Rheological properties of gamma-irradiated antimicrobial wafers and in vitro efficacy against Pseudomonas aeruginosa.

Lyophilised polysaccharide solutions and gels incorporating the broad spectrum antimicrobial compound, chlorhexidine digluconate (CHD), have potential application as self-adhering, topical delivery systems for the prophylaxis and treatment of wound infections. It is desirable to sterilise these dosage forms but they do not possess suitable thermal properties to be sterilised by autoclaving or dry heat procedures. Ionising radiation may offer a solution hence 'antimicrobial wafers' fabricated from guar (GG), xanthan (XG), karaya (KAG), sodium alginate (SA) and a 50:50 blend of SA:KAG, were gamma-irradiated (25 and 40 kGy). Wafer sterility was qualitatively determined and validated for bacterial and fungal species. The rheological properties of gels reconstituted from irradiated discs ('wafers') were measured and compared with control samples (non-irradiated) to assess changes to the flow properties. Diffusion of CHD from the resultant gels and viscous solutions, and efficacy against Pseudomonas aeruginosa, was determined using a disc diffusion test and release studies conducted in a diffusion cell apparatus. Although there was no change to cast shape, the rheological properties were drastically depleted for all irradiated samples except XG which showed no effective change in consistency, yield stress or efficacy, from the non-irradiated control. SA and SA-KAG samples displayed 'anomalous' release according to Korsmeyer-Peppas.