Issues for surgery
Risk of hypomagnesaemia if omitted.
Risk of hypermagnesemia if continued, particularly if renal impairment present.
Advice in the perioperative period
Elective and emergency surgery
Continue.
Consider checking serum magnesium, potassium, and calcium levels pre-operatively.
Post-operative advice
Restart post-operatively as soon as the next dose is due, if still required. If the patient is unable to resume their usual oral medication post-operatively, supplementation with intravenous (IV) magnesium can be considered.
If continued, consider monitoring serum magnesium.
Monitor renal function – consult product literature if renal impairment occurs post-operatively.
Patients undergoing gastrointestinal surgery
Some patients who have bowel resection surgery will have reduced magnesium absorption and will be at risk of hypomagnesaemia. The extent of magnesium malabsorption will be dependent upon the degree of resection and the remaining length of bowel following surgery.
Interactions with common anaesthetic agents
None.
Interactions with other common medicines used in the perioperative period
Magnesium is likely to affect the absorption of other oral medicines, hence manufacturers generally advise a time interval of 2 – 3 hours, if possible, between administration. See also Antimicrobials and Oral iron below.
Antimicrobials
Effects on absorption
Magnesium may affect the absorption of oral quinolones, tetracyclines and nitrofurantoin if given at the same time. Tetracycline administration should be separated from magnesium administration by 2 to 3 hours. Administration of quinolones or nitrofurantoin should be separated from magnesium administration by 3 to 4 hours.
Aminoglycosides
Aminoglycosides (e.g. gentamicin) may increase magnesium losses via the kidneys therefore an increase in magnesium dose may be necessary. Whilst single surgical prophylactic doses should not pose a problem, bear the interaction in mind if a course of antimicrobial treatment is required.
Oral iron
Magnesium may affect the absorption of oral iron if given at the same time. Administration should be separated by 3 to 4 hours.
Proton pump inhibitors
Long-term use of proton pump inhibitors has been associated with hypomagnesaemia, possibly due to disturbances in absorption. Consider switching to a histamine H2-receptor antagonist if hypomagnesaemia is refractory to treatment and it is appropriate to switch.
Further information
None relevant.
References
Summary of Product Characteristics – Magnesium (magnesium glycerophosphate) 4mmol Chewable Tablets. Colonic Pharma Ltd. Accessed via www.medicines.org.uk 16th April 2023 [date of revision of the text September 2021]
Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 10th April 2023]
Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 10th April 2023]
Magnesium. In: Brayfield A (Ed), Martindale: The complete Drug Reference. London: Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 14th July 2023]