title: Improving the therapeutic index of topical phenylephrine by reducing drop volume.
abstract: This study examined the effect of reducing eyedrop volume on the efficacy and systemic absorption of a given quantity of phenylephrine hydrochloride. Aqueous phenylephrine hydrochloride (2.5%) given in the commercially available drop volume of 32 microliters was compared with 10% aqueous phenylephrine given in an 8-microliters volume. Both preparations contained the same total amount of phenylephrine per drop. Ten subjects had both eyes dilated with each of the phenylephrine solutions according to a randomized, double-crossover sequence. The mean final pupillary diameter was nearly 1.0 mm larger for the 8-microliters drop (P = 0.0033). Nine of ten subjects achieved a larger pupillary diameter with the 8-microliters drop. Systemic absorption, as measured by plasma phenylephrine level, was similar for the two drop volumes. Thus, the 8-microliters drop achieved a significantly larger pupillary dilation without an increase in systemic absorption. Phenylephrine may have the most favorable risk-benefit ratio when administered as a high concentration in a small volume.
authors: Department of Ophthalmology, University of Texas Health Science Center, Dallas 75235.
authors: R H
authors: RH
authors: Brown
authors: T S
authors: TS
authors: Wood
authors: M G
authors: MG
authors: Lynch
authors: R D
authors: RD
authors: Schoenwald
authors: D S
authors: DS
authors: Chien
authors: L W
authors: LW
authors: Jennings
mesh_terms: D000287:Administration, Topical; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009883:Ophthalmic Solutions; D009994:Osmolar Concentration; D010656:Phenylephrine / Q000008:administration & dosage* / Q000097:blood / Q000627:therapeutic use
chemical_list: D009883:Ophthalmic Solutions; D010656:Phenylephrine