Another potentially reversible method is the reversible inhibition of sperm under guidance (RISUG). This is a clear polymer gel mixed with dimethyl sulphoxide that solidifies, causing partial obstruction and the rupture of passing sperm membranes, when injected into the vas. Phase II trials demonstrated azoospermia for at least 1 year (38).
Another critical area for contraceptive development is nonsurgical means of sterilization of both men and women. Intrauterine quinacrine is the most promising method for nonsurgical female sterilization, but the method is embroiled in controversy because it was developed in the third world and moved quickly to widespread use without adequate proof of safety (386). Approximately 100,000 women were treated with it (387). The technique is very simple: pellets containing 252 mg of quinacrine are inserted into the uterus through an IUD inserter during the proliferative phase of the cycle and again 1 month later. Intrauterine quinacrine produces sclerosis of the proximal fallopian tube. In a large trial in Vietnam, the cumulative pregnancy rate for 1,335 women who received 2 doses was 3.3 at 1 year, 10.0 at 5 years, and 12.1 at 10 years (388). Another study of almost 25,000 women found the rate of ectopic pregnancy to be 0.26 per 1,000 women treated, which was similar to surgical sterilization and the IUD, OC pills, and condoms (0.42–0.45 per 1,000) and less than nonusers of contraception (1.18 per 1,000) (389). Concern was raised that quinacrine would lead to reproductive tract cancers. Two epidemiologic studies found no apparent increased risk for cancer from previous quinacrine sterilization in humans (390,391). A study of lifetime risk in rats sterilized with intrauterine quinacrine as young adults did find an increase in reproductive tract cancer in those rats treated with eight times the human dose, but not in the rats exposed to lower doses (392).
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