Dilantin® Jeopardy: Avoiding The Dangers of Phenytoin

MedSurg Nursing, Dec, 1998 by Michael L. Schlicher

Administration

Phenytoin can be given by the following routes: IM, PO, NG, and IV. Each route, however, has certain drawbacks. Intramuscular administration has a much slower and erratic absorption rate due to the poor water solubility of phenytoin. The IM dosage must often be increased by almost 50% (Olin et al., 1996). It is also painful and can cause muscle damage. Intramuscular administration is not recommended for neonates or children (Johnson, 1993). PO administration often causes vomiting, diarrhea, and constipation. PO phenytoin can be given via nasogastric tube. However, tube feedings should be held for 1 to 2 hours before and after drug administration. As usual, flush the NG tube with 20 cc of warm tap water before and after drug administration (Mims, Toto, Luecke, & Roberts, 1996).

For emergent situations, IV administration is the preferred route. However, since phenytoin has a pH of 12 which is highly alkaline, it can be directly responsible for severe tissue damage. Intravenous use of phenytoin can also increase the risk for extravasation. Recent studies suggest that IV phenytoin can cause a vasospastic response in the injected vein due to its high pH (Hayes & Chesney, 1993). The vasospastic response predisposes dislodgement of the catheter and thereby allows infiltration of phenytoin into the tissue causing extravasation (Hayes & Chesney, 1993). When the decision to give IV phenytoin is made, staff must make sure to administer it slowly. With healthy adults, it should not be infused at a rate greater than 50 mg per minute (BeDell et al., 1996). If patients are elderly and have heart disease, the rate of administration should be slowed to 50 mg over 2 to 3 minutes. With pediatric patients, the drug should be administered at a rate not exceeding 1 to 3 mg/kg/min (Johnson, 1993). In neonates, the drug should be administered at a rate not exceeding 0.5 mg/kg/min (Johnson, 1993) (see Table 1).

Table 1.
Phenytoin Sodium/Dilantin Quick Reference Chart

     Phenytoin                   Common Dosing
      Sodium                (For Seizure Activity)
    (Dilantin)           [Contraindicated in Patients
     NO KNOWN              with Heart Block or Sinus
     ANTIDOTE                    Bradycardia)

Adults:

IV:                   Loading Dose: 10-15 mg/kg
                      Followed by maintenance dose of
                      100 mg IV every 8 hours
                      Should not exceed 50 mg/min IV
                      push in healthy adult. Elderly=50
IM:                   mg/2-3min IV push.

PO:

NG:                   100 mg-200 mg qid

Drip:
                      Loading dose: 15-18 mg/kg or 1G,
                      then 100-300 mg/day given in three
                      divided doses.

                      Same as PO; Stop feedings 1-2 hrs
                      before and after administration.
                      Flush with 20 cc of warm water.

                      Make solution 1:1 concentration.
                      Use NS only. Use filter.
                      Pump should infuse not faster than
                      50 mg/min in adult. Use good vein.

Adult:                Loading dose: 1.25 mg/kg IV Q 5
Antiarrhythmic        mins up to a total of 15 mg/kg.
(Digitalis Toxicity   Maintenance: 250 mg PO QID x 1
Arrhythmias)          day, then 250 mg PO 012 x 2 days,
                      then 300-400 mg/24 divided QD.

Neonates/Child

IV:                   Loading Dose: 15-20 mg/kg
                      Infant: IV Push not to exceed 0.5
                      mg/kg/min.
                      Child: 1-3 mg/kg/min IV push

IM:                   Not recommended for either.

PO & Suspension       Loading: 5 mg/kg/day in three
                      equally divided doses; then main-
                      tenance can be individualized for a
                      maximum up to 300 mg/day.
                      Shake suspension well.
                      Give immediately after shaking.

     Phenytoin       Therapeutic    Toxic     Half-Life     Steady
      Sodium            Serum       Serum                    State
    (Dilantin)         Levels      Levels
     NO KNOWN          (ug/ml)     (ug/ml)
     ANTIDOTE

Adults:                  10-20        >20    10-22 hours   7-10 days

IV:

IM:

PO:

NG:

Drip:

Adult:
Antiarrhythmic
(Digitalis Toxicity
Arrhythmias)

Neonates/Child

IV:

IM:

PO & Suspension

Any patient who has just been given or will be getting an IV dose of phenytoin should be placed on a cardiac monitor with continuous pulse oximetry. Oxygen, seizure precaution equipment, atropine, and a bag-valve mask should be at hand. Patients must be frequently assessed with respect to respiratory status, cardiac rhythm, and blood pressure during the injection of phenytoin and every 3 to 5 minutes thereafter. All of the assessments should be documented carefully.

In the case scenario, John developed cardiovascular collapse, hypotension, and respiratory failure from a too-rapid infusion of phenytoin. Injecting phenytoin too quickly is often the biggest and most fatal error nurses make when dealing with this drug. Use of IV phenytoin requires flushing the catheter with saline before and after a direct injection. Phenytoin should only be used with normal saline. Using D5W can cause precipitation within a few minutes of mixing. Be aware that phenytoin does NOT have a specific antidote available should extravasation take place.