1. Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 25 Drug Interactions

2. Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 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. Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 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. Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 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. Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 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. Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 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. Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 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