Thiazide + potassium-sparing Pregnancy: Routine use of diuretics in otherwise healthy pregnant women is not indicated (risk of hypovolaemia, increased blood viscosity, decreased placental perfusion). Hydrochlorothiazide crosses the placenta; use in the second and third trimester may compromise foeto-placental perfusion and cause foetal/neonatal effects (icterus, electrolyte disturbance, bone marrow depression, thrombocytopenia). Should not be used for gestational oedema, gestational hypertension or pre-eclampsia, and not for essential hypertension in pregnancy except in rare situations where no other treatment could be used. Use during breast-feeding is not recommended; if used, keep doses as low as possible.

Co-amilozide

Brand names: Moduretic

Co-amilozide is a fixed-dose combination of amiloride (a potassium-sparing diuretic) and hydrochlorothiazide (a thiazide diuretic), used in hypertension and oedema.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Hypertension: initially one Co-amilozide 2.5 mg/25 mg tablet once a day; if necessary increase to two 2.5 mg/25 mg tablets once a day or in divided doses

Route: Oral

Frequency: Once daily (or the increased dose in divided doses)

Max: Congestive heart failure and hepatic cirrhosis with ascites: dosage should not exceed four Co-amilozide 2.5 mg/25 mg tablets a day (no separate numeric ceiling is stated for hypertension beyond the two-tablet daily dose)

Source is the Co-Amilozide 2.5 mg/25 mg Tablets SPC (amiloride hydrochloride 2.5 mg with hydrochlorothiazide 25 mg). The rate of weight loss and serum electrolyte levels should determine the dosage; the most satisfactory rate of weight loss after initiation of diuresis is about 0.5-1.0 kg/day. Co-amilozide may be used alone or as an adjunct to other antihypertensive drugs; because the antihypertensive effect of those agents may be enhanced, their dose may need reducing to avoid an excessive drop in pressure. CONGESTIVE HEART FAILURE: initially one tablet a day, subsequently adjusted if required but not exceeding four tablets a day; optimal dosage determined by diuretic response and plasma potassium; once initial diuresis is achieved, dose reduction may be attempted for maintenance, which may be intermittent. HEPATIC CIRRHOSIS WITH ASCITES: initiate at a low dose; a single daily dose of two tablets may be increased gradually until effective diuresis, not exceeding four tablets a day; maintenance doses may be lower, and dose reduction should be attempted once weight is stabilised - gradual weight reduction is especially desirable in cirrhotic patients. ELDERLY: particular caution because of susceptibility to electrolyte imbalance; dosage should be carefully adjusted to renal function and clinical response. PAEDIATRIC: not recommended in children under 18 years - safety and efficacy have not been established.

Dose adjustments

Renal

Severe renal impairment, severe progressive renal disease, acute renal failure and anuria are contraindications. Thiazide diuretics become ineffective when creatinine clearance falls below 30 ml/min. Renal function, serum electrolytes and blood urea must be monitored carefully - use in impaired renal function may result in rapid development of hyperkalaemia. No numeric dose reduction is stated.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to amiloride hydrochloride, hydrochlorothiazide, other sulfonamide-derived drugs or any excipient
Hyperkalaemia (plasma potassium over 5.5 mmol/l); other potassium-conserving diuretics; potassium supplements or potassium-rich food (except in severe/refractory hypokalaemia under careful monitoring)
Concomitant use with spironolactone or triamterene
Concurrent lithium therapy
Severe hepatic failure; precoma associated with hepatic cirrhosis
Addison's disease; hypercalcaemia
Diabetic nephropathy; diabetes mellitus; blood urea over 10 mmol/l
Severe renal impairment, severe progressive renal disease, acute renal failure, anuria; patients with serum creatinine over 130 micromol/l in whom electrolytes and blood urea cannot be monitored carefully and frequently
Children under 18 years (safety not established)

Side effects

Electrolyte disturbance: hyperkalaemia (plasma potassium above 5.5 mmol/l), hyponatraemia (may be a medical emergency), hypokalaemia, hypomagnesaemia, dehydration
Nervous system: headache, dizziness, sleepiness, syncope, paraesthesia, poor taste; mental confusion, insomnia, nervousness, depression
Gastrointestinal: nausea, vomiting, diarrhoea, constipation, abdominal pain, flatulence, dry mouth, dyspepsia
Cardiovascular: arrhythmias, tachycardia, angina pectoris, orthostatic hypotension, flushing
Musculoskeletal: leg ache, muscle cramps, joint pain, back pain; general: fatigue, weakness, malaise, thirst, chest pain
Renal and urinary: nocturia, renal dysfunction including renal failure, dysuria, incontinence; reproductive: impotence (early in treatment, reversible on withdrawal)
Other: gout, anorexia, rash, pruritus, aplastic anaemia and neutropenia (amiloride), abnormal liver function (amiloride), anaphylactic reaction

Interactions

Lithium - concurrent therapy is contraindicated (SPC 4.3)
Spironolactone or triamterene, other potassium-conserving diuretics, potassium supplements or potassium-rich diet - contraindicated because of hyperkalaemia risk (SPC 4.3)
Cardiac glycosides (digitalis) - hypokalaemia can sensitise or exaggerate the cardiac response to digitalis toxicity (e.g. increased ventricular irritability); digitalis toxicity reported (SPC 4.4 and 4.8)
Other antihypertensive drugs - antihypertensive effect may be enhanced, so their dosage may need to be reduced (SPC 4.2)
Note: SPC section 4.5 was not retrieved in this source fetch - the list above is drawn from sections 4.2, 4.3, 4.4 and 4.8 only and is not complete

Clinical monograph

How it works

Hydrochlorothiazide inhibits sodium-chloride reabsorption in the distal convoluted tubule, while amiloride blocks epithelial sodium channels to reduce the associated potassium loss.

Prescribing in practice

Monitor for hyperkalaemia from the amiloride component, particularly in renal impairment or with ACE inhibitors, ARBs or potassium supplements.
Thiazides can cause hyponatraemia, hypomagnesaemia, hyperglycaemia, hyperuricaemia and may precipitate gout.
Avoid in significant renal impairment and do not combine with other potassium-sparing agents or potassium supplements.

Monitoring

Monitor serum electrolytes including potassium and sodium, with renal function and blood pressure.

Counselling the patient

Take the dose in the morning to reduce night-time urination.
Report palpitations, muscle weakness, confusion or marked dizziness.
Avoid potassium-containing salt substitutes unless advised.

Evidence & guidelines

Thiazide-type diuretics are an established option in NICE hypertension guidance; the potassium-sparing combination is used to offset thiazide-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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways