Coumadin drug-drug interactions (DDI) are frequent. Patients in permanent use of coumadin are advised to avoid traditional nonsteroidal antiinflammatory drugs to avoid risk of bleeding. New selctive cyclooxygesase 2 inhibitors arisen as potential option for treating pain and inflamation in these patients once interactions with coumadin are supposed to be lower. The CI(R)CA study was made to evaluate in a prospective fashion the occurrence of DDI with new cyclooxygenase antiinflammatory drugs and coumadin when compared to acetaminophen and placebo.

The CI(R)CA study included patient diagnosed with antiphospholipid syndrome in permanent use of coumadin. Eligible patients were invited to use in a prospective cross-over mode two weeks of celecoxib, rofecoxib, acetaminophen and placebo with two weeks of wash out between drugs. Their international normalized ratio (INR) were measured before and during the use of each study drug. The interaction with coumadin was evaluated according to increases or decreases on the INR after each medication.

Inclusion Criteria:

• PAPS on contious stable dose of coumadin
• 18 years old or older
• Younger than 65 yo
• Signed informed consent.

Exclusion Criteria:

• Renal failure
• Heart failure
• Symptomatic gastritis or peptic ulcer
• Elevated liver enzymes (>3 fold)
• Platelet count < 100,000.