Drug Overdose, Rat Poison (Warfarin Toxicity)

Major risk is hemorrhage, especially CNS or GI.

Incidence: Risk of hemorrhage in 1–7.4% of pts chronically anticoagulated. Risk is dose-related and proportional to PT prolongation. Risk of hemorrhage doubles as INR increases from 2.0–2.9 to 3.0–4.4. It further quadruples as INR increases from 3.0–4.4 to 4.5–6.9. Age is associated with increased sensitivity to warfarin and increased incidence of bleeding complications.

Rx for DVT, cerebral vessel atherosclerosis, prosthetic heart valves, mitral stenosis, and atrial fibrillation.

Bleeding

Drugs that potentiate anticoagulant effects: Antibiotics (especially metronidazole, sulfonamides, cephalosporins), NSAIDs, phenytoin, cimetidine, barbiturates, alcohol

Bleeding complications of invasive procedures.

Drug interactions.

Transient protein C deficiency preceding effect on procoagulant levels at initiation of warfarin therapy leading to thrombotic complications.

True poisoning with rodenticides (so-called super-warfarins) may result in prolonged clotting abnormality with abnormal PT values weeks to months post event because of the enormously long half-lives of these drugs.