The notion of zinc ion availability (ZIA) used here is derived from Fick's first and second laws of diffusion, but ZIA does not measure the amount of Zn²⁺ ion absorbed across biologic membranes. By calculating ZIA values for the various studies, the finding of linearity in response to treatment suggests ZIA to be a relative determinant of the amount absorbed in compliance with Fick's laws of membrane diffusion. Therefore, ZIA is defined as the potential for daily absorption of Zn²⁺ ions into oral and oropharyngeal mucosal membranes at pH 7.4 between lozenges having several different characteristics, or ZIA = KZiT, where K = 0.7697, and Zi = initial concentration of Zn²⁺ ions, and T = time.

For calculation of daily ZIA for comparative purposes between lozenge formulations, the daily ZIA value equals the constant 0.7697, times lozenge zinc dosage (mg), times fraction as Zn²⁺ ion at pH 7.4 (initial fraction before precipitation of Zn²⁺ ions by salivary proteins and absorption into oral mucosal membranes), times oral dissolution time (minutes) of lozenges, times lozenges used per day, divided by volume (ml) of saliva generated (numerically equal to total saliva generated minus lozenge weight in grams corrected for lozenge specific gravity) during each oral dissolution. Some of these facts can be determined only by studying the intra-oral dissolution/expectorations of zinc-laden saliva, or zinc-laden saliva. Linear, or at least uniform, lozenge dissolution rates occur in all lozenges tested.

To further illustrate, the ZIA value of the original 1984 Eby lozenges (Antimicrobial Agents and Chemotheraphy Volume 25, Number 1, pages 20 through 24) was set at 100 as a standard reference. The 660 mg lozenges contained 23 mg zinc gluconate initially which released 30 percent Zn²⁺ ion at pH 7.4. Lozenges dissolved in 30 minutes, and were used 9 times a day. Each lozenges generated 15 ml zinc-laden saliva. Numerically, the result is +129.92K. Therefore, to set the ZIA to 100 for the Eby lozenges as a standard; K, therefore, equals 0.7697 ml divided by minutes times mg times doses/day.