Issues for surgery
Loss of blood pressure (BP) control if omitted.
Risk of hypotension if continued.
Risk of transfusion reaction if blood transfusion laboratory not informed that patient is taking, or has recently taken, methyldopa (see Further information).
Advice in the perioperative period
Elective and emergency surgery
Continue – monitor BP.
If patient requires cross-matching for blood transfusion inform laboratory that patient is taking methyldopa as this can cause a positive direct Coombs test which would invalidate electronic issue of blood products (see Further information).
Post-operative advice
Restart post-operatively once enteral intake resumed.
Monitor BP.
Interactions with common anaesthetic agents
Hypotension
Methyldopa can increase the risk of hypotension when used concomitantly with inhalational or intravenous anaesthetics. The manufacturer of methyldopa notes that reduced doses of anaesthetic agents may be required; although, if hypotension does occur during anaesthesia, it can usually be controlled by vasopressors as the adrenergic receptors remain sensitive during treatment with methyldopa.
Interactions with other common medicines used in the perioperative period
Hypotension
Methyldopa can increase the risk of hypotension when used concomitantly with the antiemetics droperidol and prochlorperazine.
Oral iron
Concomitant administration of oral iron with methyldopa has been shown to reduce the bioavailability of methyldopa; separating administration by 2 hours only partially reduces the effect of this interaction. Monitor blood pressure and titrate methyldopa dose accordingly.
Further information
Cross-matching for blood transfusion
Treatment with methyldopa can result in a positive direct Coombs’ test (DCT) in up to 20% of patients; this may affect cross-matching for blood transfusion. A positive DCT usually occurs within 6-12 months of starting methyldopa and becomes negative within weeks or months of stopping methyldopa. If blood transfusion laboratories are not made aware a patient is taking, or has recently taken, methyldopa a positive DCT may go undetected. In the case of a positive DCT electronic issue of blood products should be disabled and conventional compatibility testing carried out to prevent a possible transfusion reaction.
References
Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 30th September 2023]
Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 30th September 2023]
Summary of Product Characteristics – Methyldopa Tablets 250mg. Aspen. Accessed via www.medicines.org.uk 30/09/2023 [date of revision of the text April 2022]