Oxicams

Oxicams

The term oxicam described the relatively new enolic acid class of 4-hydroxyl -1,2 benzothiazine carboxamide with anti-inflammatory and analgesic properties.

i. Piroxicam

Properties and uses: Piroxicam is a white or slightly yellow crystalline powder, practically insoluble in water, soluble in methylene chloride, and slightly soluble in ethanol. It is employed for acute and long-term therapy for the relief of symptoms of osteoarthritis and rheumatoid arthritis. It also possesses uricosuric action and has been used in the treatment of acute gout.

Assay: Dissolve the sample in a mixture of equal volumes of acetic anhydride and anhydrous acetic acid and titrate against 0.1 M perchloric acid. Determine the end-point potentiometrically.

Dose: Usual adult oral dose is 20 mg per day.

Dosage forms: Piroxicam capsules I.P., B.P., Piroxicam tablets I.P., Piroxicam gel B.P.

Synthesis

The two more closely related analogues are obtained by varying the heterocyclic amine used in the last step. 2-Amino thiazole thus leads to sudoxicam, while 3-amino-5-methylisoxazole affords isoxicam.

ii. Tenoxicam (Tobitil)

Properties and uses: Tenoxicam is a yellow crystalline powder, practically insoluble in water, sparingly soluble in methylene chloride, very slightly soluble in ethanol, and soluble in solutions of acids and alkalis. Used as cyclooxygenase inhibitor, analgesic, and anti-inflammatory agent.

Assay: Dissolve the sample in anhydrous formic acid, add anhydrous acetic acid, and titrate against 0.1 M perchloric acid. Determine the end point potentiometrically.

Synthesis

Dose: Dose in the case of musculoskeletal and joint disorders—such as ankylosing spondylitis, osteoarthritis and rheumatoid arthritis— and short-term management of soft tissue injury for adult is 20 mg as a single daily dose given for 7 days in acute cases. For musculoskeletal disorders and other related illnesses, the dose is a maximum of 4 mg a day up to 14 days in severe cases (short-term use).

Dosage forms: Tenoxicam injection B.P., Tenoxicam tablets B.P.

iii. Meloxicam

Metabolism: This category of drugs undergoes aromatic hydroxylation at several positions of aromatic benzothiazine ring. Sudoxicam undergoes primary hydroxylation of thiazole ring, followed by ring opening, whereas isoxicam undergoes primary cleavage reaction of benzothiazine ring

Properties and uses: Meloxicam is a pale yellow powder, practically insoluble in water, slightly soluble in acetone, soluble in dimethylformamide, very slightly soluble in ethanol and in methanol. Used as cyclooxygenase inhibitor, analgesic, and anti-inflammatory.

Assay: Dissolve the sample in a mixture of anhydrous acetic acid and anhydrous formic acid (10:1) and titrate against 0.1 M perchloric acid. Determine the end point potentiometrically.

Dosage forms: Meloxicam tablets B.P.

SAR of Oxicams

The most active analogues have substituents CH₃ on the nitrogen and electron withdrawing substituents on the anilide phenyl groups, such as Cl and CF₃.

·The introduction of heterocyclic ring in the amide chain significantly increases the anti-inflammatory activity. Example—2-thiazolyl derivative sudoxicam is more potent than indomethacin.

·The most active benzothiazine have acidities in the pKa range of 6–8.