Two years after the U.S. Food and Drug Administration (FDA) approved Onfi tablets (clobazam) as an add-on treatment for Lennox-Gastaut syndrome seizures in adults and children 2 years of age and older, the federal agency issued an Onfi SJS warning that the anti-seizure drug can cause Stevens Johnson Syndrome–a rare, but serious, skin reaction–that can result in permanent harm and death.

Onfi is a benzodiazepine medication used in combination with other drugs to treat seizures associated with Lennox-Gastaut Syndrome, a severe form of epilepsy that causes “debilitating seizures.”

The Onfi drug label and the latest patients’ medication guide changes describe the risk of serious skin reactions like Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN). According to the Onfi drug labels, the manufacturers now warn consumers that SJS and TEN can occur at any time during treatment.

“Patients taking Onfi should seek immediate medical treatment if they develop a rash, blistering or peeling of the skin, sores in the mouth, or hives,” the December 2013 FDA Onfi SJS announcement reads. “Health care professionals should discontinue use of Onfi and consider an alternate therapy at the first sign of rash, unless it is clearly not drug-related.”

According to the FDA, the likelihood of a patient developing an Onfi SJS and TEN skin reaction is greatest during the first eight weeks of treatment or when Onfi treatment is stopped and then re-started. All cases of Onfi SJS and TEN in the FDA case series have resulted in hospitalization. Additionally, one case resulted in blindness and one remaining case resulted in death.

Lennox-Gastaut, Onfi, and SJS/TEN Reactions

The National Institutes of Health (NIH) states that Lennox-Gastaut seizures usually begin before 4 years of age, ranging from 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).

“There may be periods of frequent seizures mixed with brief, relatively seizure-free periods,” according to the NIH. “Most children with Lennox-Gastaut syndrome experience some degree of impaired intellectual functioning or information processing, along with developmental delays, and behavioral disturbances. Lennox-Gastaut syndrome can be caused by brain malformations, perinatal asphyxia, severe head injury, central nervous system infection and inherited degenerative or metabolic conditions. In 30-35 percent of cases, no cause can be found.” According to FDA reports and Onfi SJS lawsuits, children and adults suffering from this already hard to manage neurological condition may also be at risk of developing SJS or TEN when taking their clobazam medication.

SJS and TEN are extremely painful skin conditions that begin with flu-like symptoms (fever, fatigue, and sore throat), later followed by lesions and ulcers forming on the mouth, lips, genital, and anal regions, and rashes covering the body. SJS rashes appear as burns and open sores, which later lead to skin sloughing off the victims body in large swaths. Painful blisters also develop on the mucous membranes, such as the eyes, nose, mouth and genitals. Onfi SJS patients may also experience joint and muscle pain, along with a sensation that their body is burning.

Up to 40 percent of people who suffer from TEN die from complications associated with the painful disease, which is quite high when compared with the 5 to 15 percent death rate of SJS victims. SJS/TEN 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.