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.
Hypovolaemia, hypotension and / or electrolyte disturbances if continued (see Interactions with common anaesthetic agents, Interactions with other common medicines used in the perioperative period and Further information).
Advice in the perioperative period
Elective and emergency surgery
Continue.
Correct electrolyte abnormalities (especially hypokalaemia and hypomagnesaemia) prior to surgery – see Further information.
Confirm which brand of metolazone the patient takes prior to admission - see Further information.
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.
For patients with diabetes mellitus, monitor blood glucose concentrations since thiazides can provoke hyperglycaemia.
Interactions with common anaesthetic agents
Hypotension
Metolazone can increase the risk of hypotension when used concomitantly with inhalational or intravenous anaesthetics.
Neuromuscular blocking drugs (NMBDs)
Metolazone may increase the response to NMBDs, probably due to their hypokalaemic effect, although there appears to be no clinical significance – monitor.
Interactions with other common medicines used in the perioperative period
Hypotension
Metolazone can increase the risk of hypotension when used concomitantly with the antiemetics droperidol and prochlorperazine.
Electrolyte disturbances
Hyponatraemia
Metolazone use is common cause of hyponatraemia – dilutional hyponatraemia may occur in patients with heart failure but may also result from sodium depletion or inappropriate antidiuretic hormone secretion (SIADH).
Concomitant use of metolazone with non-steroidal anti-inflammatory drugs (NSAIDs) increases the risk of hyponatraemia.
Concomitant use of metolazone with gabapentin increases the risk of hyponatraemia.
Hypokalaemia
Concomitant use of metolazone with corticosteroids (e.g. hydrocortisone, dexamethasone) increases the risk of hypokalaemia.
Metolazone may cause hypokalaemia; this potentially increases the risk of torsade de pointes when given with ondansetron – monitor serum potassium closely.
Non-steroidal anti-inflammatory drugs (NSAIDs)
Also see Electrolyte disturbances above.
Concomitant use of metolazone with NSAIDs increases the risk of acute renal failure (ARF).
NSAIDs can cause fluid retention and may antagonise the diuretic actions of metolazone.
Further information
Important Safety Information
MHRA/CHM advice: Xaqua® (metolazone) 5mg tablets: excercise caution when switching patients between metolazone preparations (January 2023)
The MHRA advises caution patients between different metolazone preparations due to potential differences in bioavailability and dosing instructions.
Metolazone should be prescribed and supplied by brand name, or manufacturer name, and document this clearly.
Hypokalaemia
Hypokalaemia is reported to occur in up to 34% of patients undergoing surgery (mostly non-cardiac). It is thought to significantly increase the risk of ventricular fibrillation and cardiac arrest in cardiac disease. In one study, hypokalaemia was independently associated with perioperative mortality. Care should be taken with patients taking diuretics and patients prone to developing arrhythmias. The risk of hypokalaemia is greater with thiazide diuretics than equipotent doses of other types of diuretics.
NB: Potassium supplementation alone may not be sufficient to correct hypokalaemia in patients who are also deficient in magnesium.
References
Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 13th April 2019]
Hydrochlorothiazide. In: Brayfield A (Ed), Martindale: The Complete Drug Reference. London: The Royal Pharmaceutical Society of Great Britain. Electronic version. Truven Health Analytics, Greenwood Village, Colorado, USA. Available at: http://www.micromedexsolutions.com. [Accessed 14th April 2019]
Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 3rd November 2024]
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