected for a centrally-acting analgesic, Tramadol (4 mg/kg) had no anti-inflammatory effect. Firocoxib at the dose of 5.0 mg/kg induced a certain anti-inflammatory effect (approx. 50% inhibition of oedema), but when the dose was halved to 2.5 mg/kg, it completely lost its anti-inflammatory effect. Surprisingly, when the ineffective dose of Firocoxib (2.5 mg/kg) was administered together with Tramadol (4 mg/kg), the anti-inflammatory effect reappeared, demonstrated by the fact that the oedema was significantly reduced. The extent of the anti-inflammatory effect observed with the combination of 4 mg/kg of Tramadol+2.5 mg/kg of Firocoxib is comparable with the effect induced by the higher dose of Firocoxib (5.0 mg/kg).

(20) This study clearly shows that a dose of Firocoxib which is ineffective (because it is low) acquires an unexpected, significant anti-inflammatory activity when administered with an analgesic dose of Tramadol. Consequently, the combination to which the present invention relates produces full anti-inflammatory activity with very low doses of Firocoxib, with a significant reduction in adverse effects on the liver, heart, kidney and gastrointestinal functions and clotting disorders.

(21) The compositions according to the invention can be formulated in a way suitable for oral administration to animals, and will be prepared according to conventional methods well known in pharmaceutical technology, such as those described in “Remington's Pharmaceutical Handbook”, Mack Publishing Co., N.Y., USA, using excipients, diluents, filling agents and anti-caking agents acceptable for their final use.

(22) Examples of compositions for oral administration are: water-dispersible tablets, palatable tablets, palatable boluses, oral gels or pastes, drops.