What is the role of CYP2C9 gene in prescribing warfarin?
A patient’s CYP2C9 and VKORC1 genotype can be used to help determine the optimal starting dose of warfarin. The CYP2C9 gene encodes one of the main enzymes involved in the metabolism of warfarin. Several variant CYP2C9 alleles are associated with reduced enzyme activity and lower clearance rates of warfarin.
How do you measure therapeutic effect of warfarin?
Prothrombin time (PT) — The clotting test used to measure the effect of warfarin is the prothrombin time (called pro time, or PT). The PT is a laboratory test that measures the time it takes for a clot to form. It is measured in seconds. It is particularly sensitive to the clotting factors affected by warfarin.
How often does INR need to be checked on warfarin?
How often do I need an INR? When you first start warfarin, you may need to have blood tests every few days or weekly. When your INR and warfarin dose are stable, blood tests are often done every 2 to 4 weeks, sometimes longer.
What is CYP2C9 genotype?
CYP2C9 Genotyping Of special interest are those drugs with narrow therapeutic index, such as warfarin (Coumadin®), tolbutamide, and phenytoin (Dilantin®), where impairment in CYP2C9 metabolic activity might cause difficulties in dose adjustment as well as toxicity. VKORC1 is the site of action of warfarin.
Does warfarin inhibit CYP2C9?
Although R-warfarin is not metabolized by CYP2C9, this enantiomer binds and inhibits the enzyme with a Ki of ∼8 μM (13, 14). Furthermore, warfarin alcohols are known to competitively inhibit CYP2C9 yet are not metabolized (15).
What enzyme breaks down warfarin?
The CYP2C9 enzyme breaks down (metabolizes) compounds including steroid hormones and fatty acids. The CYP2C9 enzyme also plays a major role in breaking down the drug warfarin, which thins the blood and prevents blood clots from forming.
Does warfarin affect PT or PTT?
PT: prothrombin time; aPTT: activated partial thromboplastin time; LMW heparin: low molecular weight heparin. * Warfarin has a weak effect on most aPTT reagents….
| Drug class | Vitamin K antagonists |
|---|---|
| Drug | Warfarin |
| Brand name(s) | Coumadin, Jantoven |
| PT | ↑ |
| aPTT | ↑/–* |
What is TTR in warfarin?
Time in therapeutic range (TTR) is a widely accepted metric used to evaluate the safety and efficacy of warfarin therapy. Patients with low TTR (< 65%) are at higher risk of poor outcomes, and current antithrombotic guidelines recommend interventions to improve low TTR.
What is a normal INR number?
In healthy people an INR of 1.1 or below is considered normal. An INR range of 2.0 to 3.0 is generally an effective therapeutic range for people taking warfarin for disorders such as atrial fibrillation or a blood clot in the leg or lung.
