Okuno et al. (15) studied the effect of IFN-a on drug-metabolizing activity in the human liver. Twelve patients with chronic hepatitis B received 6 x 106 IU of IFN-a intramuscularly for four weeks. IFN-a treatment reduced the O-deme-thylase and O-deethylase activities in the liver by 31% and 33%, respectively. The extent of reduction in the enzymatic activities widely varied. For example, in 2 patients, no inhibition of either enzyme was observed, whereas O-deme-thylase and O-deethylase activities in the remaining 10 patients varied from 9% to 61% and 16% to 62%, respectively.

In another study, Pageaux et al. (16) investigated the effect of therapeutic doses of IFN-a on CYP450 1A2 and 3A in patients with chronic hepatitis C. Eighteen patients with chronic hepatitis C received 3 million units (MU) of IFN-a three times a week. The results of the study indicated that IFN-a had no effect on the enzymatic activities of CYP1A2 and CYP3A.

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