Serum gamma-glutamyl transpeptidase activity in patients receiving chronic phenytoin therapy

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Abstract
To better define the incidence and range of elevated gamma-glutamyl transpeptidase (GGT) activity in patients taking a drug known to induce hepatic microsomal enzymes, GGT was measured in the sera of 58 patients before and after six months of phenytoin therapy. Enzyme activity at six months was greater than baseline in 52 of 58 patients (90%). GGT activity (normal, 0–50 units/liter) was 45.2±9.9 (mean±sem) at baseline and 135.8±18.1 after six months of therapy, a mean threefold increase (P1 pint/week. All 13 patients with elevated baseline GGT activity were regular users of alcohol and/or taking other enzyme-inducing drugs. In conclusion, increase in serum GGT activity occurs 90% of patients on long-term phenytoin therapy, most often to moderate but occasionally to high levels, and this rise in GGT activity is accentuated by regular consumption of alcohol.