From the Guidelines
Medications that can affect Prothrombin Time (PT) include warfarin, phenylbutazone, sulfinpyrazone, metronidazole, trimethoprim-sulfamethoxazole, amiodarone, and certain antibiotics such as second- and third-generation cephalosporins. These medications can either potentiate or inhibit the effect of warfarin on PT, leading to an increased or decreased risk of bleeding. For example, phenylbutazone, sulfinpyrazone, metronidazole, and trimethoprim-sulfamethoxazole can inhibit the clearance of S-warfarin, leading to an increased anticoagulant effect and a prolonged PT 1. On the other hand, medications such as barbiturates, rifampicin, and carbamazepine can increase the hepatic clearance of warfarin, leading to a decreased anticoagulant effect and a shortened PT.
- Warfarin is a vitamin K antagonist that inhibits the synthesis of vitamin K-dependent coagulation factors, including factors II, VII, IX, and X, and can affect PT 1.
- Phenylbutazone, sulfinpyrazone, metronidazole, and trimethoprim-sulfamethoxazole can inhibit the clearance of S-warfarin, leading to an increased anticoagulant effect and a prolonged PT 1.
- Amiodarone can inhibit the metabolic clearance of both the S- and R-isomers of warfarin, leading to an increased anticoagulant effect and a prolonged PT 1.
- Certain antibiotics, such as second- and third-generation cephalosporins, can inhibit the cyclic interconversion of vitamin K, leading to an increased anticoagulant effect and a prolonged PT 1.
- Direct oral anticoagulants (DOACs), such as dabigatran, rivaroxaban, apixaban, and edoxaban, can also affect PT, although the effect is generally less pronounced than with warfarin 1.
- Other medications, such as aspirin, nonsteroidal anti-inflammatory drugs, and heparin, can also affect PT by inhibiting platelet function or enhancing the anticoagulant effect of warfarin 1.
It is essential to consider the potential interactions between these medications and warfarin or DOACs when managing patients on anticoagulant therapy, as these interactions can increase the risk of bleeding or thrombosis. Regular monitoring of PT and international normalized ratio (INR) is crucial to ensure the safe and effective use of anticoagulant medications 1.
From the Research
Medications Affecting Prothrombin Time (PT)
The following medications can affect Prothrombin Time (PT):
- Warfarin: a common anticoagulant that can cause excessive prolongation of PT, especially when the dose is increased or when combined with other medications like amiodarone 2
- Amiodarone: an antiarrhythmic medication that can contribute to prolonged PT when used with warfarin 2
- Daptomycin: an antibiotic that can artificially prolong PT in a concentration-dependent manner, particularly in patients with elevated baseline PT-INR 3
- Argatroban: an anticoagulant that can prolong PT and increase INR, but its effects on PT may be minimal with extended exposure 4
- Cefotetan: an antibiotic that can cause prolonged PT, especially in patients with certain risk factors like surgery, old age, high platelet count, low albumin, or high urea and creatinine concentrations 5
- Other antibiotics: may also be associated with prolonged PT, and their effects should be assessed in large multicentre studies 5
Key Findings
- The effects of medications on PT can be influenced by various factors, including dose, combination with other medications, and patient characteristics 2, 3, 4, 5
- Monitoring PT and INR is crucial when using medications that can affect coagulation, especially in patients with liver disease or those taking anticoagulants 2, 3, 4, 6