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Drug Reference

diltiazem

Calcium channel blockers· Brands: Cardizem, Tiazac, Dilacor, Adizem, Diltia, DiltzacIVPO

Mechanism of action
Diltiazem inhibits L-type calcium channels in cardiac and smooth muscle, reducing intracellular calcium influx. This leads to coronary and peripheral vasodilatation, decreased myocardial contractility, and slowed atrioventricular conduction, lowering blood pressure and heart rate.
Pharmacokinetics
Diltiazem is well absorbed orally but undergoes extensive first-pass hepatic metabolism, resulting in a bioavailability of about 40–60%. It is highly protein bound, metabolised by CYP3A4 to active metabolites, and has a half-life of 3–7 hours. Excretion is mainly in the bile and urine. Immediate-release and extended-release formulations have different dosing schedules.
Indications & dosing

Hypertension (extended-release formulation)

Extended-release; start at 120 mg once daily, titrate to 360 mg/day as needed.

  • adult · PO: 120–360 mg once daily · Extended-release; start at 120 mg once daily, titrate to 360 mg/day as needed.

Angina (chronic stable or vasospastic, extended-release)

Extended-release; start at 120 mg once daily, may increase to 480 mg/day if required.

  • adult · PO: 120–360 mg once daily · Extended-release; start at 120 mg once daily, may increase to 480 mg/day if required.

Atrial fibrillation/flutter (rate control, extended-release oral)

Extended-release; titrate to achieve target heart rate.

  • adult · PO: 120–360 mg once daily · Extended-release; titrate to achieve target heart rate.

Atrial fibrillation/flutter (acute rate control, IV infusion)

Administer as continuous infusion after initial IV bolus.

  • adult · IV: 5–15 mg/h continuous infusion · Administer as continuous infusion after initial IV bolus.

Paroxysmal supraventricular tachycardia (acute termination)

Administer 0.25 mg/kg IV over 2 minutes; repeat with 0.35 mg/kg after 15 minutes if needed.

  • adult · IV: 0.25–0.35 mg/kg once · Administer 0.25 mg/kg IV over 2 minutes; repeat with 0.35 mg/kg after 15 minutes if needed.
Contraindications & precautions
  • Severe bradycardia · Risk of symptomatic bradycardia and complete heart block.
  • Second- or third-degree AV block without a functioning pacemaker · Diltiazem can worsen AV block.
  • Sick sinus syndrome without a pacemaker · May cause severe bradycardia or asystole.
  • Cardiogenic shock · Diltiazem may reduce cardiac output.
  • Symptomatic congestive heart failure with reduced ejection fraction · Use with caution, may worsen heart failure.
  • Concomitant use with intravenous beta-blockers · Additive negative inotropic and chronotropic effects.
  • Monitor heart rate and blood pressure during dose titration.
  • Use caution in patients with impaired hepatic or renal function; reduce dose if necessary.
  • Avoid or use with caution with other AV-node blocking agents such as beta-blockers.
  • Use caution in patients with left ventricular dysfunction or heart failure.
  • Discontinue in patients who develop symptomatic bradycardia or high-grade AV block.
  • Caution in elderly patients due to increased sensitivity to negative chronotropic effects.
Adverse effects
  • Bradycardiaserious
  • Hypotension
  • Dizziness
  • Headache
  • Flushing
  • Constipation
  • Peripheral oedema
  • AV blockserious
  • Hepatotoxicityserious
  • Gingival hyperplasia
Interactions
  • carvedilolmajorUse with caution. Assess baseline heart rate, blood pressure, ECG and left ventricular function. Consider initiating at lower doses and titrating slowly. Monitor heart rate, blood pressure and for symptoms of heart failure or syncope, particularly during the first few days after starting or changing doses. If resting heart rate falls below 50 bpm or symptomatic bradycardia occurs, reduce the dose or discontinue one of the agents.
  • apixabanmajorAvoid co-prescription where possible, or use with caution. If combined, monitor the patient closely for signs of bleeding (e.g., bruising, melaena, haematuria). Consider reducing the apixaban dose according to local guidelines or product labelling. Re-evaluate the combination if other interacting drugs or bleeding risk factors are present.
  • dabigatranmoderateIf co-administration is needed, monitor for signs of bleeding and consider reducing the dabigatran dose (e.g., 110 mg twice daily) or switching to an alternative anticoagulant. Pay particular attention to patients with CrCl <50 mL/min. Avoid this combination in severe renal impairment (CrCl <30 mL/min) or high bleeding risk.
  • digoxinmajorIf co-prescription is necessary, monitor serum digoxin concentrations and clinical response closely, especially after starting or stopping diltiazem. Consider a lower digoxin dose and adjust based on levels and renal function. Monitor heart rate, blood pressure, and ECG for signs of toxicity.
  • atorvastatinmajorAvoid co-prescription if possible. If used together, limit the atorvastatin dose (e.g., no more than 20 mg daily) and monitor patients for symptoms of myopathy. Consider alternative statins not reliant on CYP3A4, such as pravastatin or rosuvastatin. If monitoring, check creatine kinase (CK) at baseline and if symptoms occur.
  • bisoprololmajorIf possible, avoid the combination, especially in patients with heart failure, bradycardia, AV conduction disease, or hypotension. If co-prescription is necessary, start with low doses, monitor heart rate, blood pressure, and ECG regularly, and adjust doses cautiously. Consider alternatives such as a dihydropyridine calcium channel blocker or an alpha/beta blocker if appropriate. Patients should be advised to report symptoms of bradycardia, dizziness, or syncope.
  • metoprololmajorCo-prescription should be approached with caution. Measure baseline heart rate, blood pressure, and ECG. Monitor these parameters regularly, especially after dose changes. Avoid the combination in patients with marked bradycardia, second or third degree AV block without a pacemaker, or significant heart failure. Consider alternative agents or lower doses with careful titration.
  • amiodaronemajorAvoid co-prescription where possible. If the combination is necessary, monitor ECG, heart rate, and blood pressure, and consider dose reduction. Advise patients to report palpitations, dizziness, or syncope.
  • simvastatinmajorAvoid concomitant use if possible. If co-prescription is necessary, limit the simvastatin dose to a maximum of 10 mg daily, as recommended by regulatory guidelines. Monitor patients for signs of myopathy, and consider measuring creatine kinase at baseline and if symptoms develop. Advise patients to report unexplained muscle pain or weakness promptly.
  • propranololmajorAvoid co-prescription where possible, particularly in patients with heart failure, conduction disease or hypotension. If unavoidable, initiate at low doses, monitor heart rate, blood pressure and ECG regularly, and adjust therapy based on findings. Consider using a dihydropyridine calcium channel blocker instead of diltiazem if a calcium antagonist is required.
  • cyclosporinemajorConsider avoiding the combination if possible. If co-prescribed, monitor cyclosporine trough levels frequently (e.g., every 1-2 weeks initially) and adjust the cyclosporine dose to maintain therapeutic concentrations. Monitor renal function and blood pressure. Reduce cyclosporine dose by 30-50% when starting diltiazem, and re-monitor after discontinuation of diltiazem.
  • tacrolimusmajorAvoid co-prescription if possible. If necessary, reduce tacrolimus dose and monitor blood levels frequently, adjusting dose based on concentrations.
Renal & hepatic adjustment
  • eGFR 0–29: Use with caution; no specific dose adjustment recommended.
  • Hepatic impairment (mild): No dosage adjustment required; monitor for signs of toxicity.
  • Hepatic impairment (moderate): Reduce initial dose and titrate slowly; monitor liver function and adverse effects.
  • Hepatic impairment (severe): Avoid use. (avoid)
Monitoring, pregnancy & toxicity
  • Blood pressure · During dose titration and regularly.
  • Heart rate · During dose titration and regularly.
  • ECG (for bradycardia and heart block) · At baseline and during titration for arrhythmia indications.
  • Liver function tests (ALT, AST) · At baseline and periodically during treatment.
  • Signs of heart failure · Regularly.
  • Pregnancy: Diltiazem is not recommended during pregnancy, particularly in the first trimester. Use only if the potential benefit outweighs the risk to the fetus.
  • Toxicity: Bradycardia and heart block. · Supportive care; atropine for symptomatic bradycardia, cardiac pacing if severe.
  • Toxicity: Hypotension. · IV fluids, calcium gluconate, vasopressors if needed.
  • Toxicity: Cardiac failure (negative inotrope). · IV calcium gluconate, glucagon, inotropes (e.g. norepinephrine, dobutamine).
Antidotes & reversal
  • Calcium gluconate (IV) · IV calcium plus high-dose insulin-euglycaemia; cardiac pacing for bradyarrhythmia.
Clinical notes
Diltiazem is used for hypertension, chronic stable angina, and supraventricular arrhythmias. It may cause bradycardia, AV block, and worsening of heart failure. Avoid in patients with second- or third-degree AV block, severe hypotension, or systolic heart failure. Use with caution with beta-blockers, as additive effects occur; grapefruit juice increases drug levels. Doses are titrated to response, and extended-release forms are taken once daily.

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BNF; local formulary