Antiseizure Medications

Antiseizure Medication Dosing and Monitoring in the ICU

Practical Lecture Notes Based on the 2026 Narrative Review

1. Source and Scope

• Source: Webb AJ, Barlow B, Seto SL, Maciel CB, Brennan J, Cook AM. Antiseizure medication dosing and monitoring in the intensive care unit: a practical narrative review. Intensive Care Medicine. 2026. DOI: 10.1007/s00134-026-08550-y.
• Publication date reported in the supplied summary: July 15, 2026.
• Review type: Practice-oriented narrative review supported by the Research and Scholarship Committee of the Neurocritical Care Society Pharmacy Section.
• Literature search: MEDLINE from database inception through March 2026.
• Clinical scope:
  • Antiseizure medication (ASM) pharmacokinetics and pharmacodynamics in critical illness.
  • Status epilepticus (SE), seizure treatment, and seizure prophylaxis.
  • Acute kidney injury, augmented renal clearance (ARC), and hepatic dysfunction.
  • Intermittent hemodialysis, continuous renal replacement therapy (CRRT), extracorporeal membrane oxygenation (ECMO), and plasma exchange (PLEX).
  • Therapeutic drug monitoring (TDM), drug interactions, formulations, and enteral access.
• Fifteen ASMs are reviewed in detail:
  • Brivaracetam, cannabidiol, carbamazepine, cenobamate, and clobazam.
  • Lacosamide, lamotrigine, levetiracetam, oxcarbazepine, and perampanel.
  • Phenobarbital, phenytoin, topiramate, valproate, and zonisamide.
• Core principle: ICU dosing cannot be treated as routine outpatient dosing. Critical illness, organ support, and the indication can substantially change drug exposure and response.
• Evidence caution: These notes summarize the supplied review content. Many ICU recommendations are extrapolated from outpatient data, small cohorts, case reports, pharmacokinetic studies, or expert opinion.

2. Why Outpatient Dosing Can Fail in the ICU

Treatment-related changes

• Histamine-2 receptor antagonists and proton pump inhibitors raise gastric pH and may reduce absorption of weakly basic drugs.
• Vasopressors can reduce gastrointestinal perfusion and impair enteral absorption.
• Large-volume fluid resuscitation can increase the volume of distribution of hydrophilic drugs.
• Feeding tubes may adsorb selected drugs or create clinically important interactions with enteral nutrition.

Disease-related changes

• Hypothermia can reduce the metabolism of drugs that depend on esterase activity.
• Hypovolemia can reduce the volume of distribution.
• Hypoalbuminemia increases the unbound fraction of highly protein-bound drugs.
• Inflammation can increase alpha-1 acid glycoprotein and reduce the unbound fraction of basic drugs.
• Acute kidney injury reduces clearance of renally eliminated ASMs.
• ARC increases renal drug clearance and can cause subtherapeutic exposure.
• Acute hepatic injury reduces clearance of drugs that depend on hepatic metabolism.

Device-related changes

• CRRT increases clearance of dialyzable ASMs. Effluent rates above 3 L/hour may produce supraphysiologic clearance.
• Intermittent hemodialysis increases clearance of dialyzable drugs and may require a post-dialysis supplemental dose.
• ECMO can increase the apparent volume of distribution of lipophilic and highly protein-bound drugs.
• PLEX preferentially removes drugs with a small volume of distribution and high protein binding.

3. Status Epilepticus Changes Pharmacodynamics

• Persistent seizure activity produces receptor-level changes that make delayed treatment less effective.
• Calcium-sensitive NMDA and AMPA receptors are upregulated at excitatory synapses, increasing glutamate-driven excitation.
• Intracellular gamma-aminobutyric acid (GABA) stores and metabolic substrates become depleted, reducing inhibitory tone.
• Benzodiazepine-sensitive GABA-A receptors are internalized, which contributes to declining benzodiazepine effectiveness as SE continues.
• Neuronal chloride accumulation can reverse the electrochemical gradient. GABA-A receptor activation may then become excitatory rather than inhibitory.
• A loading dose has two major purposes in SE:
  • It rapidly achieves therapeutic exposure despite an expanded volume of distribution.
  • It counters the time-dependent pharmacodynamic changes of ongoing seizure activity.
• Maintenance dosing must reflect the indication:
  • Use the lower end of a dose range for prophylaxis or an isolated seizure.
  • Use the higher end, faster titration, or shorter intervals for SE when clinically appropriate.

4. Organ Function and Clearance

Acute kidney injury

• Renally cleared ASMs such as levetiracetam, lacosamide, and topiramate have reduced clearance.
• Start with a lower maintenance dose and titrate according to tolerance, clinical response, and drug concentrations when useful.
• A clinically appropriate loading dose may still be required because loading is driven mainly by the volume of distribution and urgency of seizure control.

Augmented renal clearance

• ARC is common in younger neurocritical care and trauma patients.
• It can cause underexposure to predominantly renally cleared ASMs despite an apparently normal serum creatinine.
• Consider an 8- to 24-hour urine creatinine collection when ARC is suspected.
• Higher maintenance doses or more frequent administration may be needed.

Hepatic dysfunction

• Reduce or cautiously titrate drugs that rely on hepatic metabolism when hepatic clearance is impaired.
• Avoid valproate in hepatic dysfunction because direct hepatotoxicity makes drug substitution preferable to simple dose reduction.

5. Therapeutic Drug Monitoring: Appropriate Use and Limitations

• TDM is useful when drug exposure is uncertain, but most ICU ASM targets are not validated against clinical outcomes.
• For phenytoin and valproate, measure the free concentration whenever possible in critically ill patients.
• Total concentrations can be misleading when albumin concentration or protein binding is altered.
• Correction equations are unreliable in critical illness:
  • The Winter-Tozer equation may inaccurately estimate free phenytoin.
  • The Fraser equation may inaccurately estimate free valproate.
• A published reference range should not be treated as a mandatory target when the concentration-response relationship is unproven.
• Concentrations above traditional outpatient ranges may occasionally be required for seizure control, especially in SE, but toxicity surveillance must intensify.
• Reasonable indications for TDM include:
  • Assessment of outpatient adherence at admission.
  • Suspected treatment failure or toxicity.
  • Markedly altered protein binding.
  • ARC, dialysis, CRRT, ECMO, or other major pharmacokinetic uncertainty.
  • Drug interactions expected to change exposure.
• Do not change a clinically effective and tolerated regimen solely to place a concentration inside an unvalidated reference range.

6. Overall Medication Selection Strategy

• Integrate four domains before selecting and dosing an ASM:
  • Clinical indication and urgency.
  • Concomitant medications and drug-drug interactions.
  • Renal and hepatic function.
  • Organ support devices and drug delivery route.
• Levetiracetam, fosphenytoin, and valproate have the strongest practical support as initial non-benzodiazepine choices for established SE in the reviewed material.
• Other ASMs may be used when first-line choices are unsuitable, but the evidence base is generally smaller.
• Lamotrigine is difficult to initiate acutely because it requires slow titration. Continue a patient's established regimen when feasible.
• Cenobamate also requires slow outpatient titration because of the risk of drug reaction with eosinophilia and systemic symptoms (DRESS).
• Prefer intravenous loading when an IV formulation is available and reliable exposure is essential.
• Transition to enteral therapy after access and gastrointestinal function are established.
• Screen for drug-drug interactions whenever an ASM or a major ICU medication is added, discontinued, or substantially changed.

7. High-Yield Individual Medication Notes

Brivaracetam

• Routine initiation: 50 mg twice daily.
• Acute seizure or SE loading: 100 to 400 mg IV.
• SE maintenance: 200 to 400 mg/day in two divided doses.
• Prophylaxis: 100 to 200 mg/day in two divided doses.
• It can be started directly at the target dose because tolerability is generally favorable.
• When switching from levetiracetam because of neuropsychiatric adverse effects, a brivaracetam-to-levetiracetam ratio of approximately 1:10 to 1:15 has been used.
• Renal dysfunction: No routine adjustment.
• Hepatic dysfunction: Reduce the dose; maximum 150 mg/day.
• TDM: Not routinely needed because interpatient pharmacokinetic variability is relatively low.
• Evidence note: A small 14-patient SE series reported higher loading doses among responders than nonresponders, but a concentration-guided outcome benefit remains unproven.
• Proposed but unvalidated concentration range: 0.2 to 2 µg/mL.

Lacosamide

• Routine initiation: 50 mg twice daily, titrated to 200 to 400 mg/day.
• Common ICU loading dose: 400 mg IV.
• Reported higher loading strategies: 8 to 13 mg/kg, with uncertain incremental clinical benefit.
• Maintenance: 200 to 400 mg/day, beginning 6 to 12 hours after the loading dose.
• The TRENdS trial used a 400 mg IV bolus and found acceptable efficacy and tolerability compared with fosphenytoin for nonconvulsive seizures.
• A 25-patient SE cohort reported seizure control in 50% after 400 mg versus 18% after 200 mg loading, with p = 0.2.
• Cardiac safety:
  • High loading doses may prolong the PR interval.
  • Use caution in patients with conduction disease and monitor the electrocardiogram when risk is increased.
• Severe renal dysfunction with creatinine clearance below 30 mL/min: Reduce the maintenance dose by approximately 25%.
• Hepatic dysfunction: An initial 25% reduction with close electrocardiographic monitoring is reasonable.
• Proposed reference range: 10 to 20 mg/L.
• TDM: Concentrations have not shown a clear efficacy relationship. Use mainly when toxicity is suspected.

Levetiracetam

• Routine focal seizure initiation: 500 mg twice daily, titrated to 1,500 mg twice daily.
• Convulsive SE loading in ESETT: 60 mg/kg, maximum 4,500 mg.
• Seizures not progressing to SE: A loading dose of 20 to 40 mg/kg may be sufficient.
• ICU maintenance: 1,000 to 2,000 mg every 6 to 12 hours, individualized to renal clearance and indication.
• Seizure prophylaxis: 500 to 1,000 mg twice daily.
• Higher prophylactic doses of 750 to 1,000 mg twice daily may reduce post-traumatic seizures in some studies, but findings are inconsistent.
• Renal dysfunction: Reduce the maintenance dose, using sedation and tolerance as clinical guides.
• ARC: Doses as high as 1,500 mg every 6 hours may be required to maintain exposure.
• Proposed reference range: 12 to 46 mg/L.
• TDM: Consider for suspected nonadherence, ARC, dialysis, CRRT, or otherwise unpredictable clearance.
• Concentration-toxicity correlation is weak. In a cohort of 106 patients with concentrations above 80 µg/mL, 45.3% were asymptomatic.

Phenytoin and Fosphenytoin

• Use is limited by complex pharmacokinetics, numerous interactions, formulation issues, and cardiovascular toxicity.
• Express all fosphenytoin doses as phenytoin equivalents (mg PE).
• Acute loading: 15 to 20 mg/kg.
• Obesity: If actual weight exceeds 125% of ideal body weight, calculate the loading dose using adjusted body weight.
• Maintenance: 5 to 7 mg/kg/day in divided doses, guided by TDM.
• Phenytoin has capacity-limited, zero-order elimination near the therapeutic range.
• Maintenance dose adjustments are not linear:
  • Change by only 25 to 50 mg/day at a time.
  • Recheck concentrations before making further changes.
• Typical targets:
  • Total concentration: 10 to 20 µg/mL.
  • Free concentration: 1 to 2 µg/mL.
  • Refractory epilepsy may require approximately 25 µg/mL total or 2.5 µg/mL free with close toxicity monitoring.
• When valproate is coadministered, measure free phenytoin because the drugs compete for albumin binding.

Phenobarbital

• SE loading: 15 to 20 mg/kg.
• Maintenance after SE loading: 1 to 2 mg/kg/day in divided doses.
• Ideal body weight is often used because the volume of distribution is small.
• In severe or refractory SE, actual body weight may be used with TDM guidance.
• Transition from prolonged pentobarbital infusion may require exceptionally high phenobarbital doses. The supplied review reports doses up to 120 mg/kg/day and targets above 80 to 100 mg/L in this specialized setting.
• Mild to moderate renal dysfunction: No routine adjustment.
• Estimated glomerular filtration rate below 10 mL/min/1.73 m2: Start at 50% to 66% of the usual dose.
• Mild hepatic dysfunction: No routine adjustment.
• Child-Pugh class B or C: Start at approximately 50% and titrate using tolerance and TDM.
• Phenobarbital is a strong CYP3A4 inducer and can increase alpha-1 acid glycoprotein, creating multiple interactions.
• Usual concentration range: 10 to 40 µg/mL, although selected severe cases may require higher concentrations.
• Because the half-life is long, peak and trough concentrations differ relatively little.

Valproate

• Routine initiation: 10 to 20 mg/kg/day in one to four divided doses.
• TDM-guided maintenance: 20 to 30 mg/kg/day.
• Acute seizure or SE loading: 20 to 40 mg/kg IV, maximum 3,000 mg.
• Protein binding is saturable. The free concentration can rise disproportionately relative to the total concentration.
• When coadministered with phenytoin, measure free concentrations of both drugs.
• Critical interaction with carbapenems:
  • A single carbapenem dose may reduce valproate concentration by more than 70%.
  • Dose escalation generally cannot overcome this interaction.
  • Avoid the combination and select an alternative antimicrobial or ASM when possible.
• Typical total concentration range: 50 to 100 µg/mL.
• A total concentration up to 125 mg/L has been proposed in SE.
• Free concentration target is not established. Proposed values include 5 to 15 µg/mL and up to 25 µg/mL in SE.
• Do not rely on albumin correction equations in critically ill patients. Directly measure the free concentration.
• Avoid in hepatic dysfunction because of direct hepatotoxicity.

Carbamazepine

• Difficult to initiate in the ICU because absorption is slow, pharmacokinetics are complex, and the therapeutic index is narrow.
• Initiation: 200 to 400 mg/day in two to four divided doses.
• Increase every 3 to 5 days toward 800 to 1,200 mg/day after autoinduction develops.
• Reported oral loading: 8 to 10 mg/kg, with risks of rash, gastrointestinal effects, dizziness, and somnolence.
• If oral loading is attempted, suspension may be preferable to other formulations.
• TDM is especially useful during initiation and after interruption:
  • Autoinduction may reduce exposure during continued therapy.
  • De-induction can occur after an interruption as short as 6 to 7 days and may increase toxicity when the prior dose is restarted.
• Usual concentration range: 4 to 12 µg/mL.
• Concentration-related adverse effects may appear above 8 µg/mL.
• Renal dysfunction: No empiric dose adjustment, but consider monitoring carbamazepine-10,11-epoxide.

Cenobamate

• Standard initiation: 12.5 mg once daily.
• Increase every 2 weeks toward 200 mg/day. A maximum of 400 mg/day may be used if tolerated.
• Antiseizure activity generally requires at least 50 mg/day, which is not reached until approximately week 6 with standard titration.
• This slow titration limits acute ICU use.
• DRESS generally appears 2 to 6 weeks after initial exposure.
• Faster off-label initiation has been described in refractory SE, but ICU loading safety remains uncertain.
• TDM is not routine because pharmacokinetics are relatively consistent and no validated target exists.
• Phase 3 data cited in the supplied summary reported mean steady-state concentrations of 10.8 to 19.8 µg/mL among seizure-free patients.

Clobazam

• Initiation: 5 to 10 mg once or twice daily.
• Slowly titrate toward 40 to 80 mg/day because the half-life is 36 to 42 hours.
• Reported SE dosing: 10 to 80 mg/day in divided doses.
• ICU titration can begin at 10 mg/day and increase with each administration, but delayed somnolence can emerge because of accumulation.
• Loading doses of 60 to 70 mg, approximately 1 mg/kg, have been reported but evidence is limited.
• Renal and hepatic dysfunction: No routine adjustment in the supplied review.
• CYP2C19 poor metabolizers require dose reduction because norclobazam can accumulate.
• Strong CYP2C19 inhibitors such as cannabidiol may also increase norclobazam exposure.
• TDM should include both compounds:
  • Clobazam: 30 to 300 ng/mL.
  • Norclobazam: 300 to 3,000 ng/mL.
• A typical clobazam-to-norclobazam ratio is approximately 1:10.
• The ratio does not predict efficacy, but an unusual ratio can suggest CYP2C19 poor metabolism. Norclobazam concentration may correlate with toxicity.

Oxcarbazepine

• Initiation: 150 to 300 mg twice daily.
• Increase by 300 to 600 mg/day each week to a maximum of 2,400 mg/day.
• ICU titration may be faster. Two cohorts totaling 78 patients reported that a 30 mg/kg loading dose was tolerated.
• Conversion from carbamazepine: A carbamazepine-to-oxcarbazepine ratio of approximately 1:1.5 has been used.
• Severe renal dysfunction: Start at half the target dose and titrate more slowly because 10-hydroxycarbazepine (MHD) accumulates.
• Hepatic dysfunction: No routine adjustment.
• TDM is not routine. Consider it with suspected toxicity, older age, interactions, or severe renal dysfunction.
• Proposed combined oxcarbazepine plus MHD trough range: 15 to 35 µg/mL.

Perampanel

• Routine initiation: 2 to 4 mg at bedtime.
• Weekly titration target: 6 to 12 mg/day.
• Half-life: Approximately 105 hours.
• Reported loading: 0.25 to 0.5 mg/kg, maximum 36 mg.
• One SE cohort associated a higher initial dose with SE termination (odds ratio 1.27, 95% confidence interval 1.03 to 1.57).
• Rapid ICU titration up to 32 mg/day has been reported, but safety documentation is limited.
• Delayed adverse effects can include sedation and aggressive behavior.
• Renal dysfunction: No routine adjustment.
• Mild to moderate hepatic dysfunction: Reduce the initial and maximum dose.
• Severe hepatic dysfunction: Avoid use.
• Proposed concentration range: 200 to 600 ng/mL may balance efficacy and adverse effects, but this is not a validated ICU target.
• Without loading, wait for steady state before measuring a concentration. This may require 2 to 3 weeks.

Topiramate

• Routine initiation: 50 mg/day.
• Increase weekly toward 200 to 400 mg/day in one or two divided doses.
• Reported SE strategy: 400 mg loading followed by 100 to 200 mg twice daily.
• Creatinine clearance below 70 mL/min/1.73 m2: Start at half the usual dose and titrate to tolerance.
• Hepatic dysfunction: No routine adjustment in the supplied review.
• Proposed concentration range: 5 to 20 mg/L.
• TDM has a limited role because pharmacokinetics are generally predictable.

Zonisamide

• Routine initiation: 100 mg/day.
• Increase by 100 mg every 2 weeks toward 400 mg/day.
• A 34-patient SE cohort used a 300 mg loading dose followed immediately by maintenance dosing without major reported adverse reactions.
• Renal or hepatic dysfunction: No fixed adjustment in the supplied review, but lower initial doses and slower titration may be prudent.
• Proposed concentration range: 10 to 40 mg/L.
• TDM is not routinely required.

Lamotrigine

• Initiate at 12.5 to 50 mg depending on interacting medications.
• Increase weekly and reach 200 to 400 mg/day over 6 to 8 weeks.
• Rapid titration increases the risk of Stevens-Johnson syndrome.
• If therapy is interrupted for more than five half-lives, approximately 5 days, restart the initial titration schedule.
• An 11-day rapid microinduction regimen produced rash in 15.1% of a 33-patient cohort, raising safety concerns.
• Renal and hepatic dysfunction: No routine adjustment in the supplied review.
• Proposed concentration range: 2.5 to 15 µg/mL.
• TDM is most useful when the medication history is uncertain and clinicians must determine whether therapy was recently continued.

Cannabidiol

• Routine initiation: 2.5 mg/kg twice daily.
• Increase by 5 mg/kg/day each week toward 20 mg/kg/day.
• Higher doses up to 50 mg/kg/day and faster titration have been reported.
• Limited ICU SE experience:
  • Start at 5 to 10 mg/kg/day.
  • Titrate over 1 to 2 weeks toward 25 mg/kg/day.
  • Safety and efficacy remain uncertain.
• Hepatic dysfunction: Reduce to approximately 4 to 10 mg/kg/day.
• Renal dysfunction: No routine adjustment.
• Pharmacokinetics are complex, bioavailability is low, and drug interactions are numerous.
• A proposed concentration range of 47.1 to 157 ng/mL has not been validated and observed concentrations may be higher.
• In a 100-patient outpatient cohort, responders and nonresponders had similar concentrations, although higher exposure showed a modest association with fewer seizures over 14 days.

Other ASMs to Remember

• Gabapentin and pregabalin:
  • May be used for periodic or repetitive seizures.
  • Require adjustment in renal dysfunction and kidney replacement therapy.
• Eslicarbazepine:
  • Similar considerations to oxcarbazepine.
  • Once-daily administration may be convenient.
• Vigabatrin:
  • Irreversible GABA transaminase inhibitor used for refractory epilepsy.
  • Its role in post-anoxic SE is under investigation.
  • Requires adjustment in renal dysfunction or kidney replacement therapy.
• Felbamate, stiripentol, rufinamide, tiagabine, and fenfluramine:
  • Have narrow indications.
  • In the ICU, they are most often encountered as continuation of a home regimen.

8. Dosing During Organ Support

Intermittent hemodialysis and CRRT

• No routine adjustment reported for brivaracetam, cannabidiol, carbamazepine, cenobamate, clobazam, lamotrigine, or perampanel. Much of this guidance is based on expert opinion.
• Phenytoin and valproate:
  • No routine dialysis adjustment.
  • Monitor free concentrations.
• Lacosamide:
  • Hemodialysis: Give 50% of the maintenance dose after dialysis.
  • CRRT effluent below 2 L/hour: 50 to 200 mg every 12 hours.
  • CRRT effluent 2 to 3 L/hour: 50 to 200 mg every 8 to 12 hours.
  • CRRT effluent above 3 L/hour: 100 to 200 mg every 6 to 12 hours.
• Levetiracetam:
  • Hemodialysis: Give 50% of the maintenance dose after dialysis, or use 250 to 750 mg every 12 hours as described in the review.
  • CRRT effluent below 2 L/hour: 250 to 1,000 mg every 12 hours.
  • CRRT effluent 2 to 3 L/hour: 500 to 1,250 mg every 12 hours.
  • CRRT effluent above 3 L/hour: 500 to 1,500 mg every 6 to 12 hours.
• Oxcarbazepine:
  • Slow the titration rate.
  • No other routine adjustment reported.
• Phenobarbital:
  • Hemodialysis: Give 50% of the maintenance dose after dialysis.
  • CRRT: Consider a higher initial maintenance dose of 2 to 3 mg/kg/day.
• Topiramate and zonisamide:
  • Hemodialysis: Give 50% of the maintenance dose after dialysis.
  • CRRT: Consider starting at 25 to 50 mg every 12 hours and titrate to tolerance.
  • Approximate CRRT upper doses in the review: topiramate 200 mg every 12 hours and zonisamide 300 mg every 12 hours.

ECMO

• Cannabidiol and carbamazepine may require higher doses based on limited data and expert opinion. Use TDM when possible.
• No routine adjustment reported for clobazam, lacosamide, levetiracetam, oxcarbazepine, phenobarbital, topiramate, or zonisamide.

Plasma exchange

• Administer carbamazepine and clobazam after PLEX when feasible.
• No routine adjustment reported for cannabidiol or phenobarbital.

9. Formulation and Administration Pearls

Cannabidiol

• Do not administer through a polyvinyl chloride (PVC) feeding tube because the formulation can harden and crack the tubing.
• A non-PVC tube may be used.
• The formulation contains no carbohydrate and should not disrupt ketosis.

Carbamazepine

• Do not administer oral suspension simultaneously with other medications because precipitation may occur.
• Extended-release capsules may be opened and sprinkled on soft food.
• Intact beads may be administered through a sufficiently large-bore tube.

Cenobamate

• The 12.5 mg strength is available only in prefilled titration packaging.
• A 25 mg tablet may be split.

Clobazam and Lamotrigine

• Clobazam oral film and lamotrigine orally disintegrating tablets are not absorbed through the buccal mucosa.
• The dissolved medication and saliva must be swallowed for absorption.

Lacosamide

• Maximum IV administration rate: 80 mg/minute.
• IV-to-oral conversion: 1:1.

Oxcarbazepine

• Compared with immediate-release dosing, the extended-release formulation produces approximately 19% lower peak and 16% lower trough concentrations.
• A 1:1 conversion can be used, but the extended-release dose may need to be higher based on clinical response.

Perampanel

• The IV formulation is available only in Japan according to the supplied review.
• Infuse over at least 30 minutes.

Phenobarbital

• IV formulation pH: 9.2 to 10.2.
• It is incompatible with acidic medications such as midazolam.
• The formulation contains propylene glycol. High doses may disrupt ketogenic therapy.
• Undiluted high-dose administration may cause irritation.
• Maximum IV bolus: 260 mg.
• Infusion rate: 50 to 100 mg/minute.

Phenytoin and Fosphenytoin

• Maximum phenytoin IV infusion rate: 50 mg/minute.
• Maximum fosphenytoin infusion rate: 150 mg PE/minute.
• Fosphenytoin may be administered intramuscularly.
• For enteral phenytoin:
  • Hold tube feeding for 1 hour before administration.
  • Hold tube feeding for 1 hour after administration.
• Products labeled as extended-release capsules do not use a true extended-release mechanism.
• When converting from phenytoin sodium in capsules or IV solution to phenytoin base in suspension or chewable tablets, reduce the dose by approximately 8% to 10%.
• IV phenytoin contains propylene glycol and may disrupt ketogenic therapy at high doses.
• IV phenytoin can precipitate with multiple medications and dextrose-containing fluids.

Valproate

• Maximum IV infusion rate: 500 mg/minute.
• Total daily IV-to-oral conversion: 1:1.
• Because IV therapy has no delayed absorption, divide the IV daily dose into three or four administrations.
• Conversion between extended-release and delayed-release formulations: Approximately 1:0.8 to 0.9, depending on the direction of conversion.

General enteral principle

• Do not crush or administer an extended-release formulation through a feeding tube unless product-specific information explicitly permits it.

10. Practical Bedside Framework

• Step 1: Define the indication.
  • SE requires rapid loading and aggressive maintenance.
  • Prophylaxis usually uses the lower end of the dose range.
• Step 2: Choose the agent.
  • Match spectrum, evidence, adverse-effect profile, and available route.
  • Avoid valproate in hepatic dysfunction.
  • Avoid initiating lamotrigine or cenobamate when rapid effect is required.
• Step 3: Give an appropriate loading dose.
  • Base loading primarily on urgency and volume of distribution.
  • Do not reflexively reduce a necessary loading dose solely because maintenance clearance is reduced.
• Step 4: Design maintenance therapy.
  • Account for kidney function, hepatic function, ARC, CRRT effluent rate, ECMO, PLEX, and dialysis schedule.
  • Use more frequent dosing when rapid renal clearance is expected.
• Step 5: Confirm delivery.
  • Verify formulation compatibility, feeding-tube material, nutrition holds, infusion rate, and IV compatibility.
• Step 6: Screen interactions.
  • Treat carbapenem plus valproate as a high-risk combination that usually requires avoidance rather than valproate dose escalation.
• Step 7: Monitor response and toxicity.
  • Use electroencephalography and the clinical examination as appropriate.
  • Use TDM when it answers a specific clinical question.
  • Prefer free phenytoin and free valproate concentrations in critical illness.

11. Five Executive Takeaways from the Review

• Critical illness changes ASM pharmacokinetics. Volume of distribution, organ dysfunction, ARC, CRRT, ECMO, and PLEX can all move exposure away from outpatient expectations.
• Loading doses are essential in SE because they rapidly achieve exposure and address time-dependent pharmacodynamic resistance. ICU maintenance doses and titration rates may exceed outpatient labeling.
• TDM is valuable but limited. Free phenytoin and free valproate concentrations are more informative than total concentrations, while most newer ASMs lack validated ICU concentration-response targets.
• Drug interactions must be screened proactively. Carbapenems can reduce valproate concentrations by more than 70%, and increasing valproate usually does not solve the problem.
• Evidence gaps remain substantial. Many ICU strategies are extrapolated from outpatient studies, small observational cohorts, pharmacokinetic modeling, or expert opinion.

12. Final Take-Home Message

• Do not import outpatient ASM doses and titration schedules into the ICU without reassessment.
• Treat SE early and aggressively with an appropriate loading dose.
• Reduce maintenance exposure when clearance is impaired, but increase it when ARC or high-effluent CRRT causes excessive clearance.
• Measure free phenytoin and free valproate when protein binding is altered.
• Avoid carbapenem and valproate coadministration whenever possible.
• Verify the formulation and route because administration details can determine whether the intended dose reaches the patient.
• Apply individualized clinical judgment and close monitoring because the evidence base remains incomplete.

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Educational summary based solely on the source material supplied by the user. It is not a substitute for local protocols, specialist consultation, product labeling, or patient-specific clinical judgment.