Characterization and in vivo evaluation of ocular minitablets prepared with different bioadhesive Carbopol–starch components

The purpose of this study was to evaluate different bioadhesive ocular formulations based on drum dried waxy maize® starch (DDWM), Amioca® starch and Carbopol® 974P. The concentrations of Carbopol® 974P in the mixtures varied between 5 and 25% (w/w). The rheological properties of the non-sterilized and gamma-irradiated physical blends of Carbopol® 974P with either DDWM or Amioca® were compared to those of the corresponding co-spray dried Amioca® starch/Carbopol® powders. Higher viscosity or consistency values were measured for sterilized co-spray dried powder mixtures containing an amount of Carbopol® 974P equal or above 15% (w/w) compared to the physical blends.Sustained release minitablets (Ø 2 mm, 6 mg), consisting of sodium fluorescein as model drug and the bioadhesive powders, were manufactured at a compression force of 1.25 kN. Afterwards, the tablets were sterilized with gamma-irradiation. The amount of Carbopol® in the co-spray dried powder mixtures on the one hand and gamma-irradiation on the other hand had no significant influence on the crushing strength and friability of the minitablets evaluated. However, these two factors affected the in vitro release properties of the minitablets. The slowest release was obtained with tablets containing 25% Carbopol® 974P, which unfortunately possess mucosal irritating properties. By using co-spray dried Amioca® with 15% (w/w) Carbopol® 974P, a slower release can be achieved compared to the physical mixtures of DDWM or Amioca® starch with Carbopol® 974P. Moreover, this ocular formulation is very promising and is preferred, as it did not cause any mucosal irritation and released the model drug for at least 12 h, after application in the fornix.