A 34 yo female with a history of trigeminal neuroalgia presented to the Emergency Department with a chief complaint of 5 days of severe, worsening paroxysms of pain in the left trigeminal nerve distribution. The pain was refractory to carbamazepine and gabapentin. Neurology was consulted and an unconventional therapy was recommended: 

• Trigeminal neuralgia is a chronic facial pain syndrome characterized by paroxysms of severe, lancinating pain in the trigeminal nerve distribution: usually the maxillary or mandibular branches
• The pain is typically unbearable, having been described as "the worst pain a human can endure." Before effective pharmacotherapy, patients would often resort to suicide
• First line therapy is carbamazepine at starting doses of 200 mg/day, titrated up as high as 1200 mg/day in divided doses
• Second line therapy is either gabapentin or lamotrigine. Baclofen has been used as an add-on medication in refractory cases
• Severe pain exacerbations will often prompt patients to seek care in the ED and require opiates for acute relief
• Several case reports and case series have suggested intravenous phenytoin or fosphenytoin for abortive therapy, usually reporting complete or near complete relief of pain after infusion
• The patient received 1,000 mg of phenytoin over a 1.5 hour infusion. Reported pain decreased from 9/10 to 1/10 nearly immediately. She was discharged on oral oxcarbamazepine and baclofen with neurology followup
• Conclusion: Consider intravenous phenytoin or fosphenytoin for acute pain crises in trigeminal neuralgia patients. Remember to infuse phenytoin no faster than 25-50 mg/min to avoid hypotension and bradycardia.

References
1. Cheshire, William. Fosphenytoin: An Intravenous Option for the Management of Acute Trigeminal Neuralgia Crisis.  Journal of Pain and Symptom Management 2001; 21(6): 506-510.