Saliva-resistant coating of tablets prevents oral release of penicillin: plasma but not saliva equivalence.

Abstract

To investigate saliva and plasma concentrations of penicillin after the intake of a conventional phenoxymethylpenicillin (PcV) tablet and a tablet with saliva-resistant coating (PcVsr), both containing 1 g penicillin. The study had an open randomized crossover design and involved 24 healthy subjects. Saliva and blood were sampled intermittently for 6 h after tablet intake. Within the first 10 min after tablet intake penicillin was detected in saliva in ten subjects taking PcV and in none taking PcVsr (P < 0.001). These initial saliva concentrations were short-lasting, but in some subjects 50 to 100 times higher than those following the peak concentration in plasma, i.e. at 40 min or more after swallowing. From 40 min and onwards the saliva concentrations of penicillin were very similar for the two formulations. The elimination of high initial saliva concentrations may diminish ecological disturbances of the mouth flora as well as removing the unpleasant taste of penicillin. The plasma concentrations of penicillin were similar for the two formulations throughout the 6-h sampling period and the mean ratio of the area under the plasma concentration-time curve was 99% for PcVsr in relation to PcV, the 90% confidence interval being 86-115%. The corresponding values for the maximum plasma concentration were 108% and 93 127%. The time to maximum concentration was 45 min for PcVsr and 41 min for PcV. Thus, with regard to standard criteria which are based on systemic (plasma) concentrations, the formulations were bioequivalent despite the substantial difference in initial local (saliva) concentrations. Saliva-resistant coating of tablets can prevent oral release of penicillin without affecting the plasma concentrations. From a clinical point of view both local and systemic equivalence should be established before bioequivalence is assumed.