Factors determining the passage of drugs from blood into saliva.

1. Following single oral dosing of ampicillin, cephalexin, tetracycline, erythromycin estolate, clindamycin and rifampicin to six normal volunteers, antibacterial activity was measured at 1, 3 and 6 h in serum, gingival fluid and minor gland saliva from all subjects and in parotid and submandiabular saliva from three. 2. pH values of all gingival fluid and saliva specimens were noted. 3. Partition coefficients between n-octanol and water were measured for erythromycin, clindamycin and rifampicin. Published data were used for ampicillin, cephalexin and tetracycline. 4. All antibiotics, but particularly rifampicin, were detected in gingival fluid. Only rifampicin and to a lesser degree, clindamycin were present in the other salivary constituents. 5. In studies of secretion of drugs in saliva, both the physico-chemical characteristics of the drugs and the physiological differences between individual salivary components should be considered. 6. Parotid saliva samples are likely to be of greatest value.