Injection compatibility: Suggested questions

Last updated: Friday, May 04, 2018


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?. Which ones are currently being mixed? Which drugs are you planning to mix? Although you may be asked about a specific combination, finding out what other injectable drugs are being given may highlight safe combinations to mix or identify opportunities to free up IV lines. 
  • How will the drugs be mixed? You need precise information. Will they mix in a bag, syringe or a line? What types of IV lines are in place? How long will the drugs be in contact for?
  • What are the concentrations of the drugs, and what diluents are being used? You need this information because the concentration and the diluent can affect compatibility. You may be able to advise using a lower concentration or a different diluent to ensure stability.
  • Can any IV medicines be stopped? Often it is obvious that the answer to this question is ‘no’. But you may find that an IV antibiotic is due to stop today, or that one IV medicine is not proving beneficial and could be stopped so freeing up IV access.
  • What other medication is the patient receiving? This gives you an overview of other potential ways to administer medicines – parenterally and by other routes. Check other medicines for interactions too.

The Patient


  • Are the number of intravenous access points limited? You should ask if additional IV access could be provided, and if not, why?
  • Can alternative routes of administration be considered? It will help you to know if the patient is completely nil-by-mouth, or if they cannot receive rectal medicines for example.
  • How is the patient being fed If there is an enteral feeding tube this may offer a potential alternative administration route; if TPN is being used this can create additional compatibility problems.


Going Forward


  • What will happen if the drugs can’t be mixed? It helps to know how critical the situation is so that you can offer guidance on least-worst options. For example, it’s not helpful to simply explain that drug A and drug B can’t be mixed if both are essential: what can they do instead?
  • Who will monitor the treatment? It’s important that any injectable drugs that mix are regularly monitored for signs of incompatibility, and that the patient responds to treatment as expected.