Plasma and salivary concentrations of erythromycin after administration of three different formulations

In a 6-volunteer cross-over study the pharmacokinetics of 3 erythromycin preparations were compared. A single oral dose of 500 mg of each preparation was administered at each occasion and the levels measured in timed samples of plasma and saliva. Markedly higher blood concentrations of the estolate and propionate were obtained compared to the stearate. Comparison of serum and plasma concentration of the drugs from each split sample showed no significant differences. Plasma concentrations always exceeded those in saliva but for any one preparation a similar ratio was obtained at different times. This may be useful to ascertain compliance and to measure concentration of the compounds where direct measurement in plasma is not practicable.