Bioavailability evaluation of an enteric-coated phenylbutazone formulation, and cross-over comparison with a sugar-coated product.

The relative bioavailability of enteric-coated, and commercially available sugar-coated tablets of phenylbutazone (PBZ) was studied in eight healthy volunteers. Each subject received a single oral dose of 400 mg of each preparation in a cross-over sequence. Blood samples were taken for assay of unchanged drug at intervals up to 360 hours. In an attempt fully to characterize the absorption and elimination profiles, three bioavailability parameters were evaluated; peak plasma level of PBZ, time taken to achieve peak level, and area under the plasma level-time curve. Peak plasma levels of PBZ, and area under the plasma level-time curves were not significantly different for the two products, which indicated their bioequivalence. A statistically significant (P is less than 0.001) difference in the rate of absorption of the two products was apparent, since the mean time of occurrence of the peak plasma level of PBZ for the enteric-coated tablets was 9.0 hours compared with 3.9 hours for the sugar-coated formulation. No subjective effects from the two products were noted by any of the subjects, nor were there any alterations in haematological or biochemical parameters.