Drug Interactions PDF

Drug Interactions Dr Rupinder Kaur Hashmi  Objectives Discuss Pharmacokinetic interactions. List Pharmacodynamic interactions. Comment on common Drug- Food interactions 2  Drug Interactions (D/I) It’s a modification of...

Drug Interactions Dr Rupinder Kaur Hashmi  Objectives Discuss Pharmacokinetic interactions. List Pharmacodynamic interactions. Comment on common Drug- Food interactions 2  Drug Interactions (D/I) It’s a modification of P/K or P/D properties of a drug by another drug or food item or environment or chemical administration concurrently or previously These may be  Expected but detrimental to patient  Expected & planned in order to be beneficial to patient  Unexpected, unplanned & adverse 3  Types Pharmacokinetic interaction Pharmacodynamic interaction Drug Food interaction 4  Pharmacokinetic D/I Amount of drug in blood is altered Occur at any process of time  Absorption  Distribution  Metabolism  Excretion 5  Pharmacokinetic D/I Absorption  Milk & Tetracycline: milk ↓ absorption of Tetracycline  Vit C & Fe: Vit C ↑ absorption of Fe Distribution  Indomethacin & Warfarin Metabolism  6 MP & Allopurinol Excretion  Penicillin & Probenecid  Change in urinary pH in poisoning 6  Pharmacodynamic D/I Amount of drug in blood remains the same, but its effect is altered  Synergism Additive Supraadditive/ Potentiation  Antagonism Physical Chemical Physiological/ Functional Receptor 7 Pharmacodynamic D/I: Synergism Additive:  Effect of two drugs are in same direction & add up  2+2 = 4 e.g.  Aspirin + Paracetamol: analgesic/ antipyretic  Nitrous Oxide + Ether: GA 8 Pharmacodynamic D/I: Synergism Supraadditive  Effect of combination is > individual effects of drugs  2 +2 > 4 e.g.  ACh + Physostigmine: inhibition of breakdown  Levodopa + Carbidopa: inhibition of peripheral metabolism 9  Pharmacodynamic D/I: Antagonism Physical:  Charcoal + Alkaloids Chemical:  KMnO4 oxidizes alkaloids: gastric lavage in poisoning  Chelating agents metals poisoning As, Pb Physiological/ Functional  Histamine & adrenaline on bronchial smooth muscle & BP  Glucagon & Insulin on blood sugar levels 10  Pharmacodynamic D/I: Antagonism Receptors  Reversible antagonism (Competitive/ surmountable/ equilibrium)  Noncompetitive antagonism 11  Pharmacodynamic D/I: Antagonism Reversible antagonism (Competitive/ surmountable/ equilibrium)  Ach – Atropine  Morphine – naloxone Noncompetitive antagonism  Diazepam- Bicuculline 12  Drug-Food interactions Grapefruit juice and Terfenadine Grapefruit juice and cyclosporin Grapefruit juice and felodipine Grapefruit contains : furanocoumarin compounds that can selectively inhibit CYP3A4 Changes in diet may alter drug action Alcohol with CNS-suppressant drugs may produce excessive drowsiness Phenytoin increases metabolism of vitamin D, vitamin K, and folic acid. Carbamazepine may affect metabolism of vitamin D, and folic acid, leading to possible depletion Thank you 15