Saliva levels of trimethadione and its metabolite as an index of drug metabolizing activity in rats.

1. It was investigated in normal and liver-injured rats administered with trimethadione (TMO) as to whether concentrations of TMO in plasma are able to be predicted from the corresponding saliva levels. 2. The saliva/plasma (S/P)ratio of TMO was about 1, while its metabolite 5,5-dimethyl-2,4-oxazolidinedione (DMO) showed a S/P ratio of 0.65. 3. In normal rats, there was a high correlation between saliva and plasma concentration of TMO and DMO. (TMO: r=0.966, DMO: r=0.950). 4. In liver-injured pretreated rats with carbon tetrachloride, alpha-naphthyl isothiocyanate or D-galactosamine, there was a high correlation between the saliva DMO/TMO ratio and the plasma DMO/TMO ratio after oral administration of TMO (r=0.983 at 1 h, r=0.952 at 2 h). 5. The saliva DMO/TMO ratio, as well as the plasma DMO/TMO ratio, may be utilized as an index of drug-metabolizing activity of the liver.