Single shot, long term male contraception in the offing

A new single injection male contraceptive may provide rapid, durable and potentially reversible birth control for about a year without the need for condoms, a new study has claimed, ahead of its first human clinical trial this year.

Men currently have few options for reproductive control, including condoms and vasectomy.

While condoms are widely available and useful in preventing disease when used correctly, they have an 18 per cent yearly pregnancy rate in typical use.

Vasectomy is effective, but must generally be considered permanent. There are no long-acting, reversible contraceptives currently available for men.

The new study in rabbits has confirmed that Vasalgel has the potential to fill the gap in male contraception availability.

It consists of styrene-alt-maleic acid (SMA) dissolved in dimethyl sulfoxide and could be the first long-acting, non-hormonal, potentially reversible male contraceptive to reach market, researchers said.

"Results from our study in rabbits were even better than expected. Vasalgel produces a very rapid contraceptive effect which lasted throughout the study due to its unique hydrogel properties," said Dr Donald Waller, Professor of Pharmacology and Toxicology at the University of Illinois at Chicago.

"These features are important considerations for a contraceptive product to be used in humans," said Waller, lead author of the research published in the journal Basic and Clinical Andrology.

The study provided evidence for Vasalgel's value as an effective male contraceptive. The study tested two different formulations of the test article having either 100 per cent SMA acid or 80 per cent SMA acid/20 per cent SMA anhydride.

After the gel was injected into the vas deferens of 12 rabbits, semen analysis showed that 11 rabbits were azoospermic in all samples, having no quantifiable sperm in their semen at all.

One rabbit had a few samples with very small numbers of sperm before also becoming azoospermic. Both test articles were equally effective.

The study also confirmed that the contraceptive effect was durable over the 12 month study period. The response of the vasa deferentia tissue was minimal with characteristics of a normal foreign body response.

The implant remains in a soft gel-like state, with the ability to flex and adhere to walls of the vasa deferentia.

Hydrogels allow transit of many water-soluble molecules but not larger structures such as spermatozoa.

The ability to remove the gel to return the flow of sperm - or reverse the contraceptive effect - was successfully accomplished in the rabbit model, researchers said.

Seven rabbits had the test article flushed from their vas deferens, and semen samples showed a rapid return of sperm flow, they said.

The success of the studies has paved the way for the first clinical trial in men, scheduled to launch late this year, researchers said.