Department of Rheumatology, East Surrey Hospital,
1 Department of Rheumatology, Staffordshire Rheumatology Centre, Stoke-on-Trent and
2 Department of Mathematics, University of Keele, UK
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Abstract |
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Objectives. To look at the effect of stopping FA supplementation in UK rheumatoid arthritis (RA) patients established on methotrexate <20 mg weekly and FA 5 mg daily, to report all toxicity (including absolute changes in haematological and liver enzyme indices) and to report changes in the efficacy of methotrexate.
Methods. In a prospective, randomized, double-blind, placebo-controlled study, 75 patients who were established on methotrexate <20 mg weekly and FA 5 mg daily were asked to stop their FA and were randomized to one of two groups: placebo or FA 5 mg daily. Patients were evaluated for treatment toxicity and efficacy before entry and then at intervals of 3 months for 1 yr.
Results. Overall, 25 (33%) patients concluded the study early, eight (21%) in the group remaining on FA and 17 (46%) in the placebo group (P = 0.02). Two patients in the placebo group discontinued because of neutropenia. At 9 months there was an increased incidence of nausea in the placebo group (45 vs 7%, P = 0.001). The placebo group had significantly lower disease activity on a few of the variables measured, but these were probably not of clinical significance.
Conclusions. It is important to continue FA supplementation over the long term in patients on methotrexate and FA in order to prevent them discontinuing treatment because of mouth ulcers or nausea and vomiting. Our data suggest that FA supplementation is also helpful in preventing neutropenia, with very little loss of efficacy of methotrexate.
KEY WORDS: Methotrexate, Folic acid.
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Introduction |
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The exact mechanism of action of methotrexate in RA remains uncertain. Methotrexate is an anti-folate agent. The polyglutamated derivatives of methotrexate are potent inhibitors of various enzymes, including dihydrofolate reductase and 5-aminoimidazole-4-carboxamide ribonucliotide transformalase. Inhibitory effects on cytokines, particularly interleukin-1, and on arachidonic acid metabolism, as well as effects on proteolytic enzymes, have been reported. Some might be related to the anti-folate properties of methotrexate. Overall, the drug appears to act in RA as an anti-inflammatory agent with subtle immunomodulating properties [4].
A number of researchers have investigated the relationship between folate status and toxicity/efficacy in RA patients receiving methotrexate. Morgan et al. [6] used an assay of the folate-dependent enzymatic synthesis of serine from formate and glycine (the C1 index) to compare folate status between RA patients taking methotrexate and those not taking methotrexate. They reported that the activity of the enzyme system in lymphocytes was significantly lower in the methotrexate-treated group. None of the patients in their study experienced toxicity with methotrexate treatment. They concluded that some depletion of folate coenzyme levels in lymphocytes may be necessary for a clinical response in RA, whereas excessive depletion causes toxic side-effects. Weinblatt and Fraser [7] investigated a retrospective series of patients treated with methotrexate and found that all patients with haematological toxicity were folate-deficient. They therefore concluded that haematological toxicity is related to folate depletion. It has also been suggested that other side-effects of methotrexate administration, such as gastrointestinal intolerance, mimic folate deficiency and may be related to folic acid deficiency [8].
Given this evidence of the effect of methotrexate on folate metabolism and the possible link with side-effects, the question arises as to whether supplements decrease the frequency of side-effects. A recent meta-analysis of randomized controlled trials [9] concerned with the addition of folic acid or folinic acid to methotrexate identified only two studies (67 patients treated with folic acid) that looked at folic acid; both studies were reported by the same group of US investigators [5, 8]. Both studies looked at patients starting methotrexate and folic acid concurrently. The first study followed patients for only 24 weeks, but the second study included a longer period of follow-up (48 weeks). Both studies reported the number of patients experiencing neutropenia and elevations of liver transaminases, but unfortunately the absolute levels were not included in the papers so these could not be included in the meta-analysis. The studies conducted by Morgan et al. [5, 8] were both conducted in the USA, where baseline dietary intake of folic acid may differ from that in the UK. The numbers of patients studied were small (32 and 79) and the studies may have had insufficient power to detect differences in the efficacy of methotrexate in the different treatment groups. The studies have been criticized for using a mean toxicity score, which may have resulted in some side-effects influencing the overall result more than others. The studies have also been criticized for not including hard outcome measures, such as the progression of joint erosions on X-ray [10]. No studies to date have investigated whether it is necessary to continue folic acid supplementation in the long term in patients established on methotrexate.
In summary, there is no consensus amongst rheumatologists about the necessity for folic acid supplementation for patients receiving low-dose methotrexate [4]. The purpose of our study was to expand on the work done previously and had the following objectives: (1) to look at the effect of stopping folic acid supplementation in UK patients who are established on methotrexate <20 mg weekly and folic acid 5 mg daily; (2) to report all toxicity, including absolute changes in haematological and liver enzyme indices; and (3) to report any changes in the efficacy of methotrexate.
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Materials and methods |
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Patients and methods
The subjects were patients with definite or classic RA [12] attending the Staffordshire Rheumatology Centre (SRC), UK. The laboratory and clinical data regarding disease-modifying anti-rheumatic drug (DMARD) therapy for all patients with inflammatory arthritis have been recorded on a computer drug-monitoring database at the SRC since 1987 [13]. The names of all patients (200) currently taking methotrexate were obtained from the database. Patients were excluded if they did not have RA; if they were aged under 18 yr; if they were on unstable doses of methotrexate; if they were taking methotrexate in combination with another type of DMARD; if they were not on folic acid 5 mg daily; if the total white blood cell (WBC) count was <3 x 109; if the neutrophil count was <2 x 109; or if the aspartate transaminase (AST) or alanine transaminase (ALT) concentration was outside the normal range. All suitable patients were approached about participating in the study. Seventy-five patients were recruited for the study and gave informed consent to participation. The study was approved by the North Staffordshire Health Authority Local Research Ethics Committee. During the study, each patient remained under the care of his or her rheumatologist, abstained from alcohol, and continued to receive stable doses of NSAIDs and/or prednisolone. It was required that both male and female patients should either practise contraception or have no reproductive potential.
Outcome measures
Patients were evaluated for treatment toxicity and efficacy before entry and then at intervals of 3 months for 1 yr. The assessments were carried out by two experienced metrologists (SC, JF). The primary outcome studied was the cessation of methotrexate treatment due to inefficacy or toxicity.
Secondary outcomes
Minor toxicity.
This was measured using a checklist of 24 symptoms.
Treatment efficacy.
This was evaluated with the following measures: (1) a visual analogue scale (VAS) for pain (0100 mm); (2) eight activities of daily living assessed and averaged at baseline and at 12 months using the modified Health Assessment Questionnaire and scored on a scale of 1 (no difficulty) to 4 (unable to perform) [14]; (3) the number of diarthrodial joints with swelling (maximum 50); (4) the number of tender joints (maximum 26); (5) the Ritchie index [15]; (6) the patient's and physician's global assessments of disease activity measured using a VAS (0100 mm); (7) the duration of morning stiffness expressed in minutes; (8) mean grip strength (three measurements for both hands expressed in mm Hg; (9) the proximal interphalangeal joint score [16]; and (11) the number of corticosteroid joint injections.
Laboratory assessments.
The following estimations were made at baseline and thereafter at intervals of 3 months: full blood count (FBC), WBC, absolute neutrophil count, -glutamyl transferase (GGT), AST, ALT and ESR.
Radiographic assessment.
Hand and feet radiographs were taken before starting the study and at completion. Radiographs were given Larsen scores [17] by a single blinded radiologist (JS).
Miscellaneous.
Data were also collected on current medications and doses, and Hospital Anxiety and Depression Scores were recorded [18].
Statistical analysis
All calculations were undertaken with NCSS-PASS 1992 (Dr J. L. Hintze, Kaysville, Utah, USA).
Sample size and analysis
In a recent study, 40% of patients established on long-term DMARDs reported possible adverse events over a follow-up period of 1 yr [19]. If taking folic acid reduces the number of patients experiencing adverse events to 10%, then a sample size of 32 in each group with a two-sided significance level of 5% will have a power of 80% to detect such a difference.
Comparison of data among groups
The t-test (if necessary adjusted for unequal variances) was used for approximately normal data, the MannWhitney test for non-normal data and the 2 test for categorical data.
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Results |
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Secondary outcomes |
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Treatment efficacy
Table 5 shows very little difference in treatment efficacy between the two groups. The placebo group had a significantly lower mean (SD) Ritchie index at 3 months [6.79 mm (5.61), 10.03 (6.92), P = 0.04], mean (SD) patient's global assessment at 6 months [39.75 mm (23.99), 54.37 mm (22.85), P = 0.02], mean (SD) doctor's global assessment at 6 months [28.67 mm (18.28), 41.88 mm (19.59), P = 0.01] and mean (SD) patient's global assessment at 1 yr [38.47 mm (23.19), 55.04 mm (21.05), P = 0.02].
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Laboratory assessments
Table 5 shows that the placebo group had a lower total WBC count at 3 months and 6 months than the folic acid group.
Radiographic assessment
There was no significant change in the Larsen score at 0 and 12 months: -0.5 (- 36 to 47), 0 (- 12 to 25), n = 22, 17.
Miscellaneous
There were no significant differences in numbers of patients requiring methotrexate dose changes (5/36 vs 3/29) or joint injections (6/36 vs 2/29).
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Conclusions |
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Discussion |
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Despite the fact that low-dose methotrexate has become standard therapy for RA, its mechanisms of action with respect to efficacy, as well as its side-effects, are still obscure. The rapid improvement and exacerbation after respectively introducing and discontinuing methotrexate suggests the possibility of an anti-inflammatory effect as well as an immunomodulating effect [20]. A recent review of possible mechanisms of action of methotrexate summarizes them thus: it is a folate antagonist; as folates are involved in the synthesis of purines, purine metabolism is disrupted, leading to an increase in adenosine; pyridimine metabolism is also disrupted; in addition to these pathways, the conversion of homocysteine to methionine is disrupted, leading to an increase in homocysteine [20]. Although methotrexate's antiproliferative effect is important in the treatment of malignancies, it probably does not explain its efficacy in RA [20]. Studies show that methotrexate has an immunomodulatory mode of action via effects on B- and T-cell numbers and function. Methotrexate may also modulate the production of cytokines via inhibition of polyamines or via interference with purine metabolism [20]. Cronstein [21] has recently postulated two possible biochemical mechanisms of action of methotrexate that may account for its anti-inflammatory effects: (1) inhibition of homocysteine remethylation; (2) adenosine release.
Side-effects are quite common during treatment with methotrexate. The severity varies, but most side-effects are mild, reversible, and can be treated conservatively. However in approximately 30% of patients with RA, toxicity leads to discontinuation of methotrexate therapy within 1 yr. However, although the risk of side-effects may be slightly higher in the first 6 months, the risk of all sorts of adverse effects is permanent, implying a need for long-term monitoring [20].
At least part of the side-effect profile of methotrexate seems to be directly related to its folate antagonism and its cytostatic effects, especially in tissues with a high cell turnover (bone marrow and gastrointestinal tract), which have a high requirement for purines, thymidine and methionine [20]. Most of the reported side-effects in our study were related to bone marrow and the gastrointestinal tract. Kremer et al. [22] showed accumulation of methotrexate poyglutamates in liver biopsies from patients with RA who also had folate deficiency. However, although no correlation could be shown between folate levels, methotrexate polyglutamate accumulation and transaminase elevations, this may be a possible mechanism for the liver toxicity of methotrexate.
Serum folate levels were not included in this study because the Lactobacillus casei assay that is available locally is inhibited by small concentrations of methotrexate. Folate levels can be measured by a radioimmune assay or, as in the studies by Morgan et al. [5, 6, 8], folate status can be indirectly evaluated by an assay of the activity of an enzyme system which synthesizes serine from glycine and formate and requires folate coenzymes. This activity is called the C1 index [5, 6]. Previous investigators have commented on the relationship between folate levels and methotrexate toxicity. Morgan et al. [5] found that low-normal initial folate levels in their placebo group were correlated with a high probability of eventual methotrexate toxicity [5]. A greater increase in mean corpuscular volume (MCV) was also noted in the placebo group. A further study from the same investigators also reported that low blood folate levels and increased MCV were associated with methotrexate toxicity [8]. Weinblatt and Fraser [7] did a small retrospective study of 23 patients receiving low-dose methotrexate and demonstrated an association between folate deficiency, MCV and haematological toxicity. Al-Awadhi et al. [23] looked retrospectively at 15 patients who had experienced pancytopenia related to methotrexate and reported a relationship with increasing MCV. However, a study of 200 RA patients on methotrexate reported in 1991 did not show an association between MCV elevation and adverse effects [24].
It is possible that high concentrations of adenosine and related compounds may be directly toxic. Seitz [25] suggests that this may be the mechanism for methotrexate-related headache, renal insufficiency and nodule formation. It has been observed that combined therapy with methotrexate and hydroxychloroquine may lead to a reduction in liver test abnormalities [26] and may be associated with nodule regression [27, 28]. Fries et al. [26] proposed that the ability of hydroxychloroquine to increase the size and number of lysosomes in hepatocytes stabilizes the membrane and thereby exerts its protective effect. Reduced bioavailability of methotrexate may also account for these effects [20]. Indeed, it can also be argued that folic acid reduces the side-effects of methotrexate solely by reducing its bioavailability (methotrexate blocks dihydrofolate reductase, resulting in depletion of intracellular reduced folates, and competes with dihydrofolate to inhibit the distal steps in the synthesis of nucleotides [25]). If this were the case, then it would be expected that folate supplements would diminish the efficacy of methotrexate. One reason for the design of our study (stable patients on methotrexate plus folic acid randomized to placebo or folic acid) was to better observe changes in methotrexate efficacy between the two groups. If additional folic acid was reducing the biological actions of methotrexate, then an improvement in disease control in the placebo group would have been expected. Currently, the most promising strategy to reduce the toxicity of methotrexate therapy seems to be the concomitant prescription of folic acid. More research needs to be pursued into the mechanisms of action of methotrexate to facilitate the development of further strategies to reduce toxicity [20].
Our study had several limitations. First, we had hoped to recruit more patients than previous studies to help distinguish true toxicity from the background level of symptoms reported by patients. We also hoped that a bigger cohort would clarify issues around small changes in efficacy. Unfortunately, we were able to recruit only 75 patients from our centre, suggesting that larger studies would probably need to involve several centres. We based the study on the folic acid regime used by the consultants at the Staffordshire Rheumatology Centre. This is probably not a typical regime, as a dose of folic acid of 515 mg weekly is used more widely. Future studies could be further improved by a longer follow-up time to better assess outcomes such as radiological changes.
In summary, we have reported a similar range of major and minor toxicity in our placebo group to that reported by previous studies [9]. We used a slightly higher dose of folic acid than is usually prescribed in the UK but, as reported previously, the dose of folic acid used (5 mg daily) did not seem to have a significant effect on the efficacy of methotrexate [9]. In contrast to previous studies, we have included details of haematological and biochemical parameters [9].
It is important to continue folic acid supplementation over the long term in patients on methotrexate and folic acid to help prevent patients discontinuing treatment due to mouth ulcers or nausea and vomiting. Our data suggest that folic acid supplementation is also helpful in preventing neutropenia, with very little loss of efficacy of methotrexate.
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Notes |
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References |
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