A study by Spanish researchers published in the July 15 edition of the Annals of Internal Medicine suggests that HIV-positive people may be less likely to develop resistance to anti-HIV medications if they switch their drug regimens every three months. The researchers studied 161 HIV-positive patients in Spain and Argentina over two years, breaking the study subjects into three groups--two that maintained triple drug regimens even after blood-based viral loads began to climb, indicating the development of drug resistance, and a third group that alternated between two different regimens every three months. No significant difference in the rate of drug resistance development was found between the first two study groups, but patients in the third group took four times longer to experience rising viral loads than the other study subjects. The researchers plan additional tests to see if alternating drug regimens may help stave off the development of drug-resistant virus. They also plan to use newer anti-HIV medications in upcoming research; those used in the reported study were commonly prescribed in 1999 and 2000, but are not as potent as newer medications made available since then.