Tropicamide (N-ethyly-2-phenyl-N-(4-pyridyl-methyl)-hydracrylamide) is a chemical compound.

It appears as a white powder soluble in water and stable in aqueous solution with an acid pK of about 5.0.

What it is used for and where

Medical

Tropicamide is an anticholinergic medicinal active ingredient (i.e. it exerts counter activity at the receptors of acetylcholine, a neurotransmitter of nerve cells) used in drops in eye drops to induce mydriasis (dilation of the pupil) of short duration or cycloplegia (ciliary paralysis of the eye) (1). It is absorbed fairly quickly after eye instillation, but complete recovery from mydriasis can take up to 24 hours. These drops, which stop the action of the ciliary and iris muscles, prove useful in refractive examinations, surgery and pupil dilation. 

In comparison, Tropicamide is similar to atropine, has a more rapid onset and shorter duration than other parasympatholytics, is considered less effective than cyclopentolate (2), but recovery is five times faster than cyclopentolate. With regard to the possible modification of retinal vessels, Tropicamide does not appear to alter their width (3).

Tropicamide is being developed for the treatment of sialorrhoea, a condition that causes excessive salivation (4).

Safety

Tropicamide is generally considered safe, but since it fails to give good pupil dilation when used alone, it is often combined in eye drops with phenylephrine, which different clinical cases in the literature indicate as an ophthalmic allergen (5).

• Molecular Formula     C₁₇H₂₀N₂O₂
• Molecular Weight   284.35 g/mol     
• CAS  1508-75-4
• UNII  N0A3Z5XTC6  
• EC Number   216-140-2

References_____________________________________________________________________

(1) Moghadas Sharif N, Shoeibi N, Heydari M, Yazdani N, Ghasemi-Moghaddam S, Ehsaei A. Effect of cyclopentolate versus tropicamide on anterior segment angle parameters in three refractive groups. Clin Exp Optom. 2021 Mar;104(2):151-155. doi: 10.1111/cxo.13103.

(2) Proskurina, O.V., 2002. Cycloplegic effectiveness of cyclopentolate and tropicamide preparations compared with atropinization. Vestnik Oftalmologii, 118(6), pp.42-45.

Abstract. To gain a comparative estimate of cycloplegic agents with mild effect vs conventional atropinization, a study was performed on refraction in 57 children after instillations of cyclopentolate and atropine and in 57 children after instillations of tropicamide and atropine. A difference was determined in refraction after instillation of cycloplegic agents with mild effect and atropine. It turned out that by depth of cycloplegic effect cyclopentolate is reaching that of atropine. Cyclopentolate can be used in initial study of refraction in children with hypermetropic and myopic refraction and in repeated studies of any refraction. Tropicamide is less effective cycloplegic agent than cyclopentolate and thus it can be used in initial studies of refraction in children with myopia and in repeat studies of refraction in children with myopia and hypermetropia and also in cases of intolerance of other cycloplegic agents.

(3) Frost, S., Gregory, C., Robinson, L., Yu, S., Xiao, D., Mehdizadeh, M., Burnham, S., Dehghani, C., Vignarajan, J., Kanagasingam, Y. and Schlaich, M.P., 2019. Effect of pupil dilation with tropicamide on retinal vascular caliber. Ophthalmic Epidemiology, 26(6), pp.400-407.

Abstract. Purpose: The retinal blood vessels reflect changes in the brain’s micro-circulation and these changes have been shown to correlate with the incidence of diseases such as stroke, heart disease and Alzheimer’s disease. Studies investigating the retinal vasculature routinely use pupil dilation with tropicamide to optimize image acquisition and quality. The aim of this study was to investigate the effects of tropicamide on retinal vascular parameters using retinal photography. Methods: The study was performed on 41 healthy young subjects of both sexes, using tropicamide to dilate only the right pupil, leaving the left as a control. Results: Pupil dilation with tropicamide resulted in reduced retinal vessel width measures based on standardized approaches, particularly reduced arteriolar caliber (p < .0005). However, closer investigation of the images revealed reduced fundus image magnification in the post-tropicamide images, based on reduced optic nerve head diameter (p < .0005) and longitudinal analysis with image registration and affine transformation (p < .0001). No change in vessel width parameters was observed after adjustment for image magnification. Conclusion: These results suggest that tropicamide does not change the width of the retinal vessels, however width parameters as measured by standard approaches may be reduced due to image magnification changes resulting from cycloplegia. In this study, improved optic nerve head segmentation for image scale conversion removed the magnification error. With this correction, the tropicamide intervention had no effect on vessel width parameters in young healthy people and could be utilized in future without affecting the results of retinal vascular analysis.

(4) Perez-Lloret S, Rey MV, Pavy-Le Traon A, Rascol O. Emerging drugs for autonomic dysfunction in Parkinson's disease. Expert Opin Emerg Drugs. 2013 Mar;18(1):39-53. doi: 10.1517/14728214.2013.766168. 

Abstract. Introduction: Autonomic dysfunction, including orthostatic hypotension (OH), sialorrhea, sexual dysfunction, urinary dysfunction and constipation is a common feature of Parkinson's disease (PD). Even though its treatment has been recognized as a major unmet need in PD, there is a paucity of clinical trials to assess their treatment. Areas covered: Evidence about the efficacy and safety of available treatments for autonomic dysfunction is summarized. Potential targets for upcoming therapies are then discussed in light of what is currently known about the physiopathology of each disorder in PD. Proof-of-concept trials and circumstantial evidence about treatments for autonomic dysfunction as well as upcoming clinical trials are discussed. Finally, critical aspects of clinical trials design are considered. Expert opinion: Botulinum toxin (BTX) or glycopyrrolate might be used for sialorrhea whereas macrogol could be useful in constipation. There is preliminary evidence suggesting that fludrocortisone, domperidone, droxidopa or fipamezole may be effective for the treatment of OH. Tropicamide, clonidine or radiotherapy are under development for sialorrhea. Sildenafil may be effective for the treatment of erectile dysfunction; BTX or behavioral therapy for urinary incontinence and lubiprostone and probiotics for constipation. Sound clinical trials are needed in order to allow firm evidence-based recommendations about these treatments.

(5) K Lodhi SA, Ramsali MV, Kulkarni DK, Surender P, Murty S. Safety of tropicamide and phenylephrine in pupillary mydriasis for cataract surgery. Saudi J Ophthalmol. 2022 Feb 18;35(2):108-111. doi: 10.4103/1319-4534.337859.