Photo: Kathy West/ CNPRC

A gel injection blocking the travel of sperm has been proven to be an effective birth control in monkeys – and trials in human males could be coming soon.

Sixteen rhesus males were injected with the compound, and then moved into outdoor housing with females for at least one breeding season. Seven of the 16 lived with the three to nine females for nearly two full years, according to the study, in the journal Basic and Clinical Andrology.

Among the group were males and females who had previously conceived offspring.

But no monkeys were conceived during the study period, report the team of scientists, from the California National Primate Research Center at the University of California.

“We were impressed that this alternative worked in every single monkey, even though this was our first time trying it,” said Angela Colagross-Schouten, who led the team. “Vasectomies are a routine procedure for nonhuman primate veterinarians, so to have similar or even slightly better outcomes trying a brand-new procedure is very encouraging.”

One monkey was injected improperly with the material, and developed a non-fatal sperm granuloma.

The Vasalgel compound is a heavy polymer made of styrene-alt-maleic acid dissolved in dimethyl sulfoxide. It is directly injected into the vas deferens to block sperm from proceeding outward. The scientists and developers of the compound believe that fluids are able to pass slowly through the gel, which reduces the built-up pressure in the epididymis that can be felt after vasectomy.

The theory of the inventors is that Vasalgel would be a long-term male contraceptive that would nonetheless be reversible, with another injection of sodium bicarbonate, they added.

The compound has previously been demonstrated successfully in rabbits. The Parsemus Foundation, based in Berkeley, Calif., has said that the reversal of the birth control method was also demonstrated in rabbits – though those results have not yet been published.

One other such injectable male birth control method is also under development in India. Called RISUG (short for “Reversible Inhibition of Sperm Under Guidance”), the material is a styrene maleic anhydride which doesn’t block the sperm – but instead generates pH levels that essentially hobbles the sperm’s motility before the cells reach the female reproductive tract.