Phenytoin Sodium

RECENT MAJOR CHANGES Warnings and Precautions (5.3) 2/2021

1 INDICATIONS AND USAGE Extended phenytoin sodium capsules, USP are indicated for the treatment of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. Extended phenytoin sodium capsules are indicated for the treatment of tonic-clonic (grand mal) and psychomotor (temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery. ( 1 )

2 DOSAGE AND ADMINISTRATION Adult starting dose in patients who have received no previous treatment is one 100 mg extended phenytoin sodium capsule three times a day, with dose adjustments as necessary. For most adults, the satisfactory maintenance dose will be one capsule three to four times a day. An increase, up to two capsules three times a day may be made, if necessary. ( 2.1 ) Adult once-a-day dose: If seizure control is established with divided doses of three 100 mg extended phenytoin sodium capsules daily, once-a-day dosage with 300 mg extended phenytoin sodium capsules may be considered. ( 2.1 ) Adult loading dose: reserved for patients in a clinic or hospital setting who require rapid steady-state serum levels and where intravenous administration is not desired. Refer to full prescribing information. ( 2.1 ) Pediatric starting dose is 5 mg/kg/day in two to three equally divided doses, with dosage adjustments as necessary, up to a maximum of 300 mg daily. Maintenance dosage is 4 mg/kg/day to 8 mg/kg/day. ( 2.2 ) Serum blood level determinations may be necessary for optimal dosage adjustments—the clinically effective serum total concentration is 10 mcg/mL to 20 mcg/mL (unbound phenytoin concentration is 1 mcg/mL to 2 mcg/mL). ( 2.3 ) 2.1 Adult Dosage Divided daily dosage: The recommended starting dose for adult patients who have received no previous treatment is one 100-mg extended phenytoin sodium capsule, USP by mouth three times daily. Adjust the dosage to suit individual requirements up to a maximum of two capsules three times a day. For most adults, the satisfactory maintenance dosage will be one capsule three to four times a day. Once-a-day dosage: In adults, if seizure control is established with divided doses of three 100-mg extended phenytoin sodium capsules, USP daily, once-a-day dosage with 300 mg of extended phenytoin sodium capsules, USP may be considered. Studies comparing divided doses of 300 mg with a single daily dose of this quantity indicated absorption, peak serum levels, biologic half-life, difference between peak and minimum values, and urinary recovery were equivalent. Once-a-day dosage offers a convenience to the individual patient or to nursing personnel for institutionalized patients and is intended to be used only for patients requiring this amount of drug daily. A major problem in motivating noncompliant patients may also be lessened when the patient can take this drug once a day. However, patients should be cautioned not to miss a dose, inadvertently. Only extended phenytoin sodium capsules, USP are recommended for once-a-day dosing. Inherent differences in dissolution characteristics and resultant absorption rates of phenytoin due to different manufacturing procedures and/or dosage forms preclude such recommendation for other phenytoin products. When a change in the dosage form or brand is prescribed, careful monitoring of phenytoin serum levels should be carried out. Loading dose: Some authorities have advocated use of an oral loading dose of phenytoin in adults who require rapid steady-state serum levels and where intravenous administration is not desirable. This dosing regimen should be reserved for patients in a clinic or hospital setting where phenytoin serum levels can be closely monitored. Patients with a history of renal or liver disease should not receive the oral loading regimen. Initially, one gram of extended phenytoin sodium capsules, USP is divided into three doses (400 mg, 300 mg, 300 mg) and administered at two-hour intervals. Normal maintenance dosage is then instituted 24 hours after the loading dose, with frequent serum level determinations. 2.2 Pediatric Dosage The recommended starting dosage for pediatric patients is 5 mg/kg/day by mouth in two or three equally divided doses, with subsequent dosage individualized to a maximum of 300 mg daily in divided doses. A recommended daily maintenance dosage is usually 4 mg/kg/day to 8 mg/kg/day in equally divided doses. Children …

3 DOSAGE FORMS AND STRENGTHS Extended phenytoin sodium capsules, USP are available as 200 mg or 300 mg of phenytoin sodium, USP The 200 mg capsule has a blue transparent cap and a light blue transparent body. The hard-shell gelatin capsule is filled with white to off-white powder. The capsule is printed axially with 299 in black ink on both the cap and the body. The 300 mg capsule has a light blue transparent cap and a light blue transparent body. The hard-shell gelatin capsule is filled with white to off-white powder. The capsule is printed axially with 432 in black ink on both the cap and the body. Extended phenytoin sodium capsules are available as 200 mg and 300 mg extended phenytoin sodium capsules. (3)

4 CONTRAINDICATIONS Extended phenytoin sodium capsules are contraindicated in patients with: • A history of hypersensitivity to phenytoin, its inactive ingredients, or other hydantoins [see Warnings and Precautions (5.5) ] . Reactions have included angioedema. • A history of prior acute hepatotoxicity attributable to phenytoin [see Warnings and Precautions (5.8) ]. • Coadministration with delavirdine because of the potential for loss of virologic response and possible resistance to delavirdine or to the class of non-nucleoside reverse transcriptase inhibitors. • Hypersensitivity to phenytoin, its ingredients, or other hydantoins ( 4 , 5.5 ) • A history of prior acute hepatotoxicity attributable to phenytoin ( 4 , 5.8 ) • Coadministration with delavirdine ( 4 )

6 ADVERSE REACTIONS The following serious adverse reactions are described elsewhere in the labeling: Withdrawal Precipitated Seizure, Status Epilepticus [see Warnings and Precautions (5.1) ] Suicidal Behavior and Ideation [see Warnings and Precautions (5.2) ] Serious Dermatologic Reactions [see Warnings and Precautions (5.3) ] Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity [see Warnings and Precautions (5.4) ] Hypersensitivity [see Warnings and Precautions (5.5) ] Cardiac Effects [see Warnings and Precautions (5.6) ] Angioedema [see Warnings and Precautions (5.7) ] Hepatic Injury [see Warnings and Precautions (5.8) ] Hematopoietic Complications [see Warnings and Precautions (5.9) ] Effects on Vitamin D and Bone [see Warnings and Precautions (5.10) ] Exacerbation of Porphyria [see Warnings and Precautions (5.12) ] Teratogenicity and Other Harm to the Newborn [see Warnings and Precautions (5.13) ] Hyperglycemia [see Warnings and Precautions (5.14) ] The following adverse reactions associated with the use of extended phenytoin sodium capsules were identified in clinical studies or postmarketing reports. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Body as a Whole: Allergic reactions in the form of rash and rarely more serious forms and DRESS have been observed, as has angioedema [see Warnings and Precautions (5.3 , 5.4 , 5.7) ] . Anaphylaxis has also been reported. There have also been reports of coarsening of facial features, systemic lupus erythematosus, periarteritis nodosa, and immunoglobulin abnormalities. Digestive System: Acute hepatic failure, toxic hepatitis, liver damage, nausea, vomiting, constipation, enlargement of the lips, and gingival hyperplasia. Hematologic and Lymphatic System: Hematopoietic complications, some fatal, have occasionally been reported in association with administration of phenytoin. These have included thrombocytopenia, leukopenia, granulocytopenia, agranulocytosis, and pancytopenia with or without bone marrow suppression. While macrocytosis and megaloblastic anemia have occurred, these conditions usually respond to folic acid therapy. Lymphadenopathy including benign lymph node hyperplasia, pseudolymphoma, lymphoma, and Hodgkin's disease have been reported [see Warnings and Precautions (5.9) ] . Pure red cell aplasia has also been reported. Laboratory Test Abnormality: Phenytoin may decrease serum concentrations of thyroid hormone (T4 and T3), sometimes with an accompanying increase in thyroid-stimulating hormone (TSH), but usually in the absence of clinical hypothyroidism. Phenytoin may also produce lower than normal values for dexamethasone or metyrapone tests. Phenytoin may cause increased serum levels of glucose [see Warnings and Precautions (5.14) ] , alkaline phosphatase, and gamma glutamyl transpeptidase (GGT). Nervous System: The most common adverse reactions encountered with phenytoin therapy are nervous system reactions and are usually dose-related. Reactions include nystagmus, ataxia, slurred speech, decreased coordination, somnolence, and mental confusion. Dizziness, vertigo, insomnia, transient nervousness, motor twitchings, paresthesias, and headaches have also been observed. There have also been rare reports of phenytoin-induced dyskinesias, including chorea, dystonia, tremor and asterixis, similar to those induced by phenothiazine and other neuroleptic drugs. Cerebellar atrophy has been reported, and appears more likely in settings of elevated phenytoin levels and/or long-term phenytoin use [see Warnings and Precautions (5.15) ] . A predominantly sensory peripheral polyneuropathy has been observed in patients receiving long-term phenytoin therapy. Skin and Appendages: Dermatological manifestations sometimes accompanied by fever have included scarlatiniform or morbilliform rashes. A m …

7 DRUG INTERACTIONS Phenytoin is extensively bound to plasma proteins and is prone to competitive displacement. Phenytoin is primarily metabolized by the hepatic cytochrome P450 enzyme CYP2C9 and to a lesser extent by CYP2C19, and is particularly susceptible to inhibitory drug interactions because it is subject to saturable metabolism. Inhibition of metabolism may produce significant increases in circulating phenytoin concentrations and enhance the risk of drug toxicity. Monitoring of phenytoin serum levels is recommended when a drug interaction is suspected. Phenytoin is a potent inducer of hepatic drug-metabolizing enzymes. Multiple drug interactions because of extensive plasma protein binding, saturable metabolism and potent induction of hepatic enzymes. ( 7.1 , 7.2 ) 7.1 Drugs that Affect Phenytoin Concentrations Table 2 includes commonly occurring drug interactions that affect phenytoin concentrations. However, this list is not intended to be inclusive or comprehensive. Individual prescribing information from relevant drugs should be consulted. The addition or withdrawal of these agents in patients on phenytoin therapy may require an adjustment of the phenytoin dose to achieve optimal clinical outcome. Table 2: Drugs That Affect Phenytoin Concentrations a Antacids may affect absorption of phenytoin. b The induction potency of St. John's wort may vary widely based on preparation. c Valproate sodium and valproic acid are similar medications. The term valproate has been used to represent these medications. Interacting Agent Examples Drugs that may increase phenytoin serum levels Antiepileptic drugs Ethosuximide, felbamate, oxcarbazepine, methsuximide, topiramate Azoles Fluconazole, ketoconazole, itraconazole, miconazole, voriconazole Antineoplastic agents Capecitabine, fluorouracil Antidepressants Fluoxetine, fluvoxamine, sertraline Gastric acid reducing agents H2 antagonists (cimetidine), omeprazole Sulfonamides Sulfamethizole, sulfaphenazole, sulfadiazine, sulfamethoxazole- trimethoprim Other Acute alcohol intake, amiodarone, chloramphenicol, chlordiazepoxide, disulfiram, estrogen, fluvastatin, isoniazid, methylphenidate, phenothiazines, salicylates, ticlopidine, tolbutamide, trazodone, warfarin Drugs that may decrease phenytoin serum levels Antacids a Calcium carbonate, aluminum hydroxide, magnesium hydroxide Prevention or Management: Phenytoin and antacids should not be taken at the same time of day Antineoplastic agents usually in combination Bleomycin, carboplatin, cisplatin, doxorubicin, methotrexate Antiviral agents Fosamprenavir, nelfinavir, ritonavir Antiepileptic drugs Carbamazepine, vigabatrin Other Chronic alcohol abuse, diazepam, diazoxide, folic acid, reserpine, rifampin, St. John's wort b , sucralfate, theophylline Drugs that may either increase or decrease phenytoin serum levels Antiepileptic drugs Phenobarbital, valproate sodium c , valproic acid c 7.2 Drugs Affected by Phenytoin Table 3 includes commonly occurring drug interactions affected by phenytoin. However, this list is not intended to be inclusive or comprehensive. Individual drug package inserts should be consulted. The addition or withdrawal of phenytoin during concomitant therapy with these agents may require adjustment of the dose of these agents to achieve optimal clinical outcome. Table 3: Drugs Affected by Phenytoin a The effect of phenytoin on phenobarbital, valproic acid and sodium valproate serum levels is unpredictable Interacting Agent Examples Drugs whose efficacy is impaired by phenytoin Azoles Fluconazole, ketoconazole, itraconazole, posaconazole, voriconazole Antineoplastic agents Irinotecan, paclitaxel, teniposide Delavirdine Phenytoin can substantially reduce the concentrations of delavirdine. This can lead to loss of virologic response and possible resistance [see Contraindications (4)]. Neuromuscular blocking agents Cisatracurium, pancuronium, rocuronium and vecuronium: resistance to the neuromuscular blocking action of the nonde …

8 USE IN SPECIFIC POPULATIONS • Pregnancy: Prenatal exposure to phenytoin may increase the risks for congenital malformations and other adverse developmental outcomes. ( 5.13 , 8.1 ) • Renal and/or Hepatic Impairment or Hypoalbuminemia: Monitor unbound phenytoin concentrations in these patients. ( 8.6 ) 8.1 Pregnancy Pregnancy Exposure Registry There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to antiepileptic drugs (AEDs), such as extended phenytoin sodium capsules, during pregnancy. Physicians are advised to recommend that pregnant patients taking extended phenytoin sodium capsules 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/ Risk Summary In humans, prenatal exposure to phenytoin may increase the risks for congenital malformations and other adverse developmental outcomes. Prenatal phenytoin exposure is associated with an increased incidence of major malformations, including orofacial clefts and cardiac defects. In addition, the fetal hydantoin syndrome, a pattern of abnormalities including dysmorphic skull and facial features, nail and digit hypoplasia, growth abnormalities (including microcephaly), and cognitive deficits has been reported among children born to epileptic women who took phenytoin alone or in combination with other antiepileptic drugs during pregnancy [see Data ] . There have been several reported cases of malignancies, including neuroblastoma, in children whose mothers received phenytoin during pregnancy. Administration of phenytoin to pregnant animals resulted in an increased incidence of fetal malformations and other manifestations of developmental toxicity (including embryofetal death, growth impairment, and behavioral abnormalities) in multiple species at clinically relevant doses [see Data ]. In the U.S. general population, the estimated background risk of major birth defects and of miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively. The background risk of major birth defects and miscarriage for the indicated population is unknown. Clinical Considerations Disease-associated maternal risk An increase in seizure frequency may occur during pregnancy because of altered phenytoin pharmacokinetics. Periodic measurement of serum phenytoin concentrations may be valuable in the management of pregnant women as a guide to appropriate adjustment of dosage [see Dosage and Administration (2.3 , 2.7) ] . However, postpartum restoration of the original dosage will probably be indicated [see Clinical Pharmacology (12.3) ]. Fetal/Neonatal Adverse Reactions A potentially life-threatening bleeding disorder related to decreased levels of vitamin K-dependent clotting factors may occur in newborns exposed to phenytoin in utero . This drug-induced condition can be prevented with vitamin K administration to the mother before delivery and to the neonate after birth. Data Human Data Meta-analyses using data from published observational studies and registries have estimated an approximately 2.4-fold increased risk for any major malformation in children with prenatal phenytoin exposure compared to controls. An increased risk of heart defects, facial clefts, and digital hypoplasia has been reported. The fetal hydantoin syndrome is a pattern of congenital anomalies including craniofacial anomalies, nail and digital hypoplasia, prenatal-onset growth deficiency, and neurodevelopmental deficiencies. Animal Data Administration of phenytoin to pregnant rats, rabbits, and mice during organogenesis resulted in embryofetal death, fetal malformations, and decreased fetal growth. Malformations (including craniofacial, cardiovascular, neural, limb, and digit abnormalities) were observed in rats, rabbits, and mice at doses as low as 100 m …

12.1 Mechanism of Action The precise mechanism by which phenytoin exerts its therapeutic effect has not been established but is thought to involve the voltage-dependent blockade of membrane sodium channels resulting in a reduction in sustained high-frequency neuronal discharges.

11 DESCRIPTION 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 the following structural formula: Each extended phenytoin sodium capsule, USP, for oral administration contains 200 mg or 300 mg of phenytoin sodium, USP. Each capsule also contains the following inactive ingredients: magnesium stearate, lactitol monohydrate, sodium lauryl sulfate, and talc. In addition, each of the empty gelatin capsule contains the following: gelatin, FD&C Blue # 1, FD&C Red # 40, D&C Red # 28 (200 mg) and FD&C Red # 3 (200 mg). The imprinting ink contains shellac, dehydrated alcohol, butyl alcohol, propylene glycol, strong ammonia solution, black iron oxide and potassium hydroxide. Product in vivo 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 200 mg and 300 mg meet USP Dissolution Test 3 . spl-phenytoin-structure

10 OVERDOSAGE The lethal dose in pediatric patients is not known. The lethal dose in adults is estimated to be 2 grams to 5 grams. The initial symptoms are nystagmus, ataxia, and dysarthria. Other signs are tremor, hyperreflexia, lethargy, slurred speech, blurred vision, nausea, and vomiting. The patient may become comatose and hypotensive. Bradycardia and cardiac arrest have been reported [see Warnings and Precautions (5.6) ] . Death is caused by respiratory and circulatory depression. There are marked variations among individuals with respect to phenytoin serum 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 serum 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. Irreversible cerebellar dysfunction and atrophy have been reported. Treatment: Treatment is nonspecific since there is no known antidote. The adequacy of the respiratory and circulatory systems should be carefully observed and appropriate supportive measures employed. Hemodialysis can be considered since phenytoin is not completely bound to plasma proteins. Total exchange transfusion has been used in the treatment of severe intoxication in pediatric patients. In acute overdosage the possibility of other CNS depressants, including alcohol, should be borne in mind.

16 HOW SUPPLIED/STORAGE AND HANDLING 16.1 How Supplied Extended Phenytoin Sodium Capsules, USP are available containing 200 mg or 300 mg of phenytoin sodium, USP. The 200 mg capsule has a blue transparent cap and a light blue transparent body. The hard-shell gelatin capsule is filled with white to off-white powder. The capsule is printed axially with 299 in black ink on both the cap and the body. They are available as follows: Bottle of 30 with child-resistant cap...................NDC 62756-299-83 Bottle of 100 with child-resistant cap.................NDC 62756-299-88 Bottle of 100.........NDC 62756-299-08 Bottle of 500.........NDC 62756-299-13 The 300 mg capsule has a light blue transparent cap and a light blue transparent body. The hard-shell gelatin capsule is filled with white to off-white powder. The capsule is printed axially with 432 in black ink on both the cap and the body. They are available as follows: Bottle of 30 with child-resistant cap...................NDC 62756-432-83 Bottle of 100 with child-resistant cap.................NDC 62756-432-88 Bottle of 100.........NDC 62756-432-08 Bottle of 500.........NDC 62756-432-13 16.2 Storage and Handling Store at 25°C (77°F); excursions permitted to 15° to 30°C (59° to 86°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.