Antihypertensives – enhanced hypotensive effect possible with all types. Concurrent use with ACE inhibitors or Angiotensin II receptor antagonists can result in marked falls in blood pressure, furosemide should be stopped or the dose reduced before starting an ACE-inhibitor or Angiotensin II receptor antagonists (see section 4.4). Increased risk of first dose hypotension with post-synaptic alpha-blockers (eg prazosin). Furosemide may interact with ACE inhibitors causing impaired renal function.
Aliskiren - reduces the plasma concentration of furosemide given orally. Reduced effect of furosemide might be observed in patients treated with both aliskiren and oral furosemide, and it is recommended to monitor for reduced diuretic effect and adjust the dose accordingly.
Antipsychotics – furosemide-induced hypokalaemia increases the risk of cardiac toxicity. Avoid concurrent use with pimozide. Increased risk of ventricular arrhythmias with pimozide (avoid concurrent use), amisulpride or sertindole. Enhanced hypotensive effect with phenothiazines.
In placebo-controlled trials in elderly patients with dementia, a higher incidence of mortality was observed in patients treated with furosemide plus risperidone. No consistent pattern for cause of death was observed but caution should be exercised and the risks and benefits of this combination considered prior to the decision to use.
Anti-arrhythmics (including amiodarone, disopyramide, flecainide and sotalol) - risk of cardiac toxicity (because of furosemide-induced hypokalaemia). The effects of lidocaine, tocainide or mexiletine may be antagonised by furosemide.
Cardiac glycosides – hypokalaemia and electrolyte disturbances (including hypomagnesemia) increase the risk of cardiac toxicity.
Drugs that prolong Q-T interval – increased risk of toxicity with furosemide induced electrolyte disturbances.
Vasodilators – enhanced hypotensive effect with moxisylyte (thymoxamine) or hydralazine.
Other diuretics – profound diuresis possible when furosemide given with metolazone. Increased risk of hypokalaemia with thiazides. Contraindicated with potassium sparing diuretics (e.g. amiloride spironolactone) - increased risk of hyperkalaemia (see section 4.3).
Renin inhibitors – aliskiren reduces plasma concentrations of furosemide.
Nitrates – enhanced hypotensive effect.
Lithium - furosemide reduces lithium excretion with increased plasma lithium concentrations (risk of cardio- and/or neuro-toxicity). Avoid concomitant administration unless plasma levels are monitored.
Chelating agents – sucralfate may decrease the gastro-intestinal absorption of furosemide – the 2 drugs should be taken at least 2 hours apart.
Lipid regulating drugs – Bile acid sequestrants (eg colestyramine: colestipol) – reduced absorption of furosemide – administer 2 to 3 hours apart.
NSAIDs – increased risk of nephrotoxicity (especially with pre-existing hypovolaemia/dehydration. Indometacin and ketorolac may antagonise the effects of furosemide (avoid if possible see section 4.4). In patients with dehydration or hypovolaemia, NSAIDs may cause acute renal insufficiency.
Salicylates – effects may be potentiated by furosemide. Salicylic toxicity may be increased by furosemide.
Antibiotics – increased risk of ototoxicity with aminoglycosides, polymixins or vancomycin - only use concurrently if compelling reasons. Increased risk of nephrotoxicity with aminoglycosides or cefaloridine. Furosemide can decrease vancomycin serum levels after cardiac surgery. Increased risk of hyponatraemia with trimethoprim. Concurrent use with tetracyclines may increase the risk of rising BUN (see section 4.4 – monitoring).
Antiviral – plasma concentrations of diuretics may be increased by nelfinavir, ritonavir or saquinavir.
Antidepressants – enhanced hypotensive effect with MAOIs. Increased risk of postural hypotension with TCAs (tricyclic antidepressants). Increased risk of hypokalaemia with reboxetine.
Antidiabetics – hypoglycaemic effects antagonised by furosemide.
Insulin - requirements may be increased (see section 4.4).
Antiepileptics – increased risk of hyponatraemia with carbamazepine. Diuretic effect reduced by phenytoin.
Antihistamines – hypokalaemia with increased risk of cardiac toxicity.
Antifungals – increased risk of hypokalaemia and nephrotoxicity with amphotericin.
Anxiolytics and hypnotics – enhanced hypotensive effect. Chloral hydrate or triclofos may displace thyroid hormone from binding site.
CNS stimulants (drugs used for ADHD) – hypokalaemia increases the risk of ventricular arrhythmias.
Corticosteroids – diuretic effect antagonised (sodium retention) and increased risk of hypokalaemia.
Cytotoxics – increased risk of nephrotoxicity and ototoxicity with platinum compounds/cisplatin.
Anti-metabolites – effects of furosemide may be reduced by methotrexate and furosemide may reduce renal clearance of methotrexate.
Potassium salts – contraindicated - increased risk of hyperkalaemia (see section 4.3).
Dopaminergics – enhanced hypotensive effect with levodopa.
Immunomodulators – enhanced hypotensive effect with aldesleukin. Increased risk of hyperkalaemia with ciclosprin and tacrolimus. Increased risk of gouty arthritis with ciclosporin.
Muscle relaxants – enhanced hypotensive effect with baclofen or tizanidine. Increased effect of curare-like muscle relaxants.
Oestrogens – diuretic effect antagonised.
Progestogens (drospirenone) – increased risk of hyperkalaemia and diuretic effect antagonised.
Prostaglandins – enhanced hypotensive effect with alprostadil.
Sympathomimetics – increased risk of hypokalaemia with high doses of beta2 sympathomimetics.
Theophylline – enhanced hypotensive effect.
Probenecid –effects of furosemide may be reduced by probenecid and furosemide may reduce renal clearance of probenecid.
Anaesthetic agents – general anaesthetic agents may enhance the hypotensive effects of furosemide. The effects of curare may be enhanced by furosemide.
Warfarin and clofibrate – compete with furosemide in binding to serum albumin – possibly significant if this is low (eg nephrotic syndrome).
Aminoglutethimide – concomitant use may increase the risk of hyponatraemia.
Alcohol – enhanced hypotensive effect.
Laxative abuse - increases the risk of potassium loss.
Liquorice - excess intake may increase the risk of hypokalaemia.