Gilenya, whose generic name is fingolimod, is a medication primarily used to treat relapsing forms of multiple sclerosis (MS). It works by modulating the immune system, specifically by reducing the number of certain white blood cells called lymphocytes in the bloodstream. This reduction happens because Gilenya causes these lymphocytes to be trapped in lymph nodes, preventing them from reaching the central nervous system where they could cause damage in MS. While this mechanism helps control the disease, it also has important implications for infection risk.
Because Gilenya lowers the number of circulating lymphocytes to about 20% to 30% of their normal levels, it can impair the body’s ability to fight infections. Lymphocytes are a crucial part of the immune system, responsible for identifying and attacking pathogens like viruses, bacteria, and fungi. When their numbers are reduced, the immune system is less capable of mounting an effective defense, which can lead to an increased risk of infections, some of which may be serious or even life-threatening.
Clinical studies and postmarketing experience have shown that patients taking Gilenya have a higher incidence of certain infections compared to those not on the drug. Common infections reported include bronchitis, herpes zoster (shingles), influenza, sinusitis, and pneumonia. While the overall rate of infections in patients on Gilenya is similar to placebo in some trials, the types of infections and their severity can differ. Serious infections, including disseminated herpes infections, herpes simplex encephalitis, and varicella zoster infections, have been reported. These serious infections can sometimes lead to multiorgan failure and have been fatal in rare cases, especially when patients were on higher doses or also receiving other immunosuppressive treatments like corticosteroids.
In addition to viral infections, there have been reports of fungal infections such as cryptococcal meningitis, a severe infection of the brain and spinal cord caused by the fungus Cryptococcus. This is a rare but serious complication that requires prompt diagnosis and treatment. Other infections linked to Gilenya include human papillomavirus (HPV) infections, which can cause warts, dysplasia, and even HPV-related cancers.
Because of these risks, doctors usually perform blood tests before starting Gilenya to check the patient’s immune status and monitor lymphocyte counts regularly during treatment. If a patient develops a serious infection while on Gilenya, the medication may be temporarily stopped to allow the immune system to recover. However, fingolimod has a long half-life, meaning it can take up to two months for the drug to be fully eliminated from the body, so infection risk can persist for some time after stopping the medication.
Patients are advised to report any signs of infection promptly, such as fever, cough, sore throat, or unusual skin lesions. Those with active infections, whether acute or chronic, are generally not started on Gilenya until the infection has resolved. Because of the immune system suppression, vaccinations should be up to date before beginning treatment, but live vaccines are usually avoided during therapy.
In summary, Gilenya does increase the risk of infections due to its immune-modulating effects, particularly by reducing lymphocyte counts. While many infections are mild and manageable, some can be serious or fatal, requiring careful monitoring and prompt medical attention. The benefits of controlling multiple sclerosis symptoms and relapses must be weighed against these infection risks on an individual basis by healthcare providers.
