Disclosed herein are compositions that include for example the arginine salt of carbidopa, and methods for treating neurological or movement diseases or disorders such as restless leg syndrome, Parkinson's disease, secondary parkinsonism, Huntington's disease, Parkinson's like syndrome, PSP, MSA, ALS, Shy-Drager syndrome and conditions resulting from brain injury including carbon monoxide or manganese intoxication, using substantially continuous administration of carbidopa or salt thereof together with administration of levodopa.