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Difficulty: MediumPharmacological Therapies

A client with a history of generalized seizures is prescribed phenytoin 55 mg/kg/day PO divided into 22 equal doses. The client weighs 176176 lb. The available medication is phenytoin oral suspension 125125 mg / 55 mL. How many mL should the practical nurse administer per dose? (Record answer to the nearest whole number. Do not include units in the answer.)

Answer: 8 mL

Answer

8
To find the correct volume to administer, the practical nurse must complete a multi-step calculation. First, convert the weight to kilograms: 176 lb÷2.2=80176 \text{ lb} \div 2.2 = 80 kg. Next, calculate the total daily dose: 80 kg×5 mg/kg=40080 \text{ kg} \times 5 \text{ mg/kg} = 400 mg. Because the medication is divided into two equal doses, divide the daily dose by 22, yielding 200200 mg per dose. Finally, use the available concentration (125125 mg in 55 mL) to find the volume: 200 mg125 mg×5 mL=8\frac{200 \text{ mg}}{125 \text{ mg}} \times 5 \text{ mL} = 8 mL. The practical nurse will administer 88 mL per dose.

Step-by-Step Solution

1
Convert the client's weight from pounds (lb) to kilograms (kg).
176÷2.2=80176 \div 2.2 = 80 kg
Weight-based medication prescriptions require the client's weight to be in metric units (kilograms).
2
Calculate the total daily medication dosage.
80 kg×5 mg/kg=40080 \text{ kg} \times 5 \text{ mg/kg} = 400 mg/day
The prescription specifies 55 mg of phenytoin per kilogram of body weight for the entire day.
3
Determine the amount of medication required for a single dose.
400 mg/day÷2 doses=200400 \text{ mg/day} \div 2 \text{ doses} = 200 mg/dose
The total daily dose must be divided into 22 equal doses as prescribed.
4
Calculate the liquid volume to administer using the available concentration.
200 mg125 mg×5 mL=1.6×5 mL=8\frac{200 \text{ mg}}{125 \text{ mg}} \times 5 \text{ mL} = 1.6 \times 5 \text{ mL} = 8 mL
Using the dimensional analysis or desired-over-have method ensures the correct volume of the oral suspension is administered.

Key Concept

Weight-based oral medication dosage calculation
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Topics

Pharmacological Therapies

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