Biomedical subjects

A T Florence

Publications and source records attributed to A T Florence.

At least 109 records · Page 6Linked to original sources

PubMed1976

Changes in crystallinity and solubility on comminution of digoxin and observations on spironolactone and oestradiol.

Using infrared spectroscopy, X-ray diffractometry, differential thermal analysis, scanning electron microscopy, solubility and dissolution rate measurements, it was demonstrated that the comminution of digoxin results in the appearance of an amorphous phase. The examination of spironolactone and 17 beta-oestradiol by infrared spectroscopy and differential thermal analysis showed that these compounds also undergo changes in their crystallinity on grinding. Since the dissolution characteristics of poorly soluble drugs may be complex functions of surface area and crystallinity, it is concluded that the most pertinent method for standardizing a sample of a polymorphic drug of low solubility is by means of a powder dissolution test, as the results embrace the influences of particle size, aggregation and polymorphism.

Chemistry, Pharmaceutical↗

PubMed1975

Non-ionic surfactants and membrane transport of thioridazine in goldfish.

Polysorbate 80, which has been widely used in studies of the effects of surfactants on drug absorption, increases the rate of absorption of some drugs at concentrations near its critical micelle concentration (cmc). To determine whether all non-ionic surfactants were capable of inducing this effect, the effects of six commercial non-ionic surfactants on thioridazine absorption in goldfish have been compared with the effect of polysorbate 80. The reciprocal death time (T-1) determined when the fish were immersed in the solution under study was the index of absoprtion rate used. Not all surfactants tested increased T-1. Cremophor EL (polyoxyethylated castor oil), Atlas G1295 (a polyoxyethylene fatty glyceride), Atlas G1300 (a polyoxyethylene glyceride ester) had no effect below their cmc's. Those surfactants that did increase T-1 [polysorbate 80 (a polyoxyethylene lanolin derivative), G2162 (a polyoxyethylene oxypropylene monosterate) and Renex 650 (a polyoxyethylene alkyl aryl ether)] display the concentration-dependent behaviour reported previously - a decrease in absorption rate when the surfactant concentration is increased above its cmc. The factor determining whether or not the surfactant will increas absorption rate appears to be the configuration of the surfactant molecule rather than its hydrophile-lipophile balance or its surface activity.

Animals↗

PubMed1975

Emulsion stabilization by non-ionic surfactants: the relevance of surfactant cloud point.

The effect of various additives, electrolytes and non-electrolytes, on the cloud point of non-ionic surfactants has been studied. Additives which salt-out the polyoxyethylene chains of the surfactants cause decreased stability of oil-in-water emulsions by decreasing the true hydrophile-lipophile balance (HLB) of the surfactant; additives such as sodium iodide and propanol salt-in the non-ionic surfactants and result in an increase in the effective or true HLB of the system. The latter additives do not increase the hydration of the polyoxyethylene chains but their effect must be on the structure of water so that the heat of hydration of the chains is altered. Experiments with free films of the aqueous surfactant (Brij 96) show that thinning rates are markedly affected by the additives, but there is little effect on the equilibrium thickness of the films (ca 11 nm). Nonetheless the thickness at the transition from thick film to equilibrium black film decreases with increasing cloud point of the solution indicating increased stability. The importance of structure formation in the liquid film separating the emulsion globules was demonstrated.

Chemical Phenomena↗

PubMed1975