Summary
The renal excretion and clearance of methotrexate (MTX) following high-dose (800 mg) therapy followed by folinic acid rescue was studied in 12 patients (2 female, 10 male): the mean age was 49.3±5.5 (SE), weight 68.6±3.9 (SE) and body surface area 1.8±0.1 m2. Plasma and urine were collected over 154 h at intervals of 2–24 h, and the collection times, volume, and pH of urine samples recorded. Total MTX concentrations in urine and plasma were measured by the highly specific competitive protein-binding assay method. Plasma and urinary creatinine levels were measured on an SMA-12 autoanalyser. The renal clearance of MTX was calculated for each urine collection period. Following oral administration, clearance values during the first 6 h were high at 257±8.3 (ml/min), followed by a trough in clearance of 27.9±4.2 (ml/min) in the 20- to 30-h period. This was followed by a secondary rise of MTX renal clearance to 180.4±14.6 ml/min during the 68- to 84-h period and again to 84.9±17.1 ml/min between 84 and 112 h. In the last two periods it rose to 209±57.9 ml/min. Similar fluctuations were seen following IV administration. The changes in clearance were statistically significant at the P<0.005 level. It is suggested that high concentrations of MTX in the renal tubules result in inhibition of carrier protein synthesis, leading to a fall in active tubular secretion. When MTX concentrations fall the tubular cell recovers and a secondary rise in renal clearance occurs, leading to cyclical changes in MTX elimination.
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Christophidis, N., Louis, W.J., Lucas, I. et al. Renal clearance of methotrexate in man during high-dose oral and intravenous infusion therapy. Cancer Chemother. Pharmacol. 6, 59–64 (1981). https://doi.org/10.1007/BF00253011
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DOI: https://doi.org/10.1007/BF00253011