Final answer:
After converting Mr. Doran's weight from pounds to kilograms, the calculation shows he can safely take a daily methotrexate dosage ranging from 47 to 187 mg, which corresponds to option B of the provided choices.
Step-by-step explanation:
Mr. Doran's prescribed dosage range of methotrexate for his condition is 0.625-2.5 mg/kg/day. Given that he weighs 165 pounds, we will first need to convert his weight into kilograms. There are approximately 0.453592 kilograms in a pound. Therefore, Mr. Doran's weight in kilograms is:
165 lb × 0.453592 kg/lb = 74.84308 kg
Now, using the lower end of the dosage range:
0.625 mg/kg/day × 74.84308 kg = 46.7773 mg/day
And using the higher end of the dosage range:
2.5 mg/kg/day × 74.84308 kg = 187.1077 mg/day
Therefore, rounding to the nearest whole number, Mr. Doran can safely take a range of 47 - 187 mg of methotrexate per day, which corresponds to option B.