Methotrexate (MTX) is classified pharmacologically as an antimetabolite due to its antagonistic effect on folic acid metabolism. Although its mechanism of action is uncertain, it has become the second line drug of choice for many rheumatologists
To assess the effects of folic acid and folinic acid in reducing the mucosal and gastrointestinal (GI) and haematologic side effects of low-dose of Methotrexate (MTX) in patients with Rheumatoid Arthritis (RA) and to determine whether or not folate supplementation alters MTX efficacy.
We searched the Cochrane Controlled Clinical Trial's Register (CCTR), the Cochrane Musculoskeletal Group Specialized Register and MEDLINE up to and including June 1999, using the search strategy developed by the Cochrane Collaboration (Dickersin 1994).
We also handsearched the following: (i) bibliographic references; (ii) current contents of the last 6 months; (iii) abstracts of the rheumatology meetings; and (iv) all issues of four journals; Journal of Rheumatology, Arthritis & Rheumatism, Clinical and Experimental Rheumatology, and British Journal of Rheumatology.
All languages were included. Principal investigators were also contacted in order to look for unpublished literature.
We selected all double-blind, randomized, placebo-controlled, clinical trials (RCTs), in which adult RA patients were treated with a low dose of MTX (<20 mg / week) concurrently with folate supplementation.
Data collection and analysis
Two observers extracted the data and assessed the quality of the trials. (BS, Z0) The overall treatment effect across trials was calculated using a fixed effect model. Disease activity was evaluated using standardized mean differences to ensure comparability across outcome measures. Results are presented with 95% Confidence Intervals (95% CI). Subgroup analyses were conducted evaluating different doses and sensitivity analysis looking at the quality of the trials. Publication bias was assessed with an inverted funnel plot technique. Heterogeneity of the trials was measured using a standard chi square test. Costs per month in different countries were compared.
Of the 12 trials retrieved, 7 met the inclusion criteria. The total sample included 307 patients, of which 147 were treated with folate supplementation, 80 patients with folinic acid and 67 patients with folic acid. A 79% reduction in mucosal and GI side effects was observed for folic acid [OR = 0.21 (95% CI 0.10 to 0.44)]. For folinic acid, a clinically but non-statistically significant reduction of 43% was found [OR = 0.57 (95% CI 0.28 to 1.15)]. No major differences were observed between low and high doses of folic or folinic acid. Haematologic side effects could not be analyzed, since details of each haematologic side effect by patients were not provided. No consistent differences in disease activity parameters were observed when comparing placebo and folic or folinic acid at low or high doses, although patients on high dose folinic acid had an increase in the number of tender joints, but not swollen joints. Large differences in costs across countries were found, but folinic acid was more expensive in all.
The results support the protective effect of folate supplementation in reducing MTX side effects related to the oral and GI systems. We could not determine if folic was different from folinic acid. Therefore, for folinic acid to be considered cost-effective it must be found more effective than folic acid at reducing MTX side effects.