Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Non-dihydropyridine calcium channel blocker Pregnancy: SPC §4.6, verbatim: 'There is very limited data from the use of diltiazem in pregnant patients. Diltiazem has been shown to have reproductive toxicity in certain animal species (rat, mice, rabbit). Diltiazem is contraindicated during pregnancy (see section 4.3), as well as in women of child-bearing potential not using effective contraception.' Breast-feeding: 'Diltiazem is excreted in breast milk at low concentrations. Breast-feeding while taking this drug should be avoided. If use of diltiazem is considered medically essential, an alternative method of infant feeding should be instituted.' The US label is less restrictive ('use diltiazem hydrochloride in pregnant women only if the potential benefit justifies the potential risk to the fetus') — the UK contraindication is the one that applies here.

Diltiazem hydrochloride

Brand names: Tildiem, Adizem, Slozem, Zemtard

Diltiazem is a rate-limiting (non-dihydropyridine) calcium-channel blocker used for angina and hypertension.

Adult dose

Dose: Angina: 90 mg twice daily initially, increased gradually to 120 mg twice daily or 180 mg twice daily if required. Hypertension: 120 mg twice daily.
Route: Oral — prolonged-release (SR) capsules/tablets, swallowed whole and not chewed
Frequency: Twice daily, at 12-hour intervals
SCOPE: the page's primary route (oral) for the SPC's two licensed indications, angina and hypertension. INTRAVENOUS diltiazem is NOT covered — no IV regimen appears in either fetched source — and neither source doses AF rate control, so the page's IV route and its AF indication remain unsourced. Verbatim §4.2: 'Angina Adults: The usual initial dose is 90 mg twice daily. Dosage may be increased gradually to 120 mg twice daily or 180 mg twice daily if required. Patients' responses may vary and dosage requirements can differ significantly between individual patients.' and 'Hypertension Adults: The usual dose is one Adizem-SR 120 tablet or capsule twice daily. Patients may benefit by titrating from a lower total daily dose.' Administration, §4.2: 'Oral. To be taken at 12 hour intervals. Dosage may be taken with or without food, and should be swallowed whole and not chewed. In order to avoid confusion, it is suggested that patients once titrated to an effective dose using either Adizem-SR tablets or capsules should remain on this treatment and should not be changed between different presentations. Adizem-SR capsules should not be taken at the same time as an alcoholic beverage.' Paediatric, §4.2: 'The Adizem preparations are not recommended for children. Safety and efficacy in children has not been established.' No maximum dose is stated in the UK SPC, so maxDose is left empty. For reference only, the US once-daily extended-release label says 'Individual patients may respond to higher doses of up to 480 mg once daily' and 'There is limited general clinical experience with doses above 360 mg, but doses to 540 mg have been studied in clinical trials' — a different formulation and dosing frequency, carried here as a cross-check, not as a ceiling for the twice-daily SR product.

Dose adjustments

Renal

SPC §4.2 treats renal and hepatic impairment together with the elderly: 'Elderly and patients with impaired renal or hepatic function: In the elderly, dosage should commence at 60 mg diltiazem hydrochloride twice daily and the dose carefully titrated as required' (angina). For hypertension: 'The starting dose should be 60 mg diltiazem hydrochloride twice daily, increasing to one Adizem-SR 90 mg capsule twice daily and then to one Adizem-SR 120 mg tablet or capsule twice daily if clinically indicated.' §4.4: 'Increase of plasma concentrations of diltiazem may be observed in the elderly and in patients with renal or hepatic insufficiency', and 'Cases of acute renal failure secondary to decreased renal perfusion have been reported in patients with existing cardiac disease especially reduced left ventricular function, severe bradycardia or severe hypotension. Careful monitoring of renal function is advised.'

Hepatic

Same reduced starting dose as for renal impairment — §4.2: 'Elderly and patients with impaired renal or hepatic function... dosage should commence at 60 mg diltiazem hydrochloride twice daily and the dose carefully titrated as required' (angina); for hypertension, start 60 mg twice daily, increasing to 90 mg twice daily then 120 mg twice daily if clinically indicated. §4.4 notes increased plasma concentrations of diltiazem in hepatic insufficiency.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION Patients controlled on diltiazem alone or in combination with other medications may be switched to diltiazem hydrochloride extended-release capsules, USP at the nearest equivalent total daily dose. Higher doses of diltiazem hydrochloride extended-release capsules, USP may be needed in some patients. Monitor patients closely. Subsequent titration to higher or lower doses may be necessary. There is limited general clinical experience with doses above 360 mg, but doses to 540 mg have been studied in clinical trials. The incidence of side effects increases as the dose increases with first-degree AV block, dizziness, and sinus bradycardia bearing the strongest …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-08-20. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

  • Hypersensitivity to diltiazem or to any of the excipients (§4.3)
  • Pregnancy, and women of child-bearing capacity (§4.3; §4.6 adds 'as well as in women of child-bearing potential not using effective contraception')
  • Severe bradycardia (less than 40 bpm) (§4.3)
  • Second- or third-degree heart block (§4.3)
  • Sick sinus syndrome (§4.3)
  • Decompensated cardiac failure (§4.3)
  • Left ventricular failure with pulmonary congestion (§4.3)
  • Concurrent use with dantrolene infusion, because of the risk of ventricular fibrillation (§4.3)
  • Concurrent use with lomitapide (§4.3)
  • US label additions (cross-check, may differ from UK): hypotension (systolic less than 90 mmHg), and acute myocardial infarction with pulmonary congestion documented by x-ray on admission; the US label permits sick sinus syndrome and 2nd/3rd-degree AV block 'in the presence of a functioning ventricular pacemaker'

Side effects

  • Common (§4.8): headache, dizziness, atrioventricular block (first, second or third degree; bundle branch block may occur), palpitations, flushing, constipation, dyspepsia, gastric pain, nausea, erythema, pruritus, peripheral oedema
  • Uncommon (§4.8): nervousness, insomnia, bradycardia, orthostatic hypotension, vomiting, diarrhoea, hepatic enzyme increase (AST, ALT, LDH, ALP), urticaria, malaise, fatigue
  • Rare (§4.8): thrombocytopenia, mood changes including depression, dry mouth
  • Not known (§4.8): hypersensitivity, extrapyramidal syndrome, sinoatrial block, congestive heart failure, vasculitis including leukocytoclastic vasculitis, hypotension, gingival hyperplasia, hepatitis, photosensitivity (including lichenoid keratosis at sun-exposed skin areas), angioneurotic oedema, rash, erythema multiforme (including Stevens-Johnson syndrome and toxic epidermal necrolysis), hyperhidrosis, exfoliative dermatitis, acute generalised exanthematous pustulosis, desquamative erythema with or without fever, allergic dermatitis, lupus-like syndrome, gynaecomastia
  • Acute renal failure secondary to decreased renal perfusion in patients with existing cardiac disease, especially reduced left ventricular function, severe bradycardia or severe hypotension (§4.4)
  • US label, dose-related: 'The incidence of side effects increases as the dose increases with first-degree AV block, dizziness, and sinus bradycardia bearing the strongest relationship to dose'

Monitoring

  • Heart rate — §4.4: 'The contraindications and precautions should be carefully observed and close monitoring, particularly of heart rate, should be carried out at the beginning of treatment'
  • Renal function — §4.4: 'Careful monitoring of renal function is advised' (acute renal failure secondary to decreased renal perfusion has been reported)
  • Patients with bradycardia, first-degree AV block or a prolonged PR interval 'should be observed closely' (§4.4)
  • Left ventricular function — use with caution in patients with reduced left ventricular function (§4.4)
  • Mood — 'Calcium channel blocking agents, such as diltiazem, may be associated with mood changes, including depression' (§4.4)
  • Inform the anaesthetist of ongoing diltiazem treatment before general anaesthesia (§4.4)

Clinical monograph

How it works

It blocks L-type calcium channels in cardiac and vascular smooth muscle, slowing the heart rate, reducing myocardial contractility and causing coronary and peripheral vasodilatation.

Prescribing in practice

  • Avoid combining with a beta-blocker, and use caution with other rate-limiting drugs, because of the risk of bradycardia and heart block.
  • Avoid in significant left ventricular dysfunction or heart failure owing to its negative inotropic effect.
  • It is a CYP3A4 inhibitor with many interactions, and modified-release products are brand-specific so prescribe and dispense by brand.

Monitoring

Monitor heart rate, blood pressure and for signs of heart failure, particularly after dose changes or when other cardiac drugs are added.

Counselling the patient

  • Report a slow pulse, dizziness, fainting, breathlessness or ankle swelling.
  • Do not switch between different brands of modified-release product without medical advice.

Evidence & guidelines

An established option for angina and hypertension in UK guidance (NICE), particularly where rate control is also desirable.

Reference: NICE NG136; NICE NG196; ESC AF/HT guidelines; MHRA brand-prescribing notice; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Drugs
Pathways