Calcium channel blockers · Cardiovascular
Diltiazem
Cardizem® · Tiazac®(brand names vary by market)
The calcium channel blocker that slows the heart as well as opening the arteries.
Also: modified release, capsule, injection
Mechanism
Non-dihydropyridine L-type calcium channel blocker with meaningful activity at the sinus and AV nodes as well as vascular smooth muscle: rate control and blood pressure from one molecule.
Indications
- Rate control in atrial fibrillation or flutter
- Angina, including vasospastic
- Hypertension
Formulations
Dosing concepts
Formulation
Immediate-release is several times daily; the once-daily products are not interchangeable brand for brand, and switching between them is a prescribing decision rather than a substitution.
With a beta blocker
Adding it to a beta blocker stacks two AV-nodal brakes. It is done deliberately and cautiously, never casually.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~40% (heavy first-pass)
- Half-life
- 3 to 5 h immediate-release
- Elimination
- hepatic: CYP3A4 substrate and moderate inhibitor: it raises the levels of other CYP3A4 drugs, including some statins
- Protein binding
- ~80%
Adverse effects
- Bradycardia and AV blockcommon & serious
- Peripheral oedemacommonLess than with amlodipine but still present.
- Constipationcommon
- Worsening heart failure in reduced ejection fractionseriousNegative inotropy: this class is avoided in HFrEF.
- Hepatic enzyme elevationserious
Contraindications & precautions
Contraindications
- Heart failure with reduced ejection fraction
- High-grade AV block without a pacemaker
- Severe hypotension
- Atrial fibrillation with pre-excitation
Precautions
- Concurrent beta blockade
- Hepatic impairment
- Concurrent CYP3A4 substrates
Interactions
- Beta blockers + Verapamil / diltiazemcautionBradycardia, AV block, hypotension, occasionally pacing-level.
- Amlodipine / felodipine + Strong CYP3A4 inhibitors; grapefruit (felodipine)monitorMore vasodilation: flushing, edema, hypotension.
- Simvastatin / atorvastatin + Clarithromycin, itraconazole, ritonavir (strong CYP3A4 inhibitors)avoidMyopathy up to rhabdomyolysis: muscle pain, dark urine, AKI.
Monitoring
Heart rate and blood pressure
Both are its effect and both are its toxicity
ECG for PR interval where block is a concern
AV nodal depression is dose-dependent
Symptoms of heart failure
Negative inotropy can unmask a marginal ventricle
Counselling points
- Extended-release capsules and tablets are swallowed whole.
- Constipation is common; fluid, fibre and, if needed, a laxative are part of the plan.
- Avoid grapefruit juice.
- Report a very slow pulse, fainting, or new ankle swelling.
Clinical pearls
- In atrial fibrillation with a preserved ejection fraction it is often better tolerated than a beta blocker; in a reduced ejection fraction it is the wrong drug entirely. The echo report changes the answer.
- It is a moderate CYP3A4 inhibitor, so it quietly raises simvastatin and some other substrates. The interaction is easy to forget because diltiazem does not feel like an interacting drug.
References & review
- Diltiazem product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.