D2 receptor blockade by flunarizine and cinnarizine explains extrapyramidal side effects. A SPECT study

Abstract

Twenty-six patients under treatment with the calcium channel blockers flunarizine (Fz) or cinnarizine (Cz) were examined with single-photon emission computed tomography using [123I]iodobenzamide as a ligand. The striatal dopamine D2 receptor-binding potential was determined and found to he reduced by 14 to 63% (39.5 ± 15.0%; p < 0.0001) in patients compared with age-matched control values. This reduction was larger in 12 patients with extrapyramidal symptoms and was only slowly reversible after discontinuation of treatment. Patients treated for >6 months had significantly larger reductions than patients treated for a shorter period. Parkinsonian symptoms were only seen in patients older than 50 years. Our findings prove a neuroleptic-like action of Fz and Cz, which seems to be the major reason for their extrapyramidal side effects. Older age and long-term treatment are predisposing factors for these effects. Cinnarizine, Dopamine D2 receptors, Extrapyramidal side effects, Flunarizine, Iodobenzamide, SPECT.