Why is combination therapy the treatment of choice for aids?

Answer:
HIV develops resistance to antiretroviral therapy very quickly. Using multiple drugs helps prevent the development of resistance. The current treatment protocol is known as Highly Active Antiretroviral Therapy (HAART) and uses a cocktail of nucleoside reverse transcriptase inhibitors, protease inhibitors, and possibly a newer class of drugs fusion inhibitors. Each class inhibits a different aspect of the life cycle of HIV. The likelihood that HIV will develop resistance to more than one class of drug is very low.

---