Drug Topics - January 28, 2008 - (Page H9) www.drugtopics.com JANUARY 28, 2008 DRUG TOPICS HSE 9 Interactions impact therapy 60-year-old Caucasian man, T.W., spent the night in your hospital’s cardiac unit with newonset atrial fibrillation (AF). His physician prescribed amiodarone 200 mg daily and warfarin 5 mg daily, instructing T.W. to return for follow-up in one month. The medical resident writing T.W.’s discharge orders calls the pharmacy, asking whether gabapentin A interacts with these medications. (T.W. takes 600 mg three times daily for neuropathic pain.) Checking T.W.’s chart, you find he also takes metoprolol 50 mg twice daily; sertraline 100 mg, ramipril 10 mg, and rosuvastatin 20 mg (Crestor, AstraZeneca Pharmaceuticals, LP) daily; with trazodone 50 mg at bedtime. How do you respond? cantly increase INR, potentially causing serious to fatal hemorrhagic complications. This interaction occurs rapidly and may persist for weeks due to amiodarone’s long half-life. The one-month follow-up is too long— given potential for therapeutic misadventure. INR should be checked within days of discharge. Drug interactions(s) such as amiodarone + metoprolol may increase the likelihood of hypotensive episodes, bradycardia, or cardiac arrest. Amiodarone + trazodone can cause QT prolongation. Rosuvastatin + warfarin can potentiate warfarin response, prolonging prothrombin time/INR. Sertaline + warfarin can potentiate warfarin response, prolonging prothrombin time/INR. G not interact with warfarin. However, other war- abapentin may be administered safely; it does farin drug interactions exist in this regimen. Amiodarone will likely affect warfarin metabolism because it inhibits cytochrome P-450 (CYP) 2C9 and CYP 3A4. Rosuvastatin may interact with warfarin; it is also metabolized by CYP 2C9. S-warfarin, the most potent warfarin isomer, is metabolized by CYP 2C9. R-warfarin, the less potent isomer, is metabolized by CYP 3A4 and 1A2. Both interactions have potential to increase the International Normalized Ratio (INR). In this case, warfarin is being initiated after or at the same time as interacting medications; the dose can be adjusted according to response. What is even more important to T.W. is monitoring warfarin closely upon initiation of therapy. A onemonth follow-up is too long an interval. He should follow up with an INR after three warfarin doses, with continued close follow-up and dose adjustment as needed to achieve target INR of 2.5. To achieve best possible outcomes with warfarin therapy, T.W. should be referred to an anticoagulation clinic if one is available. Beth Bryles Phillips, Pharm.D., FCCP, BCPS Clinical Associate Professor University of Georgia College of Pharmacy Athens, Ga. CHADS2 risk stratification scheme for stroke prevention in patients with AF C H A D S2 Recent congestive heart failure Hypertension Age ≥75 years Diabetes mellitus History of stroke or transient ischemic attack 1 1 1 1 2 In this scenario, health professionals performing medication reconciliation at hospital discharge should consider: Is warfarin necessary? Using the CHADS2 risk stratification scheme for stroke prevention in patients with AF, this patient has no documented risk factors. His adjusted stroke rate is 1.9, low risk with new-onset AF. Aspirin 325 mg/day as recommended by the American College of Cardiology/American Heart Association might be considered appropriate: mitigating potential for therapeutic misadventure from a severe amiodarone/warfarin drug interaction. Amiodarone and metabolites inhibit both R- and S-warfarin metabolism, with S-warfarin more strongly inhibited. In virtually all patients receiving this combination, this may signifi- Medication reconciliation would also identify therapeutic duplications: amiodarone and metoprolol are antiarrhythmics; sertaline and trazodone are antidepressants; metoprolol and ramipril are antihypertensive agents. Medication reconciliation would cause us to investigate gabapentin dosing—is this an initiating dose? Or has the patient been titrated upward to this dose and interval? What is T.W.’s renal function? Dose and interval are adjusted with renal function. James Groce, Pharm.D., CACP Professor, Campbell University School of Pharmacy Clinical Assistant Professor of Medicine, University of North Carolina School of Medicine Clinical Pharmacy Specialist-Anticoagulation Moses H. Cone Memorial Hospital Greensboro, N.C. http://www.drugtopics.com
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