UK Clinical Pharmacy Association

Folic acid

Issues for surgery

For treatment of megaloblastic anaemia – risk of increased post-operative complications secondary to anaemia if omitted for prolonged period.

For prevention of methotrexate side effects – increase in side effects if omitted pre-operatively.

For prevention of neural tube defects – potential loss of effect if omitted pre-operatively.

Advice in the perioperative period

Elective and emergency surgery 



  • For combination products follow advice as for ferrous fumarate or ferrous sulphate.

Preoperative initiation for anaemia

Screen for anaemia pre-operatively as early as possible in the patient’s pathway if surgery is anticipated to result in more than 500ml blood loss. Follow diagnostic algorithm in Centre of Perioperative Care Guidelines.

Before commencing folic acid:

  • Check vitamin B12 level – if deficient, commence vitamin B12 replacement (administration of folic acid can mask underlying B12 deficiency and may precipitate subacute combined degeneration of the spinal cord)
  • If patient prescribed phenytoin, phenobarbital, primidone or carbamazepine for epilepsy – be aware that serum antiepileptic levels may fall on commencing folic acid therapy, leading to decreased seizure control – discuss management with neurologist
  • If patient has coronary stent - see Further information.

Post-operative advice

Restart post-operatively when enteral intake resumes.

If commenced pre-operatively for treatment of folate deficiency arrange for review by General Practitioner after 4 months of treatment.

Interactions with common anaesthetic agents


Interactions with other common medicines used in the perioperative period


The manufacturers of folic acid advise that trimethoprim may reduce the effect of folic acid and this may be serious in patients with megaloblastic anaemia; however, no further information regarding the clinical significance of this interaction is available.

Further information

Patients with coronary stents

The manufacturers advise folate should not routinely be used in patients with coronary stents; however, this statement is believed to relate to the previous routine use of folate to prevent in-stent stenosis (which was disproved and possibly increased risk of in-stent stenosis). Use for treatment of folate deficiency should not be a concern.


Centre for Perioperative Care. Guideline for the Management of Anaemia in the Perioperative Pathway (September 2022). Available at: [Accessed on 17th December 2023]

Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. [Accessed on 7th December 2023]

Summary of Product Characteristics – Folic Acid 5mg Tablets. Wockhardt Uk Ltd. Accessed via 17/12/2023 [date of revision of the text July 2018]

Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. [Accessed on 28th August 2022]