Clinical Pharmacology — MCQs

Q: A 50-year-old female with rheumatoid arthritis is being considered for infliximab therapy. Which of the following tests should be performed before beginning treatment?

PPD skin test. **Explanation:** **Infliximab** is a chimeric monoclonal antibody that inhibits **Tumor Necrosis Factor-alpha (TNF-α)**. TNF-α plays a critical role in the immune system's ability to form and maintain **granulomas**, which sequester *Mycobacterium tuberculosis*. 1. **Why the PPD skin test is correct:** By inhibiting TNF-α, infliximab can cause the breakdown of existing granulomas [1], leading to the **reactivation of Latent Tuberculosis Infection (LTBI)**. This can result in severe, disseminated, or miliary tuberculosis. Therefore, all patients must be screened for TB using a PPD (Tuberculin) skin test or an Interferon-Gamma Release Assay (IGRA) [2] and a chest X-ray before initiating therapy. If LTBI is detected, prophylactic treatment (e.g., Isoniazid) must be started before the biologic. 2. **Why other options are incorrect:** * **Liver Function Tests (A):** While some biologics can cause hepatotoxicity, they are not the primary mandatory screening requirement compared to TB screening. * **Pulmonary Function Tests (C):** These are typically required for drugs causing interstitial lung disease, such as **Methotrexate** [1] or **Amiodarone**, but not routinely for Infliximab. * **Visual Examination (D):** This is mandatory for patients starting **Hydroxychloroquine** (to monitor for bull’s eye maculopathy) or **Ethambutol**, but not for TNF inhibitors. **NEET-PG High-Yield Pearls:** * **TNF-α Inhibitors:** Include Infliximab, Adalimumab, and Etanercept [1]. * **Contraindications:** Avoid TNF inhibitors in patients with **NYHA Class III/IV Heart Failure** (can worsen outcomes) and active infections. * **Screening:** Always screen for **Hepatitis B** and **TB** before starting any biologic DMARD. * **Vaccination:** Live vaccines are contraindicated while on TNF-inhibitor therapy.

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