Final answer:
AZT's effectiveness against HIV is predominantly reduced by the development of drug resistance due to the virus's high mutation rate. Combination therapy, such as HAART, has been more effective because it challenges the virus at various replication stages, making resistance development more difficult. Nonetheless, the emergence of resistant HIV strains necessitates ongoing drug development.
Step-by-step explanation:
The effectiveness of AZT as a treatment for HIV infection can become less due to the development of drug resistance. AZT works by blocking the HIV integrase enzyme, hindering the virus's ability to insert its DNA into the host cell's DNA. However, the high mutation rate of HIV facilitates the rapid emergence of drug-resistant strains when drugs are used individually, making them less effective over time. This challenge led to the adoption of Highly Active Antiretroviral Therapy (HAART), which is a combination of antiretroviral drugs attacking different stages of the virus's life cycle, thus making it more difficult for HIV to develop simultaneous resistance to multiple drugs.
To counteract resistance, doctors avoid a single-drug therapy and instead prescribe a ‘cocktail’ of multiple drugs, which often includes reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors, and other medications targeting various points of the viral replication process. Despite the use of HAART, continual development of new drugs remains critical, as resistance to current therapies can still emerge over time.