Diltiazem is a commonly prescribed calcium channel blocker used to treat conditions such as high blood pressure (hypertension), angina (chest pain), and certain types of abnormal heart rhythms (arrhythmias). It works by inhibiting the influx of calcium ions into cardiac muscle and vascular smooth muscle cells, which causes blood vessels to relax and the heart to slow down. While often effective, its powerful cardiac effects mean it carries risks of serious side effects that patients and healthcare providers must be aware of.
Severe Cardiac Complications
One of the most concerning aspects of diltiazem is its potential to cause or worsen significant heart problems due to its negative chronotropic (rate-slowing) and inotropic (contractility-reducing) effects. These severe cardiac events can be life-threatening and require immediate medical intervention.
Profound Bradycardia and Heart Block
Because diltiazem directly affects the electrical activity of the heart's conduction system, it can cause the heart rate to slow down excessively (bradycardia) or interrupt the electrical signals altogether (heart block). This is particularly risky for patients with pre-existing heart rhythm disorders, such as sick sinus syndrome, who should not take diltiazem unless they have a pacemaker. In severe cases, this can lead to a complete and potentially fatal cessation of the heartbeat. Patients should monitor their heart rate and seek medical attention if they experience excessive fatigue, dizziness, or shortness of breath.
Worsening of Heart Failure
For individuals with pre-existing impaired ventricular function, diltiazem can worsen symptoms of heart failure. Experts recommend that people with certain types of heart failure avoid diltiazem entirely, as it may exacerbate symptoms like swelling (edema), rapid weight gain, and shortness of breath without offering significant therapeutic benefits. The potential for fluid retention and a reduction in the heart's pumping strength makes careful patient selection crucial.
Acute Hepatic Injury (Liver Damage)
Diltiazem can, in rare cases, cause liver damage (hepatotoxicity), though the reaction is often idiosyncratic. The mechanism of injury is not fully understood but may be related to a hypersensitivity reaction. Symptoms of acute hepatic injury typically appear within one to eight weeks of starting therapy and are reversible upon discontinuation of the drug. Severe liver injury is possible, and patients should be aware of the warning signs.
Symptoms to watch for include:
- Loss of appetite and fatigue
- Pain in the upper right part of the abdomen
- Yellowing of the skin or eyes (jaundice)
- Unusual bruising or bleeding
- Dark urine or pale stools
Severe Skin Reactions
Although rare, diltiazem can trigger life-threatening skin reactions, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). These conditions are medical emergencies characterized by a widespread, blistering, and peeling rash that can lead to severe complications and even death.
Seek immediate emergency medical help if you experience:
- A red or purple skin rash with blistering and peeling
- Fever and a sore throat
- Burning eyes
- Swelling of the face, tongue, or throat
- Hives
Significant Drug Interactions
Diltiazem is metabolized by the cytochrome P450 3A4 enzyme system and is also an inhibitor of this pathway. This can cause serious drug interactions by increasing the plasma concentrations of other medications that rely on the same enzyme for metabolism. Combining diltiazem with other drugs that slow heart rate or lower blood pressure can dangerously increase these effects.
Table: Diltiazem Interaction Risks
| Drug Class / Drug | Potential Interaction | Resulting Risk | Reference |
|---|---|---|---|
| Statins (e.g., simvastatin) | Diltiazem inhibits CYP3A4, increasing statin levels | Myopathy, rhabdomyolysis | |
| Beta-blockers (e.g., metoprolol) | Additive effects on heart rate and conduction | Excessive bradycardia, heart block | |
| Digoxin | Diltiazem can increase digoxin plasma concentrations | Digoxin toxicity, severe bradycardia, heart block | |
| Direct Oral Anticoagulants (DOACs) (e.g., rivaroxaban, apixaban) | Increased drug exposure | Higher risk of major bleeding events | |
| Anxiolytics (e.g., midazolam, triazolam) | Diltiazem increases benzodiazepine levels | Prolonged sedation, respiratory depression |
Overdose and Hypotension
Overdosing on diltiazem can lead to a severe and rapid drop in blood pressure (hypotension), profound bradycardia, and other life-threatening complications. Symptoms can include severe dizziness, fainting, confusion, breathing difficulties, seizures, and a very slow or irregular heartbeat. It is a medical emergency that requires immediate attention.
Conclusion
While diltiazem is an important and effective medication for many cardiovascular conditions, it is not without risk. The worst side effects of diltiazem are concentrated in its significant impact on the heart's electrical system, the potential for rare but severe liver and skin reactions, and its numerous drug-drug interactions. Recognizing the warning signs of serious cardiac issues, liver damage, and skin reactions is critical for patient safety. Patients should also ensure their healthcare provider is aware of all other medications and supplements they are taking to avoid dangerous interactions. Should any symptoms of a severe reaction or overdose occur, immediate medical assistance is necessary.
For more detailed information, consult the MedlinePlus drug information page on Diltiazem.
