Specific growth rate of bacterioplankton,determined at constant temperature,as an indicator of deterioration in water quality

The specific growth rate (SGR) of natural populations of bacterioplankton, from three lowland watercourses in the northeastern part of England, was measured at intervals over 15 months using a batch-culture method. SGR of the bacteria from one watercourse showed seasonal periodicity with notably low values (<0.01 h⁻¹) in winter which coincided with acid conditions. SGR of bacteria from the other two watercourses, which were permanently circumneutral, showed irregular periodicity and notably low values were never recorded. Thus, SGR is an easily determined indicator which may be used to recognize the inhibition of bacterioplankton, which is brought about by adverse water quality, and which potentially leads to reduction in biopurification capacity. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 309–312, 1999     

Different HPMC viscosity grades as coating agents for an oral time and/or site-controlled delivery system: a study on process parameters and in vitro performances

Currently, delayed/pulsatile release and colon delivery represent topics of remarkable interest. The present paper deals with the study and development of an oral dosage form devised to release drugs following a programmed time period after administration or, when opportune design modifications are introduced, to target the colon. The system is composed of a drug-containing core and a hydrophilic swellable polymeric coating capable of delaying drug release through slow interaction with aqueous fluids. An optional external gastroresistant film is applied to overcome gastric emptying variability, thus allowing colon delivery to be pursued according to the time-dependent approach. The aim of this work was to evaluate different hydroxypropyl methylcellulose (HPMC) viscosity grades as possible materials for the attainment of the system retarding hydrophilic layer. Both the relevant suitability for application onto tablet cores by aqueous spray-coating in fluid bed and capability of delaying drug release for a programmable period were explored and compared. Methocel E50 was found to afford the best balance among different important items, i.e. process time, retarding ability, dimensions of the coated units and possibility of finely tuning the delay duration. Further results pointed out the robustness of Methocel E50-based systems, which have shown to be practically unaffected by the concentration of the employed coating solution and the pH of the release medium, as well as only poorly influenced by ionic strength, at least with regard to values encompassed in the physiological range for gastrointestinal fluids.