Chapter 25. Drug Interactions. Drug Interactions. A drug interaction can be defined as the action of an administered drug on either the effectiveness or the toxicity of another drug that is administered early, simultaneously, or later.
Chapter 25 Drug Interactions
Drug Interactions • A drug interaction can be defined as the action of an administered drug on either the effectiveness or the toxicity of another drug that is administered early, simultaneously, or later. • Not every potential drug interaction occurs in all patients. • Not every drug interaction is clinically significant. 2
Drug Interactions • Many dental drug patients take more than one drug which can increase the risk for a drug interaction. • Drug interactions may already be accounted for, and drug doses and timing are adjusted accordingly. • Over-the-counter drugs can interact with all other drugs. • A complete medical and drug history can help to minimize the problems associated with drug interactions. 3
Drug Interactions • Most drug interactions involve an alteration in the pharmacokinetics of the drug. • Drug Absorption • Drug interactions can either delay the onset of drug action or increase or decrease the amount of drug absorbed. • Rate of drug absorption is a concern when a fast onset of absorption is necessary. • An example of this would be analgesics. A rapid response is often desired when the patient is in pain. 4
Drug Interactions • Absorption • Extent of drug absorption is of concern when a drug is administered over a long period of time. • This is important because it can ultimately affect drug levels. • Distribution • Drugs that are highly protein bound can be displaced from their binding sites. • This small amount of extra drug in the bloodstream can lead to toxicity. 5
Drug Interactions • Metabolism • Many different drugs can stimulate or inhibit the metabolism of other drugs. • This can cause an increase or decrease of drug plasma levels and can lead to toxicity or reduced therapeutic effect. • Excretion • Drug interactions that involve excretion can affect the amount of drug that is either secreted or reabsorbed. • This can lead to an increased effect (toxicity) or decreased therapeutic effect. 6
Drug Interactions • Pharmacodynamic drug interactions usually occur at drug receptor sites. • They can have an antagonistic effect where no drug effect is seen. • They can have a synergistic effect where two or more drugs can come together and enhance a therapeutic or side effect. • They can have an additive effect where both drugs come together and produce an expected therapeutic or side effect. 7