Key messages
- It is unclear if azathioprine (medication that affects the body's immune response) provides more benefits overall than other medicines for multiple sclerosis, like interferon (natural proteins made by the body to treat infection). Azathioprine may reduce the number of people experiencing relapses compared to interferon.
- People taking azathioprine over two years may be more likely to experience serious harmful effects than people taking interferon.
- Future studies should last longer than two years, focus on outcomes relevant for people with multiple sclerosis (quality of life, cognitive status) and include more people with progressive multiple sclerosis (whose symptoms gradually get worse).
What is multiple sclerosis?
Multiple sclerosis is a lifelong condition, affecting the brain and spinal cord. Its symptoms vary widely, can be mild or severe and include tiredness, pain, muscle cramps and reduction or loss of sensation and strength in parts of the body.
Multiple sclerosis typically affects young people, mainly women, and people are often first diagnosed when aged between 20 and 40 years. The most common form of MS is relapsing-remitting, where symptoms come ('relapse') and go ('remit'). 'Progressive' multiple sclerosis is when symptoms gradually get worse (i.e. there is no recovery or the body struggles to recover between relapses).
How is multiple sclerosis treated?
No treatment can cure multiple sclerosis, but many available medicines can reduce relapse frequency and slow disability progression. Azathioprine is a drug used in other diseases also caused by an impaired immune response. In countries where there are fewer treatments available, azathioprine is sometimes used to treat multiple sclerosis, even though it is not currently licensed for that purpose. A previous Cochrane Review found some evidence that azathioprine could be a possible treatment compared to interferon.
What did we want to find out?
We were interested in the benefits and harms of azathioprine, either as the first treatment choice ('first choice') or when other medicines did not work or were not wanted ('switching'), compared to other treatments.
We were also interested in the effects of azathioprine compared to placebo (dummy tablet) or no treatment.
What did we do?
We searched for studies comparing azathioprine with other medicines, placebo or no treatment. We compared and summarised the results of the studies and rated our confidence in the evidence, based on factors like study methods and size. We looked for randomised controlled trials (RCTs), where participants are assigned randomly to two or more groups. This way of conducting a study is the best way to reduce the impact of non-treatment factors that could influence the results. We also looked at non-randomised studies (NRS), meaning people were put in groups in a way that was not random or that the people chose which group they wanted to be in.
What did we find?
We found 14 studies (8 randomised trials and 6 NRS) that involved 2105 participants with relapsing-remitting and progressive multiple sclerosis. Ten studies included more women with multiple sclerosis (57 to 83%) than men. The average age of onset of MS was between 29.4 and 33.4 years. The non-randomised studies and five of the RCTs were conducted in Europe; two RCTs were conducted in the USA and one RCT was conducted in Iran.
The RCTs lasted up to three years, while the NRS looked back up to 10 years.
Four studies were funded by pharmaceutical companies, five by governments or charities, and five did not report this information.
Azathioprine as a 'first choice' treatment compared to other active treatments for relapsing multiple sclerosis
Compared to interferon, over two years of treatment:
- azathioprine may reduce the number of people with relapses;
- people taking azathioprine may experience more serious harmful effects;
- azathioprine may increase nausea or vomiting (or both); and
- the effect of azathioprine on worsening disability or short-term negative side effects is very uncertain.
We found no evidence comparing azathioprine to other treatments for the outcomes of quality of life, mental health, cancer or numbers of deaths.
We found no studies that looked at azathioprine as a 'first choice' treatment compared to other active treatments for progressive multiple sclerosis, or any studies that looked at azathioprine when 'switching' from other treatments, after they did not work or were not wanted, either for people with relapsing or progressive multiple sclerosis.
The non-randomised studies provided no additional information to that already provided by RCTs.
What are the limitations of the evidence?
We are not very confident in the evidence because:
- few studies, including relatively few people and very few events, are available;
- the quality of studies is not high; and
- the evidence does not cover all the comparisons we are interested in.
How up to date is the evidence?
Our searches were conducted up to 9 August 2023; the most recent included study is from 2014.
Azathioprine has been proposed as an alternative treatment for MS when access to approved, on-label DMTs is limited, especially in resource-limited settings. The limited evidence available suggests that azathioprine may result in a modest benefit in terms of relapse frequency, with a possible increase in SAEs, when compared to interferon beta-1b, for people with relapsing-remitting multiple sclerosis. The evidence for the effect on disability progression and short-term adverse events is very uncertain. Caution is required in interpreting the conclusions of this review since our certainty in the available evidence on the benefits and harms of azathioprine in multiple sclerosis is low to very low, implying that further evidence is likely to change our conclusions.
An important limitation we noted in the available evidence is the lack of long-term comparison with other treatments and the failure of most studies to measure outcomes that are important to people with multiple sclerosis, such as quality of life and cognitive decline. This is especially the case in the evidence relevant to people with progressive forms of multiple sclerosis.
Multiple sclerosis (MS) is an immune-mediated, chronic, inflammatory demyelinating disease of the central nervous system, impacting around 2.8 million people worldwide. Characterised by recurrent relapses or progression, or both, it represents a substantial global health burden, affecting people, predominantly women, at a young age (the mean age of diagnosis is 32 years).
Azathioprine is used to treat chronic inflammatory and autoimmune diseases, and it is used in clinical practice as an off-label intervention for MS, especially where access to on-label disease-modifying treatments (DMTs) for MS is limited. Given this, a review of azathioprine's benefits and harms would be timely and valuable to inform shared healthcare decisions.
To evaluate the benefits and harms of azathioprine (AZA) for relapsing and progressive multiple sclerosis (MS), compared to other disease-modifying treatments (DMTs), placebo or no treatment. Specifically, we will assess the following comparisons.
AZA compared with other DMTs or placebo as first-choice treatment for relapsing forms of multiple sclerosis
AZA compared with other DMTs or placebo for relapsing forms of MS when switching from another DMT
AZA compared with other DMTs or placebo as first-choice treatment for progressive forms of MS
AZA compared with other DMTs or placebo for progressive forms of MS when switching from another DMT
We conducted an extensive search for relevant literature using standard Cochrane search methods. The most recent search date was 9 August 2023.
We included randomised controlled trials (RCTs) lasting 12 months or more that compared azathioprine versus DMTs, placebo or no intervention in adults with MS.
We considered evidence from non-randomised studies of interventions (NRSIs) as these studies may provide additional evidence not available from RCTS.
We excluded cluster-randomised trials, cross-over trials, interrupted time series, case reports and studies of within-group design with no control group.
We followed standard Cochrane methodology.
There were three outcomes we considered to be critical: disability, relapse and serious adverse events (SAEs, as defined in the studies). We were also interested in other important outcomes: quality-of-life (QoL) impairment (mental score), short-term adverse events (gastrointestinal disorders), long-term adverse events (neoplasms) and mortality.
We included 14 studies: eight RCTs (1076 participants included in meta-analyses) and six NRSIs (1029 participants). These studies involved people with relapsing and progressive MS. Most studies included more women (57 to 83%) than men, with participants' average age at the onset of MS being between 29.4 and 33.4 years.
Five RCTs and all six NRSIs were conducted in Europe (1793 participants); two RCTs were conducted in the USA (126 participants) and one in Iran (94 participants). The RCTs lasted two to three years, while NRSIs looked back up to 10 years. Four studies received some funding or support from commercial interests and five were funded by government or philanthropy; the other five provided no information about funding. There are three ongoing studies.
Comparison groups included other DMTs (interferon beta and cyclosporine A), placebo or no treatment. Below, we report on azathioprine as a 'first choice' treatment compared to interferon beta for people with relapsing MS. None of the studies reported on any critical or important outcome for this comparison for progressive MS. No study was retrieved comparing azathioprine to placebo or other DMTs for either relapsing or progressive MS. Furthermore, the NRSIs did not provide information not already covered in the RCTs.
Azathioprine as a first-choice treatment compared to other DMTs (specifically, interferon beta) for relapsing MS
- The evidence is very uncertain about the effect of azathioprine on the number of people with disability progression over two years compared to interferon beta (risk ratio (RR) 0.19, 95% confidence interval (CI) 0.02 to 1.58; 1 RCT, 148 participants; very low certainty evidence).
- Azathioprine may decrease the number of people with relapses over a one- to two-year follow-up compared to interferon beta (RR 0.61, 95% CI 0.43 to 0.86; 2 RCTs, 242 participants; low-certainty evidence).
- Azathioprine may result in a possible increase in the number of people with SAEs over two years in comparison with interferon beta (RR 6.64, 95% CI 0.35 to 126.27; 1 RCT, 148 participants; low-certainty evidence).
- The evidence is very uncertain about the effect of azathioprine on the number of people with the short-term adverse event of gastrointestinal disorders over two years compared to interferon beta (RR 5.30, 95% CI 0.15 to 185.57; 2 RCTs, 242 participants; very low certainty evidence).
We found no evidence comparing azathioprine to other DMTs for QoL impairment (mental score), long-term adverse events (neoplasms) or mortality.