On Dec. 3, 2013, the FDA issued a public safety warning cautioning of the risk of Stevens Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), serious and sometimes fatal skin reactions  associated with the anti-seizure medication Onfi (clobazam).

“Stevens Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), can occur at any time during Onfi treatment,” the FDA warned. “However, the likelihood of skin reactions is greater during the first [eight] weeks of treatment or when Onfi is stopped and then re-started. All cases of SJS and TEN in the FDA case series have resulted in hospitalization, one case resulted in blindness, and one case resulted in death.”

Hallmarks of Stevens Johnson Syndrome are flu-like symptoms that produce a potentially life-threatening skin disease manifested by a rash similar to a burn, open sores and skin peeling. Patients often suffer a purplish rash that spreads, painful blisters of the mucus membranes, including blisters on the eyes, nose, mouth, and genitals, sloughing off of skin in large patches, joint and muscle pain and a burning sensation all over the body.

Toxic Epidermal Necrolysis (TEN) is a more deadly form of Stevens Johnson Syndrome. Up to 40 percent of people who suffer TEN die from complications associated with the painful disease, compared with five to 15 percent of those with Stevens Johnson Syndrome (SJS). Survivors may experience lifelong health problems such as a secondary skin infection (cellulitis), sepsis (a blood infection), blindness, internal organ damage and permanent skin damage.

Onfi (“On-fee”) is an anti-seizure drug used in conjunction with other medications to treat seizures associated with Lennox-Gastaut syndrome in adults and children 2 years of age or older. Onfi belongs to a class of drugs called benzodiazepines and is a federally controlled substance because it can be abused or lead to dependence.

Lennox-Gastaut Syndrome is a severe form of epilepsy that causes debilitating seizures and begins before four years of age. According to the NIH, the seizures may be tonic (stiffening of the body, upward deviation of the eyes, dilation of the pupils, and altered respiratory patterns), atonic (brief loss of muscle tone and consciousness, causing abrupt falls), atypical absence (staring spells), and myoclonic (sudden muscle jerks).

The FDA approved Onfi for the treatment of Lennox-Gastaut in 2011. It is believed that Onfi works by enhancing the effects of a natural brain chemical which, when released, slows activity of nerve cells in the brain.

The FDA recommends that patients taking Onfi be monitored for signs and symptoms of Stevens Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) throughout the course of the medication but especially during the first two months of treatment or when therapy is stopped and then re-started. Medical attention should be sought at the first sign of rash.

Between 2011 and September 2013, according to the FDA, doctors prescribed approximately 31,000 patients prescriptions from outpatient retail pharmacies. More recent numbers indicate 151,000 Onfi prescriptions written since FDA approval.