A study by researchers at the National Institutes of Health (NIH) indicates that a steroid medication taken with an HIV protease inhibitor may increase the risk of bone damage in HIV-infected patients.

The drug interaction may also increase the risk of Cushing's syndrome, a hormonal disorder caused by prolonged exposure of the body's tissues to high levels of steroids, claims a NIH release.

The study showed that ritonavir, a protease inhibitor used to treat HIV patients, taken with the corticosteroid medication, prednisone, significantly increased the concentrations of prednisolone - the active form of prednisone in the systems of healthy volunteers.

"Physicians have noted bone lesions on scans of HIV patients treated with steroids for inflammation. We wanted to find out if the problems might be at least partially explained by an interaction between the steroids and HIV drugs," said Dr. Scott Penzak, NIH clinical center pharmacist and lead author of the study.

Corticosteroids are used to provide relief for inflamed areas of the body. They lessen swelling, redness, itching, and allergic reactions. They are used to treat a number of conditions, including severe allergies, skin problems, asthma, and arthritis.

Researchers gave ten healthy volunteers a 14-day course of low-dose ritonavir. They also gave the volunteers three doses of prednisone. One dose of prednisone was given before ritonavir was started as a baseline. A second dose was given after four days on ritonavir and a third dose was given after 14 days on ritonavir. Blood samples were taken after each dose of prednisone to determine steroid levels.

Prednisolone concentrations were 41 per cent higher than the baseline amount after the drugs were taken together four days into the ritonavir regimen and 30 per cent higher after the drugs were taken together 14 days into the regimen.

"These are statistically significant increases. They indicate that when the drugs are taken together, steroid concentrations in the body may rise to levels that cause side effects in some individuals," said Penzak.

"These results serve as a caution to clinicians treating HIV patients on concurrent steroid therapy. They may choose to start with lower steroid doses or increase their level of toxicity monitoring compared to steroid recipients who are not taking protease inhibitors," he added.

"It is these small steps that advance the safe practice of medicine. Through continued clinical research, we can improve the health of all Americans," said Dr. John Gallin, director of the NIH Clinical Center.

The study team included researchers at the NIH Clinical Center and the National Institute of Allergy and Infectious Diseases (NIAID).

The team plans to continue studies of the blood levels of individuals on steroids and other HIV medications.

The NIH Clinical Center is the clinical research hospital of the National Institutes of Health. Through clinical research, physicians and scientists translate laboratory discoveries into better treatments, therapies and interventions to improve the nation's health.