The most common adverse effect of epoetin alfa is:

A. Alteplase (Activase): Alteplase is a thrombolytic agent used to dissolve blood clots. Concurrent use with clopidogrel, an antiplatelet medication, can increase the risk of bleeding due to additive effects on clotting. Therefore, it's important to consult the doctor before using these medications together.

B. Diltiazem: Diltiazem is a calcium channel blocker used to treat hypertension and certain heart rhythm disorders. Diltiazem will decrease the level or effect of clopidogrel by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Therefore, it's advisable to consult the doctor before using these medications together.

C. Ibuprofen: Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) used to relieve pain and inflammation. Like other NSAIDs, it can increase the risk of bleeding when taken with clopidogrel. Therefore, it's important to consult the doctor before using these medications together.

D. Aspirin: Aspirin is another antiplatelet medication commonly used to prevent heart attacks and strokes. Combining clopidogrel with aspirin can increase the risk of bleeding without significantly improving outcomes in most cases. However, in some situations, such as after certain cardiac procedures, dual antiplatelet therapy (clopidogrel plus aspirin) may be prescribed under close medical supervision. Therefore, it's crucial to consult the doctor before using these medications together.

E. Coumadin (warfarin): Coumadin is an anticoagulant medication used to prevent blood clots. Concurrent use with clopidogrel can increase the risk of bleeding. Therefore, it's essential to consult the doctor before using these medications together.

A. Constipation: Constipation is not a commonly reported adverse effect of clopidogrel (Plavix). Clopidogrel is an antiplatelet medication that works by inhibiting platelet aggregation, and gastrointestinal effects such as constipation are not typically associated with its use.

B. Bruising: This is a correct answer. Bruising is a known adverse effect of clopidogrel. As an antiplatelet medication, clopidogrel inhibits platelet aggregation, which can increase the risk of bleeding and bruising.

C. Rash: Rash is a potential adverse effect of clopidogrel, although it is not as common as other side effects such as bruising or gastrointestinal symptoms. Patients taking clopidogrel should be monitored for signs of allergic reactions, including rash, which may indicate the need for further evaluation or discontinuation of the medication.

D. Headache: Headache is not a commonly reported adverse effect of clopidogrel. While some patients may experience headache while taking clopidogrel, it is not considered a frequent or significant side effect of the medication.

E. Diarrhea: Diarrhea is not a commonly reported adverse effect of clopidogrel. Gastrointestinal symptoms such as diarrhea are not typically associated with clopidogrel use, although some patients may experience gastrointestinal upset as a side effect of antiplatelet therapy.