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Drug interactions

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Drug–non-drug interactions

  • Identifying and handling possible interactions is the most common pharmacokinetics and pharmacodynamics related task for many pharmacists in pharmacies and in the hospital ward.

  • Handling interactions requires both deep knowledge and the competence to act when necessary but, more importantly, without frightening the patient unnecessarily.

Drugs may interact with the vehicle or the container, with food, with herbal medicines and with other drugs. Some of these are absolute such as the physical interactions, while others are relative with incidences rates ranging from very high to almost none.

Physical drug interactions caused by an incorrect pH, oxidising or reducing agents in the solution, exposure to light and non-reversible adsorption to container walls or excipients should be thoroughly investigated before marketing. Such interactions can easily be measured and the competence of the pharmacist may further guarantee that they do not occur.

Food interactions can be divided into food–drug interactions and drug–food interactions. Interaction with food causing lowered or delayed absorption is rare and mostly occurs with metal–ion chelate …

Correspondence to Dr Per Hartvig Honoré, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark; peh{at}

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