March 20 (Reuters) - The U.S. Food and Drug Administration said on Friday it has notified manufacturers of certain Parkinson's disease treatments to update their prescribing information with a new warning about a potential risk of seizures.

The drugs containing the ingredients carbidopa or levodopa should state that they can cause vitamin B6 deficiency and seizures associated with it, the health regulator said.

Carbidopa and levodopa are almost always taken together to treat symptoms of Parkinson's disease, a progressive nervous system disorder that occurs when brain cells produce insufficient dopamine, leading to tremors, stiffness and slow movement.

The FDA said it conducted a safety review and identified 14 cases of seizures linked to vitamin B6 deficiency in patients using these drugs. These seizures usually start in one part of the brain and then spread, potentially becoming severe and prolonged.

Healthcare professionals should evaluate vitamin B6 levels before starting patients on these drugs and consider whether supplementation is necessary, the regulator said.

Levodopa turns into dopamine in the brain, replenishing the diminished levels seen in Parkinson's disease and improving movement. Carbidopa helps ensure more levodopa reaches the brain by preventing its premature breakdown in the body.

Drugs containing these ingredients can deplete vitamin B6 levels during the process by which levodopa is converted into dopamine. Carbidopa binds to the active form of vitamin B6, resulting in additional functional loss of the vitamin, the FDA said.

Amneal AMRX.O, AbbVie ABBV.N, Organon OGN.N and Novartis NOVN.S manufacture drugs containing carbidopa or levodopa. The companies did not immediately respond to Reuters' requests for comment.

(Reporting by Christy Santhosh and Puyaan Singh in Bengaluru; Editing by Shilpi Majumdar)

((Christy.Santhosh@thomsonreuters.com;))