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Chapter 25

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.

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Chapter 25

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  1. Chapter 25 Drug Interactions

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

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