Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
ACE inhibitor Pregnancy: The use of ACE inhibitors is not recommended during the first trimester of pregnancy and is contraindicated during the second and third trimesters (known to induce human foetotoxicity - decreased renal function, oligohydramnios, skull ossification retardation - and neonatal toxicity - renal failure, hypotension, hyperkalaemia). Epidemiological evidence on first-trimester teratogenicity has not been conclusive, but a small increase in risk cannot be excluded. Unless continued ACE inhibitor therapy is considered essential, patients planning pregnancy should be changed to alternative antihypertensive treatments with an established safety profile in pregnancy; when pregnancy is diagnosed, stop immediately and, if appropriate, start alternative therapy. If exposure occurred from the second trimester, an ultrasound check of renal function and skull is recommended; infants whose mothers have taken ACE inhibitors should be closely observed for hypotension. Breast-feeding: because no information is available, imidapril is not recommended and alternative treatments with better established safety profiles are preferable, especially while nursing a newborn or preterm infant. (UK SPC §4.6)

Imidapril hydrochloride

Brand names: Tanatril

Imidapril is an angiotensin-converting enzyme (ACE) inhibitor used in the treatment of essential hypertension.

Adult dose

Dose: Essential hypertension: initially 5 mg daily; if blood pressure is not optimally controlled after at least 3 weeks, increase to 10 mg daily (the dose determined to be most effective); a small number of patients may need 20 mg daily (or, preferably, combination therapy with a diuretic should be considered)
Route: Oral
Frequency: Once daily, at about the same time of day, about 15 minutes before meals
Max: 20 mg daily (the recommended maximum dose)
Product: UK SPC via MHRA Products - IMIDAPRIL 5MG TABLETS, TANATRIL 5MG TABLETS (PL482590070), Northumbria Pharma Ltd; §2: each tablet contains 5 mg imidapril hydrochloride. §4.1: 'indicated for the treatment of essential hypertension in adults.' §4.2 Adults (verbatim): 'Treatment should be initiated with a daily dose of 5 mg. If optimum control of blood pressure has not been achieved after at least 3 weeks of treatment, the daily dose should be increased to 10 mg, the dose that has been determined to be most effective. However, for a small number of patients it may be necessary to increase the daily dose to 20 mg (the recommended maximum dose) or preferably, to consider combination therapy with a diuretic. It has not been assessed whether hypertensive patients would benefit from a combination of imidapril with other antihypertensive therapies.' ELDERLY (65 years or older): 'The initial dose is 2.5 mg once a day. The dose should be titrated according to the blood pressure response. The recommended maximum dose is 10 mg once a day.' The retrieved SPC does not say how 2.5 mg is obtained from a 5 mg tablet. PATIENTS AT INCREASED RISK FOR FIRST DOSE HYPOTENSION: 'Initiation of therapy requires, if possible, correction in salt and/or body fluids deficiencies, and discontinuation of an existing diuretic therapy for two to three days before ACE inhibition. If this is not possible, initial dose should be imidapril 2.5 mg.' Concomitant cardiac failure: initial dose 2.5 mg once a day under close medical supervision. 'Patients at high risk for severe acute first dose hypotension should be monitored medically, preferably in hospital, for up to 6-8 hours after administration of the first dose of imidapril and whenever the dose of imidapril or a concomitant diuretic is increased. The initial dose should be 2.5 mg. This also applies to patients with angina pectoris and cerebrovascular disease.' Method: oral use; 'It is recommended that the tablets be taken at about the same time of day about 15 minutes before meals, conditions under which efficacy has been demonstrated.' Children: 'The safety and efficacy of this medicine in children have not been established. No data are available.' No paediatric dose. Some sections of the product information we used were incomplete — check the full SPC.

Dose adjustments

Renal

SPC §4.2: imidapril and its active metabolite imidaprilat are predominantly excreted via the kidney; renal function should be evaluated before commencing therapy in patients suspected of renal impairment. Creatinine clearance 30-80 ml/min: reduced doses are required - recommended that treatment be initiated with 2.5 mg. Creatinine clearance 10-29 ml/min: because of limited experience (increase in the AUC of imidaprilat) imidapril should not be administered. Creatinine clearance below 10 ml/min (renal failure with or without haemodialysis): the drug is contraindicated. §4.4: not to be administered if creatinine clearance is less than 30 ml/min because of limited experience; renal function should be monitored during the first weeks of therapy; no experience in recent kidney transplantation.

Hepatic

SPC §4.2: the recommended starting dose in patients with hepatic impairment is 2.5 mg once a day. Imidapril should be used with caution in patients with hepatic impairment.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via MHRA Products — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance, to any other ACE inhibitor or to any of the excipients listed in section 6.1 (§4.3)
  • History of angioedema associated with previous ACE inhibitor therapy (§4.3)
  • Hereditary/idiopathic angioedema (§4.3)
  • Second and third trimesters of pregnancy (§4.3)
  • Renal failure with or without haemodialysis (creatinine clearance < 10 ml/min) (§4.3)
  • Concomitant use with aliskiren-containing products in patients with diabetes mellitus or renal impairment (GFR < 60 ml/min/1.73 m2) (§4.3)
  • Concomitant use with sacubitril/valsartan (§4.3)

Side effects

  • Summary: incidence of adverse events 34% with imidapril vs 36% with placebo; cough, dizziness, fatigue/somnolence, dyspepsia and vomiting occurred more frequently in the imidapril group (§4.8)
  • Common: cough (§4.8)
  • Uncommon: headache, dizziness, hypotension, rash, pruritus (§4.8)
  • Rare: insomnia, dysgeusia, postural dizziness, tinnitus, palpitations, nausea, vomiting, diarrhoea, abdominal pain, renal impairment, proteinuria, oedema, fatigue (§4.8)
  • Rare: raised alanine aminotransferase, aspartate aminotransferase, blood creatinine, blood urea and lactate dehydrogenase; decreased red blood cell count, white blood cell count and haemoglobin (§4.8)
  • Not known: oropharyngeal discomfort (§4.8)
  • Class effects: neutropenia/agranulocytosis, thrombocytopenia, pancytopenia and anaemia reported rarely with ACE inhibitors; haemolytic anaemia in G-6-PDH deficiency (§4.4, §4.8)
  • Severe hypotension may occur after initiation or a dose increase in risk groups; rarely syncope (§4.8)
  • Angioedema of the face, extremities, lips, tongue, glottis and/or larynx reported with ACE inhibitors including imidapril; can occur immediately or after months or years; laryngeal angioedema may be fatal (§4.4)
  • NOTE: the retrieved §4.8 text is truncated after the cardiac class effects; this list is not complete

Interactions

  • Potassium-sparing diuretics (spironolactone, triamterene, amiloride), potassium supplements and potassium-containing salt substitutes: significant, potentially lethal, increases in serum potassium, especially with renal impairment; ACE inhibitors must not be associated with hyperkalaemic substances except in hypokalaemia, with frequent potassium monitoring (§4.5)
  • Non-potassium-sparing diuretics: risk of sudden hypotension and/or acute renal impairment at initiation in salt/volume depletion; stop the diuretic first or start the ACE inhibitor at a low dose; monitor creatinine in the first few weeks (§4.5)
  • Lithium: increased lithium concentration, potentially toxic; use not recommended, monitor serum lithium closely if essential (§4.5)
  • NSAIDs (including aspirin at anti-inflammatory doses, COX-2 inhibitors): attenuated antihypertensive effect, risk of worsening renal function and raised potassium, especially in the elderly or with poor renal function; keep hydrated and monitor renal function (§4.5)
  • Injectable gold (sodium aurothiomalate): nitritoid reactions (flushing, nausea, vomiting, hypotension) reported rarely (§4.5)
  • Other antihypertensives, vasodilators, nitroglycerin and other nitrates: may further reduce blood pressure (§4.5)
  • Aliskiren-containing products (in diabetes or GFR < 60 ml/min/1.73 m2) and sacubitril/valsartan: contraindicated (§4.3)
  • This interaction list may be incomplete — check the full SPC.

Monitoring

  • Evaluate renal function before starting in patients suspected of renal impairment, and monitor it during the first weeks of therapy (§4.2, §4.4)
  • High-risk patients for first-dose hypotension: medical monitoring, preferably in hospital, for up to 6-8 hours after the first dose and whenever the imidapril or a concomitant diuretic dose is increased (§4.2)
  • If used with collagen vascular disease, immunosuppressant therapy, allopurinol or procainamide: white blood cell and differential counts before therapy, every 2 weeks during the first 3 months, and periodically thereafter; withdraw imidapril and other concomitant medication if neutrophils fall below 1000/mm3 (§4.4)
  • Instruct patients to report any sign of infection (e.g. sore throat, fever) so a differential white cell count can be done (§4.4)
  • Bilateral renal artery stenosis or stenosis of the artery to a single functioning kidney: start under close medical supervision with low doses, careful titration and renal function monitoring (§4.4)
  • Haemodialysis with high-flux membranes: anaphylactoid reactions reported - consider a different membrane or antihypertensive class (§4.4)
  • Monitor serum potassium with potassium-sparing diuretics/supplements and serum lithium with lithium (§4.5)

Clinical monograph

How it works

It is a prodrug converted to imidaprilat, which inhibits ACE and thereby reduces angiotensin II formation, producing vasodilatation and decreased aldosterone-driven sodium and water retention.

Prescribing in practice

  • It is contraindicated in pregnancy and in patients with a history of angioedema, and should be discontinued immediately if angioedema develops.
  • Use with caution in renal impairment, renovascular disease and volume depletion, and avoid concomitant potassium-sparing agents or potassium supplements unless potassium is monitored.
  • First-dose hypotension may occur, particularly in patients who are volume-depleted or already taking a diuretic.

Monitoring

Check renal function and serum potassium before and after starting or adjusting therapy, and monitor blood pressure.

Counselling the patient

  • Report any swelling of the face, lips, tongue or throat, or breathing difficulty, urgently.
  • A persistent dry cough may occur; mention it to your clinician.
  • Tell your clinician if you might be pregnant, and avoid potassium-containing salt substitutes unless advised.

Evidence & guidelines

ACE inhibitors are an established class for hypertension with extensive trial evidence, and NICE recommends them as a core antihypertensive option.

Reference: NICE NG136; 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