In this double-masked, placebo-controlled, parallel, randomized, single-center study, the subjects were assigned to one of four groups after a 2- to 3-week screening and entry phase. The treatment groups were (1) 8 mg RBX twice daily (n = 7); (2) 16 mg RBX per day (n = 7); (3) 16 mg RBX twice daily (n = 8); or (4) placebo (n = 7). RBX-placebo was provided so that all subjects took two identical-appearing capsules twice daily. RBX was taken orally with a meal to maximize absorption. The dose regimen lasted 28 days for all treatment groups.
During the screening and entry period of the study, patients were evaluated using the tests listed below to determine eligibility. On the day of treatment group assignment (randomization visit), subjects received the first dose of study medication and stayed at the clinic for the remainder of the day for safety assessments. Subjects returned weekly for further safety and pharmacodynamic assessments until the 28-day follow-up visit was completed.
The following systemic safety assessments were performed before randomization and at each subsequent visit: collection of adverse events, pulse, respiration, systolic blood pressure, diastolic blood pressure, temperature, urinalysis, serum creatinine, blood urea nitrogen, hematocrit, hemoglobin, mean cell volume, mean cell hemoglobin, platelet count, electrolytes, serum albumin, total protein, calcium, phosphorous, electrocardiogram, creatinine phosphokinase, lactate dehydrogenase, alanine aminotransaminase, aspartate aminotransaminase, γ-glutamyl transferase, bilirubin, and alkaline phosphatase. The following safety evaluations were performed before randomization and at the final visit: prothrombin time, partial thromboplastin time, high- and low-density lipoprotein cholesterol, total cholesterol, triglycerides, weight, serum uric acid, and fecal hemoccult. The Scheffé test was used to determine the change in leukocyte count (segmented neutrophils, bands eosinophils, basophils, and monocytes) from baseline to endpoint.
The following ocular safety assessments were performed before randomization and at each subsequent visit: visual acuity (by ETDRS protocol), D15 color testing, visual field 30-2 testing (Humphrey; Carl Zeiss Meditec, Inc., Dublin, CA), clinical cataract assessment, ETDRS retinopathy level (assessed by stereoscopic fundus photography), fluorescein angiography, comprehensive eye examination, intraocular pressure, and contrast sensitivity (Vistech, Dayton, OH) . An immunology panel (see the Methodology section) was measured before randomization and at the final visit. Tetanus toxoid was administered 2 weeks after randomization, and the tetanus titer response was measured at the last visit. Video fluorescein angiographic assessment of mean retinal circulation time and retinal blood flow was performed before randomization and at the final visit.
The trial was conducted in accordance with the Declaration of Helsinki and guidelines for Good Clinical Practice. The protocol was reviewed and approved by the Joslin Diabetes Center institutional review board, and all patients signed a written informed consent form.