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Difficulty: Very hardPharmacological and Parenteral Therapies

A client weighing 154 lbs154\text{ lbs} is experiencing continuous generalized tonic-clonic seizures. The healthcare provider orders a loading dose of intravenous phenytoin 18 mg/kg18\text{ mg/kg} to be administered at the maximum safe rate. The client currently has a single 20-gauge peripheral IV in the right forearm with a continuous infusion of 5%5\% dextrose in 0.45%0.45\% sodium chloride (D5 1/2 NS) running at 100 mL/hr100\text{ mL/hr}. Phenytoin is supplied in 50 mg/mL50\text{ mg/mL} vials.

Which action by the nurse represents the safest and most appropriate administration technique?

  1. Pause the continuous IV infusion, flush the line with 0.9%0.9\% sodium chloride, administer the 1260 mg1260\text{ mg} dose over a minimum of 2626 minutes, and flush again with 0.9%0.9\% sodium chloride before resuming.Answer
  2. B
    Attach the phenytoin syringe to the lowest Y-site of the primary IV tubing, set a syringe pump to deliver the 1260 mg1260\text{ mg} dose over 3030 minutes, and allow the primary fluid to continue running.
  3. C
    Pause the continuous IV infusion, flush the line with 0.9%0.9\% sodium chloride, administer a 2772 mg2772\text{ mg} dose over a minimum of 5656 minutes, and flush again with 0.9%0.9\% sodium chloride before resuming.
  4. D
    Pause the continuous IV infusion, flush the line with 0.9%0.9\% sodium chloride, administer the 1260 mg1260\text{ mg} dose via rapid intravenous push over 55 minutes to quickly achieve therapeutic levels, and flush again.

Answer

Pause the continuous IV infusion, flush the line with 0.9% sodium chloride, administer the 1260 mg dose over a minimum of 26 minutes, and flush again with 0.9% sodium chloride before resuming.
The correct action synthesizes accurate weight-based dosing, rate calculation, and compatibility principles. The client weighs 70 kg70\text{ kg}, requiring a total dose of 1260 mg1260\text{ mg}. Because intravenous phenytoin must not be administered faster than 50 mg/min50\text{ mg/min} to avoid severe hypotension and fatal arrhythmias, the dose must be given over a minimum of 25.225.2 minutes. Additionally, phenytoin is highly incompatible with dextrose solutions and will precipitate. Therefore, the nurse must pause the dextrose-containing primary fluid, flush the line with compatible 0.9%0.9\% sodium chloride, administer the medication slowly, and flush again before resuming the primary fluid.

Step-by-Step Solution

1
Calculate the client's weight in kilograms.
154 lbs÷2.2 lbs/kg=70 kg154\text{ lbs} \div 2.2\text{ lbs/kg} = 70\text{ kg}.
Accurate weight in kilograms is necessary for precise weight-based dosing.
2
Calculate the total ordered dose of phenytoin.
18 mg/kg×70 kg=1260 mg18\text{ mg/kg} \times 70\text{ kg} = 1260\text{ mg}.
Determines the absolute amount of medication to administer based on the provider's order.
3
Determine the minimum safe administration time.
1260 mg÷50 mg/min=25.2 minutes1260\text{ mg} \div 50\text{ mg/min} = 25.2\text{ minutes}.
Intravenous phenytoin administration must not exceed 50 mg/min50\text{ mg/min} in adults to prevent severe cardiovascular collapse.
4
Evaluate intravenous compatibility with the primary fluid.
Phenytoin is strictly incompatible with dextrose-containing solutions such as D5 1/2 NS.
Mixing phenytoin with dextrose causes immediate crystal formation and precipitation in the tubing.
5
Formulate the safe administration procedure.
Pause the primary infusion, flush thoroughly with 0.9%0.9\% sodium chloride, administer the drug over at least 25.225.2 minutes (e.g., 2626 minutes), and flush again before resuming.
This ensures no mixing of incompatible fluids and adheres to strict rate limits.

Key Concept

Phenytoin Administration: Dosage, Rate Limits, and IV Compatibility
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Topics

Pharmacological and Parenteral Therapies

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