Methotrexate catabolism to 7-hydroxymethotrexate in rheumatoid arthritis alters drug efficacy and retention and is reduced by folic acid supplementation.

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Baggott JE, Morgan SL

Methotrexate catabolism to 7-hydroxymethotrexate in rheumatoid arthritis alters drug efficacy and retention and is reduced by folic acid supplementation.

Arthritis Rheum. 2009 Aug;60(8):2257-61. doi: 10.1002/art.24685.

PubMed ID
19644884 [ View in PubMed
]
Abstract

OBJECTIVE: To assess the catabolism of methotrexate (MTX) to 7-hydroxy-MTX (7-OH-MTX) in patients with rheumatoid arthritis as well as the effect of folic acid and folinic acid on this catabolism. METHODS: Urinary excretion of MTX and its catabolite, 7-OH-MTX, was measured in 2 24-hour urine specimens collected after MTX therapy. Urine samples were collected from patients after the sixth and seventh weekly doses of MTX. MTX and 7-OH-MTX concentrations were determined by high-performance liquid chromatography mass spectrometry. Swelling and pain/tenderness indices were used to measure symptoms before and at 6 and 7 weeks of therapy. Patients received either folic acid or folinic acid supplements (1 mg/day) from week 6 to week 7. RESULTS: Folic acid inhibited aldehyde oxidase (AO), the enzyme that produces 7-OH-MTX, but folinic acid did not. Excretion of 7-OH-MTX (determined as a percentage of the dose of MTX or as mg 7-OH-MTX/gm creatinine) was not normally distributed (n=39). Patients with marked improvement in swelling and pain/tenderness indices had a lower mean 7-OH-MTX excretion level (P<0.05). Patients who received folic acid supplements had decreased 7-OH-MTX excretion (P=0.03). Relatively high 7-OH-MTX excretion was correlated with relatively high MTX excretion and with relatively low MTX retention in vivo (P<0.05) (n=35). CONCLUSION: Our findings of a non-normal distribution of 7-OH-MTX excretion suggest that there are at least 2 phenotypes for this catabolism. Decreased 7-OH-MTX formation suggests folic acid inhibition of AO and a better clinical response, while increased 7-OH-MTX formation may interfere with MTX polyglutamylation and binding to enzymes and, therefore, may increase MTX excretion and decrease MTX retention and efficacy in vivo.

DrugBank Data that Cites this Article

Drug Enzymes
DrugEnzymeKindOrganismPharmacological ActionActions
MethotrexateAldehyde oxidaseProteinHumans
Unknown
Substrate
Details