For patients for whom there is low suspicion of disease or for those simply requiring prophylaxis, a minimum of 100 mg should be
administered intravenously. For those with confirmed or highly suspected disease and for those who have "failed" the 100-mg
regimen (eg, persistent mental status changes or ocular palsy), we recommend a dosage upwards of 500 mg intravenously.
Ann Emerg Med. 2007;50:715-721.