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Study: Brimonidine significantly reduces daytime IOP
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Utilization of brimonidine in a seated position significantly lowered intraocular pressure by increasing uveoscleral outflow, according to a recent study published in the Journal of Glaucoma.
Researchers also found that brimonidine did not have the same effect at night.
Fan and colleagues conducted the double-masked, randomized, crossover study in 30 participants with ocular hypertension. According to the study, the participants self-administered 0.2% brimonidine tartrate or the placebo, artificial tears, three times daily.
Researchers measured aqueous flow by fluorophotometry, episcleral venous pressure by venomanometry, outflow facility by tonography, and both supine and seated IOP by pneumatonometry. They also calculated uveosclearal outflow mathematically, as detailed in the study.
Results showed that the brimonidine significantly lowered seated daytime and nighttime IOP as well as supine daytime IOP. The researchers concluded that the effect of the brimonidine depended upon several factors, including the position of the participant as well as the time between the last dose and measurement.
"The most plausible explanation for brimonidine’s effect on IOP is an increase in uveoscleral outflow," they reported. "The IOP reduction during the day occurred within 1 hour of the previous dose, at a time when uveoscleral outflow was increased. The insignificant decrease in IOP at night in eyes dosed with brimonidine may be because the spontaneous nighttime reduction in uveoscleral outflow, seen in healthy subjects or patients with OHT, counteracts the mechanism of action of brimonidine.
"The hypothesis that brimonidine, like prostaglandin analogs, would reduce nighttime IOP because of its effects on uveoscleral was not proven true," they continued. "A shorter duration of action of brimonidine as compared with prostaglandins may be a contributory factor. Had a dose been administered at 1 a.m., a nighttime IOP reduction might have been detected."
Disclosure: The authors have no relevant financial disclosures.
Perspective
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Scott Anthony, OD, FAAO
The importance of nocturnal intraocular pressure dynamics has surfaced as a new paradigm in glaucoma management. The push for developing a commercial 24-hour IOP monitoring device is ongoing, but we currently have very little means to track nocturnal IOP behavior.
This study sheds light on the hypotensive effects of brimonidine during sleep, which was found to be negligible in a supine position compared to placebo.
If we move into an era of improved IOP oversight, the nocturnal profile for ocular hypotensive agents will become more apparent. Until we reach that point, studies such as these may help clinicians customize glaucoma treatments by selecting those that demonstrate a greater nocturnal IOP lowering effect, which they found not to be the case with brimonidine.
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