Dilantin® Jeopardy: Avoiding The Dangers of Phenytoin

MedSurg Nursing, Dec, 1998 by Michael L. Schlicher

3. In a pediatric case, you have a child who is 6 years old and weighs 19.09 k. The doctor orders a loading dose of 15 mg/kg. You know that you can only infuse 0.5 mg/kg/min by looking at your reference chart. What is your total loading dose amount and how many minutes will it take to get the total loading dose infused?

(19.09 k x 15 mg = 286 mg

(19.09 k x 0.5 mg/min = 9.54 mg/kg/min

(286 mg divided by 9.54 mg/kg/min=29.96 or 30 minutes

(You will fill your infusion syringe with 5.72 cc of phenytoin (for a total of 286 mg), and set your infusion time for 30 minutes.

Side Effects

Improper administration of phenytoin may contribute to respiratory depression, cardiovascular collapse, and hypotension (United States Pharmacopeial, 1996). An indicator of lethal dosing can often be spotted by noticing a marked widening by 50% or more in the patient's QRS wave (Markovchick, Pons, & Wolfe, 1993). One of the more common side effects of phenytoin involves CNS depression which may include nystagmus, ataxia, slurred speech, mental confusion, motor twitching, lateral stare, numbness, and fatigue (United States Pharmacopeial, 1996). Gastrointestinal responses such as nausea, vomiting, and constipation also occur in many patients.

Women taking phenytoin may be particularly troubled by excessive growth of body hair, enlargement of their lips, and onset of acne. Phenytoin can cause birth defects (cleft lip/palate), so its use during pregnancy must be weighed against the risk of fetal damage. It is also excreted in breast milk, so nursing mothers should be properly advised (BeDell et al., 1996). In children and young adults, a measle-like rash is occasionally noted within the first 2 weeks of treatment (United States Pharmacopeial, 1996).

Patients' blood counts should be monitored closely. Blood dyscrasias can occur as a side effect of phenytoin. Finally, patients who practice poor oral hygiene are subject to gingival hyperplasia with continued use of phenytoin. Oral surgery may even be needed to cut back the excessive tissue along the gum line.

Interactions and Incompatibilities to Other Drugs

It is well documented that phenytoin interacts dangerously with many other drugs (Trissel, 1996; United States Pharmacopeial, 1996). Several drugs can cause serum phenytoin levels to either increase or decrease (see Table 4). In addition, there are a number of common drugs which can inhibit or potentiate the effects of phenytoin. For example, phenytoin has an inhibitory effect on insulin release and may raise blood sugar levels (United States Pharmacopeial, 1996). Be alert that patients on phenytoin who receive influenza vaccine may show signs of increased seizure activity (Shannon et al., 1995). All nurses should keep in mind that phenytoin is highly incompatible with dopamine, clindamycin phosphate, and aminophylline (Hayes & Chesney, 1993). Phenytoin should never be infused with any other drug.

Table 4.

Drug Interaction Reference

Drugs that Increase Serum Dilantin Levels

Cimetidine

Allopurinol