Fumaric acid ester (prodrug of monomethyl fumarate) Pregnancy: US labelling: there are no adequate data on the developmental risk associated with use in pregnant women. Available data from a pregnancy registry for dimethyl fumarate (which has the same active metabolite), observational studies and pharmacovigilance have not indicated an increased risk of major birth defects, miscarriage or other adverse maternal or fetal outcomes, with most reported exposures in the first trimester. In animal studies, administration during pregnancy or throughout pregnancy and lactation resulted in adverse effects on embryofetal and offspring development at clinically relevant exposures. A pregnancy exposure registry monitors outcomes in women exposed during pregnancy. Verify against UK SPC §4.6.

Diroximel fumarate

Brand names: Vumerity

Diroximel fumarate is an oral disease-modifying therapy for relapsing-remitting multiple sclerosis, sharing the active metabolite of dimethyl fumarate but with a potentially improved gastrointestinal tolerability profile.

Adult dose

Dose: Starting dosage 231 mg twice a day for 7 days; after 7 days the dosage should be increased to the maintenance dosage of 462 mg (administered as two 231 mg capsules) twice a day

Route: Oral — delayed-release capsules swallowed whole and intact; do not crush or chew, or sprinkle the capsule contents on food

Frequency: Twice daily

SOURCE CAVEAT: no UK SPC posology was available in the fetched bundle — this dose is taken from the US prescribing information for VUMERITY (diroximel fumarate) and must be verified against the UK SPC before publication. Temporary dosage reductions to 231 mg twice a day may be considered for individuals who do not tolerate the maintenance dosage; the recommended dosage of 462 mg twice a day should be resumed within 4 weeks, and discontinuation should be considered for patients unable to tolerate return to the maintenance dosage. Administration of non-enteric coated aspirin (up to a dose of 325 mg) 30 minutes prior to dosing may reduce the incidence or severity of flushing. If taken with food, avoid a high-fat, high-calorie meal/snack — the meal/snack should contain no more than 700 calories and no more than 30 g fat. Avoid co-administration with alcohol. BLOOD TESTS: obtain a complete blood cell count including lymphocyte count and serum aminotransferase, alkaline phosphatase and total bilirubin levels prior to treatment; repeat the CBC including lymphocyte count 6 months after initiation and then every 6 to 12 months thereafter as clinically indicated, and obtain liver tests during treatment as clinically indicated. Consider interruption if lymphocyte counts <0.5 × 10⁹/L persist for more than six months. ELDERLY: clinical studies did not include sufficient numbers of patients aged 65 years and over to determine whether they respond differently. PAEDIATRIC: safety and effectiveness have not been established in paediatric patients. Available as 231 mg delayed-release capsules. Source: US FDA prescribing information for VUMERITY (Biogen Inc.), §2 Dosage and Administration.

Dose adjustments

Renal

No dosing adjustment is recommended in patients with mild renal impairment; not recommended in patients with moderate or severe renal impairment.

Dose independently re-sourced from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Known hypersensitivity to diroximel fumarate, dimethyl fumarate, or to any of the excipients — reactions may include anaphylaxis and angioedema
Patients taking dimethyl fumarate (co-administration is contraindicated)

Side effects

Flushing — one of the most common adverse reactions (incidence for dimethyl fumarate, which has the same active metabolite, ≥10% and ≥2% more than placebo)
Abdominal pain, diarrhoea and nausea — among the most common adverse reactions; serious gastrointestinal reactions have been reported
Anaphylaxis and angioedema, which can occur after the first dose or at any time during treatment — discontinue and do not restart
Lymphopenia — obtain a CBC including lymphocyte count before initiating, after 6 months, and every 6 to 12 months thereafter
Progressive multifocal leukoencephalopathy (PML) — withhold at the first sign or symptom suggestive of PML
Herpes zoster and other serious opportunistic infections; liver injury — discontinue if clinically significant drug-induced liver injury is suspected

Interactions

Concomitant dimethyl fumarate — contraindicated, as dimethyl fumarate is also metabolised to monomethyl fumarate; diroximel fumarate may be initiated the day following discontinuation of dimethyl fumarate

Clinical monograph

How it works

It is rapidly converted to monomethyl fumarate, which is thought to activate the Nrf2 antioxidant pathway and modulate immune responses, reducing inflammatory and oxidative activity in the central nervous system.

Prescribing in practice

Monitor full blood count for lymphopenia, as prolonged severe lymphopenia is associated with progressive multifocal leukoencephalopathy (PML).
Gastrointestinal effects and flushing can occur and tend to be most prominent early in treatment.
Liver enzyme elevations can occur, so baseline and periodic liver function monitoring is recommended.

Monitoring

Check full blood count and liver function before and periodically during treatment, watching for persistent lymphopenia and new neurological features suggestive of PML.

Counselling the patient

Attend for regular blood tests to monitor white cells and liver function.
Flushing and gastrointestinal symptoms may occur, especially at first.
Report any new neurological symptoms such as weakness, confusion or changes in vision or speech.

Evidence & guidelines

Diroximel fumarate yields the same active metabolite as dimethyl fumarate, with comparative studies indicating improved gastrointestinal tolerability.

Reference: NICE TA evaluation; ABN MS-DMT; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways