<p>Pyridoxine Hydrochloride should not be given to patients receiving the drug levodopa, because the action of levodopa is antagonized by Pyridoxine Hydrochloride. However; Pyridoxine Hydrochloride may be used concurrently in patients receiving a preparation containing both carbidopa and levodopa. Concurrent use of phenytoin and folic acid may result in decreased phenytoin effectiveness.</p>