Tropicamide

Tropicamide is a muscarinic acetylcholine receptor antagonist with moderate binding selectivity for the M4 receptor subtype. In rodent models of parkinsonian tremor induced by the muscarinic agonist pilocarpine or the dopamine antagonist pimozide, tropicamide suppressed tremulous jaw movements in a dose-dependent manner. Analysis of dose-response curves revealed that tropicamide showed approximately the same potency as the nonselective muscarinic antagonist atropine for suppression of pilocarpine-induced jaw movements, but was more potent than atropine for suppression of pimozide-induced jaw movements. In contrast, atropine was more potent than tropicamide in impairing performance on visual stimulus detection and delayed nonmatch-to-position tasks. These findings demonstrate that tropicamide can exert antiparkinsonian effects distinct from its conventional ophthalmic use.

Fig. 1 Mean number of individual tremulous jaw movements after injection of pimozide or pimozide plus various doses of tropicamide or atropine. (Betz A J.; et al. 2007)

Tropicamide-loaded cubic liquid crystalline nanoparticles were prepared using ultrasound-assisted fragmentation of cubic liquid crystalline bulk phases with Pluronic F127 as dispersant. The morphology of the nanoparticles was nearly cubical as observed by transmission electron microscopy, and small angle X-ray scattering confirmed the coexistence of D and P phase cubic structures. The optimized cubic nanoparticles showed in vitro corneal permeation of tropicamide across isolated porcine cornea comparable to the commercial preparation Tropicacyl. In vivo mydriatic response study demonstrated a remarkably higher area under the mydriatic response curve for cubic nanoparticles compared to Tropicacyl.

Fig. 2 Transmission electron micrograph of tropicamide-loaded cubic nanoparticles. (Verma P, Ahuja M. 2016)