Spike in INR

I have been on Coumadin for most of the last two years following two episodes of clots in my right leg.  My INR varied between 1.8 and 2.4 and most often was between 2.0 and 2.2.  In those two years may other medications, my diet, and level of exercise remained mostly the same.  My Coumadin dose was 5mg four days a week and 7.5mg three days a week for most of the two years.  Now my INR has suddenly jumped up.  Yesterday it tested at 4.9, so my doctor had me retested today and it was 4.3.  The only difference I can identify in my routine is that my cardiologist started me on Toprol XL 25mg daily.  Any ideas why this spike could have occured?

[Encephalomalcia]

Not everyone can take Toprol XL.  Most likely this is a side effect of the Tropol.  Are you taking the generic or brand name?  Brand name is always better with heart medications.  There are other beta blockers such as "Coreg".  

[kenkeith]

Excessive INR Response:
Sometimes a patient with a stable INR shows a marked change. Possible causes are:
incorrect dosage (often associated with a prescription change) accounts for half of these unexpected changes.
drugs:
antibiotics        cardiac             anti-inflammatory      gastrointestinal  
cotrimoxazole    amiodarone          phenylbutazone          omeprazole  
erythromycin      clofibrate                piroxicam                   cimetidine  
fluconazole         propanolol                 paracetamol    
miconazole          sulfinpyrazone        
metronidazole          
isoniazid  

Tropol is not on the list, but it cannot be ruled out.  Also, gastrointestinal disorder, diarrhea episode, liver problem and heart failure should be ruled out.