di - Mechanism and Management of Common Drug Interactions...

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Unformatted text preview: Mechanism and Management of Common Drug Interactions Joseph V. Etzel, Pharm.D. Assistant Dean Associate Clinical Professor St. John’s University Objectives: At the completion of this lecture the participant should be able to: • List those factors that influence the severity of reported drug-drug interactions • Identify common drug interactions encountered in the community and institutional setting • Explain the mechanism of reported drug interactions • Develop a plan to prevent or manage potential drug interactions encountered in specific patients Drug Interaction: Definition: When the administration of one drug (precipitant drug) affects the efficacy or toxicity of a second drug (object drug) The precipitant drug may be administered simultaneously, before or after the object drug Classification of Drug Interactions • Pharmacokinetic Drug Interacitons • Pharmacodynamic Drug Interactions Factors Determining the Clinical Significance of a Reported Drug Interaction • Therapeutic index of the object drug • Duration of administration Doses of the two drugs administered • Sequence of drug administration • Interpatient variability Select Drugs with a Narrow Therapeutic Index • Digoxin (0.8 - 2.0 mcg/L) • Lithium (0.6 - 1.4 mEq/L) • Theophylline (5 - 15 mg/L0 • Phenytoin (10 - 20 mg/L) • Warfarin (measured by INR) • Tricyclic antidepressants • Oral hypoglycemic agents • Cardiac agents (procainamide, quinidine, etc) • Chemotherapeutic agents • Select antimicrobial agents • Estrogens • Cyclosporine Five Mechanisms That Lead to Diminished Drug Absorption 1. Binding in Gastrointestinal Tract 2. Direct pharmacologic interference 3. Alterations in Gastric pH 4. Alteration in Gastric Motility 5. Alteration in Gastrointestinal Flora Binding of Drugs in GI Tract Cationic agents and bile-sequestering agents may bind to form insoluble complexes in GI tract that results in incomplete drug absorption – Aluminum - Antacids – Magnesium - Sucralfate – Calcium- Polycarbophil – Zinc- Multivitamins/Minerals – Iron- Buffered meds (didanosine) Absorptive drugs (attapulgite) may have a similar effect Select Object Drugs with Diminished Absorption in Presence of Cations • Digoxin • Fluoroquinolones (Cipro, Floxin, Avalox, Tequin, Penetrex, Noroxin, Levaquin, Maxaquin) • s (except doxycycline) • Alendronate Cholestyramine, Colestipol, and other bile acid-sequestering agents • May bind to drugs in and diminish their effectiveness in a manner similar to cationic agents – Digoxin – Thyroid hormone (Synthroid, Levoxyl, etc) – Thiazide diuretics (HCTZ, hydrodiuril, etc) – Oral anticoagulants (Coumadin) – Fat soluble vitamins (A,D,E,K) and derivatives () • Space apart, monitor, or recommend alternative therapy Diminished Absorption Secondary to Direct Pharmacologic Interference • Orlistat (Xenical) – lipase inhibitor used for the management of hyperlipidemia and/or obesity – may result in malabsorption of fat soluble...
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This note was uploaded on 04/07/2011 for the course CPP 4105 taught by Professor Etz during the Spring '00 term at St. John's.

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di - Mechanism and Management of Common Drug Interactions...

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