Nandrol>65 due to reduced renal function. 2.0 mg/dL). |
| **Adding a strong CYP3A4 inhibitor** | Reduce drug X dose by ~50–70%; monitor for toxicity. |
| **Adding a strong CYP3A4 inducer** | Increase drug X dose by ~25–30% if needed; monitor therapeutic response and side effects. |
| **Patient with pre‑existing QTc >450 ms** | Avoid concomitant use unless absolutely necessary; consider alternative therapies. |

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### Practical Summary for the Emergency Room

| Situation | Action |
|-----------|--------|
| **Drug X + QT‑prolonging drug** | Check baseline ECG if possible; avoid combination or lower dose of one agent; monitor QTc >500 ms. |
| **Co‑administration with CYP3A4 inhibitor (e.g., ketoconazole, clarithromycin)** | Expect ~2–3× increase in Drug X exposure → consider dose reduction by 50% and watch for toxicity. |
| **Co‑administration with CYP3A4 inducer (e.g., rifampin, carbamazepine)** | Exposure may drop to