Minocycline is an oral antibiotic that is being evaluated as a potential treatment for relapsing-remitting multiple sclerosis (RRMS) or clinically isolated syndrome (CIS).
Minocycline was first approved in the U.S. more than 50 years ago, in 1971, for treating bacterial infections. Its use has since been extended to certain skin conditions like acne and rosacea. The antibiotic is available under a number of brand names, such as Minocin and Dynacin, as well as in generic formulations.
Multiple sclerosis (MS) is a neurodegenerative disease associated with abnormal immune and inflammatory responses against myelin, the fatty, protective sheath around nerve fibers that is critical for sending electrical signals between nerve cells.
Minocycline, a modified formulation of the natural antibiotic tetracycline, is well known for its ability to stop the growth and spread of bacteria. But the medication also has potent immunomodulatory, anti-inflammatory, and neuroprotective properties, making it a potential treatment candidate for neurodegenerative conditions such as MS.
In particular, minocycline has been shown to reduce the activation of microglia and T-cells — two types of immune cells involved in MS-associated abnormal immune attacks — and to prevent T-cells from entering the brain and spinal cord, where they could cause damage.
The therapy also can lower the production of pro-inflammatory molecules involved in myelin damage, reduce the generation of toxic oxygen radicals, and prevent nerve cell death.
Minocycline is available in tablet, foam, and injectable formulations. In clinical trials for MS, the therapy has been tested in the form of oral tablets, at a dose of 100 mg, twice a day.
After showing promise in animal models of MS, minocycline was tested alone and in combination with other therapies in clinical trials for RRMS and CIS.
GA 9014 trial
A Phase 2 clinical trial, called GA 9014 (NCT00203112), assessed minocycline as an add-on to Copaxone (glatiramer acetate) in 44 adults with RRMS. Participants were randomly assigned to receive Copaxone plus either 100 mg of minocycline or a placebo for nine months.
Results from GA 9014 showed that adding minocycline to Copaxone was generally well tolerated. It led to a reduction in the risk of relapse and in the number of new or enlarging brain lesions compared with Copaxone plus a placebo, but these differences failed to reach statistical significance.
The RECYCLINE Phase 2 trial (NCT01134627) investigated the effects of minocycline in combination with the approved MS therapy Rebif (interferon beta-1a) over nearly two years. The 305 participants, all with RRMS, were randomly selected to receive 100 mg of minocycline or a placebo, given twice daily for 96 weeks. All also received under-the-skin injections of Rebif, three times a week.
Minocycline was not significantly superior to a placebo at delaying relapses or improving other efficacy measures, the results from RECYCLINE showed. However, some trends favoring the antibiotic were observed.
A Phase 3 trial called MinoCIS (NCT00666887) evaluated whether minocycline could delay or prevent the conversion to clinically definite MS in 142 adults with CIS. These participants were randomly assigned to an oral capsule of 100 mg minocycline or a matching placebo, given twice daily for two years.
MinoCIS results indicated that significantly fewer CIS patients on minocycline than a placebo had been diagnosed with MS after six months (43% vs. 61.5%). Minocycline also significantly lowered the number and volume of brain lesions at six months. Notably, however, no significant benefits were observed after two years.
An ongoing, open-label Phase 3 trial called MinoMS-2019 (NCT04291456) is continuing to assess the safety and efficacy of minocycline (100 mg). This trial, underway in Canada, involves 148 CIS patients who experienced their first MS-like demyelinating event in the previous six months. Top-line results are expected by March 2025.
According to clinical trial data, the most common side effects of minocycline in MS patients include:
Minocycline can cause permanent teeth discoloration (yellowing or graying) during tooth development in children, occurring from the second half of pregnancy to the age of 8. It is therefore not recommended for children younger than 8 and should only be used in these patients if other alternative medications are contraindicated or unlikely to be effective.
While there are no well-controlled studies on the use of minocycline in pregnant women, the therapy can cross the placenta and cause damage to a developing fetus. Patients who become pregnant while on minocycline should discuss the potential harm to the fetus with their healthcare provider.
Minocycline also can pass into breast milk and cause serious side effects in nursing infants. Patients on minocycline should discuss with their healthcare team whether to continue taking the drug or to breastfeed.
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Minocycline is an antibiotic that is also believed to have anti-inflammatory and neuroprotective effects. It is being evaluated in clinical trials in relapsing-remitting multiple sclerosis and clinically isolated syndrome. Results have shown that it may help slow disease progression and reduce relapses in MS patients by lowering disease-associated inflammation and subsequent nerve cell death.
Minocycline has shown promising results in MS Phase 2 and Phase 3 trials. These results may encourage the launch of additional studies to confirm the antibiotic’s benefits in relapsing forms of MS. It may still take several years before a potential approval is granted by the U.S. Food and Drug Administration.
Based on animal data, minocycline is not recommended for use during pregnancy due to possible fetal harm. People of childbearing age should use effective contraception while on this medication. Patients should talk with their healthcare provider if they become pregnant, plan to become pregnant, or are breastfeeding or plan to do so while on minocycline.
In clinical trials in multiple sclerosis patients, the earliest signs of minocycline’s effects were reported at six months. In one small trial involving 10 patients with relapsing-remitting MS, the treatment significantly lowered the number of inflammatory lesions by 84% at six months. In a larger trial, called MinoCIS, the antibiotic also significantly lowered the proportion of patients converting from clinically isolated syndrome to clinically definite MS at six months.
Hair loss and weight gain have not reported as side effects of minocycline in clinical trials for multiple sclerosis, but hair loss is mentioned as a common side effect of minocycline in other indications. Patients should talk with their healthcare team if such events occur.
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