Protein S
Protein S is a naturally occurring anticoagulant protein in the blood that serves as a cofactor for activated protein C, playing a critical role in preventing excessive blood clot formation. This medication is primarily used to treat or prevent thrombosis in patients diagnosed with hereditary or acquired Protein S deficiency, which increases susceptibility to dangerous blood clots.
Protein S is an anticoagulant therapy used to prevent blood clots in individuals with Protein S deficiency.
Key facts at a glance
- RxNorm
- 34822
- Generic
- Protein S
- Class
- unclassified
- Brands
- Kcentra, Balfaxar
- Availability
- rx
- Lactation
- unknown
- Routes
- —
- Forms
- injection
- Regions
- US, EU, CN, JP
- Monitoring
- —
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Protein S is indicated for the prevention and treatment of venous thromboembolism (including deep vein thrombosis and pulmonary embolism) in patients with confirmed Protein S deficiency. It may also be used in cases of acquired deficiency due to conditions such as liver disease, disseminated intravascular coagulation, or certain infections.
Protein S serves as an essential cofactor for activated protein C (APC), enhancing APC's ability to inactivate coagulation factors Va and VIIIa. This action prevents the propagation of blood clots and maintains normal hemostatic balance in the circulatory system.
Protein S therapy requires careful monitoring of coagulation parameters. Treatment is contraindicated in patients with known hypersensitivity, active bleeding, or severe thrombocytopenia. Regular assessment of Protein S levels is recommended during therapy to ensure adequate anticoagulation. The underlying cause of deficiency should be identified when possible.
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 20, 2026. · Read our editorial policy