Effect of formulation on dissolution and bioavailability of phenytoin tablets

Bioavailability of different phenytoin tablets was calculated from saliva phenytoin levels in healthy human volunteers in a single dose study. Tablets containing different excipients and either phenytoin free acid or sodium phenytoin were chose on the basis of an in vitro dissolution rate study of different tablets. Tablets containing phenytoin precipitated with polysorbate 80 showed faster in vitro dissolution and also higher bioavailability than tablets prepared with phenytoin free acid with different excipients. In vivo studies showed that proper formulation of a tablet containing the free acid form of phenytoin can give rise to the same bioavailability than that of sodium phenytoin. In vitro dissolution of the formulation reflected in vivo bioavailability.