Diroximel Fumarate

Multiple Sclerosis (MS) is a chronic, debilitating neurological disease that can lead to profound cognitive and physical symptoms, severely affecting quality of life. It is the main cause of neurological disability not caused by trauma in the young adult population of both North America and Europe. Relapsing-remitting forms of MS lead to neurological symptoms that resolve and recur periodically. More than 80% of patients suffering from this disease have relapsing-remitting MS.

Diroximel fumarate is a drug used for the treatment of relapsing forms of Multiple Sclerosis (MS).

Diroximel fumarate is indicated for the treatment of relapsing forms of multiple sclerosis (MS) in adults; specifically active secondary progressive disease and clinically isolated syndrome, as well as relapsing-remitting MS.

• Active secondary progressive Multiple Sclerosis
• Clinically Isolated Syndrome (CIS)
• Relapsing Remitting Multiple Sclerosis (RRMS)

Diroximel fumarate relieves the neurological symptoms of relapsing MS with less gastrointestinal effects than its bioequivalent counterpart, dimethyl fumarate. It is important to note that diroximel fumarate can cause angioedema, anaphylaxis, hepatotoxicity, flushing, lymphopenia, and Progressive Multifocal Leukoencephalopathy (PML).

Discontinue diroximel fumarate immediately if PML is suspected or if anaphylaxis or angioedema occur. Liver function and total bilirubin should be tested prior to initiating diroximel fumarate and during treatment. A complete blood count (CBC) should be obtained prior to starting diroximel fumarate, after the first 6 months of administration, and at subsequent intervals of 6 to 12 months following this period. Suspend treatment if lymphocyte counts are measured to be less than 0.5 × 109/L for more than 6 months.

Currently, the mechanism of action of this drug in MS is not fully understood. Diroximel fumarate is hypothesized to regulate cell signaling pathways, causing beneficial immune and neuroprotective effects. Monomethyl fumarate (MMF) is the active metabolite of diroximel fumarate, and activates the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway in humans. This pathway occurs as a response to oxidative stress in cells.

In addition to the above, MMF is a nicotinic acid receptor agonist in the laboratory setting. The relevance of this finding to the treatment of MS is unknown at this time. The mechanism by which this drug leads to less gastrointestinal effects is purported to be due to its lack of a methanol leaving group in its chemical structure, and substitution with inert 2-hydroxyethyl succinimide.

Diroximel fumarate is rapidly absorbed in the gastrointestinal tract following administration, like its bioequivalent drug, dimethyl fumarate. The median Tmax of monomethyl fumarate (MMF) after oral administration ranges from 2.5-3 hours with a mean Cmax of 2.11 mg/L. The bioequivalent drug, dimethyl fumarate, administered to healthy volunteers also shows a similar mean Tmax and Cmax.

The average steady state concentration of this metabolite is estimated at 8.32 mg.hr/L after it is administered twice a day in patients with MS. The mean AUC0–∞ of the active metabolite is 88mg × min L−1. Food appears to significantly reduce the Cmax of diroximel fumarate's active metabolite, MMF, when compared to administration in the fasted state.

The apparent volume of distribution ranges from 72L to 83L. Monomethyl fumarate (MMF), the active metabolite of diroximel fumarate, crosses the blood brain barrier.

Plasma protein binding of MMF, the active metabolite of diroximel fumarate, ranges from 27-45%.

Monomethyl fumarate is eliminated as carbon dioxide through expired breath. Negligible amounts, under 0.3% of the ingested dose, are measured in urine. The inactive metabolite, 2-hydroxyethyl succinimide (HES), representing 58-63% of the ingested dose, is excreted in urine.

The terminal half-life of monomethyl fumarate (MMF), diroximel fumarate's active metabolite, is estimated to be 1 hour.

No clearance information is available on the FDA label for diroximel fumarate, however, clinical study results for its active metabolite, monomethyl fumarate show a mean apparent total clearance from the plasma after oral administration of 1.54 mgL−1.

Currently, an MSDS for diroximel fumarate is unavailable. The MSDS for its bioequivalent counterpart, dimethyl fumarate, indicates an oral LD50 of 2,240 mg/kg in rats.

There is no information regarding overdose on the FDA label for diroximel fumarate. Cases of overdose with its bioequivalent counterpart, dimethyl fumarate, have been reported in the literature, and symptoms reflect the adverse effects of this drug. These symptoms include nausea, vomiting, diarrhea, and flushing, among others. Currently there is no antidote to an overdose with diroximel fumarate or dimethyl fumarate. Symptomatic and supportive management are the only options up to this date if an overdose should occur.

• Avoid alcohol.
• Take with or without food. If taken with food, the meal/snack should contain no more than 700 calories and no more than 30 g fat. Taking diroximel fumarate with food may reduce the adverse effect of flushing.

• A complete blood cell count (CBC), including lymphocyte count
• Serum aminotransferase, alkaline phosphatase, and total bilirubin levels