(First Priority) Pributazone Boluses are used for the relief of inflammatory conditions associated with the musculoskeletal system in horses. Pributazone Boluses are a non-steroidal anti-inflammatory drug (NSAID). Each Pributazone bolus contains 1 gram phenylbutazone. The dosage of Pributazone Boluses is recommended at 1-2 boluses per 500 lbs body weight daily, given orally. Dosage is usually reduced as symptoms regress. Phenylbutazone.