Lyophilised wafers as vehicles for the topical release of chlorhexidine digluconate--release kinetics and efficacy against Pseudomonas aeruginosa.

There is a requirement to deliver accurate amounts of broad spectrum antimicrobial compounds locally to exuding wounds. Varying amounts of exudate complicates this process by limiting the residence and therefore efficacy of active substances. Minimum bactericidal concentrations (MBC) of antimicrobials are necessary to suppress infection and lessen the chances of resistant strains of potentially pathogenic bacteria from prevailing. Polysaccharide wafers can adhere to exudating wound beds, absorbing fluids and forming highly viscous gels that remain in situ for prolonged periods of time to release sustained amounts of antimicrobial. In this study, five different formulations were produced containing the antimicrobial, chlorhexidine digluconate (CHD). Absorption of simulated wound fluid, resultant rheological properties of gels and efficacy against plated cultures of Pseudomonas aeruginosa were measured and compared. CHD reduced the 'water uptake' of wafers by 11-50% (w/w) and decreased the rheological consistency of non-SA containing gels by 10-65%. Release studies indicated that karaya wafers gave the highest sustained release of CHD, >60 μg/mL in 24 h, well in excess of the MBC for P. aeruginosa. Release kinetics indicated an anomalous diffusion mechanism according to Korsmeyer-Peppas, with diffusion exponents varying from 0.31 to 0.41 for most wafers except xanthan (0.65).