Anticonvulsant hypersensitivity: an unfortunate case of triple exposure to phenytoin

Journal of Family Practice, Nov, 1997 by Cara E. Brown, Gregory D. Smith, Thomas Coniglione

5. Elevated urea nitrogen.[1,2,9]

Less common findings documented include myopathy, eosinophilic pneumonitis, joint effusions, serum sickness, polyarteritis nodosa, and lymphoma.[4,10,11] Depending on the cluster of signs seen, the differential diagnosis often includes collagen vascular diseases, malignancies (eg, lymphoma), and infections (eg, mononucleosis, rubella, and staphylococcal scalded skin syndrome.) [7,9,11]

Reported mortality rates have been quite high if hepatitis (5% to 50%) or toxic epidermal necrolysis (15% to 25%) develops.[12,13] Death from toxic epidermal necrolysis usually occurs because of fluid and electrolyte imbalances or sepsis. Most often, full dermatologic resolution occurs within 2 to 4 weeks, but normalization of the liver function tests may take 3 months.[6]

Treatment consists of discontinuation of anti-convulsant medication, supportive measures, and high-dose oral corticosteroids. Treatment with high-dose oral corticosteroids has never been validated by a double-blind controlled study because many consider it the standard of care and report a prompt resolution of dermatologic problems. Acetaminophen is contraindicated because of increased possibility of hepatotoxicity. If toxic epidermal necrolysis occurs, it should be treated like a burn with infection prevention, fluid and electrolyte support, and admission to a burn unit depending on the extent of desquamation.

Challenge doses of even 1 mg have caused recurrent anticonvulsant hypersensitivity; and since the risk of mortality is high, do not give to a challenge dose or any arene-oxide-producing drug; If a challenge dose is readministrated unknowingly, a reoccurrence of anticonvulsant hypersensitivity happens within 24 hours and toxic epidermal necrolysis is more likely.[9] In earlier trials of diagnostic rechallenge, severe reactions developed even with a 1-mg dose of phenytoin. Our patient's case reaffirms that severe reactions occur with repeat drug exposure; the amount of surface area and the number of sites increased dramatically between our patient's second and third exposure. No other case of more than two exposures has been reported. Documentation of three exposures has been found, and since the first documented reaction occurred within 24 hours of exposure, our patient must have been exposed previously at least once more, making a minimum of four total exposures.

MedicAlert. bracelet indicating her drug allergy. Wearing this bracelet should be recommended, especially to all patients with anticonvulsant hypersensitivity because these patients may present post-ictal or in status epilepticus. Unlike imitations available at some drug stores, MedicAlert supplies the only identification jewelry that provides instant identification and a lifelong medical file that may be updated. These files are available in emergent situation to physicians and other emergency medical responders by a 24-hour worldwide collect-call phone system. Identification emblems are also widely used by patients with chronic conditions such as diabetes mellitus, Alzheimer's, hemophilia, and hearing impairments. Except for a few sponsored memberships, patient cost includes a $35 registration fee and $15 annual renewal fee. Physicians can receive a display with brochures free of charge from 1-800-ID-ALERT (1-800-825-3785.) As a nonprofit 3.8-million-member organization endorsed by the American Academy of Family Physicians the MedicAlert Foundation claims that 80,000 American lives have been saved since 1956; this claim is based on a membership survey in which 5% reported that MedicAlert "saved my life."[13,14]