Issues for surgery
For treatment of hypertension – loss of blood pressure (BP) control if omitted.
For treatment of oedema – risk of fluid retention and increased risk of exacerbation of symptoms in heart failure patients if omitted.
For ascites – risk of exacerbation of symptoms if omitted.
Risk of hyperkalaemia due to impaired renal perfusion or tissue damage from surgical trauma if continued (see Further information).
Advice in the perioperative period
Continue, including combination products.
Correct electrolyte abnormalities prior to surgery
Combination products*:
- co-amilofruse (amiloride and furosemide) - see also Furosemide drug monograph
- co-amilozide (amiloride + hydrochlorothiazide)
- amiloride + bumetanide - see also Bumetanide drug monograph
- amiloride + hydrochlorothiazide + timolol - see also Timolol drug monograph
*If necessary, consideration should be given to prescribing the components of combination products as separate medicines perioperatively. However, some components of combination products do not exist as individual medicines (e.g. hydrochlorothiazide). If there is any doubt about the need to continue / withhold component agents of a combination product, advice should be sought from an anaesthetist.
Post-operative advice
Monitor urea and electrolytes (U&E’s) and BP. Dosage reduction should be considered in patients with hypovolaemia, hypotension, or electrolyte disturbances.
Interactions with common anaesthetic agents
Hypotension
Amiloride can increase the risk of hypotension when used concomitantly with inhalational or intravenous anaesthetics.
Interactions with other common medicines used in the perioperative period
Hypotension
Amiloride can increase the risk of hypotension when used concomitantly with the antiemetics droperidol and prochlorperazine.
Non-steroidal anti-inflammatory drugs (NSAIDs)
NSAIDs may antagonise the antihypertensive and / or diuretic effects of amiloride.
NSAIDs may increase the risk of acute renal failure (ARF), especially in dehydrated or elderly patients, and hyperkalaemia (see Further information). Patients receiving amiloride and NSAIDs should be adequately hydrated and have their renal function monitored.
Both amiloride and NSAIDs increase the risk of hyponatraemia.
Corticosteroids
Corticosteroids (e.g. dexamethasone) may potentially decrease antihypertensive effects of amiloride due to sodium and fluid retention.
Low molecular weight heparin (LMWH)/Unfractionated heparin (UFH)
Amiloride and LMWH/UFH can increase the risk of hyperkalaemia (see Further information). The risk increases with LMWH duration of use – the manufacturers recommend monitoring of serum electrolytes in patients before starting LMWH therapy, and regularly thereafter particularly if treatment is prolonged beyond seven days.
Further information
Hyperkalaemia
Patients who have undergone surgery are at increased risk of hyperkalaemia due to a number of factors, including increased potassium release from cells due to tissue damage, reduced urinary excretion (e.g. due to volume depletion), or exogenous potassium load (e.g. blood transfusions). The risk of hyperkalaemia may be further compounded in patients taking potassium-sparing diuretics, especially in elderly patients, patients with renal insufficiency and patients with diabetes. Serum potassium levels should be monitored.
References
Ayach T, Nappo RW, Paugh-Miller JL, Ross EA. Postoperative Hyperkalaemia. Eur J Intern Med. 2015; 26(2):106-11
Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 6th May 2019)
Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 6th May 2019]
Summary of Product Characteristics – Amiloride 5mg Tablets. Wockhardt UK Ltd. Accessed via www.medicines.org.uk 06/05/2019 [date of revision of the text October 2015]
The Joint Task Force on non-cardiac surgery: cardiovascular assessment and management of the European Society of Cardiology (ESC) and the European Society of Anaesthesiology (ESA). 2014 ESC/ESA Guidelines on non-cardiac surgery: cardiovascular assessment and management. European Heart Journal. 2014; 35:2383-2431