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DOSAGE AND ADMINISTRATION
Because of the increased risk of adverse cardiovascular reactions associated with rapid administration, intravenous administration should not exceed 50 mg per minute in adults. In pediatric patients, the drug should be administered at a rate not exceeding 1-3 mg/kg/min or 50 mg per minute, whichever is slower.
As non-emergency therapy, Dilantin should be administered more slowly as either a loading dose or by intermittent infusion. Because of the risks of cardiac and local toxicity associated with intravenous Dilantin, oral phenytoin should be used whenever possible.
Because adverse cardiovascular reactions have occurred during and after infusions, careful cardiac monitoring is needed during and after the administration of intravenous Dilantin. Reduction in rate of administration or discontinuation of dosing may be needed.
Because of the risk of local toxicity, intravenous Dilantin should be administered directly into a large peripheral or central vein through a large-gauge catheter. Prior to the administration, the patency of the IV catheter should be tested with a flush of sterile saline. Each injection of parenteral Dilantin should then be followed by a flush of sterile saline through the same catheter to avoid local venous irritation due to the alkalinity of the solution.
Dilantin can be given diluted with normal saline. The addition of parenteral Dilantin to dextrose and dextrose-containing solutions should be avoided due to lack of solubility and resultant precipitation.
Treatment with Dilantin can be initiated either with a loading dose or an infusion:
A loading dose of parenteral Dilantin should be injected slowly, not exceeding 50 mg per minute in adults and 1-3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients.
For infusion administration, parenteral Dilantin should be diluted in normal saline with the final concentration of Dilantin in the solution no less than 5 mg/mL. Administration should commence immediately after the mixture has been prepared and must be completed within 1 to 4 hours (the infusion mixture should not be refrigerated). An in-line filter (0.22-0.55 microns) should be used.
Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution or container permit.
The diluted infusion mixture (Dilantin plus normal saline) should not be refrigerated. If the undiluted parenteral Dilantin is refrigerated or frozen, a precipitate might form: this will dissolve again after the solution is allowed to stand at room temperature. The product is still suitable for use. A faint yellow coloration may develop, however this has no effect on the potency of the solution.
In adults, a loading dose of 10 to 15 mg/kg should be administered slowly intravenously, at a rate not exceeding 50 mg per minute (this will require approximately 20 minutes in a 70-kg patient).
The loading dose should be followed by maintenance doses of 100 mg orally or intravenously every 6-8 hours.
In the pediatric population, a loading dose of 15-20 mg/kg of Dilantin intravenously will usually produce plasma concentrations of phenytoin within the generally accepted therapeutic range (10-20 mcg/mL). The drug should be injected slowly intravenously at a rate not exceeding 1-3 mg/kg/min or 50 mg per minute, whichever is slower.
Continuous monitoring of the electrocardiogram and blood pressure is essential. The patient should be observed for signs of respiratory depression.
Determination of phenytoin plasma levels is advised when using Dilantin in the management of status epilepticus and in the subsequent establishment of maintenance dosage.
Other measures, including concomitant administration of an intravenous benzodiazepine such as diazepam, or an intravenous short-acting barbiturate, will usually be necessary for rapid control of seizures because of the required slow rate of administration of Dilantin.
If administration of Parenteral Dilantin does not terminate seizures, the use of other anticonvulsants, intravenous barbiturates, general anesthesia, and other appropriate measures should be considered.
Intramuscular administration should not be used in the treatment of status epilepticus because the attainment of peak plasma levels may require up to 24 hours.
Nonemergent Loading and Maintenance Dosing
Because of the risks of cardiac and local toxicity associated with intravenous Dilantin, oral phenytoin should be used whenever possible. In adults, a loading dose of 10 to 15 mg/kg should be administered slowly. The rate of intravenous administration should not exceed 50 mg per minute in adults and 1-3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients. Slower administration rates are recommended to minimize the cardiovascular adverse reactions. Continuous monitoring of the electrocardiogram, blood pressure, and respiratory function is essential.
The loading dose should be followed by maintenance doses of oral or intravenous Dilantin every 6-8 hours.
Ordinarily, Dilantin should not be given intramuscularly because of the risk of necrosis, abscess formation, and erratic absorption. If intramuscular administration is required, compensating dosage adjustments are necessary to maintain therapeutic plasma levels. An intramuscular dose 50% greater than the oral dose is necessary to maintain these levels. When returned to oral administration, the dose should be reduced by 50% of the original oral dose for one week to prevent excessive plasma levels due to sustained release from intramuscular tissue sites. Monitoring plasma levels would help prevent a fall into the subtherapeutic range. Serum blood level determinations are especially helpful when possible drug interactions are suspected.
IV Substitution For Oral Phenytoin Therapy
When treatment with oral phenytoin is not possible, IV Dilantin can be substituted for oral phenytoin at the same total daily dose. Dilantin capsules are approximately 90% bioavailable by the oral route. Phenytoin is 100% bioavailable by the IV route. For this reason, plasma phenytoin concentrations may increase modestly when IV phenytoin is substituted for oral phenytoin sodium therapy. The rate of administration for IV Dilantin should be no greater than 50 mg per minute in adults and 1-3 mg/kg/min (or 50 mg per minute, whichever is slower) in pediatric patients.
Serum concentrations should be monitored and care should be taken when switching a patient from the sodium salt to the free acid form. Dilantin® Kapseals® and Dilantin Parenteral are formulated with the sodium salt of phenytoin. The free acid form of phenytoin is used in Dilantin-125 Suspension and Dilantin Infatabs. Because there is approximately an 8% increase in drug content with the free acid form over that of the sodium salt, dosage adjustments and serum level monitoring may be necessary when switching from a product formulated with the free acid to a product formulated with the sodium salt and vice versa.
Dosing in Special Populations
Patients with Renal or Hepatic Disease
Due to an increased fraction of unbound phenytoin in patients with renal or hepatic disease, or in those with hypoalbuminemia, the interpretation of total phenytoin plasma concentrations should be made with caution. Unbound phenytoin concentrations may be more useful in these patient populations.
Phenytoin clearance is decreased slightly in elderly patients and lower or less frequent dosing may be required.
A loading dose of 15-20 mg/kg of Dilantin intravenously will usually produce plasma concentrations of phenytoin within the generally accepted therapeutic range (1020 mcg/mL). The drug should be injected slowly intravenously at a rate not exceeding 13 mg/kg/min or 50 mg per minute, whichever is slower.
N 0071-4488--47 (Steri-Dose® 4488) Dilantin ready-mixed solution containing 50 mg phenytoin sodium per milliliter is supplied in a 2-mL sterile disposable syringe(22 gauge x 1 ¼ inch needle). Packages of ten syringes.
N 0071-4488-45 Dilantin ready-mixed solution containing 50 mg phenytoin sodium per milliliter is supplied in 2-mL Steri-Vials®. Packages of twenty-five.
N 0071-4475-45 Dilantin ready-mixed solution containing 50 mg phenytoin sodium per milliliter is supplied in 5-mL Steri-Vials. Packages of twenty-five.
Caution-Federal law prohibits dispensing without prescription.
Warning- Manufactured with CFC-12, which harms public health and environment by destroying ozone in the upper atmosphere.
Distributed by : Parke- Davis, Division of Pfizer Inc, NY,NY 10017. February 2013
Last reviewed on RxList: 3/20/2013
This monograph has been modified to include the generic and brand name in many instances.
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