Epinephrine for the treatment of anaphylaxis: do all 40 mg sublingual epinephrine tablet formulations with similar in vitro characteristics have the same bioavailability?

Epinephrine autoinjectors are underutilized in the first aid emergency treatment of anaphylaxis in the community; so non-invasive sublingual epinephrine administration is being proposed. In order to determine the effect of changing excipients on the bioavailability of sublingual epinephrine, four distinct fast-disintegrating epinephrine 40 mg tablet formulations, A, B, C and D, were manufactured using direct compression. All formulations were evaluated for tablet hardness (H), disintegration time (DT) and wetting time (WT). In a prospective 5-way crossover study, four sublingual formulations and epinephrine 0.3 mg i.m. as a control were tested sequentially in a validated rabbit model. Blood samples were collected before dosing and at intervals afterwards. Epinephrine plasma concentrations were measured using HPLC-EC. All tablet formulations met USP standards for weight variation and content uniformity, and resulted in similar mean H, DT and WT (n=6). The area under the curve (AUC), maximum concentration (C(max)) and time at which C(max) was achieved (T(max)) did not differ significantly after the sublingual administration of formulation A and epinephrine 0.3 mg i.m. The AUC after B, C and D were significantly lower (p<0.05) than after epinephrine 0.3 mg i.m. These results suggest that the selection of excipients used in these tablet formulations can affect the bioavailability of sublingually administered epinephrine.