Glyceryl Trinitrate [GTN], Isosorbide Dinitrate, Isosorbide Mononitrate

  Issues for Surgery

For treatment of angina – exacerbation of symptoms if omitted.

Risk of tachycardia and hypotension if continued.

  Advice in the Perioperative period

Elective and Emergency Surgery 

Continue – monitor heart rate and blood pressure (BP).

Post-operative Advice

Restart post-operatively as soon as next dose is due.

  Interaction(s) with Common Anaesthetic Agents


Nitrates can increase the risk of hypotension when used concomitantly with inhalational or intravenous anaesthetics1, 2.


Isosorbide dinitrate can act as a physiological antagonist to noradrenaline / norepinephrine3.

  Interaction(s) with other Common Medicines used in the Perioperative Period


Nitrates can increase the risk of hypotension when used concomitantly with the antiemetics droperidol and prochlorperazine1, 2, 3.

  Further Information


Many patients on long-acting or transdermal nitrates rapidly develop tolerance (with reduced therapeutic effects). Reduction of blood-nitrate concentrations to low levels for 4-12 hours each day usually maintains effectiveness. If tolerance is suspected during use of transdermal patches, they should be left off for 8-12 hours (usually overnight)1, 4.

For patients on modified-release (MR) isosorbide dinitrate or standard release isosorbide mononitrate (ISMN), the second of the two daily doses should be given no later than 8 hours after the morning dose. MR preparations of ISMN should only be given once daily, and used in this way do not produce tolerance1.

Ensure that nitrate-based medicines are prescribed accurately and appropriately.



  1. Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. [Accessed on 5th May 2019]
  2. Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. [Accessed on 5th May 2019]
  3. Summary of Product Characteristics – Isosorbide Dininitrate 20mg Tablets. Accord-UK Ltd. Accessed via 02/10/2019 [date of revision of the text June 2015]
  4. Summary of Product Characteristics – Minitran® (glyceryl trinitrate) 5 mg/ 24h, Transdermal Patch. Mylan Products Limited. Accessed via 05/05/2019 [date of revision of the text July 2018