drug interactions
Introduction
Instructor: Gretchen K. Garofoli, PharmD, BCACP, CTTS, FAPhA
Learning Objectives
Define the term "drug interaction"
Identify foods that commonly interact with medications
Categorize different types of drug interactions
Determine the significance of drug interactions
Utilize drug interaction identification software
Definition of Drug Interaction
Drug Interaction: A pharmacologic or clinical response to a combination of drugs that differs from the expected effects of the individual drugs when taken alone. (Source: Tatro DS, Drug Interaction Facts, 1992)
Types of Interactions
Pharmacokinetic
What the body does with the drug:
Absorption: How the drug is taken up by the body
Distribution: How the drug spreads in the body
Metabolism: How the drug is broken down by the body
Excretion: How the drug is eliminated from the body
Common interactions involve Cytochrome P450 (CYP 450) enzymes.
Pharmacodynamic
What the drug does to the body:
Additive, synergistic, or antagonist effects between drugs.
Categories of Substances Impacting Drug Interactions
Prescription medications
Over-the-counter medications
Herbals and supplements
Substances: Cigarettes, alcohol
Foods: E.g., grapefruit juice, spinach
Medical Conditions
Risk Factors for Drug Interactions
Patients on multiple medications
Patients consulting multiple physicians and using multiple pharmacies
Usage of narrow therapeutic index medications
Age: Pediatric and elderly patients
Decreased renal or liver function
Alcohol consumption
Tobacco usage
Specific dietary habits
Use of herbal supplements
Severity of Drug Interactions
Severe
Major
Moderate
Minor
Common Drug-Drug Interactions
MAOIs with other serotonergic drugs
Potassium-sparing diuretics with ACE-Is/ARBs
Bactrim® with warfarin
Clarithromycin with digoxin or some statins
Oral contraceptives with enzyme inducers
Interactions involving narrow therapeutic index medications
Calcium Carbonate and Proton Pump Inhibitors
Iron and Levothyroxine
Common Drug-Disease Interactions
Inappropriate medications in the Elderly
Beer’s List medications
Beta-Blockers in asthmatic patients
Pioglitazone in patients with heart failure
Nasal decongestants in patients with high blood pressure
Metformin causing Vitamin B12 Deficiency
Common Drug-Food Interactions
Tetracycline with milk
Iron and levothyroxine with milk/calcium
Warfarin with Vitamin K foods (spinach, kale, etc.)
Statins with grapefruit juice
Benzodiazepines, APAP, metronidazole with alcohol
MAOIs with tyramine foods (chocolate, aged cheeses, sausage)
Drug Interaction Software
Available platforms include:
Lexicomp®
MICROMEDEX®
Clinical Pharmacology®
Epocrates®
Handling Drug Interaction Alerts
Monitor for medications with lingering effects, such as:
Amiodarone, fluoxetine, MAOIs
Exercise caution with CYP450 Inhibitors/Inducers discontinuation
Understand that class alerts may not apply to all medications within the class
Example Patient Medication List
Duloxetine 60 mg
Isosorbide MN ER 30 mg
Januvia 50 mg
Omeprazole 20 mg
Aspirin 81 mg
Clopidogrel 75 mg
Atorvastatin 40 mg
Drug Interaction Case Studies
Testing Your Skills 1
Scenario: Patient on clarithromycin and simvastatin
Testing Your Skills 2
Scenario: Patient on tramadol and Zoloft
Testing Your Skills 3
Scenario: Patient on amoxicillin and Ortho Tri-Cyclen
Common Issues in Drug Interaction Programs
May fail to identify significant interactions
May generate unnecessary alerts
The Pharmacist's Role
Assess clinical significance of drug interactions
Evaluate the necessity of overriding alerts
Analyze drug interaction reports for relevance
Counsel patients on potential interactions and outcomes
Stay updated with literature for new interactions