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Phenytoin Sodium
Overview
What is Phenytoin Sodium?
Phenytoin sodium is an antiepileptic drug. Phenytoin sodium is related to the barbiturates in chemical structure, but has a five-membered ring. The chemical name is 5,5-Diphenylhydantoin sodium salt, having a molecular weight of 274.25 and having the following structural formula and molecular formula:
Each extended phenytoin sodium capsule, USP, for oral administration, contains 100 mg phenytoin sodium, USP. Each capsule also contains the following inactive ingredients: colloidal silicon dioxide, hydroxyethyl cellulose, magnesium oxide, magnesium stearate, microcrystalline cellulose, povidone and sodium lauryl sulfate. In addition, each of the empty gelatin capsules contains the following: D&C Red No. 28, D&C Red No. 33, FD&C Blue No. 1, gelatin, sodium lauryl sulfate and titanium dioxide.
The imprinting ink contains the following: black iron oxide, D&C Yellow No. 10 Aluminum Lake, FD&C Blue No. 1 Aluminum Lake, FD&C Blue No. 2 Aluminum Lake, FD&C Red No. 40 Aluminum Lake, propylene glycol and shellac glaze.
Product performance is characterized by a slow and extended rate of absorption with peak blood concentrations expected in 4 to 12 hours as contrasted to prompt phenytoin sodium capsules, USP with a rapid rate of absorption with peak blood concentration expected in 11⁄2 to 3 hours.
Extended phenytoin sodium capsules, USP 100 mg meet
What does Phenytoin Sodium look like?
What are the available doses of Phenytoin Sodium?
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What should I talk to my health care provider before I take Phenytoin Sodium?
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How should I use Phenytoin Sodium?
Extended phenytoin sodium capsules are indicated for the control of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery.
Phenytoin serum level determinations may be necessary for optimal dosage adjustments (see and ).
Serum concentrations should be monitored in changing from extended phenytoin sodium capsules, USP, to prompt phenytoin sodium capsules, USP, and from the sodium salt to the free acid form.
Extended phenytoin sodium capsules are formulated with the sodium salt 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 product formulated with the sodium salt and vice versa.
What interacts with Phenytoin Sodium?
Extended phenytoin sodium capsules are contraindicated in those patients who are hypersensitive to phenytoin or other hydantoins.
What are the warnings of Phenytoin Sodium?
Acetaminophen and codeine phosphate tablets contain sodium metabisulfite, a sulfite that may cause allergic-type reactions including anaphylactic symptoms and life-threatening or less severe asthmatic episodes in certain susceptible people. The overall prevalence of sulfite sensitivity in the general population is unknown and probably low. Sulfite sensitivity is seen more frequently in asthmatic than in nonasthmatic people.
Suicidal Behavior and Ideation
Antiepileptic drugs (AEDs), including phenytoin sodium, may increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Patients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.
Pooled analyses of 199 placebo-controlled clinical trials (mono- and adjunctive therapy) of 11 different AEDs showed that patients randomized to one of the AEDs had approximately twice the risk (adjusted Relative Risk 1.8, 95% CI:1.2, 2.7) of suicidal thinking or behavior compared to patients randomized to placebo. In these trials, which had a median treatment duration of 12 weeks, the estimated incidence rate of suicidal behavior or ideation among 27,863 AED-treated patients was 0.43%, compared to 0.24% among 16,029 placebo-treated patients, representing an increase of approximately one case of suicidal thinking or behavior for every 530 patients treated. There were four suicides in drug-treated patients in the trials and none in placebo-treated patients, but the number is too small to allow any conclusion about drug effect on suicide.
The increased risk of suicidal thoughts or behavior with AEDs was observed as early as one week after starting drug treatment with AEDs and persisted for the duration of treatment assessed. Because most trials included in the analysis did not extend beyond 24 weeks, the risk of suicidal thoughts or behavior beyond 24 weeks could not be assessed.
The risk of suicidal thoughts or behavior was generally consistent among drugs in the data analyzed. The finding of increased risk with AEDs of varying mechanisms of action and across a range of indications suggests that the risk applies to all AEDs used for any indication. The risk did not vary substantially by age (5 to 100 years) in the clinical trials analyzed.
Table 1 shows absolute and relative risk by indication for all evaluated AEDs.
The relative risk for suicidal thoughts or behavior was higher in clinical trials for epilepsy than in clinical trials for psychiatric or other conditions, but the absolute risk differences were similar for the epilepsy and psychiatric indications.
Anyone considering prescribing phenytoin sodium or any other AED must balance this risk with the risk of untreated illness. Epilepsy and many other illnesses for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior. Should suicidal thoughts and behavior emerge during treatment, the prescriber needs to consider whether the emergence of these symptoms in any given patient may be related to the illness being treated.
Patients, their caregivers, and families should be informed that AEDs increase the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of the signs and symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm. Behaviors of concern should be reported immediately to healthcare providers.
There have been a number of reports suggesting a relationship between phenytoin and the development of lymphadenopathy (local or generalized) including benign lymph node hyperplasia, pseudolymphoma, lymphoma, and Hodgkin’s Disease. Although a cause and effect relationship has not been established, the occurrence of lymphadenopathy indicates the need to differentiate such a condition from other types of lymph node pathology. Lymph node involvement may occur with or without symptoms and signs resembling serum sickness, e.g., fever, rash, and liver involvement.
In all cases of lymphadenopathy, follow-up observation for an extended period is indicated and every effort should be made to achieve seizure control using alternative antiepileptic drugs.
Acute alcoholic intake may increase phenytoin serum levels while chronic alcohol use may decrease serum levels.
In view of isolated reports associating phenytoin with exacerbation of porphyria, caution should be exercised in using this medication in patients suffering from this disease.
| Indication | Placebo Patientswith Eventsper 1,000 Patients | Drug Patientswith Eventsper 1,000 Patients | Relative Risk:Incidence of Eventsin DrugPatients/Incidence inPlacebo Patients | Risk Difference:Additional DrugPatients withEvents per 1,000Patients |
| Epilepsy | 1 | 3.4 | 3.5 | 2.4 |
| Psychiatric | 5.7 | 8.5 | 1.5 | 2.9 |
| Other | 1 | 1.8 | 1.9 | 0.9 |
| Total | 2.4 | 4.3 | 1.8 | 1.9 |
Usage in Pregnancy
Clinical
A. Risks to Mother
An increase in seizure frequency may occur during pregnancy because of altered phenytoin pharmacokinetics. Periodic measurement of plasma phenytoin concentrations may be valuable in the management of pregnant women as a guide to appropriate adjustment of dosage (see ). However, postpartum restoration of the original dosage will probably be indicated.
B. Risks to the Fetus
If this drug is used during pregnancy, or if the patient becomes pregnant while taking the drug, the patient should be apprised of the potential harm to the fetus.
Prenatal exposure to phenytoin may increase the risks for congenital malformations and other adverse developmental outcomes. Increased frequencies of major malformations (such as orofacial clefts and cardiac defects), minor anomalies (dysmorphic facial features, nail and digit hypoplasia), growth abnormalities (including microcephaly), and mental deficiency have been reported among children born to epileptic women who took phenytoin alone or in combination with other antiepileptic drugs during pregnancy. There have also been several reported cases of malignancies, including neuroblastoma, in children whose mothers received phenytoin during pregnancy. The overall incidence of malformations for children of epileptic women treated with antiepileptic drugs (phenytoin and/or others) during pregnancy is about 10%, or 2-to 3-fold that in the general population. However, the relative contributions of antiepileptic drugs and other factors associated with epilepsy to this increased risk are uncertain and in most cases it has not been possible to attribute specific developmental abnormalities to particular antiepileptic drugs.
Patients should consult with their physicians to weigh the risks and benefits of phenytoin during pregnancy.
C. Postpartum Period
A potentially life threatening bleeding disorder related to decreased levels of vitamin K-dependent clotting factors may occur in newborns exposed to phenytoin . This drug-induced condition can be prevented with vitamin K administration to the mother before delivery and to the neonate after birth.
Preclinical
Increased resorption and malformation rates have been reported following administration of phenytoin doses of 75 mg/kg or higher (approximately 120% of the maximum human loading dose or higher on a mg/m basis) to pregnant rabbits.
What are the precautions of Phenytoin Sodium?
General
The liver is the chief site of biotransformation of phenytoin; patients with impaired liver function, elderly patients, or those who are gravely ill may show early signs of toxicity.
A small percentage of individuals who have been treated with phenytoin have been shown to metabolize the drug slowly. Slow metabolism may be due to limited enzyme availability and lack of induction; it appears to be genetically determined.
Phenytoin should be discontinued if a skin rash appears (see section regarding drug discontinuation). If the rash is exfoliative, purpuric, or bullous, or if lupus erythematosus, Stevens-Johnson Syndrome, or toxic epidermal necrolysis is suspected, use of this drug should not be resumed and alternative therapy should be considered. (See .) If the rash is of a milder type (measles-like or scarlatiniform), therapy may be resumed after the rash has completely disappeared. If the rash recurs upon reinstitution of therapy, further phenytoin medication is contraindicated.
Phenytoin and other hydantoins are contraindicated in patients who have experienced phenytoin hypersensitivity (see ). Additionally, caution should be exercised if using structurally similar compounds (e.g., barbiturates, succinamides, oxazolidinediones and other related compounds) in these same patients.
Hyperglycemia, resulting from the drug's inhibitory effects on insulin release, has been reported. Phenytoin may also raise the serum glucose level in diabetic patients.
Osteomalacia has been associated with phenytoin therapy and is considered to be due to phenytoin's interference with Vitamin D metabolism.
Phenytoin is not indicated for seizures due to hypoglycemic or other metabolic causes. Appropriate diagnostic procedures should be performed as indicated.
Phenytoin is not effective for absence (petit mal) seizures. If tonic-clonic (grand mal) and absence (petit mal) seizures are present, combined drug therapy is needed.
Serum levels of phenytoin sustained above the optimal range may produce confusional states referred to as "delirium," "psychosis," or "encephalopathy," or rarely irreversible cerebellar dysfunction. Accordingly, at the first sign of acute toxicity, plasma levels are recommended. Dose reduction of phenytoin therapy is indicated if plasma levels are excessive; if symptoms persist, termination is recommended. (See .)
Information for Patients
Patients taking phenytoin should be advised of the importance of adhering strictly to the prescribed dosage regimen, and of informing the physician of any clinical condition in which it is not possible to take the drug orally as prescribed, e.g., surgery, etc.
Patients should also be cautioned on the use of other drugs or alcoholic beverages without first seeking the physician's advice.
Patients should be instructed to call their physician if skin rash develops.
The importance of good dental hygiene should be stressed in order to minimize the development of gingival hyperplasia and its complications.
Patients should be informed of the availability of a Medication Guide, and they should be instructed to read the Medication Guide prior to taking phenytoin sodium. Patients should be instructed to take phenytoin sodium only as prescribed.
Suicidal Thinking and Behavior
Patients, their caregivers, and families should be counseled that AEDs, including phenytoin sodium, may increase the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm. Behaviors of concern should be reported immediately to healthcare providers.
Patients should be encouraged to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry if they become pregnant. This Registry is collecting information about the safety of antiepileptic drugs during pregnancy. To enroll, patients can call the toll free number 1-888-233-2334 (see ).
Laboratory Tests
Phenytoin serum level determinations may be necessary to achieve optimal dosage adjustments.
Drug Interactions
There are many drugs which may increase or decrease phenytoin levels or which phenytoin may affect. Serum level determinations for phenytoin are especially helpful when possible drug interactions are suspected. The most commonly occurring drug interactions are listed below.
Drug Enteral Feeding/Nutritional Preparations Interaction
Literature reports suggest that patients who have received enteral feeding preparations and/or related nutritional supplements have lower than expected phenytoin plasma levels. It is therefore suggested that phenytoin not be administered concomitantly with an enteral feeding preparation. More frequent serum phenytoin level monitoring may be necessary in these patients.
Drug/Laboratory Test Interactions
Phenytoin may decrease serum concentrations of T. It may also produce lower than normal values for dexamethasone or metyrapone tests. Phenytoin may cause increased serum levels of glucose, alkaline phosphatase, and gamma glutamyl transpeptidase (GGT).
Care should be taken when using immunoanalytical methods to measure plasma phenytoin concentrations.
Carcinogenesis
See section for information on carcinogenesis.
Pregnancy
Pregnancy Category D
See .
To provide information regarding the effects of exposure to phenytoin sodium, physicians are advised to recommend that pregnant patients taking phenytoin sodium enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry. This can be done by calling the toll free number 1-888-233-2334, and must be done by patients themselves. Information on the registry can also be found at the website http://www.aedpregnancyregistry.org/.
Nursing Mothers
Infant breast-feeding is not recommended for women taking this drug because phenytoin appears to be secreted in low concentrations in human milk.
Pediatric Use
See .
What are the side effects of Phenytoin Sodium?
Central Nervous System:
A predominantly sensory peripheral polyneuropathy has been observed in patients receiving long-term phenytoin therapy.
Gastrointestinal System:
Integumentary System:
Hemopoietic System:
Connective Tissue System:
Immunologic:
What should I look out for while using Phenytoin Sodium?
Extended phenytoin sodium capsules are contraindicated in those patients who are hypersensitive to phenytoin or other hydantoins.
Abrupt withdrawal of phenytoin in epileptic patients may precipitate status epilepticus. When, in the judgment of the clinician, the need for dosage reduction, discontinuation, or substitution of alternative antiepileptic medication arises, this should be done gradually. However, in the event of an allergic or hypersensitivity reaction, rapid substitution of alternative therapy may be necessary. In this case, alternative therapy should be an antiepileptic drug not belonging to the hydantoin chemical class.
What might happen if I take too much Phenytoin Sodium?
The lethal dose in pediatric patients is not known. The lethal dose in adults is estimated to be 2 to 5 grams. The initial symptoms are nystagmus, ataxia, and dysarthria. Other signs are tremor, hyperreflexia, lethargy, slurred speech, nausea, vomiting. The patient may become comatose and hypotensive. Death is due to respiratory and circulatory depression.
There are marked variations among individuals with respect to phenytoin plasma levels where toxicity may occur. Nystagmus, on lateral gaze, usually appears at 20 mcg/mL, ataxia at 30 mcg/mL, dysarthria and lethargy appear when the plasma concentration is over 40 mcg/mL, but as high a concentration as 50 mcg/mL has been reported without evidence of toxicity. As much as 25 times the therapeutic dose has been taken to result in a serum concentration over 100 mcg/mL with complete recovery.
How should I store and handle Phenytoin Sodium?
ZERIT Capsules should be stored in tightly closed containers at 25° C (77° F). Excursions between 15° C and 30° C (59° F and 86° F) are permitted (see USP Controlled Room Temperature). ZERIT for Oral Solution should be protected from excessive moisture and stored in tightly closed containers at 25° C (77° F). Excursions between 15° C and 30° C (59° F and 86° F) are permitted (see USP Controlled Room Temperature). After constitution, store tightly closed containers of ZERIT for Oral Solution in a refrigerator, 2° C to 8° C (36° F to 46° F). Discard any unused portion after 30 days. ZERIT Capsules should be stored in tightly closed containers at 25° C (77° F). Excursions between 15° C and 30° C (59° F and 86° F) are permitted (see USP Controlled Room Temperature). ZERIT for Oral Solution should be protected from excessive moisture and stored in tightly closed containers at 25° C (77° F). Excursions between 15° C and 30° C (59° F and 86° F) are permitted (see USP Controlled Room Temperature). After constitution, store tightly closed containers of ZERIT for Oral Solution in a refrigerator, 2° C to 8° C (36° F to 46° F). Discard any unused portion after 30 days. Extended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central PharmacyExtended Phenytoin Sodium Capsules, USP are available containing phenytoin sodium equivalent to 100 mg of phenytoin, USP.The 100 mg capsule is a hard-shell gelatin capsule with a light lavender opaque cap and white opaque body filled with one white to off-white capsule-shaped tablet. The capsule is axially printed with over in black ink on both the cap and body. They are supplied by as follows:Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]Protect from light and moisture.Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.U.S. Patent No. 6,274,168U.S. Patent No. 6,620,432Mylan Pharmaceuticals Inc.Morgantown, WV 26505This Product was Repackaged By:State of Florida DOH Central Pharmacy
Clinical Information
Chemical Structure
No Image foundClinical Pharmacology
Phenytoin is an antiepileptic drug which can be used in the treatment of epilepsy. The primary site of action appears to be the where spread of seizure activity is inhibited. Possibly by promoting sodium efflux from neurons, phenytoin tends to the threshold against hyperexcitability caused by excessive stimulation or environmental changes capable of reducing membrane sodium gradient. This includes the reduction of posttetanic potentiation at synapses. Loss of posttetanic potentiation prevents cortical seizure foci from detonating adjacent cortical areas. Phenytoin reduces the maximal activity of brain stem centers responsible for the tonic phase of tonic-clonic (grand mal) seizures.
The plasma half-life in man after oral administration of phenytoin averages 22 hours, with a range of 7 to 42 hours. Steady-state therapeutic levels are achieved at least 7 to 10 days (5 to 7 half-lives) after initiation of therapy with recommended doses of 300 mg/day.
When serum level determinations are necessary, they should be obtained at least 5 to 7 half-lives after treatment initiation, dosage change, or addition or subtraction of another drug to the regimen so that equilibrium or steady-state will have been achieved. Trough levels provide information about clinically effective serum level range and confirm patient compliance and are obtained just prior to the patient's next scheduled dose. Peak levels indicate an individual's threshold for emergence of dose related side effects and are obtained at the time of expected peak concentration. For extended phenytoin sodium capsules peak serum levels occur 4 to 12 hours after administration.
Optimum control without clinical signs of toxicity occurs more often with serum levels between 10 and 20 mcg/mL, although some mild cases of tonic-clonic (grand mal) epilepsy may be controlled with lower serum levels of phenytoin.
In most patients maintained at a steady dosage, stable phenytoin serum levels are achieved. There may be wide interpatient variability in phenytoin serum levels with equivalent dosages. Patients with unusually low levels may be noncompliant or hypermetabolizers of phenytoin. Unusually high levels result from liver disease, congenital enzyme deficiency, or drug interactions which result in metabolic interference. The patient with large variations in phenytoin plasma levels, despite standard doses, presents a difficult clinical problem. Serum level determinations in such patients may be particularly helpful. As phenytoin is highly protein bound, free phenytoin levels may be altered in patients whose protein binding characteristics differ from normal.
Most of the drug is excreted in the bile as inactive metabolites which are then reabsorbed from the intestinal tract and excreted in the urine. Urinary excretion of phenytoin and its metabolites occurs partly with glomerular filtration but more importantly by tubular secretion. Because phenytoin is hydroxylated in the liver by an enzyme system which is saturable at high plasma levels, small incremental doses may increase the half-life and produce very substantial increases in serum levels, when these are in the upper range. The steady-state level may be disproportionately increased, with resultant intoxication, from an increase in dosage of 10% or more.
Non-Clinical Toxicology
Extended phenytoin sodium capsules are contraindicated in those patients who are hypersensitive to phenytoin or other hydantoins.Abrupt withdrawal of phenytoin in epileptic patients may precipitate status epilepticus. When, in the judgment of the clinician, the need for dosage reduction, discontinuation, or substitution of alternative antiepileptic medication arises, this should be done gradually. However, in the event of an allergic or hypersensitivity reaction, rapid substitution of alternative therapy may be necessary. In this case, alternative therapy should be an antiepileptic drug not belonging to the hydantoin chemical class.
The liver is the chief site of biotransformation of phenytoin; patients with impaired liver function, elderly patients, or those who are gravely ill may show early signs of toxicity.
A small percentage of individuals who have been treated with phenytoin have been shown to metabolize the drug slowly. Slow metabolism may be due to limited enzyme availability and lack of induction; it appears to be genetically determined.
Phenytoin should be discontinued if a skin rash appears (see section regarding drug discontinuation). If the rash is exfoliative, purpuric, or bullous, or if lupus erythematosus, Stevens-Johnson Syndrome, or toxic epidermal necrolysis is suspected, use of this drug should not be resumed and alternative therapy should be considered. (See .) If the rash is of a milder type (measles-like or scarlatiniform), therapy may be resumed after the rash has completely disappeared. If the rash recurs upon reinstitution of therapy, further phenytoin medication is contraindicated.
Phenytoin and other hydantoins are contraindicated in patients who have experienced phenytoin hypersensitivity (see ). Additionally, caution should be exercised if using structurally similar compounds (e.g., barbiturates, succinamides, oxazolidinediones and other related compounds) in these same patients.
Hyperglycemia, resulting from the drug's inhibitory effects on insulin release, has been reported. Phenytoin may also raise the serum glucose level in diabetic patients.
Osteomalacia has been associated with phenytoin therapy and is considered to be due to phenytoin's interference with Vitamin D metabolism.
Phenytoin is not indicated for seizures due to hypoglycemic or other metabolic causes. Appropriate diagnostic procedures should be performed as indicated.
Phenytoin is not effective for absence (petit mal) seizures. If tonic-clonic (grand mal) and absence (petit mal) seizures are present, combined drug therapy is needed.
Serum levels of phenytoin sustained above the optimal range may produce confusional states referred to as "delirium," "psychosis," or "encephalopathy," or rarely irreversible cerebellar dysfunction. Accordingly, at the first sign of acute toxicity, plasma levels are recommended. Dose reduction of phenytoin therapy is indicated if plasma levels are excessive; if symptoms persist, termination is recommended. (See .)
Central Nervous System:
A predominantly sensory peripheral polyneuropathy has been observed in patients receiving long-term phenytoin therapy.
Gastrointestinal System:
Integumentary System:
Hemopoietic System:
Connective Tissue System:
Immunologic:
Reference
This information is obtained from the National Institute of Health's Standard Packaging Label drug database.
"https://dailymed.nlm.nih.gov/dailymed/"
While we update our database periodically, we cannot guarantee it is always updated to the latest version.
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Clonazepam Description Each single-scored tablet, for oral administration, contains 0.5 mg, 1 mg, or 2 mg Clonazepam, USP, a benzodiazepine. Each tablet also contains corn starch, lactose monohydrate, magnesium stearate, microcrystalline cellulose, and povidone. Clonazepam tablets USP 0.5 mg contain Yellow D&C No. 10 Aluminum Lake. Clonazepam tablets USP 1 mg contain Yellow D&C No. 10 Aluminum Lake, as well as FD&C Blue No. 1 Aluminum Lake. Chemically, Clonazepam, USP is 5-(o-chlorophenyl)-1,3-dihydro-7-nitro-2H-1,4-benzodiazepin-2-one. It is a light yellow crystalline powder. It has the following structural formula: C15H10ClN3O3 M.W. 315.72Tips
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Interactions
Interactions
A total of 440 drugs (1549 brand and generic names) are known to interact with Imbruvica (ibrutinib). 228 major drug interactions (854 brand and generic names) 210 moderate drug interactions (691 brand and generic names) 2 minor drug interactions (4 brand and generic names) Show all medications in the database that may interact with Imbruvica (ibrutinib).