Neurocritical Care Society Issues Seizure Prevention Guidelines for Aneurysmal Subarachnoid Hemorrhage

Every year, hundreds of thousands of people worldwide survive the sudden rupture of a brain aneurysm, only to face an anxious question that has haunted neurologists for decades: should they be given powerful antiseizure drugs to prevent seizures that may never come? Now, after more than four years of painstaking evidence synthesis, the Neurocritical Care Society has issued its first formal guideline dedicated to that very question, and its conclusions are striking in their humility. A ten-member panel of physicians, pharmacists, and nurses, writing in the journal Neurocritical Care, concludes that the evidence base for seizure prophylaxis in aneurysmal subarachnoid hemorrhage is so thin that no strong recommendation of any kind can be made—leaving the most consequential prescribing decisions in this population resting on conditional suggestions drawn from just ten studies.

Aneurysmal subarachnoid hemorrhage, the bleeding that occurs when a weakened vessel at the base of the brain bursts into the space surrounding it, carries a reported incidence of early seizures ranging from 8 to 24 percent. The widespread adoption of continuous electroencephalography in neurocritical care units has only complicated the picture, revealing a hidden burden of nonconvulsive seizures and even nonconvulsive status epilepticus that would otherwise go undetected. These silent electrical storms matter: patients with a high burden of electrographic seizures show measurably worse cognitive and functional outcomes. Known risk factors for early seizures include older age, rupture of an aneurysm in the anterior circulation, hydrocephalus requiring drainage of cerebrospinal fluid, seizures occurring before hospital arrival, higher clinical grade on admission, surgical clipping of the aneurysm, and the presence of a thick subarachnoid clot.

Against this backdrop, clinicians have long prescribed prophylactic antiseizure medications, but with little rigorous justification. Most of the supporting evidence comes from observational cohort studies, and professional societies have hedged accordingly. The earlier American Heart Association guidelines suggested considering prophylactic medication during the post-bleed period while warning against long-term use; the 2023 revision offered only a weak recommendation for patients with high-seizure-risk features; and the Neurocritical Care Society’s own comprehensive management guidelines from 2023 conspicuously made no statement on prophylaxis at all. The new guideline panel, formed in October 2019 and co-chaired by A. Shaun Rowe of the University of Tennessee Health Science Center and Jennifer A. Frontera of New York University Grossman School of Medicine, set out to close this gap using the Grading of Recommendations Assessment, Development, and Evaluation methodology, the international standard for translating evidence into clinical guidance.

The panel structured its work around three carefully framed questions, each following the population, intervention, comparator, and outcome format. First, in adult patients hospitalized with aneurysmal subarachnoid hemorrhage who have never had a clinical or electrographic seizure, should an antiseizure medication be given at all? Second, if treatment is chosen, should clinicians prefer levetiracetam or phenytoin and its water-soluble prodrug fosphenytoin? Third, if treatment is chosen, should it last a short period of three days or less, or extend beyond three days? The outcomes judged critical were early seizures, defined as occurring within fourteen days of hemorrhage or during hospitalization; late seizures at or beyond fourteen days; and adverse events attributable to the drugs themselves. Mortality and functional and cognitive outcomes, scored on instruments such as the modified Rankin Scale, were rated as important but not decisive.

The literature search, initially spanning databases including PubMed, Medline, Embase, Emcare, and the Cochrane Library from 1946 through July 2020 and updated through September 2024, retrieved nearly two thousand articles. Only ten survived the screening process, and just seven entered the meta-analyses. That winnowing alone tells the story: an intervention applied to tens of thousands of patients annually worldwide rests on a handful of small, nonrandomized investigations. Risk of bias was assessed with the Cochrane RoB-2 tool for randomized trials and the ROBINS-I instrument for nonrandomized studies, and all meta-analyses used random-effects models with heterogeneity flagged at an I-squared value of fifty percent or greater.

On the first question, the pooled evidence was sobering. Two nonrandomized studies encompassing 437 patients compared antiseizure medication with no treatment, and the meta-analysis found no significant reduction in early seizures, with a relative risk of 0.72 and a confidence interval spanning from 0.37 to 1.41. No study at all examined late seizures in this comparison. Adverse events, documented in a single study of 84 patients, were numerically more than four times as common in the treated group—nine of forty-four versus two of forty—though the difference fell just short of statistical significance with a p value of 0.06. Functional outcomes at discharge and six months showed no meaningful difference. The panel’s verdict: antiseizure medication may be used or withheld, a conditional recommendation grounded in low-quality evidence, with the observation that clinicians may reasonably favor treatment in high-risk patients such as those with high-grade hemorrhage, intraparenchymal clot, hydrocephalus, or surgical clipping.

The drug comparison proved equally murky. Three nonrandomized studies addressed early seizure prevention, but two reported zero events, leaving essentially one study to drive the finding. That investigation showed fewer early seizures with phenytoin or fosphenytoin—a relative risk of 2.46 favoring phenytoin against levetiracetam with a confidence interval of 1.09 to 5.55. Yet the safety picture ran the other way. In a study by Shah and Husain, patients on phenytoin or fosphenytoin experienced dramatically more elevated transaminases, at 30.1 percent versus zero percent, more thrombocytopenia at 11.5 percent versus zero, and more unexplained fever. A separate case-control study of 259 patients, excluded from the meta-analysis because of medication-switching confounding, linked phenytoin to worse functional outcomes and more delayed cerebral ischemia. There was also a mechanistic concern: phenytoin induces CYP3A4, the enzyme that metabolizes nimodipine, the drug given to all these patients to prevent delayed brain ischemia, potentially undermining its effectiveness. The panel suggested either agent could be used, conditional on very low quality evidence, but its expert commentary notes that most practitioners prefer levetiracetam for its favorable safety profile and fewer drug interactions.

The dosing problem received particular attention. Levetiracetam clearance is known to be enhanced in these patients because of augmented renal clearance, meaning standard doses of 500 milligrams twice daily may leave blood levels far below therapeutic targets. Population pharmacokinetic work cited in the guideline found that patients with augmented renal clearance may require as much as 1500 milligrams twice daily, and studies in broader neurocritical care populations suggest that doses of 750 to 1000 milligrams twice daily or total daily doses exceeding 1000 milligrams achieve better target levels and fewer seizures. The panel’s expert guidance explicitly raises the possibility of higher dosing or loading strategies and recommends serum level monitoring where feasible, acknowledging that apparent failures of levetiracetam prophylaxis may partly reflect systematic underdosing.

On duration, the evidence tilted cautiously toward brevity. A single small randomized trial of 84 patients comparing three days of levetiracetam with continued treatment until discharge found no difference in in-hospital seizures but more sedation-related discontinuation in the extended group; it was terminated early for slow enrollment and thus underpowered. A retrospective study of 449 patients comparing three-day phenytoin with multiweek courses found the short course reduced hypersensitivity reactions from 8.8 percent to 0.5 percent without any increase in hospital or long-term seizures. Conversely, another retrospective comparison of short-course levetiracetam against extended phenytoin showed more seizures with levetiracetam, though the levetiracetam dose used was low for this population. The pooled analysis favored extended treatment for seizure prevention with a relative risk of 2.45 for short courses, but the adverse event data favored short courses emphatically, with a relative risk of 0.06 for complications. Reconciling these competing signals, the panel suggested individualized decisions, and its practical commentary states plainly that prophylaxis should generally not continue beyond three days in patients without seizures or high-risk electroencephalographic findings, such as elevated scores on the validated 2HELPS2B risk instrument.

Perhaps the most striking feature of the guideline is its candor about what remains unknown. The authors note that the evidence base consists almost entirely of nonrandomized studies with inconsistent seizure definitions, variable drug regimens, minimal drug-level monitoring, and little systematic capture of adverse events or long-term cognitive outcomes. They call for large randomized controlled trials with standardized prophylaxis regimens, therapeutic drug titration, combined clinical and electrographic seizure surveillance, data safety monitoring boards, and subgroup analyses of low- versus high-grade hemorrhage. They also point to troubling signals that phenytoin exposure itself is associated with functional and cognitive disability after subarachnoid hemorrhage, independent of any seizure-prevention benefit. For a field that has prescribed prophylactic anticonvulsants reflexively for decades, the message is paradoxically both liberating and unsettling: doing nothing may be as defensible as treating, and when treatment is chosen, a short, carefully dosed course of levetiracetam—guided where possible by the electroencephalograph rather than tradition—represents the current best judgment of expert consensus in the face of genuinely sparse science.