Methotrexate (MTX) remains the first-line disease-modifying antirheumatic drug (DMARD) and a staple of most combination therapies for people with rheumatoid arthritis (RA).1 Folic acid is coprescribed with MTX; however, there has been debate over its effects on the therapeutic efficacy of MTX. There is no consensus about the optimal dose.2
The rationale for folic acid supplementation relates to the action of MTX as a folate antagonist. The aim is to prevent or decrease the adverse effects of folate deficiency (eg, megaloblastic anemia, cytopenias). Several studies have reported a reduction in MTX-related adverse effects, particularly liver function abnormalities, with folic acid supplementation.3,4 A Cochrane review reported a reduction in gastrointestinal adverse effects and hepatotoxicity with folic acid supplementation.5,6 Cessation of folic acid has been associated with occurrence of adverse effects.7
While the benefits of supplementation are supported, the potential for interference with the therapeutic efficacy of MTX has been less well studied. In a study of folic/folinic acid supplementation, there was no apparent reduction in MTX efficacy, although MTX dose was higher in participants taking folic/folinic acid compared with placebo.3 In a post hoc analysis of 2 randomized controlled trials, participants who received folic acid were less likely to achieve ACR 20%, 50%, or 70% at 52 weeks.8 In people with RA starting MTX, RBC folate decreases and a smaller decrease in RBC folate was associated with a smaller decrease in DAS28.9 We have observed that people with RA with higher RBC folate concentrations have more active disease.10
The optimal dose of folic acid remains to be determined. Morgan et al4 reported no difference in efficacy with folic acid 5 mg weekly compared with 27.5 mg weekly or placebo although abnormalities in liver function tests were more common in the placebo group. Dhir et al11 reported no difference in efficacy or toxicity at 6 months with folic acid 10 mg versus 30 mg weekly.
The aim of this study was to determine whether a reduction in supplemental folic acid results in improved disease control in people with RA and/or increased MTX-related adverse events.
This was a 24-week pilot randomized double-blind controlled trial. The study was conducted at a single center with participants enrolled between February 2011 and August 2013. Ethical approval was obtained from the Upper South A Regional Ethics Committee (URA/10/09/070), New Zealand. Written informed consent was obtained from each participant. The trial was registered with the Australian New Zealand Clinical Trials Registry (ANZCTR12610000739011).
People with RA as defined by ARA criteria12 receiving MTX with folic acid 5 mg weekly for 3 months or more and at a stable dose for 1 month or more were recruited. Participants had active RA as defined by DAS28 of 3.2 or greater required a change in treatment as determined by the treating clinician. Participants were excluded if they had a change in dose or introduction of another DMARD, nonsteroidal anti-inflammatory agent or oral steroid within the preceding month, or intra-articular steroid injection within 1 month before enrolment.
Randomization and Blinding
The randomization sequence was generated electronically by an independent statistician. The randomization sequence was stratified by intramuscular (IM) steroid use and arranged in permuted blocks of size 8. Participants were randomized on a 1:1 ratio to continue folic acid 5 mg weekly (high dose) or reduce folic acid to 0.8 mg weekly (low dose) to be taken four days after MTX. The randomization sequence was sent to the unblinded study pharmacist who prepared study medication and provided it to the blinded study coordinator.
Study Treatment and Procedures
Participants were allowed a single intramuscular steroid injection (triamcinolone 80 mg) at baseline if required. Participants were seen at weeks 0, 4, 8, 16, and 24. Disease activity was assessed using standard clinical parameters comprising: swollen joint count, tender joint count, physicians' global score, patient pain, and fatigue visual analogue scales. Participants answered standardized questions related to MTX adverse effects. Full blood count, liver function tests, RBC folate, and MTX polyglutamate concentrations (MTXPGs), measured as previously described,13 were also determined.
The primary outcome measures were change in DAS28 at 6 months and occurrence of MTX associated adverse effects. Secondary outcome measures were the relationship between change in RBC folate and change in RA disease activity and the relationship between change in RBC folate and change in RBC MTX polyglutamate concentrations.
Sample Size and Power
Assuming a standard deviation of change in DAS28 over 6 months of 1.5, a sample size of 32 participants per group would achieve more than 90% power to show a difference in DAS28 greater than 1.2 between low-dose and high-dose groups as statistically significant (2-tailed α = 0.05).
Standard descriptive statistics including means, medians, ranges, frequencies, and percentages were used to describe the presenting features by randomized group. Comparison of changes between randomized groups was undertaken using a general linear model, which included baseline level as a covariate. Associations between the changes in RBC folate, DAS28, and MTX polyglutamates were tested using Spearman nonparametric correlation coefficients. Treatment emergent adverse events were compared between randomized groups using χ2 and Fisher exact tests as appropriate. A 2-tailed p value less than 0.05 was taken to indicate statistical significance.
Forty participants were recruited, all received the allocated treatment and completed the 24-week study visit. Recruitment was ceased after 40 participants due to ongoing recruitment difficulties, which were the result of the effects of the Christchurch Earthquake on February 22, 2011, and government changes in access to biologic DMARDs for people with RA. Baseline demographics are outlined in Table 1.
There was no significant difference in the change in DAS28 between the high- and low-dose groups at 24 weeks (−0.13 [95% confidence interval (CI), −0.69 to 0.43] vs −0.25 [−0.87 to 0.37], respectively [p = 0.78]). The mean difference in the change between low- and high-dose groups was 0.11 (95% CI, −0.73 to 0.95). Baseline IM steroid had no effect on this result (p = 0.83). The mean (95% CI) change in RBC folate between week 0 and 24 was +87.9 (−28.5 to 204.3) nmol/L in the high-dose group and −113.3 (−246.6 – 20.1) nmol/L in the low-dose group (p = 0.03).
There was no relationship between change in RBC folate and change in DAS28 irrespective of randomization (r = 0.02, p = 0.92). There was no significant association between change in RBC folate and change in total RBC MTXPG concentrations (MTXPG1–5) or MTXPG3–5 within randomized groups or for all participants (MTXPG1–5r = −0.07, p = 0.70; MTXPG3–5r = −0.14, p = 0.41). For the group as a whole, there was no association between change in DAS28 and change in MTXPG3–5 (r = −0.20; p = 0.22). There was no significant association between change in RBC MTXPG3–5/folate ratio and change in DAS28 (r = −0.15; p = 0.38).
One participant in each group had a transient reduction in neutrophil count (1.7 and 1.5 × 109/L in the high- and low-dose folate groups, respectively). Five participants in each group had hemoglobin below the lower limit of normal, whereas 2 participants in the high-dose group and 6 participants in the low-dose group had a reduction in lymphocytes (<0.5× lower limit of normal). Six participants in the low-dose and 2 in the high-dose group had an increase in alanine trasaminase (ALT) above the upper limit of normal (ULN) (Fisher exact test p = 0.11). In 5 of these, the increase in ALT was less than 1.5× ULN. In the remaining 3, there was a transient increase in ALT (1.5–2× ULN). One participant in the low-dose group had a transient increase in AST (<1.5× ULN). There was no significant difference in other MTX-related adverse events between randomized groups (Table 2).
In this study of people with active RA receiving MTX, no significant improvement in DAS28 (mean difference in the change to week 24: 0.11 [95% CI, −0.73 to 0.95]) was achieved by a reduction in supplemental folic acid despite the associated fall in RBC folate concentrations.
There are several potential reasons for the absence of a demonstrable effect. First, the decrease in RBC folate achieved in this study may not have reached the undefined threshold for an effect to occur. Second, there was no significant change in RBC MTXPG concentrations, which some have suggested may be associated with disease activity.14 Third, the baseline DAS28 was relatively low, which may have made it difficult for any differences to be observed. Fourth, the difference in high versus low folic dose may have been insufficient to observe any difference in effect and a third arm with very high folic acid, that is, 10 mg or more weekly may have revealed differences. Finally, the study may have been underpowered due to recruitment difficulties; however, the 95% CI for the difference in the change still excludes our a priori target of a difference in the DAS28 change of 1.2, suggesting that this not the case.
The relationships between MTX, folic acid, and disease activity are complex and interrelated. Both MTX and folate act intracellularly where they undergo serial polyglutamation utilizing the same pathway.15 The intracellular half-life of each agent is influenced by its degree of polyglutamation. It has been shown that MTX therapy is associated with falls in intracellular folate polyglutamates, and that those achieving more modest improvements in disease activity have relatively smaller falls in intracellular folate polyglutamates.9 Although this observation suggests there is a therapeutic ratio between RBC MTXPGs and folate polyglutamates, this has not been shown. Low baseline RBC folate levels have been associated with a lack of response after 3 months of MTX.16 This suggests RBC folate concentration may be a marker of the ability to transport or retain MTX intracellularly. However, our previous report showed no association between RBC folate and RBC MTX polyglutamate concentrations17 and the findings of the present study do not lend support to this suggestion. Thus there must be other mechanisms accounting for the observed effects.
Studies comparing folic acid between 5 and 30 mg/wk have shown no difference in efficacy.4,11 Taking these data together, it seems that if there is any effect of folic acid on MTX efficacy it is not dose related.
The reduction in adverse effects associated with folic acid is more consistent in the literature. In the current study, although numerically more individuals receiving low-dose folic acid had a transient rise in transaminases, this did not reach statistical significance. This is in keeping with a previous study where low RBC folate concentrations were not associated with adverse effects.11 However, given the observed trend in abnormal liver function tests, the current recommendation of at least 5 mg weekly of folic acid remains appropriate.
There are several limitations to this study. There were substantial difficulties in recruitment, which resulted in the study being underpowered. This was at least in part due to widening of access to biological therapies in New Zealand after the study commenced, which resulted in a lower DAS28 score at study entry. This may have made any difference between randomized groups more difficult to observe. Access to biologic therapies means some people who would have been considered eligible for the study before the increased access were not considered appropriate after the widening of access. Second, there was no placebo group for ethical reasons. Given the results of this study, a further larger clinical trial does not seem warranted.
Results from this study and the available literature suggest that if supplemental folic acid affects disease activity this is not dose related. The prevention of MTX-related adverse effects remains the primary reason for coprescribing folic acid with MTX.
This study was funded by Arthritis New Zealand. We acknowledge the support of Christchurch Hospital Pharmacy.
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