Effects of polysorbate 80 on the absorption and distribution of oral methotrexate (MTX) in mice.

This study is part of a programme of work aimed at improving the bioavailability of oral methotrexate (MTX). In preliminary experiments no significant effect of non-ionic surfactant polysorbate 80 (Tween 80) on absorption of 0.5 mg MTX X kg-1 in NMRI mice was observed except when the drug was given together with 6% polysorbate 80 in solution. Absorption from a higher dose of 3 mg MTX X kg-1 was increased when the drug was administered with 2% or 6% polysorbate 80. Plasma MTX measurements confirmed the significantly higher levels of MTX with 6% polysorbate 80 PO. In subsequent experiments, when Porton mice were used and 4 mg MTX X kg-1 was administered PO, higher plasma and brain levels of MTX were measured in animals given the drug with 6% polysorbate 80, suggesting the enhancement of MTX uptake by this non-ionic surfactant. Although the amount of MTX in the liver and kidney of mice given MTX with polysorbate 80 were not significantly different from the amounts in mice given MTX alone, the lower observed levels suggested that polysorbate 80 perhaps facilitates the elimination of the drug from these organs. The amount of plasma MTX in mice measured 1 h after oral administration of various MTX doses in the presence of 6% polysorbate 80 were significantly higher than the levels in mice given the drug without surfactant, but the significantly higher amounts of MTX in the brain were only observed following the doses of 2 and 6 mg MTX X kg-1.