Vasectomy Success -- March 5, 2003

Research Triangle Park, NC — Two chemicals already commonly used in the medical field also effectively inhibit sperm function, a new study confirms. This makes them good candidates to both inhibit and help wash away residual sperm after a vasectomy, which could decrease the time between vasectomy and sterility.

The purpose of a vasectomy is to sever the tubes (each called a vas deferens, or vas for short) that carry sperm from the testicles to the penis. In contrast to tubal ligation in women, which is immediately effective, vasectomy can take up to three months to take full effect.

"It probably takes two or three weeks for residual sperm that are downstream from the vasectomy site to be flushed out," says Dr. David Sokal, an associate medical director at Family Health International (FHI) and coauthor of the study, published in the March issue of the journal Contraception. A technique called vas irrigation can be used during a vasectomy to wash away these leftover sperm, but no chemical has been approved by the U.S. Food and Drug Administration for this purpose.

To identify potential vas irrigants, a small team of researchers from FHI and the CONRAD program at the Eastern Virginia Medical School in Norfolk, VA, tested the ability of five different chemicals to inhibit sperm function. Using sperm from human volunteers, the researchers determined each chemical's effects on three sperm functions: motility, viability, and ability to penetrate cervical mucus.

The chemical that most effectively inhibited all three functions is called diltiazem, a calcium-channel blocker that is already commonly used to treat high blood pressure and chest pain. After just 15 minutes, diltiazem killed about 85 percent of the sperm and completely inhibited all sperm motility and ability to penetrate cervical mucus. Another calcium-channel blocker tested in the study — nicardipine — appears to work on different calcium channels or through a different mechanism, as it did not effectively inhibit sperm function.

The second compound that showed promise is called methylene blue. While it did not kill sperm as effectively as diltiazem, it completely inhibited sperm motility after two hours and completely blocked penetration of cervical mucus after only 15 minutes. Since methylene blue is commonly used to dye the vas during other surgical and diagnostic procedures, it would likely be safe as a vas irrigant.

The identification of candidate vas irrigants is a small step toward improving the effectiveness and acceptability of vasectomy by reducing the risk of pregnancy in the postvasectomy period, says Dr. Sokal. The next step is to proceed to animal safety studies and then on to phase I clinical trials of diltiazem and methylene blue, both of which have been patented by FHI for use as vas irrigants.

Identification and evaluation of an effective vas irrigant might enable a man to become sterile immediately after a vasectomy. But for now, clinicians must continue to recommend that men use condoms or other contraceptives for at least three months after vasectomy. "If they do not, there may be a significant risk of pregnancy," says Dr. Sokal.

Dr. Sokal also notes that even with vas irrigation, some surgeons might still recommend a three-month waiting period before confirming vasectomy success, because of the chance of recanalization. A recanalization is a spontaneous reconnection of the two ends of the vas that can occur following a vasectomy, often within a month or two. Recent research from FHI has shown that the risk of recanalization appears to be related to the surgical technique used for vasectomy. The use of more effective surgical techniques, such as fascial interposition and cautery, can reduce this risk.

Additional coauthors on the study are Dr. Gustavo F. Doncel and Barbara L. Wood, both of the CONRAD program, and Dr. Pingili Reddy of FHI. To read FHI's online materials on vasectomy, see http://www.fhi.org/en/topics/listings/sterilizationlist.html.

Reference
Wood BL, Doncel GF, Reddy PR, Sokal DC. Effect of diltiazem and methylene blue on human sperm motility, viability and cervical mucus penetration: potential use as vas irrigants at the time of vasectomy. Contraception 2003;67(3):241-45.

FHI is dedicated to improving lives, knowledge, and understanding worldwide through a highly diversified program of research, education, and services in family health and HIV/AIDS prevention and care. Since our inception in 1971, FHI has formed partnerships with national governments and local communities in dozens of countries throughout the developing world to support lasting improvements in the health of individuals and the effectiveness of entire health systems.