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Dr. Coleman is an assistant professor of pharmacy practice and director of the pharmacoeconomics and outcomes studies group at the University of Connecticut School of Pharmacy.
BD, a 65-year-old man with heart failure, comes to the pharmacy with a prescription for fluoxetine HCl (Prozac) 20 mg a day and tells you that he has been very depressed lately because of his worsening heart failure symptoms. The fourth-year pharmacy intern is working that day and asks if she can enter the prescription and review the patient's medication profile, because she just completed a school examination on heart failure. Under the watchful eye of the precepting pharmacist, the intern reviews the patient's profile and finds that he is currently taking carvedilol (Coreg) 25 mg twice a day. The student is concerned because she recognizes an interaction between BD's current medications and his new prescription.
What is the mechanism behind the interaction, and what is the significance of it? What should the intern/pharmacist do?
BA, a 62-year-old man who suffered a myocardial infarction a year ago, comes into your pharmacy to pick up his prescription for atorvastatin 80 mg once daily. When he goes to pay for his prescription, he also hands the pharmacist a bottle of the storebrand baby aspirin and a similar-sized bottle of Bayer Aspirin with Heart Advantage. He mentions to the pharmacist that his physician stressed that, because he had a heart attack, it was important for him to take an 81-mg tablet of aspirin every day. He has been using the store-brand aspirin for the last year, but when he drew it off the shelf today, he noticed this new type of aspirin in a fancy box. BA wants to know what is different about this aspirin and whether he should be using this one instead?
Prozac is an inhibitor of the cytochrome P450 (CYP450), isoenzyme CYP2D6, whereas Coreg is a substrate for this isoenzyme. Consequently, the initiation of Prozac in BD could result in increased blood levels of Coreg, placing BD at a higher risk for hypotension, bradycardia, and heart block. The intern and pharmacist should contact the prescribing physician and advise him or her about the potential drug interaction and to recommend a different antidepressant other than Prozac or Paxil (which are both potent CYP2D6 inhibitors).
The pharmacist should tell BA that Bayer Aspirin with Heart Advantage is a new product that contains 81 mg of aspirin and 400 mg of phytosterols (plant sterols) per tablet. Phytosterols have a similar function in plants as cholesterol in humans and, when ingested, can decrease the absorption of dietary cholesterol. Current cholesterol treatment guidelines recommend that patients ingest 2 g/day of phytosterols, because they can help lower a patient's bad (low-density lipoprotein) cholesterol by as much as 10%. It is important for the pharmacist to point out to BA that this product is not a replacement for his atorvastatin, however, and that taking 1 tablet of Bayer Aspirin with Heart Advantage will not be sufficient for him to reach the recommended phytosterol intake (only providing 400 mg of the recommended 2000 mg/day). The pharmacist can alert the patient that phytosterols also are currently added to other commonly consumed foods, such as margarine, orange juice, and granola bars.