A 48-year-old woman with hepatic cirrhosis (Child-Pugh Class B) is prescribed metoprolol 50 mg daily for hypertension. After 3 days, she develops severe bradycardia (HR 42/min) and hypotension (BP 88/54 mmHg). Serum albumin is 2.8 g/dL. What is the most appropriate next step?

Explanation

## Pharmacokinetic Basis Metoprolol is a lipophilic beta-blocker that undergoes extensive hepatic metabolism (first-pass and systemic). In hepatic cirrhosis, reduced hepatic blood flow and impaired metabolic capacity lead to: - Increased bioavailability (reduced first-pass metabolism) - Prolonged half-life and drug accumulation - Reduced protein binding due to hypoalbuminemia (2.8 g/dL) - Increased free (active) drug concentration **Key Point:** Hepatic impairment increases metoprolol exposure dramatically. Child-Pugh Class B cirrhosis requires dose reduction of 25–50% to prevent toxicity. ## Volume of Distribution & Protein Binding **High-Yield:** Metoprolol is highly protein-bound (95%). In cirrhosis with hypoalbuminemia, free drug concentration increases, amplifying beta-blockade and causing severe bradycardia and hypotension. ## Management Algorithm ```mermaid flowchart TD A[Metoprolol toxicity<br/>in cirrhosis patient<br/>HR 42, BP 88/54]:::outcome --> B{Hepatic function?}:::decision B -->|Reduced clearance<br/>+ Hypoalbuminemia| C[Withhold metoprolol]:::action C --> D[Measure serum level<br/>if available]:::action D --> E[Reduce dose by 50%<br/>after stabilization]:::action E --> F[Monitor HR & BP<br/>Recheck in 24-48 hrs]:::action B -->|Acute toxicity| G[Supportive care<br/>Consider atropine if<br/>symptomatic bradycardia]:::urgent G --> H[Do NOT increase dose]:::urgent ``` **Clinical Pearl:** Symptomatic bradycardia (HR < 50 with hypotension) in a cirrhotic patient on beta-blockers is a sign of drug accumulation, not inadequate dosing. The correct response is dose reduction, not escalation. ## Why Serum Level Measurement Matters 1. Confirms drug accumulation (elevated concentration despite standard dose). 2. Guides safe dose reduction strategy. 3. Helps predict time to steady state after dose adjustment. ## Pharmacokinetic Parameters in Cirrhosis | Parameter | Normal | Cirrhosis (Child B) | | --- | --- | --- | | Hepatic clearance | ~5.5 mL/kg/min | ~2–3 mL/kg/min (↓ 50–60%) | | Half-life (metoprolol) | 3–4 hours | 7–10 hours (↑ 2–3×) | | Protein binding effect | Low impact | High impact (↓ albumin) | | Bioavailability | ~25% | ~50–70% (↑ first-pass loss) | | Recommended dose | 50 mg daily | 25 mg daily (50% reduction) |