Modification of electrostatic charge on inhaled carrier lactose particles by addition of fine particles.

Triboelectrification affects particle adhesion and agglomeration and hence the formulation, manufacture, and use of dry powder inhaler (DPI) devices. Electrostatic charge measurement of two component mixes of spray-dried or crystalline lactose fine particles (< 10 microns) 0, 5, 10, 15, 20, and 30% w/w with spray-dried or crystalline lactose 63-90 microns, respectively, has been undertaken using a system incorporating pneumatic transport of the mixed powders to a stainless steel cyclone charging device. The magnitude of charge on the mixes was shown to decrease with increased fine particle content, and there was no significant difference in charge for each concentration between spray-dried and crystalline lactose. Both the variation of charge and powder adhesion to the cyclone surface increased with increase in fine particle content. The proportion of fine particles in carrier systems in DPIs may thus have an important role where triboelectrification is involved.

An investigation of the parameters influencing the bioadhesive properties of Myverol 18-99/water gels.

An in vitro assessment was undertaken of the parameters influencing the bioadhesive strength of lyotropic liquid crystalline gels formed by the monoglyceride blend Myverol 18-99 and water. The gels were found to bind more strongly to a dry Perspex surface than to moist mucosal tissue and were shown to be weaker bioadhesives than Carbopol 934P and sodium alginate. The works of adhesion and forces of detachment were independent of contact time, were reduced by the presence of surface water and increased with an increase in the compression force, suggesting that interpenetration was not the mechanism of bioadhesion. The bioadhesion of Myverol 18-99/water gels appeared to be due to secondary chemical bonds, such as van der Waals forces, but was limited by their cohesive strength. An in vivo gel retention assessment by gamma scintigraphy showed that the gels were retained within the vaginal cavity for a period of at least 6 h.

The in vitro release of some antimuscarinic drugs from monoolein/water lyotropic liquid crystalline gels.

PURPOSE: To investigate the potential use of a monoolein/water lyotropic liquid crystalline gel for the vaginal delivery of the antimuscarinic drugs, propantheline bromide and oxybutynin hydrochloride to treat urinary incontinence, using Myverol 18-99 as a commercially available grade of monoolein. METHODS: The influence of propantheline bromide and oxybutynin hydrochloride on the phase structure of Myverol 18-99/water gels was investigated using polarising microscopy. The in-vitro release of the antimuscarinic drugs from Myverol 18-99/water gels was determined and the release pattern interpreted with the aid of results from swelling studies and partition coefficient determinations. RESULTS: Myverol 18-99 forms gels with lyotropic liquid crystalline structures in the presence of water. The addition of propantheline bromide and oxybutynin hydrochloride promoted the formation of gels with a lamellar phase structure. The gels absorbed water at a rate inversely proportional to their initial water content until they reached an equilibrium water content of approximately 40% w/w whilst maintaining their physical integrity. The release of the antimuscarinic drugs was sustained over a period of approximately 18 hours and followed square root of time kinetics indicating that the rate of release was diffusion controlled. CONCLUSIONS: The in-vitro release behaviour of Myverol 18-99/water gels suggested that they are suitable carriers to deliver propantheline bromide or oxybutynin hydrochloride. The results of swelling studies indicated that a confined area, such as the vaginal cavity, would be a suitable site of administration.

Photo-oxidation of tetracycline adsorbed on hydroxyapatite in relation to the light-induced staining of teeth.

In an attempt to understand the chemistry of the light-induced staining of children's teeth by tetracycline, we studied the photo-chemical behavior of tetracycline adsorbed on hydroxyapatite, as a simple model of enamel. Tetracycline was strongly bound by hydroxyapatite to give a pale yellow material which, under ultraviolet light, showed a bright yellow fluorescence (lambda max 525 nm). On exposure of this material to the radiation from a medium-pressure mercury lamp, the fluorescence gradually disappeared, and a red-purple product was formed. Photo-acoustic spectroscopy was employed to follow the disappearance of tetracycline and the concomitant formation of the red-purple product, the spectrum of which (lambda max 530 nm) led to the conclusion that it was 4 alpha, 12 alpha-anhydro-4-oxo-4-dedimethylaminotetracycline (AODTC). This assignment was supported by the observation that 1 mole of oxygen was absorbed per mole of adsorbed tetracycline converted to the red-purple product. It is suggested that the formation of AODTC on hydroxyapatite probably takes place by a mechanism of photo-oxidation similar to that already proposed for solutions of tetracycline, and that the formation of AODTC in children's teeth is responsible for the light-induced staining caused by tetracycline.