Serum, tear, and aqueous azithromycin concentrations are reported in nanograms per milliliter. Biopsy specimens are reported in nanograms per milligram of wet tissue weight. Table 1 shows the azithromycin levels in serum, tear, aqueous, and conjunctival specimens for all study times. The mean serum, tear, and aqueous concentrations with SDs and coefficients of variation are displayed for the sampling points of 3, 6, and 12 hours and 1, 2, 3, and 4 days. Occasional high SD and coefficient of variation values reflect a sample mean in which the number of samples comprising the mean was small (n=3). Concentrations are expressed in nanograms per milliliter for serum, tear, and aqueous samples. Time point statistics are derived from 5 patient samples, except for day 1 tear samples, which could be obtained from only 4 patients, and day 2 and day 3 tear samples, which could be collected from only 3 patients. For aqueous samples, day 3 and day 4 samples could be collected from only 4 patients. Mean biopsy specimen concentrations, with SD and coefficient of variation values, are represented for the sampling points of 1, 2, 3, 4, 6, 8, 10, 12, and 14 days. Concentrations are expressed in nanograms per gram for conjunctival biopsy specimens. Time point statistics are derived from 5 patient samples, except for days 1 and 3, on which 4 conjunctival specimens were collected. Mean accuracy for all quality control samples tested in conjunction with the patient sample run was more than ±10% off their expected target result. Figure 1 displays azithromycin pharmacokinetic profiles in serum, tear, aqueous, and conjunctival specimens. All samples are expressed using a common concentration axis of log micrograms per milliliter vs time in days. The ranges of azithromycin concentration for serum, tear, aqueous, and conjunctival specimens were 21 to 974 ng/mL, 82 to 2892 ng/mL, 10 to 69 ng/mL, and 0.7 to 32 µg/g, respectively, over the sampling time specified. The terminal elimination phase rate constant (Kel) of azithromycin in serum was estimated using least squares methods as the slope of the logarithm of the concentration against the time curve. All samples between 24 and 96 hours were used in its calculation. The apparent rate constant for the elimination in serum was approximately 0.02 per hour, corresponding to a half-life of 44 hours (half-life=log natural/Kel). Table 2 shows ratios of tear fluid, aqueous humor, and conjunctival tissue relative to serum values obtained for the time point and patient value of the ratio. The values in Table 2 are expressed as the mean ratio of the other component (tear, aqueous, or conjunctival) value relative to the time points concentration in serum. Mean ratios were greater in conjunctival tissue samples than in tear, serum, or aqueous samples. Mean concentrations of azithromycin in conjunctival tissue to mean serum concentration ratios were 288, 57, 174, and 257 at 1, 2, 3, and 4 days after administration of azithromycin, respectively.