Plasma methotrexate levels in patients with gestational trophoblastic neoplasia treated by two methotrexate regimens

Plasma methotrexate levels were measured in six patients with nonmetastatic and three patients with "low-risk" metastatic gestational trophoblastic neoplasia who were treated by two different methotrexate regimens. Five patients were treated with 16 cycles consisting of methotrexate, 1 mg/kg (days 1, 3, 5, and 7) followed in 24 hours by citrovorum factor, 0.1 mg/kg (days 2, 4, 6, and 8). Cycles alternated between intravenous and intramuscular administration. Statistical differences in plasma levels were found at 1 and 48 hours between the two routes of administration but probably were not of clinical importance. The plasma levels at the time of citrovorum factor administration were below that necessitating citrovorum factor rescue. Four patients were treated with alternating cycles of intravenous or intramuscular methotrexate, 0.5 mg/kg for 5 consecutive days without citrovorum factor. A total of 15 cycles demonstrated no difference in plasma levels at 1, 12, and 24 hours between intravenous and intramuscular administration. Statistical differences in plasma methotrexate levels were noted between the two methotrexate regimens only with intramuscular administration but were not of clinical importance. The reduced toxicity of the methotrexate-citrovorum factor may be due to the scheduling of the methotrexate and not to the citrovorum factor.