FDA Warns of Rare but Serious Drug Reaction to Antiseizure Medicines

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The medicines, levetiracetam and clobazam, may a cause life-threatening reaction to patients if not caught and treated quickly.

On Nov. 28, 2023, FDA released a warning concerning the antiseizure medicines levetiracetam (Keppra, Keppra XR, Elepsia XR, Spritam) and clobazam (Onfi, Sympazan). These medicines can cause a rare but serious reaction called Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), which can be life-threatening if not diagnosed and treated quickly. The reaction often starts off as a rash but can quickly progress, leading to injury to internal organs, hospitalization, and even death. Because of this, FDA is mandating that warnings about this risk be added to the prescribing information and patient medication guides for levetiracetam and clobazam.

DRESS can include fever, rash, swollen lymph nodes, or injury to organs including the liver, kidneys, lungs, heart, or pancreas. It can develop two to eight weeks after starting the medicines, and symptoms and intensity can vary widely. DRESS can also be confused with other serious skin reactions, such as Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis. Affected patients are advised to find immediate medical attention if DRESS is suspected during treatment with levetiracetam or clobazam.


Levetiracetam is an antiseizure medicine for solo use or use with other medicines to control certain types of seizures in adults and children such as myoclonic seizures, partial seizures, or tonic-clonic seizures. It has been approved by FDA for 24 years, and an estimated 12 million prescriptions were given in the United States in 2022. Clobazam, which has been FDA-approved for 12 years, is a benzodiazepine (a class of medicines that depresses the central nervous system) indicated for use with other medicines to control seizures for patients two years or older for a specific severe form of epilepsy called Lennox-Gastaut syndrome. In 2022, around 779,000 prescriptions for Clobazam were dispensed in the US.

Sources: FDA, FDA