Phenylbutazone: what the FDA reviewed for dog products

Phenylbutazone Tablets, USP 100 mg Phenylbutazone Tablets, USP 200 mg NADA 094-170, Supplemental approval, January 12, 2001; sponsor Cronus Pharma Specialities India Private Ltd.; species: Dogs; foi_id 328; FDA PDF

Indication

Relief of inflammatory conditions associated with the musculoskeletal system in dogs.

Dose regimen

20 mg/lb of body weight (200 mg/10 lb) daily, maximum 800 mg per day, oral (tablet), in three divided doses daily, relatively high dose for the first 48 hours, then reduce gradually to the lowest maintenance dose producing the desired clinical response

ORALLY 20 mg/lb. of body weight (200 mg/10 lb.) in three divided doses daily. Maximum dose is 800 mg per day regardless of weight.

Effectiveness

In vitro comparative dissolution of the new 200 mg tablet vs the approved 100 mg tablet (12 units each; samples at 10-45 minutes) used as a surrogate for in vivo bioequivalence because phenylbutazone is a BCS Class II compound and the formulations are proportionally identical; primary endpoint: Dissolution profile similarity factor f2 >= 50; result: f2 = 61.80 (using the 10-25 minute points), meeting the >= 50 criterion; tablet size change judged not to affect dissolution, so in vivo absorption expected to be comparable at the same mg/kg dose

For this dataset, the Similarity Factor (f2) = 61.80 For curves to be considered similar, the f2 value should be greater than or equal to 50.

Extraction notes: Supplemental approval (2001) adding a 200 mg tablet strength; no animal studies. Animal safety refers to the original NADA 094-170 FOI summary (1974). No Species/Class field; 'Dogs' from the indication. Product name in the catalogue lists both 100 mg and 200 mg tablets; the supplement concerns the 200 mg tablet.