Relationship of prostaglandin efficacy with race

It has been indicated in prior studies that there is a link between a patient's ethnicity and the efficacy of prostaglandin analogues. In a study performed by Dr P.A. Netland et al. it was reported that travoprost was significantly better than latanoprost or timolol at lowering intraocular pressure (IOP) in black patients.¹

"Netland and the Travoprost Study Group had reported that travoprost was more effective than latanoprost in lowering IOP in black patients," said Dr Catherine Birt when discussing her initial reasons for performing her study to examine this possible relationship. "Netland et al. later published a reanalysis of two studies, pooling data to examine the response to travoprost in black and non-black patients. These data showed that travoprost lowered mean IOP further in black patients than in non-black patients by an average of 8.1 mmHg compared to 7.0 mmHg respectively."

Considering the results from previous studies, Dr Birt (Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada) and her team were able to perform a prospective randomized investigator-masked multicentre investigation on the relationship between prostaglandin efficacy and patient race.

The investigatormasked, multicentre comparison involved testing three prostaglandins on 83 patients from 9 different sites with either newly diagnosed openangle glaucoma or elevated IOP after a 'washout' period. Each patient was randomized to receive either latanoprost, travoprost or bimatoprost but assignment was balanced by racial group and study site.

"Ethnicity of the patient was based on a self report system, not DNA or other objective markers," added Dr Birt. "The investigators were masked to the drug assignment of the participants which was made on the basis of a randomization schedule, balanced for ethnicity and drug assignment, produced for each participating site by the biostatistician."

Patients completed follow-ups at 2, 6, 12 and 24 weeks, with local side effects assessed each time.

Surprise results

"All three of the prostaglandin drugs were highly effective at lowering IOP. No differences in effect between the drugs or between members of different racial groups were detected, and no interaction between drug and ethnicity was detected," revealed Dr Birt. "Our null hypothesis stated that there would be no ethnic-based difference in IOP lowering effectiveness, and/or safety profile, between the three medications; the alternative hypothesis was that such a difference existed."

The findings did show a significant IOP decrease from baseline to 12 weeks and from baseline to 24 weeks. No interaction was found between racial group and the prostaglandins used. Dr Birt highlighted. "This was in keeping with the null hypothesis. Based on the Netland results, we had expected to find that travoprost was more effective in the African-derived patients, but this is not the result our data supported."

The surprising results may be due to the fact that the study size sample was smaller than desired. Dr Birt claimed, "Our sample size was smaller than required; with unlimited time and money a larger study could be done; a multicentre study in different areas of the world would also be an interesting way of examining this question, but with significant logistical difficulties."

In conclusion, Dr Birt's investigation showed that all three prostaglandins are equally successful in lowering IOP. Dr Birt said, "By increasing uveoscleral outflow and lowering IOP, prostaglandins are highly effective for relieving pressure in open-angle glaucoma patients."

Dr Catherine Birt is a glaucoma specialist and belongs to the Toronto Area Glaucoma Society, Canada. She can be contacted by E-mail: catherine.birt@sunnybrook.ca

Dr Birt has indicated she is a speaker/consultant to Alcon, Allergan, Merck, and Pfizer.

Reference

1. P.A. Netland et al., Am. J. Ophthalmol., 2001;132(4):472–484.