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Clinical importance of interactions

Clinical importance of interactions. Combinations. Possitive interaction: summation 1+1 =2 poten tiation 1+1=3 Negative interaction: decreased effect. 5R. Right drug – drug for the diagnosis Right dose – estimated therapeutic dose

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Clinical importance of interactions

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  1. Clinical importance of interactions

  2. Combinations Possitive interaction: summation 1+1=2 potentiation 1+1=3 Negative interaction: decreased effect

  3. 5R • Right drug – drug for the diagnosis • Right dose – estimated therapeutic dose • Right time – drugs at developped disease loose effectivity • Right form - drugs as insulin must be administered as s.c. injection, if administered perorally, they dissolve in GIT • Right patient – is the one who needs the drug and we know his risk profile

  4. Factors Increasing Risk of Drug Interactions • Polypharmacy • Polymorbidity • Treatment lasting long time • Chronic disease • Combination of drugs with similar effect • Low therapeutic index • Simultaneous ordination of more drugs by different physicians • Abuses • Self-treatment

  5. Drugs with High Risk • Peroral antidiabetics • Peroral anticoagulants • Heart glykosides • Antiepileptic drugs • Antimanic drugs • NSA • Antibiotics

  6. Division according to the level at which they arise: • pharmaceutic – physical and chemical incompatibility • pharmacocinetic – absorption distribution biotransformation excretion • pharmacodynamic

  7. Absorption • pH in GIT – antacids • motility of GIT – prokinetics antidiarrhoea drugs drugs causing obstipation

  8. Distribution • Insufficiency of plasmatic proteins – hepatopathy • Binding to plasmatic proteins • Benzodiazepine site • Warfarin site

  9. Biotransformation • Enzyme system CYP 450 • Inductors • E.g. barbiturates, hydantoin antiepileptics ... • Also cigarette smoke • Inhibitors • E.g. azol antimycotics, diltiazem ... • Also grapefruit juice

  10. Pharmacodynamic Interactions • Most often potentiation of sedative effect on CNS (benzodiasepines and alcohol) • Also potentiation of bradycardia (verapamil a betablockers) • Dangerous simultaneous administration of warfarin and aspirin

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