Interactions: Managing and monitoring

Last updated: Thursday, November 23, 2017


In clinical practice there are a number of strategies by which you can help reduce the chances of an interaction affecting a patient:

Prescription review. Screening by a pharmacist is a significant means by which interactions are prevented, detected, and addressed. Medicines reconciliation is also important for ensuring that all medicines taken by a patient are documented, and then any interactions are more likely to be picked up. Addressing polypharmacy may reduce the number of drugs taken and thereby lessen the risks of interactions.

Choice of drug. Different drugs in the same class have differing potentials to interact (e.g. clarithromycin is a potent inhibitor of CYP3A4, but azithromycin is not). Swapping to either another drug in the same class or a different class of drug with the same indication may avoid an interaction.

Withholding one medicine. Sometimes the safest approach may be to withhold one medicine or delay starting it to avoid an interaction. For example, consider a patient on simvastatin who requires clarithromycin for a chest infection. In this situation, the clinical urgency of treating the infection, may make it acceptable to temporarily stop the statin until the clarithromycin course has been completed.

Dose reduction. Some interactions tend to increase the activity of one medicine fairly reliably. In this situation you may be able to reduce the dose of that medicine. For example, one strategy if itraconazole is essential for a patient on sirolimus, may be to reduce the sirolimus dose and monitor its levels. However, in practice you would seek expert approval and guidance before doing this.

Monitoring and communication. If a potentially interacting combination must be used, knowing the possible outcome may allow the patient to be monitored for potential adverse effects. You need to plan ahead and appreciate where the patient will be if monitoring is required. For example, it's easier to ensure an inpatient is monitored for cardiac side effects than a patient who is due to go home in an hour. Think about who will do the monitoring and how, and talk to the patient or their carer about this as well as healthcare staff.

Ask specialists. Clinical pharmacists in a specialist field often have a good working knowledge of practical ways to avoid, monitor, or reduce the effects of potentially interacting combinations of drugs. Listen to Michelle Cerrato, Lead Pharmacist for Cardiovascular and Thoracic Care at University Hospital Southampton, as she explains how to manage medicines that affect the QT interval:


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