Summary
The protein binding of methotrexate by serum from eight normal volunteers was assessed by continuous ultrafiltration at pH 7.4 and 37°C. Methotrexate concentrations were measured by radioimmunoassay and the data analysed by the method of Scatchard. The major binding protein was albumin which bound 87.3% of the drug in serum. Analysis of the Scatchard plots indicated two distinct groups of binding sites. Class I was found to have 0.16±0.05 (S D) binding sites with an intrinsic association constant of 71.15±35.98 (S D)×104 M−1: Class II had 2.01±0.93 (S D) binding sites and an affinity of 0.18±0.15×104 M−1. No great change in the percentage of methotrexate bound occurred until the total concentration of the drug exceeded 50 µMol 1−1.
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Steele, W.H., Lawrence, J.R., Stuart, J.F.B. et al. The protein binding of methotrexate by the serum of normal subjects. Eur J Clin Pharmacol 15, 363–366 (1979). https://doi.org/10.1007/BF00558441
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DOI: https://doi.org/10.1007/BF00558441