Source / episode info
- **Episode:**237
- **Title:**Divine Intervention Episode 237 – HIV and The USMLE.
- **Published:**2020-05-20
- Source:Episode page
One-liner
This episode provides a comprehensive review of HIV virology, detailing the pathogenesis from CD4 binding to reverse transcription; outlining opportunistic infection staging based on declining CD4 counts; and reviewing key prophylactic regimens and the mechanisms/toxicities of various antiretroviral drug classes.
High-yield summary
- Pathogenesis: HIV uses its glycoproteins (GP120 for host attachment, GP41 for fusion) to bind to CD4+ T-cells via CCR5 or CXCR4 receptors. The viral RNA is converted into double-stranded DNA by reverse transcriptase and integrated into the host genome by integrase.
- AIDS Definition: AIDS is defined as being HIV positive and having an AIDS-defining illness (e.g., Pneumocystis, MAC, Kaposi sarcoma). While CD4 < 200 cells/mm³ was historically used, OIs are the defining factor today.
- OI Staging & Prophylaxis: Specific prophylactic regimens must be initiated based on falling CD4 counts: TMP-SMX for Pneumocystis (CD4 < 200) and Toxo (Toxoplasma gondii) (CD4 < 100); Itraconazole for endemic fungi (Histoplasmosis/Coccidioidomycosis).
- ART Toxicity: NRTIs are associated with mitochondrial toxicity, leading to lactic acidosis and lipodystrophy. Protease inhibitors can cause metabolic syndrome.
- Diagnostic Testing: The fourth-generation ELISA is preferred as it detects both HIV antibodies and the P24 antigen, offering high sensitivity and specificity for screening. Confirmation requires a Western Blot.
Learning objectives
- Describe the virological cycle of HIV, including key enzymes and glycoproteins.
- Correlate specific opportunistic infections with declining CD4+ T-cell thresholds.
- Select appropriate prophylactic regimens for common OIs (PCP, Crypto, Toxo) based on patient risk factors and CD4 count.
- Identify the major drug classes used in ART (NRTIs, NNRTIs, PI, etc.) and their associated toxicities/mechanisms of action.
- Understand the guidelines for HIV diagnosis (ELISA vs. Western Blot) and post-treatment monitoring.
Board exam buzzwords