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CEREBYX® (fosphenytoin sodium) Adverse Reactions

6 ADVERSE REACTIONS

The following serious adverse reactions are described elsewhere in the labeling:

6.1 Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The more important adverse clinical reactions caused by the IV use of CEREBYX or phenytoin are cardiovascular collapse and/or CNS depression. Hypotension can occur when either drug is administered rapidly by the IV route. The rate of administration is very important; for CEREBYX, it should not exceed 150 mg PE/min [see Warnings and Precautions (5.2)]. The adverse reactions most commonly observed with the use of CEREBYX in clinical trials were nystagmus, dizziness, pruritus, somnolence, and ataxia. With one exception, these reactions are commonly associated with the administration of IV phenytoin. Pruritus, however, was seen much more often following CEREBYX administration and occurred more often with IV CEREBYX administration than with IM CEREBYX administration. These reactions were dose and rate related; most alert patients (41 of 64; 64%) administered doses of ≥15 mg PE/kg at 150 mg PE/min experienced discomfort of some degree. These sensations, generally described as itching, burning, or tingling, were usually not at the infusion site. The location of the discomfort varied with the groin mentioned most frequently as a site of involvement. The paresthesia and pruritus were transient events that occurred within several minutes of the start of infusion and generally resolved within 10 minutes after completion of CEREBYX infusion. Some patients experienced symptoms for hours. These reactions did not increase in severity with repeated administration. Concurrent adverse events or clinical laboratory change suggesting an allergic process were not seen [see Warnings and Precautions (5.10)]. Approximately 2% of the 859 patients who received CEREBYX in premarketing clinical trials discontinued treatment because of an adverse event. The adverse events most commonly associated with withdrawal were pruritus (0.5%), hypotension (0.3%), and bradycardia (0.2%).

Dose and Rate Dependency of Adverse Reactions Following IV CEREBYX: The incidence of adverse reactions tended to increase as both dose and infusion rate increased. In particular, at doses of ≥15mg PE/kg and rates ≥150 mg PE/min, transient pruritus, tinnitus, nystagmus, somnolence, and ataxia occurred 2 to 3 times more often than at lower doses or rates.

Incidence in Controlled Clinical Trials

All adverse events were recorded during the trials by the clinical investigators using terminology of their own choosing. Similar types of events were grouped into standardized categories using modified COSTART dictionary terminology. These categories are used in the tables and listings below with the frequencies representing the proportion of individuals exposed to CEREBYX or comparative therapy.

Incidence in Controlled Clinical Trials - IV Administration to Adult Patients with Epilepsy or Neurosurgical Patients: Table 4 lists adverse reactions that occurred in at least 2% of patients treated with IV CEREBYX at the maximum dose and rate in a randomized, double-blind, controlled clinical trial where the rates for phenytoin and CEREBYX administration would have resulted in equivalent systemic exposure to phenytoin.

TABLE 4. Adverse Reaction Incidence Following IV Administration at the Maximum Dose and Rate to Adult Patients with Epilepsy or Neurosurgical Patients (Events in at Least 2% of CEREBYX-Treated Patients)
BODY SYSTEMIV CEREBYXIV Phenytoin*
  Adverse EventN=90N=22
*
The study was not designed to assess comparative safety.
BODY AS A WHOLE
  Pelvic Pain40
  Asthenia20
  Back Pain20
  Headache25
CARDIOVASCULAR
  Hypotension89
  Vasodilatation65
  Tachycardia20
DIGESTIVE
  Nausea914
  Tongue Disorder40
  Dry Mouth45
  Vomiting29
NERVOUS
  Nystagmus4459
  Dizziness3127
  Somnolence2027
  Ataxia1118
  Stupor85
  Incoordination45
  Paresthesia40
  Extrapyramidal Syndrome40
  Tremor39
  Agitation30
  Hypesthesia29
  Dysarthria20
  Vertigo20
  Brain Edema25
SKIN AND APPENDAGES
  Pruritus495
SPECIAL SENSES
  Tinnitus99
  Diplopia30
  Taste Perversion30
  Amblyopia29
  Deafness20

Incidence in Clinical Trials - IV Administration to Pediatric Patients with Epilepsy or Neurosurgical Patients: The overall incidence of adverse reactions and the types of adverse reactions seen were similar among children and adults treated with CEREBYX. In an open-label, safety, tolerability, and pharmacokinetic study of fosphenytoin in pediatric subjects (neonates through age 16), the following adverse reactions occurred at a frequency of at least 5% in 96 subjects treated with intravenous CEREBYX: vomiting (21%), nystagmus (18%), ataxia (10%), fever (8%), nervousness (7%), pruritus (6%), somnolence (6%), hypotension (5%), and rash (5%).

Incidence in Controlled Trials - IM Administration to Adult Patients with Epilepsy: Table 5 lists adverse reactions that occurred in at least 2% of CEREBYX-treated patients in a double-blind, randomized, controlled clinical trial of adult epilepsy patients receiving either IM CEREBYX substituted for oral phenytoin or continuing oral phenytoin. Both treatments were administered for 5 days.

TABLE 5. Adverse Reaction Incidence Following Substitution of IM CEREBYX for Oral Phenytoin in Adult Patients with Epilepsy (Events in at Least 2% of CEREBYX-Treated Patients)
BODY SYSTEMIM CEREBYX Oral Phenytoin*
  Adverse EventN=179N=61
*
The study was not designed to assess comparative safety.
BODY AS A WHOLE
  Headache95
  Asthenia93
DIGESTIVE
  Nausea50
  Vomiting30
HEMATOLOGIC AND LYMPHATIC
  Ecchymosis75
NERVOUS
  Nystagmus158
  Tremor1013
  Ataxia88
  Incoordination85
  Somnolence710
  Dizziness53
  Paresthesia43
  Reflexes Decreased35
SKIN AND APPENDAGES
  Pruritus30

Adverse Events During Clinical Trials in Adult and Pediatric Patients

CEREBYX has been administered to approximately 900 individuals during clinical trials. Adverse events seen at least twice are listed in the following, except those already included in previous tables and listings. Events are further classified within body system categories and enumerated in order of decreasing frequency using the following definitions: frequent adverse events are defined as those occurring in greater than 1/100 individuals; infrequent adverse events are those occurring in 1/100 to 1/1000 individuals.

Body as a Whole: Frequent: fever, injection-site reaction, infection, chills, face edema, injection-site pain; Infrequent: sepsis, injection-site inflammation, injection-site edema, injection-site hemorrhage, flu syndrome, malaise, generalized edema, shock, photosensitivity reaction, cachexia, cryptococcosis.

Cardiovascular: Frequent: hypertension; Infrequent: cardiac arrest, migraine, syncope, cerebral hemorrhage, palpitation, sinus bradycardia, atrial flutter, bundle branch block, cardiomegaly, cerebral infarct, postural hypotension, pulmonary embolus, QT interval prolongation, thrombophlebitis, ventricular extrasystoles, congestive heart failure.

Digestive: Frequent: constipation; Infrequent: dyspepsia, diarrhea, anorexia, gastrointestinal hemorrhage, increased salivation, liver function tests abnormal, tenesmus, tongue edema, dysphagia, flatulence, gastritis, ileus.

Endocrine: Infrequent: diabetes insipidus.

Hematologic and Lymphatic: Infrequent: thrombocytopenia, anemia, leukocytosis, cyanosis, hypochromic anemia, leukopenia, lymphadenopathy, petechia.

Laboratory Test Abnormality: Phenytoin (the active metabolite of CEREBYX) may cause increased serum levels of glucose and alkaline phosphatase.

Metabolic and Nutritional: Frequent: hypokalemia; Infrequent: hyperglycemia, hypophosphatemia, alkalosis, acidosis, dehydration, hyperkalemia, ketosis.

Musculoskeletal: Frequent: myasthenia; Infrequent: myopathy, leg cramps, arthralgia, myalgia.

Nervous: Frequent: reflexes increased, speech disorder, dysarthria, intracranial hypertension, thinking abnormal, nervousness; Infrequent: confusion, twitching, Babinski sign positive, circumoral paresthesia, hemiplegia, hypotonia, convulsion, extrapyramidal syndrome, insomnia, meningitis, depersonalization, CNS depression, depression, hypokinesia, hyperkinesia, paralysis, psychosis, aphasia, emotional lability, coma, hyperesthesia, myoclonus, personality disorder, acute brain syndrome, encephalitis, subdural hematoma, encephalopathy, hostility, akathisia, amnesia, neurosis.

Respiratory: Frequent: pneumonia; Infrequent: pharyngitis, sinusitis, hyperventilation, rhinitis, apnea, aspiration pneumonia, asthma, dyspnea, atelectasis, cough increased, sputum increased, epistaxis, hypoxia, pneumothorax, hemoptysis, bronchitis.

Skin and Appendages: Frequent: rash; Infrequent: maculopapular rash, urticaria, sweating, skin discoloration, contact dermatitis, pustular rash, skin nodule.

Special Senses: Infrequent: visual field defect, eye pain, conjunctivitis, photophobia, hyperacusis, mydriasis, parosmia, ear pain, taste loss.

Urogenital: Infrequent: urinary retention, oliguria, dysuria, vaginitis, albuminuria, genital edema, kidney failure, polyuria, urethral pain, urinary incontinence, vaginal moniliasis.

6.2 Postmarketing Experience

The following adverse reactions have been identified during post-approval use of fosphenytoin. 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: Anaphylaxis, angioedema [see Warnings and Precautions (5.7)]

Laboratory Test Abnormality: Phenytoin or CEREBYX may decrease serum concentrations of T4. It may also produce lower than normal values for dexamethasone or metyrapone tests. Phenytoin may also cause increased serum levels of gamma glutamyl transpeptidase (GGT).

Nervous System Disorders: Dyskinesia

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