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Medication Interactions
Elizabeth Rash PhD, ARNP, FNP-C
UCF College of Nursing
CFP Physicians Group
Medication Interactions
• Good and Bad
– Synergism
• Ex. Codeine + acetaminophen or ibuprofen =
increased pain relief
– Adverse drug events (ADEs)
A
B
Unidirectional
A
B
Bidirectional
Adverse Drug Events (ADEs)
• The numbers (U.S. Prescribing 2003)
• 3.4 billion Rx filled
–10.1 million/yr for <65y
–23.5 million/yr for >65y
Adverse Drug Events (ADEs)
• 701,547 patients treated for ADEs in EDs
(2004-2005)
– 116,318 hospitalized
– 1/3 2o allergic reactions
– 1/3 2o unintentional overdose
– 2/3rds considered to be potentially
preventable
Adverse Drug Events (ADEs)
• Most ADEs 2o 5 classes of drugs:
– Insulins
– Opioids (narcotics)
– Anticoagulants
– Amoxicillin containing antibiotics
– Antihistamine containing cold products
JAMA 2006
Adverse Drug Events (ADEs)
• 21.3% > 65yr (community dwelling) at
least 1 inappropriate Rx drug
• 23% of nursing home admissions due to
medication problems
(J. Am. Pharm. Assoc.:Nov 2002)
Polypharmacy vs. Polymedicine
: increased number of drugs for
increased number of medical problems (may
be appropriate)
– Ex. Treating high blood pressure or diabetes with
drugs with different mechanisms of action
inappropriate use of drugs
– Ex. Medication duplication or treating the side
effects of one drug with another
Drug Interactions: What?
• Other drugs
– Coumadin® and Erythromycin increase bleeding
• Food
– Grapefruit and Verapamil increase toxicity
• Herbs and supplements
– St. John’s Wort and Zoloft® increase serotonin
crisis risk
• Other medical conditions or diseases
– Prednisone® and Diabetes increase blood sugar
Drug Interactions: How?
• Absorption
–Can slow down or speed up how
rapidly the drug gets into the blood
stream
• Ex. antacids + tetracycline
Drug Interactions: How?
• Metabolism enzymes
– Inducers: speed the metabolism of another
drug and can cause ineffectiveness
– Inhibitors: slow the metabolism of another
drug and can cause toxicity or
ineffectiveness
• Plavix® and PPIs (Prilosec®)
– PPI inhibits the action of Plavix® a Prodrug that
does not work until it Is metabolized
Drug Interactions: How?
• Receptors
– Some drugs block the tissue receptors that stop
other drugs or chemicals from having action on
that tissue
• Could be good or bad
– Ex. Antihistamines (Claritin®) block allergens on
the histamine receptors stopping allergic reactions

– Ex. Antihistamines (Ditropan®) block the
cholinergic receptors and interfere with
Alzheimer’s drugs like Aricept from working 
Drug Interactions: How?
• Elimination
– Taking an aspirin (acidic pH) with Zegerid®
(basic pH) may cause more rapid
elimination of the aspirin and decrease its
effect
Drug Interactions: How?
• Timing
– NSAIDs (Motrin®) interfere with the
platelet benefits of a preventive Aspirin.
• If taking both, take the aspirin first and wait at least 2
hours before taking the Motrin®
Common Drug Interactions
• Antifungal drugs that end in "-azole”, Itraconazole or
Sporanox®)
• Some antibiotics (end in "-mycin” Erythromycin®)
• Antacids cimetidine (Tagamet®)
• Drugs that prevent convulsions, (Dilantin® and
Tegretol®).
• Cholesterol drugs such as statins (Lipitor®)
• Blood thinning drugs (Coumadin®)
Drug Interactions: Preventing ADEs
•
•
•
•
•
Brown bag or drug list to all providers
ID bracelets
Use 1 pharmacy
Pharmacist consultation
Communicate side effects and don’t stop
abruptly without discussing with provider
• Follow instructions
Questions?
Thank you!
CFP Physicians Group
985 SR 436 Casselberry Fl 32707
(407) 831-5252
http://cfpphysiciansgroup.com/