Name: Metoprolol (Lopressor)
Class: Cardioselective b1-Blocking Agent
Mechanism: Selective blockade of b1 (heart, kidney) w/rel. sparing of b2. No a effect.
Absorption: Good oral (>95%). Bioavailability ~50%. Plasma levels vary 10x btwn. patients.
Dist.: 12% bound to protein. Metabolism.: Hepatic Excretion, t½: Short t½ (3-4 hr).
Toxicity/S.E.s: CV—hypotension, bradycardia, c/i for CHF or AV block. Resp—c/i in asthmatics, COPD, bronchitis, allergic rhinitis. Metabolism—caution w/diabetics (masks signs of hypoglycemia: tachycardia). CNS—weakness, fatigue, nightmares, depression. GI—n/v (uncommon). Hypersens—rash, hematologic disorders (rare).
Utility: Hypertension (¯ CO ® ¯ BP; blocks renin release). Angina pectoris (prophylactic ® exercise tolerance due to ¯ O2 demand). Cardiac arrhythmias (esp. supravent. tachyarrhyths). Acute MI (prophylaxis and reduction of infarct size and failure). Pheochromocytoma (in comb. w/alpha blocker). Essential tremor. Migraine headache (prophylaxis). Performance anxiety.
Special Features: Abrupt w/drawal may trigger MI. Cardioselectivity not great. May be advantageous in asthmatic or diabetic hypertensives.