Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Loop diuretic + potassium-sparing Pregnancy: §4.6, Pregnancy: animal work in general shows no hazardous effect of furosemide, and there is clinical evidence of safety in the third trimester, but furosemide crosses the placental barrier and 'It must not be given during pregnancy unless there are compelling medical reasons. Treatment during pregnancy requires monitoring of foetal growth.' 'The safety of Amiloride Hydrochloride has not been established and is therefore not recommended for use during pregnancy.' Breast-feeding: furosemide passes into breast milk and may inhibit lactation, it is not known whether amiloride is excreted in breast milk, and 'Breastfeeding must be avoided during treatment with Co-Amilofruse' — §4.3 contraindicates the product in breast-feeding women.

Co-amilofruse

Brand names: Frumil, Lasoride

Co-amilofruse is a fixed-dose combination of amiloride (a potassium-sparing diuretic) and furosemide (a loop diuretic), used for oedema where potassium conservation is desirable.

Adult dose

Dose: Oedema where a prompt diuresis is required and potassium conservation matters — including congestive cardiac failure (§4.1) — CO-AMILOFRUSE 2.5/20 mg TABLETS ONLY: one or two tablets. §4.2 Adults, verbatim: 'One or two tablets to be taken in the morning.' SCOPE OF THIS ENTRY: 2.5/20 mg is the only strength in this bundle and the tablet count above is that strength's posology. Co-amilofruse is marketed in more than one strength; every other strength has its own SPC and its own tablet-count posology, none of which is sourced here. Confirm the strength on the prescription before applying this dose.
Route: Oral. §4.2 Method of administration, verbatim: 'Oral administration.' The tablet combines amiloride hydrochloride with furosemide (both actives are named through §4.3–§4.8); no section in this bundle states which of the 2.5 mg and 20 mg belongs to which active, so that split is not asserted here.
Frequency: Once daily, taken in the morning (§4.2).
Max: Two tablets of Co-Amilofruse 2.5/20 mg, taken in the morning. §4.2 states no adult dose above 'One or two tablets to be taken in the morning' and gives no titration ceiling of its own.
NOT FOR UNDER-18s. §4.2 Paediatric population, verbatim: 'Not recommended for children under 18 years of age as safety and efficacy have not been established', and §4.3 goes further — 'Co-Amilofruse is contraindicated in children and adolescents less than 18 years of age, as safety in this age group has not been established.' paedDose is therefore null by design, not by omission. ELDERLY — §4.2, verbatim: 'The dosage should be adjusted according to diuretic response; serum electrolytes and urea should be carefully monitored.' DOSE-RELEVANT INTERACTIONS FROM §4.4/§4.5: (a) ACE inhibitors and angiotensin II receptor antagonists — 'A marked fall in blood pressure and deterioration in renal function may be seen when ACE inhibitors or angiotensin II receptor antagonists are added to furosemide therapy, or their dose level increased. The dose of Co-Amilofruse should be reduced for at least three days, or the drug stopped, before initiating the ACE inhibitor or angiotensin II receptor antagonist or increasing their dose.' (b) Sucralfate — 'Oral Co-Amilofruse and sucralfate must not be taken within 2 hours of each other'. (c) 'Where indicated, steps should be taken to correct hypotension or hypovolaemia before commencing therapy' (§4.4). (d) §4.4 also directs that the drug be discontinued before a glucose tolerance test. TRUNCATION CAVEAT: §4.4 and §4.8 both stop at the source-fetch limit, so the warnings and adverse reactions recorded on this page are partial. §4.2 itself is complete.

Dose adjustments

Renal

§4.2 gives NO renal dose adjustment. The renal handling in this SPC is by contraindication and monitoring instead: §4.3 contraindicates a creatinine clearance below 30 ml/min per 1.73 m², anuria, renal failure with anuria not responding to furosemide, and renal failure from nephrotoxic or hepatotoxic poisoning or associated with hepatic coma; §4.4 requires frequent serum potassium checks below a creatinine clearance of 60 ml/min per 1.73 m², notes that serum potassium may rise later in treatment in impaired renal function, and states that furosemide is not recommended for diuresis as part of preventative measures against radiocontrast-induced nephropathy in patients at high risk.

Hepatic

§4.2 gives NO hepatic dose adjustment. §4.3 contraindicates precomatose states associated with cirrhosis and renal failure associated with hepatic coma. §4.4 requires particularly careful monitoring in 'patients with hepatic cirrhosis together with impaired renal function' and, for hypoproteinaemia such as in nephrotic syndrome, states that 'Cautious dose titration is required'. §4.8 records hepatic encephalopathy in patients with hepatocellular insufficiency.

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

Contraindications

  • Hypersensitivity to the active substances or to any of the excipients listed in section 6.1, or to sulphonamides or sulphonamide derivatives
  • Hypovolaemia or dehydration (with or without accompanying hypotension)
  • Impaired renal function with a creatinine clearance below 30 ml/min per 1.73 m² body surface area
  • Anuria, or renal failure with anuria not responding to furosemide
  • Renal failure as a result of poisoning by nephrotoxic or hepatotoxic agents, or renal failure associated with hepatic coma
  • Hyperkalaemia
  • Severe hypokalaemia
  • Severe hyponatraemia
  • Concomitant potassium supplements or potassium-sparing diuretics
  • Precomatose states associated with cirrhosis
  • Addison's disease
  • Breast-feeding women
  • Children and adolescents less than 18 years of age — safety in this age group has not been established

Side effects

  • Frequency not known — eosinophilia and haemoconcentration; occasionally thrombocytopenia; rarely leucopenia and, in isolated cases, agranulocytosis, aplastic anaemia or haemolytic anaemia; bone marrow depression is a rare complication and necessitates withdrawal of treatment
  • Frequency not known — paraesthesia
  • Frequency not known — hepatic encephalopathy in patients with hepatocellular insufficiency
  • Frequency not known — dizziness, fainting, loss of consciousness and headache
  • Frequency not known — serum calcium may be reduced, with tetany observed in very rare cases
  • Frequency not known — blood cholesterol and triglycerides may rise during furosemide treatment, usually returning to normal within six months on long-term therapy
  • Frequency not known — glucose tolerance may be impaired; metabolic control may deteriorate in diabetes and latent diabetes mellitus may become manifest
  • Electrolyte and water balance disturbance — serum potassium may fall early in treatment because furosemide acts first, then rise later as amiloride takes effect, especially in impaired renal function
  • Metabolic alkalosis, or metabolic acidosis to which amiloride may contribute; pre-existing metabolic alkalosis (e.g. in decompensated cirrhosis) may be aggravated
  • Warning signs of electrolyte disturbance — increased thirst, headache, hypotension, confusion, muscle cramps, tetany, muscle weakness, disorders of cardiac rhythm and gastrointestinal symptoms
  • Hypovolaemia and dehydration, especially in elderly patients
  • Increases in blood creatinine and blood uric acid
  • Pseudo-Bartter syndrome in the context of misuse and/or long-term use of furosemide
  • SOURCE NOTE: §4.8 ENDS AT THE SOURCE-FETCH LIMIT part-way through the creatinine/uric-acid sentence.
  • This side-effect list may be incomplete — check the full SPC.

Interactions

  • Cardiac glycosides, other diuretics, antihypertensives and other drugs with blood-pressure-lowering potential — a more pronounced fall in blood pressure must be anticipated; their dosage may need adjustment
  • ACE inhibitors and angiotensin II receptor antagonists — marked fall in blood pressure and deterioration in renal function; reduce the Co-Amilofruse dose for at least three days, or stop it, before initiating or increasing them
  • Potassium salts, drugs which reduce potassium excretion, NSAIDs and ACE inhibitors — with the amiloride component, serum potassium may rise and hyperkalaemia may occur
  • Nephrotoxic drugs — their toxic effects may be increased by a potent diuretic such as furosemide
  • Sucralfate — must not be taken within 2 hours of oral Co-Amilofruse; it decreases furosemide absorption from the intestine and so reduces its effect
  • Lithium — serum levels may rise, increasing lithium toxicity including cardiotoxic and neurotoxic effects; monitor levels and adjust the lithium dose
  • Risperidone — in placebo-controlled trials in elderly patients with dementia a higher incidence of mortality was seen with furosemide plus risperidone (7.3%) than with risperidone alone (3.1%) or furosemide alone (4.1%); weigh risks and benefits before combining
  • SOURCE NOTE: eMC does not expose §4.5 as a separate section heading, so this interaction text arrives inside the fetched §4.4 block — which ENDS AT THE SOURCE-FETCH LIMIT mid-way through the risperidone entry. This list is therefore INCOMPLETE.

Monitoring

  • Serum sodium, potassium, creatinine and glucose — §4.4: 'Regular monitoring... is generally recommended during therapy; particularly close monitoring is required in patients at high risk of developing electrolyte imbalances or in case of significant additional fluid loss'
  • Frequent serum potassium checks where creatinine clearance is below 60 ml/min per 1.73 m², or where co-prescribed drugs may raise potassium (§4.4)
  • Urinary output — §4.4: 'Urinary output must be secured'; patients with partial obstruction of urinary outflow, e.g. prostatic hypertrophy or impaired micturition, have an increased risk of acute retention and require careful monitoring
  • Blood pressure — symptomatic hypotension leading to dizziness, fainting or loss of consciousness can occur, particularly in the elderly and in patients on other hypotensive drugs (§4.4)
  • Serum lithium levels where lithium is co-prescribed, adjusting the lithium dose where necessary
  • Elderly — §4.2: 'The dosage should be adjusted according to diuretic response; serum electrolytes and urea should be carefully monitored'
  • Foetal growth if the product is unavoidably continued in pregnancy (§4.6)

Clinical monograph

How it works

Furosemide inhibits the sodium-potassium-chloride co-transporter in the loop of Henle to produce a brisk diuresis, while amiloride blocks distal epithelial sodium channels to limit potassium loss.

Prescribing in practice

  • Monitor for hyperkalaemia, which can be precipitated by the amiloride component especially in renal impairment or with ACE inhibitors, ARBs or potassium supplements.
  • The combination can cause hypotension, dehydration and other electrolyte disturbances such as hyponatraemia.
  • Use with caution in renal impairment and avoid concurrent potassium-sparing diuretics or potassium supplements.

Monitoring

Monitor serum electrolytes, particularly potassium and sodium, alongside renal function and fluid status.

Counselling the patient

  • Take the dose earlier in the day to avoid disturbed sleep from passing urine.
  • Report muscle weakness, palpitations, confusion or excessive thirst.
  • Avoid potassium-containing salt substitutes unless advised otherwise.

Evidence & guidelines

Loop diuretics are an established symptomatic treatment for fluid overload; the potassium-sparing combination reflects standard UK practice to mitigate diuretic-induced hypokalaemia.

Reference: 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