PARIS • A gel squirted into the sperm ducts of monkeys has been effective at preventing pregnancy, according to a new study which offers hope of a solution for men reluctant to go under the knife for family planning.

While several birth control options exist for women, the race is on for a non-surgical, long-term and reversible male contraceptive without the side effects of hormonal changes.

Researchers in the US are developing one possible option, dubbed Vasalgel, which has proven effective in rabbits and now also in rhesus monkeys - more closely related and anatomically similar to humans. Vasalgel is a polymer gel injected directly into the vas deferens, creating a blockage in the tube that transports sperm from the testes out through the penis.

In an experiment at the California National Primate Research Centre, 16 adult male monkeys were treated. They were housed with females, and monitored for up to two years.

"Treated males have had no conceptions since Vasalgel injections," the research team wrote in the journal Basic And Clinical Andrology, published yesterday.

"The presence of Vasalgel appears to be well tolerated and placement resulted in minimal complications," the researchers wrote.

One monkey of the 16 had symptoms of sperm granuloma, a build-up in the vas deferens which is a common complication in about 60 per cent of human vasectomies.

Not yet tested in monkeys, the reversibility of the method was tested in earlier experiments in rabbits, when the gel was successfully flushed out with solution of sodium bicarbonate.

Preparations are under way for a clinical trial in humans, said the Parsemus Foundation, a non-profit organisation funding the product's development.

AGENCE FRANCE-PRESSE