A once-a-month pill to help women battle the bone-weakening disease osteoporosis (search) has been approved by the Food and Drug Administration.

Boniva will be the first monthly osteoporosis medication, said Dr. Ronald Emkey of Radiant Research in Reading, Pa., which conducted trials of the drug. Current medications are taken weekly.

Boniva, approved late Thursday, is being jointly promoted by the drug companies, GlaxoSmithKline and Roche.

The companies estimate that 44 million Americans over age 50 suffer from osteoporosis

Known as ibandronate sodium, the 150 milligram tablets are intended for both treatment and prevention of postmenopausal osteoporosis. The drug is expected to go on sale, by prescription, in April.

The companies said they were setting up a patient support program to help patients remember to take the drug every month and to stay on the medication.

In trials over three years the drug reduced the number of new vertebral fractures in women with osteoporosis and increased bone density in women who had not developed the disease. The most common side effects reported were abdominal pain, high blood pressure, upset stomach, joint pain, nausea and diarrhea.