why is l-dopa usually given in combination with carbidopa
Carbidopa/levodopa It is primarily used to improve the symptoms of Parkinson's disease but does not change the course of the disease.[1] It can take two to three weeks of treatment before benefits are seen.[2] Each dose then begins working in about ten minutes with a duration of effect of about five hours.[2][3]
Methyl tert-butyl ether In the US it has been used in gasoline at low levels since 1979, replacing tetraethyl lead as an antiknock (octane rating) additive to prevent engine knocking. Oxygenates also help gasoline burn more completely, reducing tailpipe emissions and dilute or displace gasoline components such as aromatics (e.g., benzene). Before the introduction of other oxygenates and octane enhancers, refiners chose MTBE for its blending characteristics and low cost.