Interactions with the protein binding of 7-hydroxy-methotrexate in human serum in vitro

Thrombocytopenia after a single test dose of methotrexate

Low dose methotrexate (MTX) can cause numerous gastrointestinal, pulmonary, central nervous system, and hematologic toxicities. Risk factors include folate deficiency, decreased renal function, older age, increased mean corpuscular volume or concomitant use of trimethoprim-sulphamethoxazole, probenecid, or nonsteroidal antiinflammatory drugs (NSAIDs). We describe a case of isolated thrombocytopenia after a single oral dose of MTX in a 36-year-old woman with sarcoidosis. She had rheumatoid arthritis and her only other medications included NSAIDs. One week after her first oral dose of 7.5 mg MTX, diffuse petechiae developed on her chest, abdomen, and extremities; she had a platelet count of 25,000/mm3. Nine days after discontinuation of both MTX and the NSAID, her platelet count increased to 189,000/mm3.

Clinical pharmacokinetics of naproxen

Naproxen is a stereochemically pure nonsteroidal anti-inflammatory drug of the 2-arylpropionic acid class. The absorption of naproxen is rapid and complete when given orally. Naproxen binds extensively, in a concentration-dependent manner, to plasma albumin. The area under the plasma concentration-time curve (AUC) of naproxen is linearly proportional to the dose for oral doses up to a total dose of 500 mg. At doses greater than 500 mg there is an increase in the unbound fraction of drug, leading to an increased renal clearance of total naproxen while unbound renal clearance remains unchanged. Substantial concentrations of the drug are attained in synovial fluid, which is a proposed site of action for nonsteroidal anti-inflammatory drugs. Relationships between the total and unbound plasma concentration, unbound synovial fluid concentration and therapeutic effect have been established. Naproxen is eliminated following biotransformation to glucuroconjugated and sulphate metabolites which are excreted in urine, with only a small amount of the drug being eliminated unchanged. The excretion of the 6-O-desmethylnaproxen metabolite conjugate may be tied to renal function, as accumulation occurs in end-stage renal disease but does not appear to be influenced by age. Hepatic disease and rheumatoid arthritis can also significantly alter the disposition kinetics of naproxen. Although naproxen is excreted into breast milk the amount of drug transferred comprises only a small fraction of the maternal exposure. Significant drug interactions have been demonstrated for probenecid, lithium and methotrexate.

Alterations in methotrexate pharmacokinetics by naproxen in the rat as measured by microdialysis

Reports of a potentially life-threatening interaction between the antifolate methotrexate (MTX) and drugs belonging to the NSAID class instigated a study of MTX pharmacokinetics by a microdialysis technique in the presence and absence of the NSAID naproxen in anesthetized rats. After pretreatment with naproxen, the animals received either 750 or 1,000 mg/kg MTX as a 6 h continuous intravenous infusion. During infusions, microdialysis effluents were obtained from probes situated intravenously, intrahepatically and intrarenally. In all three compartments, time-concentration AUCs for both MTX and its major extracellular metabolite, 7-hydroxymethotrexate (7-OH-MTX), increased about two-fold in the presence of naproxen. The mechanisms responsible for the MTX-NSAID interaction are briefly discussed. The study demonstrate that the microdialysis technique offers a means to investigate pharmacokinetic drug-drug interactions.

Ornithine decarboxylase induction in mouse kidney as indicator of renal damage. Differential nephrotoxic effect of anticancer antifolate drugs

High doses of folate and its quinazoline analogue with antitumour activity, N10-propargyl-5,8-dideazafolic acid (CB 3717), caused severe renal damage in mice, leading in the case of folate to death. The mouse kidneys increased in weight, which was accompanied by time- and dose-dependent induction of ornithine decarboxylase (ODC) activity. In contrast, methotrexate (MTX) had negligible effect on mouse kidneys except when applied together with the non-steroidal antiinflammatory drug, indomethacin.

Effect of aspirin and sulindac on methotrexate clearance

The pharmacokinetics of low dose methotrexate (MTX) were evaluated in 12 rheumatoid arthritis patients in the presence and absence of steady-state levels of salicylic acid (ASA) and sulindac (SU). Using a Latin square design, patients were given MTX plus ASA (mean 3.4 g/day), MTX plus SU (mean 400 mg/day), or MTX alone. On a background of at least one year of regular MTX therapy, patients received 10 mg/m2 MTX iv (mean 17.8 mg) given after at least 2 weeks of treatment with each of the above regimens. Plasma concentrations of MTX and 7-hydroxymethotrexate (7-OH-MTX) were measured using HPLC. No differences in MTX clearance (Cl) were found comparing MTX alone, MTX + ASA, and MTX + SU. However, if one particular subject that had a very low clearance when receiving MTX alone was excluded, there was a statistically significant decrease in MTX clearance when either ASA or SUL were present. It is also noteworthy that ASA significantly increased the exposure of the subject to 7-OH-MTX and, to a lesser extent, so did sulindac. Since 7-OH-MTX has been shown to be an active metabolite when given for cytotoxic effects at higher doses and because it has been show to be nephrotoxic at doses a thousand-fold greater than used in rheumatoid arthritis, nonsteroidal anti-inflammatory drugs should be used cautiously with MTX until further large scale safety studies are conducted. The data indicate that if a clinically significant interaction were to occur, ASA is more likely than SU to interact with MTX.