Generic Name

Verapamil Hydrochloride

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Classification

FDA Approved Indications

• Hypertension
• Angina pectoris
• Ventricular rate control in atrial fibrillation or flutter

Mechanism of Action

Verapamil inhibits calcium ion influx across the cell membrane of vascular smooth muscle and cardiac muscle, leading to decreased myocardial contractility, conduction velocity, and oxygen demand. It relaxes coronary and peripheral blood vessels, reducing blood pressure and decreasing cardiac workload.

Dosage and Administration

Adult: Typically 80-160 mg three times daily; may be adjusted based on response. Extended-release formulations (Calan SR, Verelan) usually taken once daily at similar total daily doses.

Pediatric: Use not generally recommended; consult specific pediatric guidelines.

Geriatric: Start at lower doses due to increased sensitivity and comorbidities; monitor closely.

Renal Impairment: No specific adjustment; use with caution and monitor response.

Hepatic Impairment: Use with caution; dose adjustment may be necessary due to decreased metabolism.

Pharmacokinetics

Absorption: Well absorbed orally but subject to first-pass metabolism.

Distribution: Widely distributed; cross blood-brain barrier.

Metabolism: Extensively metabolized by the liver, primarily via CYP3A4.

Excretion: Metabolites primarily excreted in urine; a small amount excreted unchanged in feces.

Half Life: 3-7 hours for immediate-release; longer for extended-release formulations.

Contraindications

• Hypersensitivity to verapamil
• Acute myocardial infarction with left ventricular failure
• Uncompensated heart failure
• 2nd or 3rd degree AV block
• Sick sinus syndrome (unless a functioning pacemaker)

Precautions

• Use with caution in left ventricular systolic dysfunction
• Monitor blood pressure and cardiac rhythm
• Use cautiously in elderly and patients with hepatic impairment
• Pregnancy category C; benefits should outweigh risks
• Lactation: caution advised; verify safety

Adverse Reactions - Common

• Headache (Common)
• Dizziness (Common)
• Flushing (Common)
• Bradycardia (Common)
• Constipation (Common)

Adverse Reactions - Serious

• Atrioventricular block (Rare)
• Heart failure (Rare)
• Severe hypotension (Rare)
• Pulmonary edema (Rare)

Drug-Drug Interactions

• Beta-blockers (additive bradycardia and AV block)
• Digitals (digoxin)
• Other hypotensives
• CYP3A4 inhibitors and inducers

Drug-Food Interactions

• Grapefruit juice (may increase serum levels)

Drug-Herb Interactions

• St. John's Wort (may reduce efficacy)

Nursing Implications

Patient/Family Teaching

• Take medication exactly as prescribed; do not skip doses.
• Monitor and report signs of dizziness, swelling, or irregular heartbeat.
• Avoid grapefruit juice during therapy.
• Caution about sudden position changes to prevent falls.
• Do not discontinue abruptly to avoid rebound hypertension or arrhythmia.

Special Considerations

Black Box Warnings:

• Potential for severe hypotension and cardiac failure

Genetic Factors: CYP3A4 polymorphisms may affect metabolism.

Lab Test Interference: May cause false positive urinary catecholamine tests.

Overdose Management

Signs/Symptoms: Severe hypotension, bradyarrhythmias, conduction abnormalities, cardiovascular collapse.

Treatment: Supportive measures including IV fluids, vasopressors, atropine, and calcium gluconate; continuous cardiac monitoring.

Storage and Handling

Storage: Store in a tight, light-resistant container at room temperature (15-30°C).

Stability: Stable under recommended conditions, check expiration date.