The clinician must maintain a high level of suspicion for central nervous system infections even if not all of the classic signs are present, because prompt treatment may make a difference in patient outcome. If bacterial meningitis is suspected, a CT scan of the head should be obtained prior to lumbar puncture if there is papilledema, a focal neurologic exam, or if the patient is comatose. In bacterial meningitis, empiric antibiotics should be chosen based on a patient's risk factors and should be started immediately. Depending on the resistance patterns of the institution, Streptococcus pneumoniae may be resistant to penicillins and cephalosporins. Corticosteroids are of uncertain benefit in bacterial meningitis and may decrease the penetration of antibiotics into the central nervous system. The dosage for acyclovir treatment in herpes simplex encephalitis is 10 to 15mg/kg every 8 hours. Subdural empyema is a neurosurgical emergency. Brain abscesses should be surgically drained if they exceed 2.5 centimeters.