Background: D-Decarboxylase inhibitors, such as carbidopa or benserazide, have been used as adjunct therapy in Parkinson disease shortly after levodopa synthesis in the 1960s. These compounds increase intracerebral drug concentration and decrease adverse effects by blocking peripheral conversion to dopamine. Skin rash as part of an allergic reaction was previously described in subjects who were using levodopa in combination with carbidopa or benserazide; however, etiology was never clear. Allergic reactions to carbidopa have not previously been reported.
Methods: We report a case of a 77-year-old woman with a diagnosis of idiopathic Parkinson disease, who developed autonomic and dermatological signs: conjunctival injection, rhinorrhea, excessive sweating, hypertension, and pruritic generalized rash, among others, immediately after carbidopa/levodopa administration regardless of the manufacturer. Treatment with dexamethasone combined with chloropyramine hydrochloride resulted in complete resolution of the hypersensitivity reaction each time it presented. The autonomic and dermatological manifestations did not reappear after treatment was replaced with benserazide/levodopa.
Conclusions: To the best of our knowledge, this is the first case report of an allergic reaction specific to carbidopa. Our case highlights the importance of identifying the source of a hypersensitivity drug response, whether it is caused by the active component or by the excipients.