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A doctor ordered oral warfarin for a patient with a history of phlebitis. In the past, this patient needed only small doses of warfarin to stabilize her condition. So the doctor prescribed an initial dose of 1 mg. But when he wrote the order, he put a decimal point after the 1 and added a O. Unfortunately, a line on the order form obscured the decimal point. To the pharmacist who received a copy of the order, and to the unit secretary and nurse who kept the original, the order looked like 10 mg. That's what the patient received.
Two days later, the patient's prothrombin time was 38 seconds. (Her control time was 12 seconds.) The doctor ordered phytonadione (vitamin K1, AquaMEPHYTON) to reverse the effects of the overdose.
This error could have been avoided if the doctor had simply written the order as 1 mg, not 1.0 mg. The decimal point and the zero serve no purpose. The order can easily be misinterpreted, especially if the decimal point is hard to see or, as in this case, if it's on top of a line on the order form. (These lines on a form, by the way, may also cut off the tops of 7s, so they end up looking like 1s).
A carbonless form with lines only on the original may also have prevented this error. If there were no lines on his copy, the pharmacist probably would have noticed the decimal point and dispensed the correct dose. But the easiest solution is to simply eliminate unnecessary decimal points and zeros.