The FDA detected 14 cases of vitamin B6 deficiency–linked seizures and two deaths in patients with Parkinson’s disease taking carbidopa/levodopa drugs. Both AbbVie and Novartis market levodopa-based products.
Products containing levodopa and carbidopa, a common drug combination for treating Parkinson’s disease, could trigger seizures, the FDA has found.
The agency conducted a safety review of drugs carrying these compounds and found 14 cases of seizures linked to vitamin B6 deficiency, according to a safety alert on Friday. In all of these cases, levodopa doses exceeded 1,000 mg per day. Seizures were typically focal-onset, meaning they started in a limited region of the brain. They then spread to include both hemispheres, leading to convulsions and causing emergencies in some cases.
Two patients died, both of whom had had low vitamin B6 levels and poorly controlled seizures, the FDA said. Nine patients were given vitamin B6 supplementation, which in all cases led to the resolution of their seizures.
All 14 cases of carbidopa/levodopa-linked seizures were detected through post-marketing surveillance or found in the medical literature, “so there are likely additional cases about which we are unaware,” the FDA said.
While the safety signals arose in those taking oral formulations and enteral suspensions of carbidopa/levodopa, the regulator did not dismiss the possibility that other products—such as injectables or those that use additional compounds to enhance the original drug combo—could carry the same risk. “Biological plausibility suggests there may be a similar risk across all drug products containing carbidopa/levodopa,” the FDA wrote.
The agency has already notified all manufacturers of drugs carrying carbidopa/levodopa, asking them to update the labels of their respective products to carry warnings for vitamin B6 deficiency-associated seizures. In the meantime, healthcare professionals should assess their patients’ vitamin B6 levels at baseline and throughout treatment, and consider supplementation as needed, the FDA recommended.
Levodopa is a synthetic drug that, once it reaches the brain, is converted into dopamine, a neurotransmitter that is deficient in patients with Parkinson’s disease. Levodopa’s therapeutic benefits for Parkinson’s were first established in the 1960s, and the first drug that combined it with the decarboxylase inhibitor carbidopa—which improved its efficacy and safety—entered the market in 1975.
The combo remains in use today. In October 2024, the FDA approved AbbVie’s Vyalev , a levodopa-based therapy for advanced Parkinson’s disease. The product contains foscarbidopa and foslevodopa, prodrugs that can be given continuously over 24 hours as a subcutaneous infusion. Novartis also owns a carbidopa/levodopa product in Stalevo, which additionally uses entacapone to sustain heightened levels of the drug in the bloodstream.
The industry is now opening up new therapeutic avenues for Parkinson’s disease, however. Eli Lilly in January scooped up Ventyx Biosciences for $1.2 billion, gaining access to a pipeline of drugs that target the NLRP3 inflammatory cascade, an underlying pathway driving the condition. Also looking at an immune-centered approach to Parkinson’s is AC Immune, which in December 2025 demonstrated slower disease progression in patients treated with its anti-alpha-synuclein therapy.
