Serum Concentration of Phenylbutazone in Tests for Antiphlogistic Activity and under Clinical Treatment

Abstract

OWING to marked individual variations in the rate of metabolic transformation in man, the daily doses of phenylbutazone used in therapy show a relatively wide range. Burns et al.¹ found a biological half-life for phenylbutazone ranging from 1.5 to 6 days, and correspondingly found plateau plasma concentrations ranging from 60 to 150 mg/1. in different individuals. After an initial dose of 800 mg orally followed by 200 mg four times daily, Wilson et al.² found plasma concentrations from 50 to 100 mg/1. and consider these concentrations necessary for therapeutic effect. Currie³ found 80–110 mg/1. at the beginning of the therapy and later under maintenance dose-levels of 46–80 mg/l. Bruck et al.¹ are of the opinion that, in order to avoid side-effects, plasma concentrations should not exceed 100 mg/l., and during treatment they maintained concentrations of between 50 and 90 mg/1. They propose that treatment should begin with 200 mg per day orally, and that the dose should increase by 100 mg daily until the response is satisfactory.