FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

Why is ritonavir ineffective when used alone in HIV treatment?

1. It is rapidly metabolized by CYP3A isozymes.

2. It has low bioavailability.

3. It does not target HIV effectively.

4. It causes severe side effects.

The correct answer is: It is rapidly metabolized by CYP3A isozymes.

Ritonavir, when used alone in HIV treatment, is ineffective primarily because it is rapidly metabolized by CYP3A isozymes. This rapid metabolism leads to suboptimal plasma levels of the drug, thus limiting its efficacy against the virus. Ritonavir was initially developed as a protease inhibitor, but its short half-life and quick breakdown in the body make it inadequate for monotherapy. In contrast, when used in combination with other antiretroviral agents, ritonavir can act as a booster. It inhibits the metabolism of these drugs when taken together, allowing for increased drug concentrations and enhanced therapeutic effectiveness. This characteristic highlights the importance of combining ritonavir with other medications to achieve better control of HIV. While bioavailability is a relevant consideration in the context of drug administration, ritonavir is primarily effective with its role in combination therapy rather than due to low bioavailability. Furthermore, although ritonavir does have a safety profile that can include side effects, this aspect does not singularly account for its ineffectiveness when used alone; rather, the rapid metabolism plays a critical role in its performance as a treatment candidate.