Final answer:
The calculation based on 108 lbs b.w. and a dosage of 25 mg/kg/day q6h results in a needed dose of 306.25 mg per administration. One 300-mg tablet of quinidine matches the required dose closely.
Step-by-step explanation:
A doctor orders a dosage of quinidine for an adult patient weighing 108 lbs at a dosage of 25 mg/kg/day, to be administered every 6 hours (q6h). To calculate the dose for each administration, we need to convert the patient's weight to kilograms (1 kg = 2.20462 lbs), which results in approx. 49 kg (108 lbs / 2.20462). Multiplying the patient's weight in kilograms by the dosage per kilogram gives us the total daily dose in milligrams:
49 kg x 25 mg/kg/day = 1225 mg/day
Since the medication is to be administered q6h (four times a day), the total daily dose should be divided by four to obtain the dose per administration:
1225 mg/day ÷ 4 = 306.25 mg/dose
The closest available tablet size is a 300-mg tablet, which suggests that each dose would consist of one 300-mg tablet. However, the exact prescription should be confirmed with the doctor since the calculated dose is slightly over the tablet strength. The stock supply of quinidine in 300-mg tablets is convenient as it closely matches the calculated dose needed.