Equiphen Paste (Phenylbutazone) is a synthetic, non-hormonal, anti-inflammatory, antipyretic compound useful in the management of inflammatory conditions. The apparent analgesic effect is probably related mainly to the anti-inflammatory properties of the compound.

Chemically, phenylbutazone is a 4-butyl-1, 2-diphenyl-3, 5-pyrazolidine-dione. It is a pyrazolone derivative, entirely unrelated to the steroid hormones.