Side Effects of Verapamil
Verapamil's most common side effects include constipation, peripheral edema, hypotension, bradycardia, and AV block, with serious cardiovascular complications possible in patients with heart failure or severe left ventricular dysfunction. 1
Cardiovascular Side Effects
The most clinically significant adverse effects of verapamil involve the cardiovascular system due to its negative inotropic and chronotropic properties:
Common Cardiac Effects
- Hypotension: Occurs in approximately 2.5% of patients, resulting from verapamil's vasodilatory properties 2. This can manifest as dizziness or symptomatic hypotension, though severe drops below normal are uncommon in hypertensive patients 1
- Bradycardia and conduction abnormalities: Verapamil slows AV nodal conduction, causing asymptomatic first-degree AV block and transient bradycardia in many patients 1. Higher degrees of AV block occur less frequently (0.8%) but require dose reduction or discontinuation 1
- Peripheral edema: Common to all calcium channel blockers, this occurs due to arterial vasodilation 3, 4
Critical Cardiovascular Warnings
Heart failure exacerbation is the most serious concern - verapamil developed congestive heart failure or pulmonary edema in 87 of 4,954 patients (1.8%) in clinical trials 1. The drug should be avoided in:
- Patients with severe left ventricular dysfunction (ejection fraction <30%) 1
- Patients with moderate to severe heart failure symptoms 1
- Any patient with ventricular dysfunction receiving concurrent beta-blockers 1
In patients with hypertrophic cardiomyopathy and severe symptoms (orthopnea, paroxysmal nocturnal dyspnea) combined with marked outflow obstruction, verapamil has caused death due to augmented outflow obstruction, pulmonary edema, and cardiogenic shock 5. The vasodilating properties can predominate over negative inotropic effects in these vulnerable patients 5.
Gastrointestinal Effects
- Constipation: The most common non-cardiovascular side effect 5, 6. This is particularly problematic in elderly patients and is considered a potentially inappropriate medication (PIM) in people ≥75 years with chronic constipation 7
- Nausea and gastrointestinal upset: Reported across multiple studies 3, 6
Hepatic Effects
Elevated liver enzymes can occur with verapamil use 1:
- Transaminase elevations with or without concomitant increases in alkaline phosphatase and bilirubin
- Some elevations are transient and may resolve despite continued treatment
- Several cases of hepatocellular injury have been proven by rechallenge, with half showing clinical symptoms (malaise, fever, right upper quadrant pain) 1
- Periodic liver function monitoring is prudent 1
Neurological Effects
- Dizziness, headache, and malaise 3, 4
- Blurred vision 8
- In overdose situations, confusion and altered mental status can occur 9
Metabolic and Other Effects
- Weight gain and fluid retention 6
- Gingival hyperplasia (rare) 8
- Skin reactions: Rash, flushing, and in rare cases with adjuvant therapy, skin rashes 3, 10
Special Populations and Situations
Renal Impairment
Patients with chronic renal insufficiency or end-stage renal disease are at increased risk for verapamil toxicity 11. Four reported cases developed:
- Varying degrees of AV heart block
- Hypotension
- Hyperkalemia
- Metabolic acidosis
- Hepatic dysfunction
Sustained-release verapamil should be used with extreme caution in renal impairment, as accumulation of verapamil or its metabolites can lead to severe toxic effects 11.
Elderly Patients
Older patients experience greater antihypertensive effects due to decreased baroreceptor response and age-related increases in drug exposure 7. Falls are a particular concern due to hypotension 7.
Dangerous Drug Interactions
- Beta-blockers: Combination can cause profound bradycardia and hypotension; verapamil is contraindicated in patients already on beta-blockers in certain situations 12, 1
- Digoxin: Verapamil increases digoxin levels by 50-75%, requiring dose reduction 1
- Accessory pathway syndromes (WPW): Verapamil is absolutely contraindicated in atrial fibrillation/flutter with WPW, as it can precipitate ventricular fibrillation by increasing conduction through the accessory pathway 12, 13, 1
Overdose
Even modest overdoses can be fatal, particularly with sustained-release formulations 14. A case report documented fatal toxicity from only 720 mg (3 tablets) in a patient with preexisting renal and cardiac disease, with postmortem cardiac blood levels of 6000 ng/mL 14. Overdose presents with severe hypotension, bradycardia, heart block, and potential cardiovascular collapse 9, 6.
Clinical Monitoring Recommendations
Based on the evidence, patients on verapamil require:
- Blood pressure monitoring (especially during initiation) 7, 3
- ECG monitoring for conduction abnormalities 7
- Periodic liver function tests 1
- Renal function assessment, particularly in elderly or those with baseline renal impairment 11
- Careful attention to constipation management, especially in elderly patients 7, 5