Thiopurine methyltransferase activity in a sample population of black subjects in Florida

Thiopurine methyltransferase (TPMT), is an enzyme detected in the human red blood cell that catalyzes the S-methylation of thiopurine drugs and is known to exist as a genetic polymorphism in white subjects. Investigations in this laboratory of red blood cell TPMT showed interethnic differences also existed in North American black subjects. A sample group of black subjects in Florida had a mean activity of 8.64 +/- 3.47 U/ml red blood cells and an antimode of 6.5 units, which represented values significantly lower than those obtained for both the mean activity and the antimode in other populations. The findings of this study suggest the possibility that TPMT activity may be under genetic control in North American black subjects and that this ethnic group may be at greater risk of experiencing thiopurine-induced toxicity caused by the lower overall mean activity of the enzyme.

Clinical and pharmacological study of intrahepatic artery infusion of thiotepa

Twenty patients with primary or metastatic liver cancer were treated on a clinical and pharmacological study with intrahepatic artery infusion of Thiotepa. Toxicity was tolerable and included nausea and fatigue. Uncommon side effects were myelosuppression, abdominal pain and anemia. One patient with gallbladder cancer had a partial response for 11 (+) months. Recommended dose of Thiotepa for future Phase II clinical trials is 1.0 mg/kg. Pharmacokinetics of intrahepatic Thiotepa revealed an extraction ratio similar to that reported for cisplatin. The data suggest increased hepatic clearance for Thiotepa either by binding or metabolism.

Lidocaine pharmacokinetics during water immersion in normal humans

Water immersion produces a marked diuresis, natriuresis, and kaliuresis in association with suppression of the renin-aldosterone system. These effects are mediated primarily by an increase in central blood volume. Consequently, this redistribution and the resultant marked increase in cardiac output is associated with alterations in the circulating levels of several volume regulatory hormones, including plasma renin activity and plasma aldosterone. Although the changes in these blood hormonal levels probably reflect perturbation of hormonal release, it is conceivable that the above-mentioned central hemodynamic modifications result in an altered splanchnic blood flow, thereby modulating hormonal clearances. We assessed the effects of immersion on hepatic blood flow by determining the pharmacokinetics of single doses of lidocaine administered intravenously. Seven normal male subjects were studied during a time-control period and during water immersion to the neck. The clearance of lidocaine was unaltered by immersion, suggesting that the presumed marked central hypervolemia and increased cardiac output was not associated with changes in splanchnic blood flow.