A 37-year-old patient suffering from obliterating vascular endarteritis of lower limbs takes daily 60 microgram/kilogram of phenylin. Because of presentations of convulsive disorder (craniocerebral trauma in anamnesis) he was prescribed phenobarbital. Withholding this drug caused nasal hemorhage. What is this complication connected with?

Answer options

1. Aliphatic hydroxylation of phenobarbi-tal
2. Induction of enzymes of microsomal oxidation in liver caused by phenobarbital
3. Conjugation of phenylin with glucuronic acid
4. Oxidative deamination of phenylin
5. Inhibition of microsomal oxidation in liver caused by phenobarbital

Explanation

Phenobarbital causes a decrease in anticoagulant activity as measured by the prothrombin time. Phenobarbital also induces hepatic microsomal enzymes resulting in increased metabolism and decreased anticoagulant response of oral anticoagulants (e.g. Phenylin, warfarin).