* Boxed warnings added to Solvay, Auxilium gels

* Serious side effect reported in young children

NEW YORK (Reuters) - The U.S. Food and Drug Administration said on Thursday it will require strong warnings to be added to two testosterone replacement gel products after numerous reports of troubling side effects in children who were exposed to the medicines.

Very young children who came into contact with the male hormone gel experienced inappropriate enlargement of the penis or clitoris, premature development of pubic hair, advanced bone age, increased libido, and aggressive behavior, the FDA said.

The so-called “black box” warnings will be included on the labels for Solvay’s AndroGel and Auxilium Pharmaceuticals Inc’s Testim.

The testosterone replacement therapies come in gel form and are typically administered by rubbing the product on the upper arm or shoulder. Under the current label, patients are advised to wash their hands after using the product and to cover the treated skin with clothing.

As of December 1, 2008, the FDA said it had received reports of eight cases of secondary exposure to testosterone in children ranging in age from nine months to five years, primarily due to direct contact between the treated skin and the child. Additional reports of potential secondary exposures are under review, the agency said.

In at least one case, a child was hospitalized and underwent surgery due to a delay in recognizing the cause of the symptoms, the FDA said.

The gels are intended for use in men who either no longer produce testosterone or produce it in very low amounts.

“These drugs are approved for an important medical need, but can have serious, unintended side effects if not used properly,” Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research, said in a statement.

“We must ensure that the adults using them are well-informed about the precautions needed to protect children from secondary exposure.”

In most cases, the signs and symptoms regressed when the child no longer was exposed to the product, although the agency said in a few cases, enlarged genitalia did not fully return to age-appropriate size and bone age remained modestly greater than the child’s chronological age.

The required label changes will provide additional information about the risk of secondary exposure and the steps that should be taken to reduce the risk, the FDA said.

Some 1.4 million prescriptions for AndroGel and 370,000 prescriptions for Testim were filled by U.S. retail pharmacies in 2007, according to data cited by the FDA.