Hexobarbital Rifampicin

Rifampin has been shown to inerease stereoselectively the oral elear-ances of both hexobarbital enantiomers after administration of the racemate, although the degree of stereoseleetivity in the interaction was age dependent [159]. In both young and elderly volunteers, the oral CL of the S(-l-) enantiomer increased with rifampicin pretreatment, by about tenfold in each group. The oral CL of the R(—) enantiomer, however, increased by 74-fold and 19-fold in young and elderly subjects, respectively. Therefore, the inductability of metabolism of R-hexobarbital is diminished with aging [159]. 

Phenobarbital possibly modestly increases the clearance of rifampicin. The effect of rifampicin on phenobarbital levels is unknown, but note that rifampicin markedly increased the clearance of another barbiturate hexobarbital, used as a marker of drug metabolism. 

In one study, the serum levels of rifampicin were reduced by 20 to 40% in 12 of 15 patients taking phenobarbital 100 mg daily. In another study, although phenobarbital 100 mg daily for 7 days reduced the mean half-life of a single 600-mg dose of rifampicin by 15%, this was not statistically significant. However, in a further 5 patients with cirrhosis of the liver, phenobarbital did reduce the half-life of rifampicin by a mean of 2.2 hours. The effect of rifampicin on phenobarbital levels does not appear to have been studied, but rifampicin markedly increased the clearance of another barbiturate hexobarbital, used as a marker of drug metabolism. " ... 

Zilly W, Breimer DD, Richter E. Induction of drug metallism in man after rifampicin treatment measured by increased hexobarbital and tolbutamide clearance. EurJ Clin Pharmacol (1975) 9,219-27. 

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See also in sourсe #XX -- [ ]

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