Phenytoin administration

A suggestion to minimize interaction is to hold tube feeding 1-2 hours before and after phenytoin, but this has no proven benefit Adjust tube feeding rate to account for time held for phenytoin administration Monitor phenytoin serum concentrations and clinical response closely Consider switching to IV phenytoin route if unable to reach therapeutic serum concentration Consider holding tube feeding before and after administration... 

The concurrent administration of lidocaine with cimeti-dine but not ranitidine may cause an increase (15%) in the plasma concentration of lidocaine. This effect is a manifestation of cimetidine reducing the clearance and volume of distribution of lidocaine. The myocardial depressant effect of lidocaine is enhanced by phenytoin administration. 

Because of the increase in A-V transmission observed with phenytoin administration, it should not be given to patients with atrial flutter or atrial fibrillation. Phenytoin will probably not restore normal sinus rhythm and may dangerously accelerate the ventricular rate. 

An understanding of absorption, binding, metabolism, and excretion is more important for phenytoin than it is for most drugs. Following oral administration, phenytoin absorption is slow but usually complete, and it occurs primarily in the duodenum. Phenytoin is highly bound (about 90%) to plasma proteins, primarily plasma albumin. Since several other substances can also bind to albumin, phenytoin administration can displace (and be displaced by) such agents as thyroxine, triiodothyronine, valproic acid, sulfafurazole, and salicylic acid. 

Acute adverse effects seen after phenytoin administration usually result from overdosage. They are generally characterized by nystagmus, ataxia, vertigo, and diplopia (cerebellovestibular dysfunction). Higher doses lead to altered levels of consciousness and cognitive changes. 

Phenytoin administration during pregnancy may produce a constellation of congenital abnormalities, including cleft palate. This has been ascribed to phenytoin-arene oxide reactivity with cellular DNA in tissues lacking the protective effects of HYEl (21,22). 

A number of methods to minimize the interaction between phenytoin and continuous enteral feeding have been suggested, but no consensus exists. Some clinicians choose holding the feeding for 1 to 2 hours before and after phenytoin administration to minimize the interaction. But since this has not been proven effective and may result in suboptimal nutrition, others choose not to interrupt the feeding. 

If hypotension occurs with intravenous phenytoin administration, immediately stop the infusion and administer intravenous fluids and pressors (see p 16) if necessary. 

A. Rapid intravenous phenytoin administration (S 50 mg/min in adults or 1 mg/kg/min in children) may produce hypotension, atrioventricular block, and... 

RD. Influence of chronic phenytoin administration on the pharmacokinetics and pharmaco-(fynamics of vecuronium. (1999) 83,183P-184P. 

Begg EJ, Chinwah PM, Webb C, Day RO, Wade DN. Enhanced metabolism of mexiletine after phenytoin administration. BrJ Clin Pharmacol ( 9S2) 14, 219-23. 

Wong YWJ, Yeh C, Thyrum PT, The effects of concomitant phenytoin administration on the steady-state pharmacokinetics of quetiapine. J Clin Psychopharmacol (2001) 21, 89-93. 

Schweitzer EJ, Canafax DM, Gillingham KJ, Najarian JS, Matas AJ. Phenytoin administration in kidney recipients on CSA immunosuppression. J Am Soc Nephrol (1991) 2, 816. 

Scumpia AJ, Yahsou J, Cajina J, Cao C. Purple glove syndrome after intravenous phenytoin administration presenting in the emergency department. J Emerg Med February 2013 44(2) e281-3. 

Concurrent administration of auranofin with phenytoin may increase phenytoin blood levels. 

Additive bone marrow depressive effects occur when the miotic inhibitor drugs are administered with other anti-neoplastic dragp or radiation therapy. Administration of vincristine with digoxin results in a decreased therapeutic effect of tlie digoxin and decreased plasma digoxin levels. There is a decrease in serum concentrations of phenytoin when administered widi vinblastine... 

Age-related variations in central nervous system (CNS) neurotransmitter production and receptor sensitivity are the most likely explanations for the pharmacodynamic differences observed between children and adults following administration of psychotropic medications [39a], Children have lower phenobarbital ratios than adults, and the ratio increases with gestational age [40,41]. Conversely, a lower therapeutic range for children has been identified for cyclosporine, phenytoin, and digoxin [42]. 

SA Varia, VJ Stella. Phenytoin prodrugs VI In vivo evaluation of a phosphate ester prodrug of phenytoin after parenteral administration to rats. J Pharm Sci 73(8) 1087-1090, 1984. 

Fig. 15 Effect of phenytoin (PHT) particle size on (a) dissolution in simulated gastric fluid, pH 1.2, 37°C and (b) bioavailability in human volunteers after oral administration of 300 mg PHT. Dark circles lot with particle size range 74-350 /u.m open circles lot with particle size range 177-350 /am. (From Ref. 64.)...

The answer is g. (KatzungT pp 399-400J Phenytoin is one of the most commonly used antiepileptic agents. Chronic administration has been reported to cause adverse reactions, such as ataxia, dizziness, nystagmus, gingival hyperplasia, hirsutism, and megaloblastic anemia. 

In nonacute situations, phenytoin may be initiated in adults at oral doses of 5 mg/kg/day and titrated upward. Subsequent dosage adjustments should be done cautiously because of nonlinearity in elimination. Most adult patients can be maintained on a single daily dose, but children often require more frequent administration. Only extended-release preparations should be used for single daily dosing. 

Phenytoin is associated with pain and burning during infusion. Phlebitis may occur with chronic infusion, and tissue necrosis is likely on infiltration. Intramuscular administration is not recommended. 

Continuous ECG, blood pressure, and respiratory status monitoring is recommended for all loading doses of fosphenytoin. Serum phenytoin concentrations should not be obtained for at least 2 hours after IV and 4 hours after intramuscular administration of fosphenytoin. 

An EEG is a key tool that allows practitioners to determine when abnormal electrical activity has been aborted and may assist in determining which anticonvulsant was effective. Vital signs must be monitored during the infusion. It may also be necessary to monitor the ECG in some patients. The infusion site must be assessed for any evidence of infiltration before and during administration of phenytoin. 

After intraperitoneal administration, the phenytoin-lipid conjugates were at best equipotent with phenytoin in protection mice against seizures... 

G. K. E. Scriba, D. M. Lambert, Bioavailability of Phenytoin and Anticonvulsant Activity after Oral Administration of Phenytoin-Ws-hydroxyisobutyrate to Rats , Pharm. Res. 1997, 14, 251-253. 

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