What are the side effects of intravenous metoprolol?

Side Effects of Intravenous Metoprolol

The most common side effects of IV metoprolol are hypotension and bradycardia, occurring in approximately 27% and 16% of patients respectively, with cardiogenic shock being the most serious risk, particularly in the first 24 hours after administration. 1, 2

Cardiovascular Side Effects (Most Common and Serious)

Hypotension

• Systolic blood pressure <90 mmHg occurs in 27.4% of patients receiving IV metoprolol 2
• Hypotension is the most frequent side effect and is typically transient but requires immediate management 3
• Risk is highest in patients with baseline systolic BP <120 mmHg 1, 4

Bradycardia

• Heart rate <40 bpm develops in 15.9% of patients 2
• Symptomatic bradycardia (HR <60 bpm with dizziness or lightheadedness) represents an absolute contraindication to continued therapy 4
• Continuous heart rate monitoring is essential during IV administration 4

Conduction Abnormalities

• Second- or third-degree heart block occurs in 4.7% of patients 2
• First-degree heart block (PR interval ≥0.26 seconds) develops in 5.3% of patients 2
• PR interval >0.24 seconds is an absolute contraindication to IV metoprolol 1, 4

Cardiogenic Shock

• Early IV metoprolol increases cardiogenic shock risk by 11 per 1000 patients treated, especially during days 0-1 1, 5
• Risk factors include age >70 years, systolic BP <120 mmHg, heart rate >110 bpm or <60 bpm, and Killip class >1 1, 4
• The COMMIT trial demonstrated a 30% relative increase in cardiogenic shock overall 4

Heart Failure

• Heart failure symptoms occur in 27.5% of patients 2
• Cold extremities and peripheral edema develop in approximately 1% of patients 2
• Decompensated heart failure is an absolute contraindication to IV administration 1, 5

Respiratory Side Effects

Bronchospasm

• Wheezing and dyspnea occur in approximately 1% of patients 2
• Active asthma or reactive airway disease represents an absolute contraindication 1, 4, 5
• Even cardioselective beta-blockers lose selectivity at therapeutic doses and can precipitate bronchospasm 6
• Continuous auscultation for bronchospasm is required during IV administration 4

Dyspnea

• Dyspnea of pulmonary origin occurs in fewer than 1% of patients 2
• Shortness of breath has been reported in approximately 3% of patients 2

Central Nervous System Side Effects

Common CNS Effects

• Tiredness occurs in approximately 10% of patients and is reported in about 1% during myocardial infarction treatment 2
• Dizziness develops in about 10% of patients 2
• Headache, vertigo, and sleep disturbances have been reported 2

Less Common CNS Effects

• Depression occurs in about 5% of patients 2
• Mental confusion and short-term memory loss have been reported 2
• Hallucinations, visual disturbances, and reduced libido have been reported, though drug relationship is unclear 2

Gastrointestinal Side Effects

• Nausea and abdominal pain occur in fewer than 1% of patients during myocardial infarction treatment 2
• Diarrhea develops in about 5% of patients 2
• Vomiting is a common occurrence 2
• Dry mouth, gastric pain, constipation, flatulence, and heartburn occur in about 1% of patients 2

Dermatologic and Hypersensitivity Reactions

• Pruritus or rash occur in about 5% of patients 2
• Rash and worsened psoriasis have been reported, though drug relationship is unclear 2
• Very rare reports of photosensitivity and worsening of psoriasis 2

Metabolic and Miscellaneous Effects

• Unstable diabetes has been reported, though drug relationship is unclear 2
• Claudication has been reported 2
• Very rare reports of hepatitis, jaundice, and non-specific hepatic dysfunction in postmarketing experience 2
• Isolated cases of transaminase, alkaline phosphatase, and lactic dehydrogenase elevations 2

Critical Monitoring Requirements During IV Administration

Continuous monitoring must include: 4, 5

• Heart rate monitoring continuously
• Blood pressure checks frequently during and after each bolus
• Continuous ECG monitoring
• Auscultation for new rales (pulmonary congestion)
• Auscultation for bronchospasm

Common Pitfalls to Avoid

• Never administer the full 15 mg IV dose rapidly or as a single bolus, as this significantly increases hypotension and bradycardia risk 4
• Do not administer IV metoprolol in patients with decompensated heart failure—wait until clinical stabilization 4
• Do not assume fever or tachycardia is benign; rule out sepsis and alcohol withdrawal before beta-blockade 4
• Avoid in patients with pre-excited atrial fibrillation, as it may paradoxically accelerate ventricular response 4

High-Risk Patient Populations

Patients at increased risk for adverse effects include: 1, 4

• Age >70 years
• Systolic BP <120 mmHg at presentation
• Heart rate >110 bpm or <60 bpm
• Killip class II-III (signs of heart failure)
• Increased time since symptom onset in acute MI

For high-risk patients, consider esmolol instead, with a maintenance infusion of 50-300 mcg/kg/min, allowing for rapid titration and shorter duration of action due to its ultra-short half-life (10-30 minutes) 4