Kinetics of oral and intravenous mexiletine: lack of effect of cimetidine and ranitidine.

The pharmacokinetics of mexiletine, a Class I antiarrhythmic drug, was investigated in 6 healthy volunteers after single oral doses and 15 min intravenous infusions of 3 mg/kg. Cimetidine and ranitidine are commonly used H2-receptor antagonists, which interact adversely with many drugs, e.g. inhibition of the metabolism of Class I antiarrhythmics such as lidocaine and quinidine by cimetidine. To investigate the effects of the two drugs on the kinetics of mexiletine, cimetidine 800 mg.day-1 or ranitidine 600 mg.day-1 were administered orally for one week. Neither H2-receptor antagonist altered the distribution and elimination of mexiletine, nor did they affect its overall kinetics, or excretion of the metabolites para- and 4-OH-methylmexiletine after oral and intravenous administration of mexiletine.

Clinical results and pharmacokinetics of high-dose cytosine arabinoside (HD ARA-C).

Four patients with acute nonlymphoblastic leukemia and one malignant teratoma refractory to conventional chemotherapy were treated with high doses of cytosine arabinoside (HD ARA-C). They received up to 12 cycles of 1.8 to 3 g/m2 every 12 hours applied by 2-hour infusions. A total of 55 HD ARA-C infusions was performed. All leukemic patients responded. A complete clearance of blasts from the bone marrow was observed in two patients following 8-12 cycles of 3 g/m2. However, relapses occurred after three and seven weeks, in one case with resistance to HD ARA-C. The patient with malignant teratoma did not respond. No severe toxicity emerged even after repeated applications. Adverse reactions included moderate nausea and vomiting (4 patients), diarrhea (2 patients), hepatic dysfunction (1 patient), bone pain (1 patient), blurred vision (1 patient), conjunctivitis (1 patient), and exanthema with partial epidermiolysis (1 patient). Granulocytopenia occurring between 3-8 days after having started the therapy, subsided within 4-25 days. Plasma levels of ARA-C and the metabolite uracil arabinoside (ARA-U) were monitored. At steady state plasma concentrations of ARA-C were 32-97 microM (8-24 micrograms/ml). ARA-C disappeared from the plasma mono- or biphasic with a terminal half-life (t50%) of 7.8-12.6 minutes. The total clearance (Cl) of ARA-C varied between 1.7 and 2.9 liters/kg . h, and the distribution volume (Vss) between 0.44 and 0.86 liters/kg. Cerebrospinal fluid (CSF) levels of ARA-C reached 10-15% of steady state concentrations in plasma.