Manufacturer advises monitor concentration and adjust dose. The period effect between each crossover was determined to assess the effect of the previous exposure to phenytoin on the area under the concentrationtime curve auc. Therapeutic drug monitoring of phenytoin is carried out to ensure effective and. Drug monitoring in patients with epilepsy should not be routinely performed unless. Oct 28, 2019 phenytoin frequently produces gingival hyperplasia, especially in children, which occasionally is so severe that it may require surgical removal.
Monitoring of phenytoin concentration among patients with chronic use will be helpful in. Phenytoin extended capsules and parenteral phenytoin are formulated with the sodium salt of phenytoin. Phenytoin is eliminated via hepatic metabolism and should be used with caution in any patient with hepatic dysfunction. Pharmacokinetic monitoring of antiepileptic drugs grupo aula. Patients receiving phenytoin infusions require close haemodynamic monitoring. Besides, when the patient receive another drug such as valproic acid which can compete whith phenytoin for proteing binding.
An audit of therapeutic drug monitoring tdm of anticonvulsants was performed to assess both its use and misuse in the management of patients with epilepsy. Phenytoin base eg, oral suspension, chewable tablets contains 8% more drug than phenytoin sodium 92 mg base is equivalent to 100 mg phenytoin sodium. Bioavailability is dependent upon particle size and problems of generic inequivalence have therefore arisen, particularly in scandinavia. An audit of therapeutic drug monitoring of anticonvulsants. Some of the factors complicating phenytoin dosing include a narrow therapeutic window, high degree of. Phenytoin is primarily metabolized by cyp 2c9 and 2c19, and carbamazepine induces all cyp 2c hepatic isoenzymes. A guide to therapeutic drug monitoring melissa faye. Clinically important displacement can be caused by bilirubin and. Phenytoin and marijuana drug interactions a study of fda. Clinical decision support of therapeutic drug monitoring. Phenytoin sodium is related to the barbiturates in chemical structure, but has a fivemembered ring. Therapeutic drug monitoring of phenytoin is carried out to ensure effective and safe levels.
When a change in the dosage form or brand is prescribed, careful monitoring of phenytoin serum levels should be carried out. Naranjo and who causality assessment was done, indicating a probable relationship between the patients symptoms and her use of phenytoin. Evidencebased implementation of free phenytoin therapeutic. A case report vineetha bharathan menon1, justin kurian1, krishna undela1. Mar 05, 2011 current issues of therapeutic drug monitoring tdm in children in hong kong dr albert chan, md consultant chemical pathologist, pmh director, ha toxicology reference lab. Phenytoin induced toxicity leads to ataxia, nystagmus, gingival hypertrophy, nodular skin lesions and hirsutism. Pd analysis was performed by evaluating the clinical response to phenytoin therapy, adverse drug reaction monitoring, and causality categorization using the. It is a medicine that has been approved by the food and drug administration to treat tonic clonic grand mal and complex partial seizures. Phenytoin is poorly soluble in water and is therefore commonly given as phenytoin sodium salt, which dissolves more readily. This table is an expanded version of that publication and newly revised for 20182019 by steven w. Updated with approvals from wirral drug and therapeutics committee.
Mar 28, 2019 this drug may be administered by iv or im injection. Please see full prescribing information and medication guide. Phenytoin levels may take up to an hour to be reported and treatment in status. This drug may be administered by iv or im injection. Dailymed phenytoin sodium capsule, extended release. Our results indicated that total phenytoin serum concentration is not a reliable therapeutic goal for drug monitoring in severelyill head trauma patients even in. Translating phenytoin therapeutic drug monitoring for potential. Therapeutic drug monitoring of phenytoin in critically ill. Phenytoin suspchewable tab therapeutic drug monitoring phenytoin displays nonlinear saturation kinetics, hence a small increase in dose may result in a much larger increase in serum level hypoalbuminaemia will increase the amount of free phenytoin. Phenytoin is a relatively insoluble weak acid, usually administered as the sodium salt. Clinical guideline for the use of phenytoin in epilepsy final. May 16, 2019 phenytoin extended capsules and parenteral phenytoin are formulated with the sodium salt of phenytoin.
Therapeutic drug monitoring phenytoin has a narrow therapeutic index and has nonlinear kinetics. Dailymed extended phenytoin sodium phenytoin sodium capsule. Monitoring of phenytoin concentration among patients with chronic use will be helpful in prevention, early identification and resolution of. Feb 14, 2012 therapeutic drug monitoring of phenytoin by measurement of plasma concentrations is often employed to optimize clinical efficacy while avoiding adverse effects. Drug interactions with phenytoin nervous system home page.
Baer, md, and first published in the april 1982 issue of mlo. Phenytoin while effort has been made to contact all owners this has not always been possible. Dilantin is a prescription medicine used to treat certain types of seizures called tonicclonic grand mal and psychomotor temporal lobe seizures and to prevent and treat seizures that happen during or after brain surgery. Therapeutic drug monitoring of phenytoin by measurement of plasma. Inhibition of metabolism may produce significant increases in circulating phenytoin concentrations and enhance the risk of drug toxicity. Dec, 2012 phenytoin is a relatively insoluble weak acid, usually administered as the sodium salt. Phenytoin is a potent inducer of hepatic drugmetabolizing enzymes. Clinical pharmacokinetics of phenytoin springerlink. Evidencebased implementation of free phenytoin therapeutic drug monitoring. Dilantin phenytoin sodium food and drug administration. Some of the factors complicating phenytoin dosing include a narrow therapeutic window, high degree of protein binding, and nonlinear pharmacokinetics.
All phenytoin infusions are to be initiated using hospital medication and infusion filter supplies. A comparison of phenytoinloading techniques in the. The rights of drug administration must be followed. Phenytoin will not be carried by the qas flight team. These interactions may potentially affect the level of phenytoin in your blood, raise your risk of side effects, or decrease the effectiveness of some medicines. Csf mtx concentrations were significantly lower in samples from patients younger than 7 years. This is most commonly accomplished by measurement of total phenytoin plasma concentrations. The concept of critical values for drug levels was originally developed by the late daniel m.
Oct 18, 2012 drug interactions with phenytoin are a frequent occurrence, although their clinical relevance has often been overemphasised. Over a four week period all samples received for phenytoin, carbamazepine, sodium valproate and phenobarbitone assays were included in the audit. Guideline for use of injectable phenytoin in adults. Find patient medical information for phenytoin oral on webmd including its uses, side effects and safety, interactions, pictures, warnings and user ratings. Probably the most important of such interactions are those resulting in inhibition of phenytoin metabolism. The basic assumptions underlying therapeutic drug monitoring are that drug metabolism varies from patient to patient and that the plasma level of a drug is more closely related to the drug s therapeutic effect or toxicity than is the dosage.
All phenytoin results are reported in the following panel, with an adjusted phenytoin value. Indications for therapeutic drug monitoring of methotrexate administration of methotrexate in high doses with calcium folinate coexistence of kidneys and liver failure, the presence of exudation in body cavities concomitant administration of other drugs increasing the toxicity of methotrexate salicylates. Prescribing issues associated with anticonvulsant medications. Guide for drug level monitoring of commonly used medications.
Phenytoin is predicted to decrease the exposure to modafinil and modafinil is predicted to increase the concentration of phenytoin. The correct therapeutic dose of phenytoin should be determined by seizure control and clinical toxicity, not by serum drug levels. Therapeutic drug monitoring of phenytoin is necessary to ensure therapeutic and nontoxic levels. Routine therapeutic drug monitoring of anticonvulsants has limited clinical usefulness except phenytoin therapeutic drug monitoring tdm has traditionally been used to guide treatment decisions for patients with epilepsy. A comparison of phenytoinloading techniques in the emergency. Phenytoin is a drug prescribed to treat or prevent the recurrence of certain types of seizures see epilepsy, including complex partial seizures impaired consciousness that is preceded, accompanied, or followed by psychological symptoms or generalized tonicclonic seizures involve abrupt loss of consciousness, respiratory arrest, muscle. Therapeutic, drug monitoring, carbamazepine, valproic acid, phenytoin, digoxin. The compounds listed in table 4 do not interfere with the emit 2000 phenytoin assay when. This table highlights the key areas of concern only. Monitoring of free phenytoin concentrations may be beneficial in patients with aids, hypoalbuminemia and renal impairment.
However, serum drug levels should only be taken when there is a clear indication to. Dilantin infatabs phenytoin dose, indications, adverse. Involved in multiple drug interactions because of extensive plasma protein binding, saturable metabolism, and potent hepatic enzymeinducing properties. A small percentage of individuals metabolize phenytoin slowly. The drug has a moderately large volume of distribution and is approximately 90% bound to plasma proteins. Phenytoin interactions bnf content published by nice. Parenteral medication prescriptions and the drug are to be checked with a second registered or endorsed enrolled nurse prior to administration. Phenytoin is an antiepileptic drug which can be used in the treatment of epilepsy.
Serum mtx concentrations at the end of infusion were assessed by routine therapeutic drug monitoring. The laboratory should actively be involved in the therapeutic drug. Nhs tayside phenytoin prescribing and monitoring guideline. The point estimate ratio of aucot for the third dose relative to the first dose was 81. Total phenytoin concentration is not well correlated with active free. Patients treated with any aed for any indication should be monitored for the. Current issues of therapeutic drug monitoring tdm in children in hong kong dr albert chan, md consultant chemical pathologist, pmh director, ha toxicology reference lab. The qas would welcome notification from any holder who has been omitted or incorrectly acknowledged. Monitoring of phenytoin serum levels is recommended when a drug interaction is suspected. Check albumin level concurrently with phenytoin level albuminadjusted phenytoin level may be higher than reported i. Drugs with a narrow therapeutic index where therapeutic drug levels do not differ greatly from levels. Certain medications including paroxetine, cimetidine, and carbamazepine may potentially cause drug interactions with phenytoin.
Drug interactions are reported only by a few people who take phenytoin and marijuana together. The effect of adding carbamazepine to chronic phenytoin will result in a reduction of phenytoin level, due to an increase efficiency of 2c9 and 2c19 metabolism. Supratherapeutic levels are required to control seizures in some cases. Type of epilepsy adverse effects interactions monitoring notes sodium valproate. This medicine is available in different forms, including dilantin, phenytek, or generic phenytoin. Clinically important displacement can be caused by. Current issues of therapeutic drug monitoring tdm in. Antiepileptic drugs aeds decrease seizure frequency and severity in. See what the interactions are, when they happen and for which people. Phenytoin may be given intravenously to patients who cannot receive the drug orally or who require rapid onset of drug effect. Look up information on diseases, tests, and procedures. Clinical decision support of therapeutic drug monitoring of phenytoin.
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. A serum phenytoin level is recommended several days after starting drug therapy, and again after 2 to 3 weeks to evaluate for delayed toxicity. A small change in dosing can result in a large change in blood levels. Section 6 therapeutic drug monitoring kieran hand consultant pharmacist antiinfectives the objectives of this section are. Guidelines for therapeutic drug monitoring q pulse reference no. Dailymed extended phenytoin sodium phenytoin sodium.
Phenytoin is a potent inducer of hepatic drug metabolizing enzymes. Clinical decision support of therapeutic drug monitoring of. Clinical guideline for the use of phenytoin in epilepsy page 4 of 12 3. Therapeutic drug monitoring of phenytoin by measurement of plasma concentrations is often employed to optimize clinical efficacy while avoiding adverse effects. In these patients, the monitoring of serum phenytoin concentrations should be based on the unbound fraction of the drug. Pharmacokinetic characteristics of antiepileptic drugs aeds. Compounds whose chemical structure or concurrent therapeutic use would suggest possible crossreactivity have been tested. Due to its large surface area, the small intestine is the main site of phenytoin absorption. However, this medicine can make absence or petit mal seizures happen more frequently. Phenytoin dilantin, dilantin125 is an oral and injectable drug prescribed for the treatment of seizures. Drug interactions with phenytoin are a frequent occurrence, although their clinical relevance has often been overemphasised. The chemical name is sodium 5,5diphenyl2, 4imidazolidinedione, having the following structural formula. The emit 2000 phenytoin assay measures the total proteinbound plus unbound phenytoin concentration in serum or plasma. Nov 20 page 1 of 10 medicines formulary therapeutic drug monitoring contents.
Phenytoin causes dose related side effects at normal doses on chronic use. To test your ability to monitor serum levels for drugs with a narrow therapeutic. This can result in difficulties in dose adjustment and interpretation of levels. Apr 22, 2019 inhibition of metabolism may produce significant increases in circulating phenytoin concentrations and enhance the risk of drug toxicity. Prescribing issues associated with common anticonvulsant medications1, 6, 7, 8 multiple drug interactions and adverse effects may occur with all anticonvulsants.
The study is created by ehealthme based on reports of 5 people who take the same drugs from food and drug administration fda, and is updated regularly. The related drug information index provides comprehensive access to all drug information related to a specific drug types of content include full prescribing information, drug summaries, full prescribing information continuing medication education full pi cme, medication guides, risk evaluation and mitigation strategies rems summaries, rems continuing medication education rems cme, and. Ecg, heart rate, blood pressure and respiratory function. Clinical guideline for the use of phenytoin in epilepsy. Each dilantin 100 mg extended oral capsulecontains 100 mg phenytoin sodium. Hypoalbuminemia, renal failure, and interactions with other highly proteinbound drugs e. However, total phenytoin levels can be misleading in patients with factors such as low plasma albumin that alter the free unbound.