HYGROTON

What it is

Hygroton 25 is a tablet containing 25 mg of chlortalidone as the active ingredient. Chlortalidone is a sulfonamide-derived benzothiadiazine (thiazide)-related diuretic with a long duration of action.

Approved indications

— Essential arterial hypertension, as long as creatinine clearance is greater than 30 mL/min, as primary therapy or in combination with other antihypertensive agents. — Stable, chronic heart failure of mild to moderate degree (functional class II, III), as long as creatinine clearance is greater than 30 mL/min. — Ascites due to cirrhosis of the liver in stable patients under close control.

Dosing overview

A single dose daily or every other day given in the morning with food is recommended. For a given dose, the full effect is reached after 3 to 4 weeks.

Key safety warnings

Sulphonamide derivatives such as chlortalidone can cause an idiosyncratic reaction resulting in choroidal effusion with visual field defect, acute transient myopia and acute angle-closure glaucoma, with symptoms typically occurring within hours to weeks of drug initiation. Untreated acute angle-closure glaucoma can lead to permanent vision loss. Treatment with thiazide diuretics has been associated with electrolyte disturbance such as hypokalaemia, hypomagnesaemia, hypercalcaemia and hyponatraemia. Hypokalaemia can sensitise the heart or exaggerate its response to the toxic effects of digitalis. With 25 mg per day, the decrease in serum potassium concentrations averages 0.7 mmol/L. For chronic treatment, serum potassium concentrations should be checked initially and then after 3 to 4 weeks. In patients with impaired hepatic function or progressive liver disease, especially in patients with liver cirrhosis, minor changes in the fluid and electrolyte balance due to thiazide diuretics may precipitate hepatic coma.

Contraindications

— Anuria, severe renal failure (creatinine clearance lower than 30 mL/min) and hepatic failure. — Hypersensitivity to chlortalidone and other sulfonamide derivatives or to any of the excipients in Hygroton 25. — Refractory hypokalaemia, hyponatraemia and hypercalcaemia. — Symptomatic hyperuricaemia (history of gout or uric acid calculi). — Hypertension during pregnancy. — Conditions involving enhanced potassium loss, such as salt-losing nephropathies and prerenal (cardiogenic) impairment of kidney function. — Untreated Addison's disease.

PBS listing

Hygroton 25 mg tablet is listed on the PBS with 2 items as unrestricted and restricted listings, with an ex-manufacturer price of A$3.66.

Regulatory history

Hygroton 25 (chlortalidone 25 mg tablet) was first registered on the ARTG on 2 August 1991.