PAREMYDÒ Solution combines the effects of the adrenergic agent, hydroxyamphetamine hydrobromide, and the anticholinergic agent, tropicamide.

Hydroxyamphetamine hydrobromide is an indirectly-acting sympathomimetic agent which, when applied topically to the eye, causes the release of endogenous norepinephrine from intact adrenergic nerve terminals resulting in mydriasis. Since hydroxyamphetamine hydrobromide has little or no direct activity on the receptor site, dilation does not usually occur if there is damage to the presynaptic nerve terminal, e.g., Horner's Syndrome. However, it is not known whether damage to the presynaptic nerve terminal will influence the extent of mydriasis produced by PAREMYDÒ. Hydroxyamphetamine hydrobromide has minimal cycloplegic action.

Tropicamide is a parasympatholytic agent which, when applied topically to the eye, blocks the responses of the sphincter muscle of the iris and the ciliary muscle to cholinergic stimulation, producing dilation of the pupil and paralysis of the ciliary muscle. Tropicamide produces short-duration mydriasis. Although cycloplegia occurs with higher doses of tropicamide, there is evidence with 0.25% tropicamide that full cycloplegia does not occur.

Since both these agents act on different effector sites, their simultaneous use produces an additive mydriatic effect. PAREMYDÒ provides diminished pupil responsiveness to light, facilitating ophthalmoscopy. The onset of action with PAREMYDÒ occurs within 15 minutes, followed by maximum effect within 60 minutes after instillation of one drop. Clinically significant dilation, inhibition of pupillary light response, and partial cycloplegia last 3 hours, with recovery beginning at approximately 90 minutes and with complete recovery occurring in most patients in 6 to 8 hours. However, in some cases complete recovery may take up to 24 hours. Effectiveness may differ slightly in patients with light and dark irides, with those patients with light irides experiencing a slightly greater mydriasis.

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