During the initial stage of treatment, INR is checked daily; intervals between tests can be lengthened if the patient manages stable therapeutic INR levels on an unchanged warfarin dose. Newer point-of-care testing is available and has increased the ease of INR testing in the outpatient setting. Instead of a blood draw, the point-of-care test involves a simple finger prick. Maintenance dose
Recommendations by many national bodies, including the American College of Chest Physicians, have been distilled to help manage dose adjustments.The maintenance dose of warfarin can fluctuate significantly depending on the amount of vitamin K1 in the diet. Keeping vitamin K1 intake at a stable level can prevent these fluctuations. Leafy green vegetables tend to contain higher amounts of vitamin K1. Green parts of members of the family Apiaceae, such as parsley, cilantro, and dill are extremely rich sources of vitamin K; cruciferous vegetables such as cabbage and broccoli, as well as the darker varieties of lettuces and other leafy greens, are also relatively high in vitamin K1. Green vegetables such as peas and green beans do not have such high amounts of vitamin K1 as leafy greens. Certain vegetable oils have high amounts of vitamin K1. Foods low in vitamin K1 include roots, bulbs, tubers, and most fruits and fruit juices. Cereals, grains, and other milled products are also low in vitamin K1. Self-testing
Anticoagulation with warfarin can also be monitored by patients at home. International guidelines on home testing were published in 2005.
When warfarin (or another 4-hydroxycoumarin derivative) is given during the first trimester—particularly between the sixth and ninth weeks of pregnancy—a constellation of birth defects known variously as fetal warfarin syndrome (FWS), warfarin embryopathy, or coumarin embryopathy can occur. FWS is characterized mainly by skeletal abnormalities, which include nasal hypoplasia, a depressed or narrowed nasal bridge, scoliosis, and calcifications in the vertebral column, femur, and heel bone, which show a peculiar stippled appearance on X-rays. Limb abnormalities, such as brachydactyly (unusually short fingers and toes) or underdeveloped extremities, can also occur. Common nonskeletal features of FWS include low birth weight and developmental disabilities. Second trimester and later
Warfarin administration in the second and third trimesters is much less commonly associated with birth defects, and when they do occur, are considerably different from FWS. The most common congenital abnormalities associated with warfarin use in late pregnancy are central nervous system disorders, including spasticity and seizures, and eye defects. Because of such later pregnancy birth defects, anticoagulation with warfarin poses a problem in pregnant women requiring warfarin for vital indications, such as stroke prevention in those with artificial heart valves. According to the American College of Chest Physicians, warfarin may be used in lactating women who wish to breastfeed their infants. Available data does not suggest that warfarin crosses into the breast milk. Similarly, INR levels should be checked to avoid adverse effects. Adverse effects
Bleeding
The only common side effect of warfarin is hemorrhage.