SPS resources
SPS provides advice on Interactions (SPS page).
Articles on general principles include:
- Understanding drug interactions (SPS page) – which covers pharmacodynamic and pharmacokinetic interactions
- Understanding enzyme or transporter-based drug interactions (SPS page) – which includes cytochrome P450 interactions
Articles on some interactions for some specific medicines and drug classes include:
- Considerations and interactions with GLP-1 receptor agonists (SPS page)
- Managing interactions with direct oral anticoagulants (DOACs) (SPS page)
- Managing interactions with methotrexate (SPS page)
- Using clopidogrel with proton pump inhibitors (PPIs) (SPS page)
- Using folic acid and phenytoin safely (SPS page)
We also provide advice on managing interactions between complementary products and conventional medicines (SPS page)
Other resources
In addition to our own resources, we recommend the following resources. They are free to access unless otherwise indicated.
Resources are listed in the likely order you might prefer to use them. However, this depends on the nature of the question you are looking to answer.
British National Formulary
The BNF and BNFC provide information on interactions between pairs of medicines. How to find information depends on the way you access them.
Pairs of medicines
BNF drug interactions and BNFC drug interactions provide an A to Z list of monographs. Each monograph lists the interactions for that medicine. The list can be filtered by drug name to check for interactions.
Multiple medicines
Accessing the BNF or BNFC as a mobile app or via Medicines Complete (via NHS England OpenAthens), allows you to search multiple medicines simultaneously.
NHS healthcare professionals in England can register for a free NHS England OpenAthens account. Once registered, log in to Medicines Complete using the option NHS England, then go to BNF interactions.
Using BNF information
The BNF provides information for each pair of interacting drugs. Entries for non-pharmacodynamic interactions describe action to be taken, based on advice from manufacturers or authorities such as the MHRA. For these, the likely severity of the interaction (if not managed) and type of evidence for the interaction are noted.
Pharmacodynamic interactions are listed without noting likely severity or evidence type. Tables of pharmacodynamic effects are included in all versions on the BNF and in Appendix 1 of the print version. The tables list medicines with the same pharmacodynamic effect but are not exhaustive. Examples include:
- Table 4: Drugs with antiplatelet effects
- Table 5: Drugs that cause bradycardia
- Table 7: Drugs that cause hypotension
- Table 8: Drugs that prolong the QT interval
- Table 9: Drugs with antimuscarinic effects
Summaries of Product Characteristics
Product information is available via electronic Medicines Compendium and MHRA. SmPCs list interactions with other medicinal products and other forms of interaction in section 4.5.
Other useful SmPC sections include:
- contraindications (4.3)
- special warnings and precautions for use (4.4)
- pharmacodynamic properties (5.1)
- pharmacokinetic properties (5.2)
Stockley’s Drug Interactions
Available to subscribers via Medicines Complete, monographs in Stockley’s Drug Interactions describe the evidence, mechanism, clinical importance and management of over 5,000 drug interactions.
Stockley’s Interaction Checker allows users to search for interactions between multiple medicines. Brief information is provided for each pair of interacting drugs, with links to full Stockley monographs.
QT-interval interactions
Access to US site CredibleMeds is free but users must be registered. It provides a searchable database of medicines that prolong the QT interval and/or induce Torsades de Pointes (TdP).
Drugs are categorised according to risk: known risk, possible risk or conditional risk of TdP.
A page showing therapeutic options not on the QT drugs list shows, by indication, medicines that are not in one of the QT risk categories.
Questions around TdP risk, including the criteria used to assign the risk category to drugs in the database, are answered in FAQs for Healthcare Professionals.
Contraceptive medicines interactions
HIV drug interactions
The interactive HIV interaction checker allows users to select HIV drugs and co-medications, including some herbal supplements.
Results are graded from ‘these medicines should not be co-administered’ to ‘no clinically significant interaction expected’ and note if further monitoring or dose adjustment are required.
The prescribing resources section of the site provides further information including summary tables of drugs interactions and fact sheets for HIV medicines.
Viral hepatitis drug interactions
The hepatology drug interaction checker provides information on interactions with medicines used in chronic hepatitis C infection. Users can select hepatology drugs and co-medications.
Results are graded from ‘these medicines should not be co-administered’ to ‘no clinically significant interaction expected’ and note if further monitoring or dose adjustment are required.
The prescribing resources section of the site provides further information including summary tables of drug interactions and fact sheets for hepatitis medicines.
Cancer drug interactions
The interactive Cancer drug interaction checker allows users to select cancer medicines and co-medications.
Results are graded from ‘medicines should not be co-administered’ to ‘no clinically significant interaction expected’ and note if further monitoring or dose adjustment are required.
The checker is no longer being maintained and was last updated in June 2022. Do not rely on it as a sole source of information.
Further advice
If the information is not available on the SPS website or the information resources listed, or if your clinical scenario is complex, we would suggest you seek further advice from our Medicines Advice service (SPS page).
Training resources
If you would like more information on how to approach answering questions on drug interactions, we recommend:
Medicines Learning Portal
The Medicines Learning Portal is aimed at trainee hospital pharmacists but the content is also relevant to clinical primary care healthcare professionals. The portal includes a tutorial on drug interactions which provides advice on:
- questions to ask when considering questions relating to drug interactions
- mechanisms of drug interactions
- managing and monitoring drug interactions
- how to talk to patients about drug interactions
Update history
- Republished
- Full review and update.
- Title amended
- Published