Phenytoin drug monitoring

As phenytoin has a narrow therapeutic index therapeutic drug monitoring to establish therapeutic levels is mandatory. Dose and concentration dependent adverse effects are nausea, vomiting, tremor, confusion, headache and dizziness, nystagmus and ataxia. 

PHENYTOIN DRUG DEPENDENCE THERAPIES - DISULFIRAM t phenytoin levels Inhibited metabolism Monitor phenytoin levels closely... 

TELITHROMYCIN PHENYTOIN 1 levels of these drugs, with risk of therapeutic failure Induction of hepatic metabolism 1. Avoid co-administration of telithromycin for up to 2 weeks after stopping phenytoin 2. With the other drugs, monitor for l clinical efficacy and t dose as required... 

Lau AH, Kronfol NO. Effect of continuous hemofiltration on phenytoin elimination. Ther Drug Monitor 1994 16 53-7. 

S226 Brettfeld, C., Gobrogge, R., Massoud, N., Munzenberger, P., Nigro, M. and Sarnaik, A. (1989). Evaluation of Ames Seralyzer for the therapeutic drug monitoring of phenobarbital and phenytoin. Ther. Drug Monit. 11, 612-615. 

Wing, D.S. Duff, H.J. The impact of a therapeutic drug monitoring program for phenytoin. Ther. Drug Monit. 1989, 11 (1), 32-37. 

Tests for fosphenytoin serum concentration are not available commercially and are of no clinical value. Serum phenytoin concentrations are the end point for therapeutic drug monitoring, and the desired serum concentration range is the same as that when phenytoin is administered (10 to 20 mg/L). Because fosphenytoin cross-reacts with several immunoassays for phenytoin to cause a 1.2- to 6-fold overestimation of phenytoin concentration, blood should not be obtained for at least 2 hours after intravenous and 4 hours after intramuscular administration. In order to minimize in vitro conversion to phenytoin, blood should be collected in tubes containing EDTA, and samples should be refrigerated as soon as possible. ... 

Anticonvulsants Phenytoin, lamotrigine Therapeutic drug monitoring recommended may require anticonvulsant dose increase. 

Gatti, G., Crema, F., Attardo-Parrinello, G., Fratino, P, Aguzzi, F., and Perucca, E., Serum protein binding of phenytoin and valproic acid in insulin-dependent diabetes mellitus, Then Drug Monitor., 9, 389, 1987. 

Levine, M. and Chang, T., Therapeutic drug monitoring of phenytoin. Rationale and current status, Clin. Pharmacokinet., 19 341-358, 1990. 

Callaghan N, Duggan B, O Hare J, O DriscoU D. Serum levels of phenobarbitone and phe-nylethylmalonamide with primidone used as a single d and in combination with carbamazepine or phenytoin. In Johannessen SI et al. Antiepileptic Therapy Advances in Drug Monitoring. New York Raven Press 1980, 307-13. 

Burger DM, Meenhorst PL, Mulder JW, Kraaijeveld CL, Koks CHW, Bult A, Beijnen JH. Therapeutic drug monitoring of phenytoin in patients with the acquired immunodeficiency syndrome. TherDnigMonit 99A) 16, 616-20. 

Therapeutic drug monitoring Anticonvulsants Carbamazepine Phenytoin Ethosuximide Primidone Phenobarbitone Valproic acid... 

HYDANTOINS Fhenytoin is the most commonly prescribed anticonvulsant because of its effectiveness and relatively low toxicity. However, a genetically linked inability to metabolize phenytoin has been identified. For this reason, it is important to monitor serum concentrations of the drug on a regular basis to detect signs of toxicity Fhenytoin is administered orally and parenterally. If the drug is administered parenterally, the IV route is preferred over the intramuscular route because erratic absorption of phenytoin causes pain and muscle damage at the injection site... 

The effects of buspirone are decreased when the drug is administered with fluoxetine Increased serum levels of buspirone occur if the drug is taken with erythromycin or itraconazole Should any of these combinations be required, the dosage of buspirone is decreased to 2.5 mg BID, and the patient is monitored closely. Venlafaxine blood levels increase with a risk of toxicity when administered witii MAOIs or cimetidine There is an increased risk of toxicity when trazodone is administered with the phenothiazines and decreased effectiveness of trazodone when it is administered with carbamazepine Increased serum digoxin levels have occurred when digoxin is administered with trazodone There is a risk for increased phenytoin levels when phenytoin is administered witii trazodone... 

While generally not of major concern, omeprazole may inhibit the metabolism of warfarin, diazepam, and phenytoin lansoprazole may decrease theophylline concentrations. Drug interactions with omeprazole are of particular concern in patients who are considered slow metabolizers, as are approximately 3% of the Caucasian population. Unfortunately, it is unclear which patients have the polymorphic gene variation that makes them slow metabolizers.17 The metabolism of esomeprazole may also be altered in patients with this polymorphic gene variation. Patients on potentially interacting drugs should be monitored for development of drug-related problems. 

Isoniazid Carbamazepine, phenytoin Decreased metabolism of other agents (nausea, vomiting, nystagmus, ataxia) Monitor drug SDC... 

Ideally, unbound (versus total) drug concentrations should be monitored, especially for drugs that have a narrow therapeutic range, are highly protein bound (free fraction less than 20%), and have marked variability in the free fraction (e.g., phenytoin, disopyramide). 

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