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| The UK Society for Intravenous Anaesthesia |
| Based in the UK - as a resource for Anaesthesia Worldwide |
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Annual Scientific Meeting, Belfast; November 2000. Beneficial interactions JPH Fee Professor of Anaesthetics Queen’s University of Belfast Drug interactions may occur as the result of synergy, additivity, potentiation, or inhibition. The nature of the interaction may reflect the underlying mechanism so that two drugs acting on the same receptor are likely to have an additive rather than a synergistic effect. Alternatively, two drugs acting at related receptor sites, such as the GABA/benzodiazepine receptor complex, may exhibit synergy. Isobolograms, based on dose-response curves of drugs given separately and in combination, are widely used to study drug interactions.Interactions between propofol and other intravenous agents may be synergistic1 or additive2. Interactions between propofol and opioids are more marked during surgery than during induction of anaesthesia3. Propofol interferes with opioid metabolism to increase circulating concentrations of opioid; conversely, alfentanil reduces the clearance of propofol4. The main objective of combining propofol with other drugs is to reduce propofol and opioid dosage so that the same anaesthetic effect can be achieved without compromising cardiovascular stability5. Beneficial consequences of lower dosages include shortened recovery times and fewer unpleasant opioid-related side effects6. The concept of optimal propofol-opioid concentrations with optimised combined infusion regimens is now well established. References: 1. McAdam LC, MacDonald JF, Orser BA. Isobolographic analysis of the interactions between midazolam and propofol at GABA(A) receptors in embryonic mouse neurons. Anesthesiology 1998;89:1444-54. 2. Vinik HR, Bradley EL, Kissin I. Isobolographic analysis of propofol-thiopental hypnotic interaction in surgical patients. Anesthesia & Analgesia 1999; 88;667-70. 3. Mora CT, Henson M, Bailey J et al. Propofol plasma concentration affects alfentanil requirements for cardiac surgery. Anesthesiology 1992;77:A408. 4. Vuyk J. TCI: supplementation and drug interactions. Anaesthesia 1998;53(Suppl.1):35-41. 5. Billard V, Moulla F, Bourgain JL et al. Hemodynamic response to induction and intubation; propofol/fentanyl interaction. Anesthesiology 1994;81:1384-93. 6. Vuyk J, Lim T, Engbers FH et al. The pharmacokinetic interaction of propofol and alfentanil during lower abdominal surgery in women. Anesthesiology 1995;83:8-22. |
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