- treatment of seizures which are unresponsive to phenobarbital
- an antiarrhythmic agent, which has been useful in the treatment of ventricular arrhythmias, associated with digoxin toxicity
- phenytoin acts as an anticonvulsant by limiting the development and spread of seizure activity. More effective than phenobarbital in stopping the spread of seizure activity; less active than phenobarbital in suppressing focal activity
- phenytoin acts as an antiarrhythmic agent by decreasing cardiac automaticity and prolonging the refractory period
- because phenytoin exhibits "zero order" kinetics, a small change in dose may result in an unexpectedly large increase in serum concentration
- bilirubin can displace phenytoin from albumin binding sites; this will create difficulty in the interpretation of serum concentrations, which are normally measured and reported as total drug (ie. free + bound)
- ACUTE, following IV administration: hypotension, bradycardia, ventricular fibrillation, vasodilation; venous irritation; pain, thrombophlebitis, skin rash. Observe IV site carefully. Extravasation may cause tissue inflammation and necrosis.
If extravasation does occur, HYALURONIDASE may be used as follows: Dilute the 150 units/mL concentration to 15 units/mL with 0.9% NaCl. Inject the 15 units/mL dilution at 5 separate sites (0.2 mL per site) around the periphery of the extravasation
- GI side effects: vomiting, constipation
- other side effects that may be seen with chronic use include toxic hepatitis, gingival hyperplasia, hyperglycemia and osteoporosis
Precautions and Nursing Implications
- monitor IV site closely; to avoid local tissue injury use dilute solutions of phenytoin, flush the IV catheter with 0.9% NaCl before and after phenytoin administration and try to avoid small hand, wrist or foot veins
- do not stop phenytoin abruptly, this may precipitate seizures (withdrawal)
- do not mix phenytoin with any solution containing dextrose because it will precipitate
- clear IV butterfly or angiocath tubing with saline 0.5 mL before and after drug administration
- recommended blood serum levels: 40-80 micromol/L (10-20 micrograms/mL)
- observe ECG tracings for cardiac arrhythmias, (eg. ventricular fibrillation) while administering phenytoin
- DO NOT give IM
- oral absorption is poor in neonates
- use with caution in asphyxiated infants because of increased risk of cardiac arrest
- DRUG INTERACTION with Phenobarbital - levels of phenytoin may increase or decrease (usually decrease); therefore monitor Phenytoin levels closely
- also likely to interact with other medications which are metabolized in the liver (eg. may decrease serum concentrations of theophylline)
**a 0.22 MICRON IN-LINE FILTER IS REQUIRED DUE TO THE POTENTIAL OF DRUG PRECIPITATION. **
AS AN ANTICONVULSANT
- 10-20 mg/kg IV
A stat dose may be given in this manner: Phenytoin must be administered slowly. In neonates phenytoin should be administered at a rate not exceeding 1 to 3 mg/kg/min. The administration of the drug may be made easier by dilution (must be with saline solution eg. NaCl 0.9 %) to 5 mg/mL. See last page for instructions.
- 2 to 4 mg/kg IV q12h
- administered by slow IV infusion at a concentration of 5 mg/mL
- IV SOLUTION MUST BE SALINE
- do NOT give IM
ORAL MAINTENANCE DOSE
- 2 to 4 mg/kg po q12h
- absorption of phenytoin is highly variable and often very poor in infants. Doses up to 15 mg/kg/day have been used; anecdotal reports show that even higher doses have been required in certain cases. If these doses are used, the increases should occur slowly and serum levels monitored very closely
- if an infant has a feeding tube, the tube should be flushed with 0.9% NaCl before AND after administration of phenytoin to minimize adsorption to the tube; to minimize poor absorption hold feedings for 2 hours before and after phenytoin administration, if possible
AS AN ANTIARRHYTHMIC
- 5 to 10 mg/kg IV, for ventricular tachycardia, especially if due to digoxin toxicity
- note that phenytoin is rarely used in neonates for this purpose
- 25 mg/mL suspension for oral use (keep at room temperature; shake well prior to each use)
- 50 mg/mL, 2 mL ampoule for IV use
- the IV solution may be diluted to 5 mg/mL as follows:
ADD 1mL OF PHENYTOIN 50 mg/mL
TO 9mL OF SODIUM CHLORIDE 0.9%
TO PRODUCE FINAL CONCENTRATION OF
50 mg/10mL (5mg/mL)
=_______mL of 5mg/mL SOL'N
NOTE THAT A SALINE SOLUTION (eg. NaCl 0.9%) MUST BE USED THE DILUTION SHOULD BE USED WITHIN 1 HOUR AFTER PREPARATION
THE IV SOLUTION MAY BE FURTHER DILUTED TO AS LOW AS 1mg/mL
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- Drugs Dex, Denver, Colorado, 1992.
- Trissel L.A.: Handbook on Injectable Drugs, American Society of Hospital Pharmacists 1988.
- Krogh CME et al (ed): Compendium of Pharmaceuticals and Specialties, Canadian Pharmaceutical Association, 1992.
- Gomella TL (Ed): Neonatology - Management, Procedures, On-Call Problems, Diseases, Drugs, 1992, Appleton and Lange, Norwalk, Connecticut.
- Personal Communication with John Kettlewell, Department of Pharmacy, The Hospital for Sick Children, Toronto, 1 March 1990.
- Volpe JJ: Neurology of the Newborn, Sanders, Toronto, 1987.
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