Pharmacokinetics of erythrocyte methotrexate after high-dose methotrexate.

Erythrocyte methotrexate (MTX) concentrations were determined in 10 patients with metastatic osteogenic or soft tissue sarcoma after 52 cycles of high-dose methotrexate (HDMTX). In contrast to serum MTX, pharmacokinetics of erythrocyte MTX showed three distinct phases: A rapid decrease to a nadir 2-3 days after MTX was followed by a significant rise of erythrocyte MTX until days 10-14. Subsequently there was a third phase, with a definite decrease of erythrocyte MTX concentrations with half-lives of 30-40 days. Short-term repititions of HDMTX had considerable influence on the first two phases of the kinetics. Each curve surpassed that of the previous therapy, and erythrocyte MTX concentrations increased continuously to the values measured at the end of the HDMTX infusion. The following mechanisms of MTX enrichment in erythrocytes is discussed: In erythro- and normoblasts MTX is converted to polyglutamate forms, which are retained inside the cell and are probably the reason for the relatively high sensitivity to MTX. Upon resumption of erythropoiesis the release of freshly prepared erythrocytes containing MTX and predominantly MTX polyglutamates causes the renewed increase in blood MTX levels.

Pharmacokinetics of reduced folates after short-term infusion of d, 1-folinic acid.

After the use of d,1-folinic acid (d,1-CHO-THF), pharmacokinetic measurements should take into account 1-CHO-THF and its metabolite 1-methyltetrahydrofolic acid (1-CH3-THF) as well as d-CHO-THF. For this purpose, we developed a simple and rapid assay by combining reversed-phase HPLC to determine total levels of d,1-CHO-THF and CH3-THF and chiral HPLC to separate the biologically active 1-CHO-THF from the inactive d-CHO-THF. We investigated the pharmacokinetics after short-term infusion of 300 mg d,1-CHO-THF in ten healthy volunteers. With a mean of 56.5 min, 1-CHO-THF exhibits a rapid body clearance of 222 ml/min, about 60% of which is caused by metabolism to CH3-THF and 40%, by renal excretion. CH3-THF has a terminal half-life of 208 min and a total body clearance of 88.9 ml/min, which is essentially the same as the renal clearance. Due to the lower clearance of CH3-THF, its AUC (2,132 microM x min) exceeds that of 1-CHO-THF (1445 microM x min) by approximately 50%. In contrast to that of the reduced 1-folates, the total body and renal clearance of d-CHO-THF is very low, with values of 13.2 and 12.9 ml/min, respectively. This results in a very high AUC of 24, 269 microM x min, which is higher by factors of 17 and 11 than those of 1-CHO-THF and CH3-THF, respectively. The implications of the distinct kinetics of the reduced 1-folates and d-CHO-THF for the efficacy of folinic acid/5-fluorouracil therapy and adequate protocols for the treatment of advanced colorectal cancer are discussed.

Pharmacokinetics of methotrexate during regional hyperthermia in a pig model.

In the pig model, regional hyperthermia in the gluteus was combined with the infusion of 150 mg MTX over a period of 100-120 min. The pharmacokinetic data reveal that this approach is capable of simulating the situation that is necessary and achievable in medium-dose MTX therapy of human tumours. Under MTX infusion, serum levels in the region of 10(-5) M are attained. As an expression of a renal and hepatic MTX excretion, high levels of MTX are found both in the urine and in the bile. Especially high concentrations of MTX are found in the liver and kidney tissue. In the normothermic and hyperthermic muscle, very low MTX levels are found. The pharmacokinetic data obtained show that the selected model is suitable for the future investigation of the effect of regional hyperthermia and MTX on transplanted tumours.

Methotrexate and methotrexate polyglutamates in human sarcoma metastases after high-dose methotrexate therapy.

The methotrexate concentrations in the lungs or cutaneous metastases of patients with osteogenic or soft-tissue sarcoma were determined at different times after a high-dose methotrexate therapy. The levels in the metastases were 0.964 to 2.96 X 10(-7) molar six to nine days after the end of MTX infusion. They were thus 7.8 to 28 times higher than the corresponding serum levels. At the same time, an appreciable rise of dihydrofolate reductase activity was observed in the metastases. After chromatographic separation over Sephadex G15, MTX polyglutamates could be demonstrated in all tumor samples investigated so far; these amounted up to 68.3% of the total MTX. Taking into account the slower efflux of MTX polyglutamates compared to unchanged MTX, a new hypothesis for the principle of action of high-dose methotrexate therapy is discussed: the very high MTX doses lead to such high intracellular MTX concentrations even in transport-resistant tumor cells that at least part of the MTX is converted into MTX polyglutamates. Unchanged MTX flows relatively rapidly out of the cells, whereas the MTX polyglutamates only break down very slowly and thus can be cytostatically effective over a long period of time.

Ferrokinetics after high-dose methotrexate therapy.

After high-dose methotrexate with doses ranging from 2-10 g/m2, ferrokinetics were performed in 11 patients with different tumors. Iron-III-citrate-59Fe was injected at methotrexate serum concentrations ranging between 2.7 x 10(-7) -1.3 x 10(-8) M. With MTX levels greater than or equal to 4.2 x 10(-8) M the plasma iron clearance was always retarded, and the plasma iron turnover was diminished in 5 of 6 patients with levels of 3.1-8.9 x 10(-8) M at the time of the injection. In all cases with MTX concentrations greater than or equal to 5 x 10(-8) M the 59Fe-utilization as the measure of effective erythropoiesis was reduced pathologically below normal range. These results show that the erythropoiesis resumes its normal extent even in case of normal methotrexate clearance only when the methotrexate serum concentrations have fallen down below 5 x 10(-8) and that erythropoiesis is more sensitive against methotrexate toxicity than the granulocytopoiesis.