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Difficulty: HardPharmacological and Parenteral Therapies

A hospitalized adult weighing 176 lb176\text{ lb} experiences a prolonged seizure. The healthcare provider orders an intravenous loading dose of phenytoin at 15 mg/kg15\text{ mg/kg}. The client currently has a single peripheral intravenous line continuously infusing 5%5\% dextrose in half-normal saline at 75 mL/hr75\text{ mL/hr}. Given that the maximum safe administration rate for intravenous phenytoin is 50 mg/min50\text{ mg/min}, which of the following describes the most appropriate method to administer this medication?

  1. A
    Stop the primary infusion, flush the line with 0.9%0.9\% sodium chloride, administer 1,200 mg1,200\text{ mg} of phenytoin over 15 minutes15\text{ minutes}, and flush again with 0.9%0.9\% sodium chloride.
  2. B
    Administer 1,200 mg1,200\text{ mg} of phenytoin via the Y-port closest to the client while the primary dextrose infusion continues, ensuring the phenytoin infuses over at least 24 minutes24\text{ minutes}.
  3. Stop the primary infusion, flush the line with 0.9%0.9\% sodium chloride, administer 1,200 mg1,200\text{ mg} of phenytoin over at least 24 minutes24\text{ minutes}, and flush again with 0.9%0.9\% sodium chloride.Answer
  4. D
    Stop the primary infusion, flush the line with 0.9%0.9\% sodium chloride, administer 2,640 mg2,640\text{ mg} of phenytoin over at least 53 minutes53\text{ minutes}, and flush again with 0.9%0.9\% sodium chloride.

Answer

The nurse must stop the dextrose infusion, flush the line with normal saline (0.9%0.9\% sodium chloride), administer the correct dose of 1,200 mg1,200\text{ mg} over a minimum of 24 minutes24\text{ minutes}, and follow with another normal saline flush.
The correct action demonstrates accurate synthesis of three critical nursing concepts: dosage calculation, IV fluid compatibility, and safe administration rates. First, the client weighs 80 kg80\text{ kg} (176 lb÷2.2176\text{ lb} \div 2.2), which makes the correct loading dose 1,200 mg1,200\text{ mg} (80 kg×15 mg/kg80\text{ kg} \times 15\text{ mg/kg}). Second, because the maximum rate is 50 mg/min50\text{ mg/min}, dividing the total dose (1,200 mg1,200\text{ mg}) by the maximum rate (50 mg/min50\text{ mg/min}) confirms the medication must be infused over an absolute minimum of 24 minutes24\text{ minutes}. Finally, because phenytoin precipitates in dextrose, the primary dextrose infusion must be paused, and the line must be thoroughly flushed with compatible 0.9%0.9\% sodium chloride before and after the dose is given.

Step-by-Step Solution

1
Convert the client's weight from pounds to kilograms.
176 lb÷2.2 lb/kg=80 kg176\text{ lb} \div 2.2\text{ lb/kg} = 80\text{ kg}.
Phenytoin dosing is strictly weight-based using the metric system.
2
Calculate the total required milligram dose of the medication.
80 kg×15 mg/kg=1,200 mg80\text{ kg} \times 15\text{ mg/kg} = 1,200\text{ mg}.
To ensure the client receives the exact prescribed therapeutic loading dose.
3
Calculate the absolute minimum safe infusion time.
1,200 mg÷50 mg/min=24 minutes1,200\text{ mg} \div 50\text{ mg/min} = 24\text{ minutes}.
Intravenous phenytoin must never be administered faster than 50 mg/min50\text{ mg/min} in adults to prevent severe cardiovascular toxicity, such as hypotension and fatal arrhythmias.
4
Determine intravenous fluid compatibility and correct the administration sequence.
Stop the continuous dextrose infusion and use 0.9%0.9\% sodium chloride to clear the line before and after medication delivery.
Phenytoin immediately precipitates when mixed with dextrose-containing solutions, requiring a compatible normal saline flush to prevent line occlusion or embolism.

Key Concept

Safe Parenteral Administration of High-Risk Anticonvulsants
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Topics

Pharmacological and Parenteral Therapies

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