This study evaluates the pharmacokinetic profile of levetiracetam in critically ill patients who have suffered a subarachnoid hemorrhage. The patients will be evaluated for development of augmented renal clearance and the effects and duration of effects this may have on levetiracetam clearance.

Inclusion Criteria:

• Patients diagnosed with non-traumatic subarachnoid hemorrhage requiring levetiracetam for seizure prophylaxis or treatment
• Presentation to University of Colorado Hospital within 48 hours of subarachnoid hemorrhage
• Adults ages 18 to 89 years
• Anticipated length of stay ≥ 48 hours
• Informed consent provided by the patient or patient's designated medical proxy

Exclusion Criteria:

• Pregnancy
• Patients receiving renal replacement therapy
• Brain death or imminent brain death expected ≤48 hours
• Patient with history of nephrectomy or renal transplant

Patients who have suffered a non-traumatic subarachnoid hemorrhage requiring strict intake and output monitoring and admission to the neuro-intensive care unit