The US Food and Drug Administration (FDA) announced today that it has approved the use of Pfizer's Rapamune (sirolimus) in the treatment of lymphangioleiomyomatosis (LAM).

LAM is a rare progressive form of lung disease that results in a proliferation of disorderly smooth muscle growth throughout the lungs, in thebronchioles, alveolar septa, perivascular spaces, and lymphatics.

The disease causes obstruction of small airways leading to pulmonary cyst formation and pneumothorax and lymphatics (leading to chylous pleural effusion).

FDA's decision has marked Rapamune as the first drug that has been ever approved by the administration for treatment of the rare disease, which primarily affects women of childbearing age.

LAM is a disease which, according to Reuters, affects two to five women per million throughout the world. According to LAM Foundation, the disease's symptoms are similar to those of asthma, emphysema and other lung conditions.

Rapamune was originally approved as an immunosuppressive agent in 1999. It is presently available both as a tablet as well as oral solution.

The drug was first used to prevent organ rejection in patients over the age of 13 who were receiving kidney transplants.

It has been found that the safety and efficacy of Rapamune for LAM treatment were studied in a clinical trial. Researchers during the trial compared the drug to a placebo in 89 patients over the period of 12 months.

The most commonly reported side-effects of the drug as highlighted in clinical trial include mouth and lip ulcers, diarrhea, abdominal pain, nausea, sore throat, acne, chest pain, leg swelling, upper respiratory tract infection, headache, dizziness, muscle pain and elevated cholesterol levels.

Some of its serious side-effects include hypersensitivity and swelling (edema) that was observed in renal transplant patients during trials.