Interactions: Suggested questions

Last updated: Monday, November 20, 2017


They may not apply to every situation you come across, but there are some questions you should be thinking about in practice.

The Medicine


  • Which drugs are involved, and is the patient already taking both of them? Commonly, a patient already taking one medicine is prescribed a second one which may interact. In practice it’s often easier to change the new drug if you can.
  • What is the indication for the medicines involved? This enables you to advise on alternative treatment if necessary, and sometimes the indication will affect the remedial action or monitoring required.
  • How long have they been taken for?  If a patient has been stable on a combination for a long time without ill effects there may be no need to change the prescription.
  • If there is an interaction, is there any reason why alternative drugs can’t be used to avoid it?  Sometimes alternatives that are less likely to interact have already been prescribed or were not tolerated.

The Patient


  • If the patient is already taking both drugs, have any problems been identified or investigated? You need to know if the combination has already made the patient ill, or if the prescriber is worried about a particular aspect.
  • Is the patient taking any other drugs? It’s important to have the full picture to avoid potential interactions that may have been missed. 
  • What is the patient’s liver and renal function like? This can affect clearance which may make the patient more prone to interactions or adverse effects.
  • Has a healthcare professional or patient read a warning about the combination? Sometimes e-prescribing systems or websites flag up interactions indiscriminately; they are not always relevant.

Going Forward


  • If any monitoring would be required, who would do this? If your advice is to continue with a potentially interacting combination, or to change a medicine, you need to ensure the patient will be monitored by e.g. blood tests, checking efficacy, looking out for side effects. Who will do this? Does a GP know what to do if the patient is going home? You should talk to the patient about this too.