Expert: Mary E Scott, RPh, CGP - 8/23/2007

Question
Hi!  My mother, age 54, is on the following meds for various conditions.  Would you review the following list & tell me of any interactions to watch out for?  (I'm particularly concerned about warfarin interactions.)

Warfarin (Coumadin)               2.5 mg / qd 4 days
                                   5 mg / qd 3 days
Metoprolol Succinate (Toprol XL)  100 mg / bid
Lansoprazole (Prevacid)            30 mg / qd
Bumetanide  (Bumex)                 2 mg / bid
Potassium Chloride (K-dur)         20 mg / bid
Allopurinol                       100 mg / bid
Prednisone                         10 mg / qd
Paroxetine HCL (Paxil)             10 mg / qd
Levothyroxine sodium (Levoxyl)   .175 mg / qd
Amlodipine (Norvasc)                5 mg / qd
Simvastatin (Zocor)                80 mg / qd
Aspirin                            81 mg / qd
Fentanyl patch (Duragesic)        100 mcg/ hr

She also takes the following meds on an as needed basis:

Acetaminophen/oxycodone 5/325  (Percocet)
Methocarbamol (Robaxin)   750
Metolazone (Zaroxolyn)      5 mg
Simethicone
Ibuprofen
Charcoal caps

Thank you for your time & attention.

Sincerely,
Shanon, concerned daughter  

Answer
Hi,Shanon!
Prednisone can increase the blood-thinner effect of warfarin, especially if she is not taking it on a routine basis. If she has been taking the same dose day in and day out, it's not a problem.
The aspirin can also increase warfarin's effect, but again, if her doctor feels she needs it, and it is taken routinely, it's not a problem.
Allopurinol and Zocor can also increase warfarin's effect.
These meds are maintenance drugs, so if she stops one, or the dosage changes, the dose of the warfarin may have to be increased.
The prn (as needed) meds could pose a problem. Ibuprofen can increase the risk of bleeding when taken with warfarin,and there is an interaction with aspirin, causing the cardio-protective effect of aspirin to be lost.
Charcoal caps should not be taken at the same time as her other meds since they bind to other drugs and cause them not to work.
How often does she get her INR (measurement of how warfarin is working)checked? It should be checked monthly,and more often if her meds are being changed.And remember, dietary changes,such as an increase in green, leafy vegetable consumption or the addition of dietary supplements (Ensure,Boost,etc)can affect warfarin,also! Hope this helps, Mary