- D C Brater: Department of Medicine, Indiana University Medical Center, Indianapolis, USA.
Torasemide is a lipophilic anilinopyridine sulphonylurea derivative that acts as a high ceiling loop diuretic and has been used for the treatment of both acute and chronic congestive heart failure (CHF) and hypertension. Torasemide is similar to other loop diuretics in terms of its mechanism of diuretic action; namely, blockade of Na+/K+/2Cl- cotransport in the thick ascending limb of the loop of Henle. It has high bioavailability (> 80%), as does bumetanide, but a longer elimination half-life (3 to 4 hours) than either bumetanide or furosemide (frusemide). In the treatment of chronic CHF, oral torasemide (5 to 20 mg/day) has been shown to be an effective diuretic. Patients treated with torasemide for up to 1 year have reduced bodyweight, improved pulmonary haemodynamics, and decreased CHF severity. Intravenous torasemide (20 to 60mg as a single dose) has been shown to be as effective as furosemide in the treatment of acute CHF, and resulted in significant diuresis, bodyweight loss, and improved pulmonary haemodynamics and exercise performance. 'Non-diuretic' dosages (2.5 to 5 mg/day) of oral torasemide have been used to treat essential hypertension, both as monotherapy and in combination with other antihypertensive agents. When used in these dosages, torasemide lowered diastolic blood pressure (DBP) to below 90mm Hg in 8 to 12 weeks in 70 to 80% of patients. With dose doubling, this level of efficacy occurred in more than 90% of hypertensive patients. Clinical trials have established that blood pressure can be maintained at this level for at least 1 year with low dose torasemide. Torasemide is well tolerated in dosages up to 20 mg/day for at least 1 year. The most commonly reported adverse effects are those associated with loop diuretics in general. These include transient hypokalaemia, hyperuricaemia, dizziness, headache, gastrointestinal disturbances, orthostatic hypotension and fatigue. Adverse effects are comparable with those of other diuretics and rarely necessitate drug withdrawal.