Midamor (amiloride) is a therapy used to increase potassium levels in patients with high blood pressure and heart conditions. Research has suggested that Midamor may have a neuroprotective effect in multiple sclerosis (MS).
The drug is currently being investigated as a potential treatment for primary progressive MS (PPMS) and secondary progressive MS (SPMS) patients.
How Midamor works
MS is a condition where the body’s immune system begins to attack the protective layer called myelin that surrounds nerve cells in the brain and spinal cord. As the myelin becomes damaged, nerve cells are no longer able to send signals efficiently, resulting in a range of symptoms.
A protein called acid-sensing ion channel 1 (ASIC1) is over-expressed in acute MS lesions. This causes sodium to easily enter and accumulate inside nerve cells, which in turn triggers the excessive release of calcium. High concentrations of calcium are toxic for nerve cells.
Midamor is a sodium channel blocker. It can stop sodium from entering the nerve cells, which in turn reduces the release of calcium. Therefore, Midamor could have a neuroprotective function in MS patients.
Midamor in clinical trials
A pilot study involving 14 patients with primary progressive multiple sclerosis (PPMS) showed that participants taking Midamor for three years experienced less nerve damage, less loss of brain volume, and a slower increase in disability compared to the year prior to treatment.
A Phase 2 trial called ACTION (NCT01802489) in 46 patients with MS was completed in September 2016. The trial aimed to assess the effect of Midamor in treating optic neuritis, where significant nerve cell loss in the eye results in poor vision. However, Midamor did not appear to provide any significant protection to the optic nerve.
Another Phase 2 study, called MS-SMART (NCT0190259) is testing the safety and effectiveness of three different drugs – riluzole, Midamor, and fluoxetine — over a two-year period in 440 people with SPMS.
Study participants are assigned one of the three drugs or a placebo, and their response to the treatment is being measured as a change in the rate of brain volume loss using magnetic resonance imaging (MRI). This study is ongoing but not currently recruiting participants. Results are expected by the end of 2018.
Common side effects caused by Midamor include diarrhea, headache, loss of appetite, nausea, and weakness. The side effects of Midamor in patients with MS is currently unknown. The pilot study reported worsening bladder problems in two of the 14 participants, which led those patients to leave the trial.
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