Drugdrug interactions

DRUG/DRUG INTERACTIONS IN PHARMACOLOGY

Overview

  • Understanding various drug interactions is crucial in nursing pharmacology.

Learning Objectives

  • Identify common drug-drug or drug-food interactions.

  • Differentiate between drug reactions and drug incompatibility.

  • Recognize antagonistic, potentiating, additive, and synergistic effects in drug interactions.

  • Apply pharmacokinetics knowledge in describing drug interactions.

Definitions

Drug Incompatibility

  • Chemical or Physical Reaction: Occurs between two or more drugs in vitro.

  • Altered Effect: The effect of the drug may be modified at any pharmacokinetic phase.

Drug Interactions

  • The ability of one drug to alter the response of another when given together.

  • Can occur at any phase of pharmacokinetics.

  • May have therapeutic (beneficial) or non-therapeutic (adverse) effects.

PHARMACOKINETICS REVIEW

  • Assessment of Drug Interaction Points:

    • Absorption

    • Distribution

    • Metabolism

    • Excretion

DRUG INTERACTIONS AT DIFFERENT PHASES

Absorption

  • Example: Tetracycline + calcium = unabsorbable drug complex in the gut.

  • Example: Psyllium (Metamucil) with oral drugs leads to poor absorption.

Distribution

  • Example: ASA + warfarin = competition for protein binding.

    • One drug can 'bump off' the other, increasing the free active drug concentration.

Metabolism

  • Example: Rifampin + warfarin = increased warfarin dosage needed.

    • Rifampin induces liver enzymes, leading to faster metabolism of warfarin.

Excretion

  • Example: Digoxin + quinidine = competition for kidney excretion sites.

    • Digoxin may become toxic due to resorption into circulation.

  • Example: Sodium bicarbonate + amphetamines = slowed excretion of amphetamines due to alkaline urine.

Site of Action

  • Example: Beta blockers + beta adrenergic drugs = competition at receptor sites.

    • One may cause bronchospasm, while another causes bronchial relaxation.

TYPES OF DRUG INTERACTIONS

Additive Interaction

  • Definition: Combined drug effects equal the sum of individual effects.

    • Mathematical representation: 1 + 1 = 2.

Potentiating Interaction

  • Definition: One drug enhances the effect of another.

    • Mathematical representation: A + B = 2A + B.

Synergistic Interaction

  • Definition: Combined drugs produce an effect greater than expected.

    • Mathematical representation: 1 + 1 = 10.

Antagonistic Interaction

  • Definition: One or both drugs nullify each other's effects.

    • Mathematical representation: 1 + 1 = 0.

PRACTICE DRUG INTERACTIONS

  • Azithromycin + Imipenem: Identify type of interaction and effects.

  • Caffeine + Aspirin: Understand expected actions and therapeutic effects.

  • Narcan + Morphine: Evaluate type of interaction and potential effects.

  • Coumadin + Aspirin: Identify expected effects and therapeutic vs. non-therapeutic outcomes.

  • St. John’s Wort + General Anesthesia: Analyze expected effects and interactions.

  • Heparin + Protamine Sulfate: Review expected effects and interactions.

SUMMARY

  • Nurses must have knowledge of potential drug-drug interactions for enhanced therapy and to minimize safety risks.