Usual therapeutic range: around 2.5 (range 2.0 to 3.0)
Causes for an INR above the therapeutic range (INR > 3):
(1) initial dose too high
(2) failure to recheck the patient after a dose adjustment
(3) large dose adjustment if subtherapeutic
(4) insufficient dose adjustment if supratherapeutic
(5) drug interaction (norfloxacin, metronidazole, clarithromycin, isoniazid, omeprazole, tramadol, ceftriaxone, cimetidine, allopurinol, azithromycin, corticosteroids, efavirenez)
(6) overcompliance
(7) herbal interaction
Causes for an INR being below the therapeutic range (INR < 2):
(1) initial dose too low
(2) failure to recheck the patient after a dose adjustment
(3) large dose adjustment if supratherapeutic
(4) insufficient dose adjustment if subtherapeutic
(5) drug interaction (rifampin, nevirapine, neurobion, 6-mercaptopurine, corticosteroids, efavirenez)
(6) patient noncompliance with medication
(7) patient noncompliance with restrictions on vitamin K intake (green leafy vegetables, vitamins)
(8) suboptimal patient education
(9) herbal interaction
