US regulators have waved a green flag for the use of Pfizer’s Rapamune to treat the ultra-rare, progressive and often fatal lung disease lymphangioleiomyomatosis (LAM).

Rapamune (sirolimus) is the first drug approved to treat the disease, which mostly affects women of childbearing age and is characterised by abnormal growth of smooth muscle cells that invade lung tissues and blood/lymph vessels. This causes destruction of the lung, resulting in airflow obstruction and thus limiting the delivery of oxygen to the body.

Originally cleared in the US in 1999 as an immunosuppressive agent to help prevent organ rejection, Rapamune’s approval for LAM was based on data from a trial involving 89 patients randomised to receive the drug or placebo, which showed that those given the drug for one year experienced stabilisation of lung function.

On the safety side, the most commonly reported side effects associated with the drug were mouth and lip ulcers, diarrhoea, abdominal pain, nausea, sore throat, acne, chest pain, leg swelling, upper respiratory tract infection, headache, dizziness, muscle pain and elevated cholesterol. Serious side effects including hypersensitivity and swelling have been observed in renal transplant patients, the US Food and Drug Administration noted.

According to the US National Library of Medicine, only between two and five women per million women worldwide are known to have the disease.