Laser Doppler Flowmetry Study of Systemic Vasoconstriction after Topical 2.5% Phenylephrine Eye Drops

Abstract

Abstract: : Purpose: To study the systemic vasoconstrictive effects of topical 2.5% phenylephrine. Methods: Prospective Study. After IRB approval, subjects were recruited to undergo monitoring of peripheral blood flow with laser Doppler flowmetry via a surface probe applied to right index finger. Each subject was monitored for five minutes at baseline. Then, each received one drop of proparacaine solution in each eye; and monitoring was continued for two minutes. Next, one drop of 2.5% phenylephrine was administered in each eye; and monitoring was continued for an additional five minutes. Changes in flow were analyzed with paired t–test. Results: Ten subjects volunteered to participate in the study. Analysis of laser Doppler flowmetry data at the level of the finger showed a significant vasoconstrictive response to both proparacaine and phenylephrine. At the time of proparacaine administration, blood flow at the index finger dropped a mean of 50% from baseline (p<0.001). Within 30 seconds, blood flow in all of the subjects returned to baseline. At the time of phenylephrine administration, blood flow decreased by 52% (p<0.001). In contrast to proparacaine, phenylephrine also caused a sustained vasoconstrictive effect that lasted 2 to 3 minutes after the drops were administered (p<0.001). Conclusions: This study indicates that administration of 2.5% phenylephrine causes a significant systemic vasoconstrictive response, which lasts for 2–3 minutes. In contrast, proparacaine causes vasoconstriction for only 30 seconds. The vasoconstrictive effect of proparacaine may be because of a sympathetic response to eye drop administration. While this suggests that the peripheral vasoconstrictive effect of phenylephrine 2.5% is not more than the administration of proparacaine, one must take into account the more sustained nature of the phenylephrine–induced response. Patients at high risk for coronary ischemia thus may need to be observed for several minutes after receiving topical phenylephrine.

Keywords: pharmacology • blood supply • drug toxicity/drug effects