The Saliva and plasma concentrations of rifampicin were determined following oral administration of 600mg of the drug to healthy human subjects. Rifampicin is a zwitterion with PKa's of 1.7 and 7.9. The saliva-plasma concentration ratios calculated on the basis of the PKa of 1.7 was 1.6346. The saliva concentrations were much higher than tha MICs of a variety of organisms, indicating the possible usefulness of rifampicin in the treatment of susceptible ora-pharyngeal and nasopharyngeal pathogens. After 24 hrs, when rifampicin was completely absent in the urine, the saliva and plasma concentrations also had fallen almost to zero.
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