Adult and children dose of phenetoin
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Now I have comprehensive data from the Harriet Lane Handbook, FDA labeling, and the Family Medicine textbook. Here is the full, detailed answer:
Phenytoin Dosing
ADULTS
Status Epilepticus (IV)
| Parameter | Dose |
|---|---|
| Loading dose | 10-20 mg/kg IV (usual 15-20 mg/kg) |
| Max infusion rate | 50 mg/min (slower if elderly or cardiac risk) |
| Maintenance dose | 100 mg IV/oral every 6-8 hours |
Non-emergent Loading & Maintenance (IV/Oral)
| Parameter | Dose |
|---|---|
| Loading dose (oral, hospitalized) | 1000 mg divided as 400 mg, then 300 mg, then 300 mg q2h |
| Loading dose (IV) | 10-15 mg/kg IV at max 50 mg/min |
| Maintenance (oral capsules) | 100 mg 3 times daily (300 mg/day) or 300 mg once daily |
| Maintenance (IV) | 100 mg IV every 6-8 hours |
| Range | 200-500 mg/day, adjusted by levels |
Oral Maintenance by Weight
- 4-7 mg/kg/day in 1-3 divided doses (adjusted to therapeutic level)
CHILDREN (Pediatric)
Status Epilepticus (IV)
| Age | Loading Dose | Max Infusion Rate |
|---|---|---|
| All pediatric ages | 15-20 mg/kg IV | 1-3 mg/kg/min or 50 mg/min (whichever is slower) |
Maintenance Dose (Oral or IV)
| Age Group | Dose |
|---|---|
| Neonates | 5 mg/kg/day divided q12h |
| Infants/Children < 6 years | 5 mg/kg/day in 2-3 divided doses (max 300 mg/day) |
| Children > 6 years | 7.5-9 mg/kg/day in 2-3 divided doses |
| Adolescents | 300 mg/day (same as adult) |
Children generally require higher mg/kg doses than adults due to faster hepatic metabolism.
NEONATAL DOSING (from Harriet Lane Handbook)
- Loading dose: 15-20 mg/kg IV
- Maintenance: 5 mg/kg/day divided every 12 hours
- Rate: not to exceed 1-3 mg/kg/min
Therapeutic Drug Monitoring
| Level | Target |
|---|---|
| Total phenytoin | 10-20 mcg/mL (mg/L) |
| Free (unbound) phenytoin | 1-2 mcg/mL |
Monitor free levels in: hypoalbuminemia, renal failure, pregnancy, elderly patients (reduced protein binding)
Key Practical Points
- Non-linear (Michaelis-Menten) kinetics: Small dose increases near the therapeutic range can cause disproportionately large rises in serum levels - dose changes should be small (25-50 mg increments)
- IV rate warning: Rapid IV infusion causes hypotension, bradycardia, and cardiac arrhythmias - always monitor ECG and BP
- IM route: NOT recommended (painful, erratic absorption, crystal precipitation)
- Oral bioavailability: Capsules (sodium salt) and tablets/suspension (acid form) are NOT interchangeable mg-for-mg - 100 mg capsule ≈ 92 mg free acid
- Drug interactions: Numerous - enzyme inducer (CYP2C9, CYP3A4); levels altered by carbamazepine, valproate, fluconazole, and many others
- Fosphenytoin (prodrug): Dosed in phenytoin sodium equivalents (PE); can be given faster IV (150 mg PE/min in adults) and can be given IM
Sources
- The Harriet Lane Handbook, 23rd ed., p. 1888-1904 (pediatric/neonatal dosing)
- Textbook of Family Medicine, 9th ed., Table 41-12
- FDA Dilantin Label
- Drugs.com Phenytoin Dosage Guide (reviewed Mar 2026)
Status epilepticus
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Here is a complete, evidence-based overview of Status Epilepticus:
Status Epilepticus
Definition
A seizure lasting ≥5 minutes OR two or more seizures without recovery of consciousness between them. After 5 minutes, seizures are unlikely to self-terminate, are harder to control with antiepileptics, and begin causing neuronal damage. This is a neurological emergency - treatment should begin immediately.
After 20 minutes: hypotension, hypoxia, metabolic acidosis, hyperthermia, hypoglycemia, cardiac dysrhythmias, and pulmonary edema commonly develop.
Classification
| Type | Description |
|---|---|
| Convulsive SE | Tonic-clonic motor activity with altered consciousness |
| Nonconvulsive SE (NCSE) | Comatose or fluctuating mental status, no overt seizures - diagnosed by EEG |
| Refractory SE | Persists despite adequate doses of two antiepileptic agents (>60 min) |
| Super-refractory SE | Continues or recurs ≥24h after general anaesthetic agent initiation |
Common Causes
- Subtherapeutic antiepileptic drug levels (most common in known epileptics)
- Acute stroke or CNS injury
- Anoxia / hypoxia
- Metabolic abnormalities (hypoglycemia, hyponatremia, hypocalcemia)
- Alcohol or drug intoxication / withdrawal
- CNS infections (meningitis, encephalitis)
- Preexisting neurologic conditions
Immediate Stabilization (0-5 min)
- Airway: Position to maximize ventilation, prevent aspiration; nasopharyngeal airway if needed; consider intubation if prolonged
- Breathing: O2 by mask/nasal cannula; bag-valve-mask if inadequate ventilation
- Circulation: Large-bore IV access; cardiac monitor, pulse oximetry, BP monitoring
- Glucose: Bedside glucose immediately; give IV dextrose if hypoglycemic
- Labs: Electrolytes, calcium, magnesium, glucose, renal/liver function, CBC, toxicology screen, antiepileptic drug levels, pregnancy test (if applicable)
- Temperature: Monitor continuously; treat hyperthermia with cooling
- Do NOT perform LP during active SE; delay CT scan until seizures controlled
Treatment Algorithm
Phase 1 - First-Line: Benzodiazepines (0-10 min)
Terminate seizures 70% of the time. Give as early as possible - delays >10 min increase mortality, seizure duration, and complications.
| Drug | Adult Dose | Pediatric Dose | Route |
|---|---|---|---|
| Lorazepam (preferred if IV available) | 2-4 mg IV (0.1 mg/kg); repeat once in 5 min | 0.05-0.1 mg/kg IV | IV |
| Midazolam (preferred if no IV access) | 10 mg IM/IN | 0.2 mg/kg IM; 0.3 mg/kg IN | IM, IN, IV |
| Diazepam | 5-10 mg IV; repeat q5 min (max 30 mg) | 0.2-0.5 mg/kg IV (max 10 mg) or 0.5 mg/kg rectal | IV, rectal |
- Lorazepam: onset 3 min, duration 12-24 hours (preferred IV agent)
- Diazepam: onset 2 min, duration only 15-60 min (shorter - seizures may recur)
- IM midazolam = as effective as IV lorazepam in pre-hospital trials; preferred when no IV access
- Give second benzodiazepine dose only after 5 min of continued seizure activity after first dose
Phase 2 - Second-Line Antiepileptics (start within 20 min)
Start simultaneously with or immediately after benzodiazepines. No single agent is definitively superior.
| Drug | Adult Dose | Infusion Rate | Notes |
|---|---|---|---|
| Fosphenytoin (preferred over phenytoin) | 20 mg PE/kg IV | up to 150 mg PE/min | Can give IM; fewer cardiac/infusion side effects |
| Phenytoin | 20 mg/kg IV | max 50 mg/min (25 mg/min safer) | Not in glucose solutions; cardiac monitor mandatory |
| Levetiracetam | 20-60 mg/kg IV (typically 2000-4500 mg) | over 15 min | Fewest side effects, no interactions; rapidly gaining favor |
| Valproic acid | 20-40 mg/kg IV | 3-6 mg/kg/min | Contraindicated in liver disease, thrombocytopenia, suspected metabolic disease; not with phenytoin |
| Lacosamide | 200-400 mg IV | over 15 min | Alternative with limited data |
Phase 3 - Refractory SE: Anesthetic Infusions (<30-60 min target)
Requires intubation, Neuro ICU admission, and continuous EEG monitoring.
| Drug | Loading Dose | Infusion Rate |
|---|---|---|
| Midazolam | 0.2 mg/kg IV | 0.05-2 mg/kg/h, titrate to seizure cessation |
| Propofol | 1 mg/kg IV | 1-10 mg/kg/h (risk of propofol infusion syndrome at >40 mg/kg/h) |
| Phenobarbital | 20 mg/kg IV | 50-75 mg/min |
| Ketamine | - | 5 mg/kg/h infusion (emerging evidence) |
| Pentobarbital | 5-15 mg/kg | 0.5-5 mg/kg/h |
Pediatric-Specific Notes (Harriet Lane Handbook)
- Diazepam IV: Neonate: 0.1-0.3 mg/kg q15-30 min (max 2 mg); Child <5 yr: 0.2-0.5 mg/dose q2-5 min (max 5 mg); Child ≥5 yr: 1 mg/dose q2-5 min (max 10 mg)
- Rectal diazepam: 0.5 mg/kg; widely used by EMS in children
- Buccal midazolam: 0.5 mg/kg (max 10 mg) - more effective than rectal diazepam in children
- Children metabolize antiepileptics faster - weight-based dosing is essential
Nonconvulsive SE - Key Points
- Suspect in: prolonged postictal state, subtle motor signs (twitching, eye deviation, blinking), unexplained coma or confusion
- Diagnosis requires EEG
- Treat similarly to convulsive SE once diagnosed
Prognosis
Mortality increases with:
- Delayed diagnosis/treatment
- Age >60 years
- No prior seizure history
- Nonconvulsive SE (often missed)
- Underlying etiology severity
Sources:
- Tintinalli's Emergency Medicine, 9th ed., Ch. 171 (primary)
- Rosen's Emergency Medicine, 9th ed., Ch. 169
- Harriet Lane Handbook, 23rd ed. (pediatric dosing)
- 2025 Surgical Critical Care SE Management Guidelines
- ENLS Status Epilepticus Protocol v6.0, July 2024
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