PubMed Health⌕ Search

Biomedical subjects

R L Schnaare

Publications and source records attributed to R L Schnaare.

18 recordsLinked to original sources
PubMed1992

Effect of surfactant phase in perfluorocarbon emulsification efficiency.

The effect of preparation temperature on the emulsification efficiency of perfluoro-3-butyltetrahydrofuran (FC-75) was investigated. Polyoxyethylene (POE) oleyl ether surfactants were used as the emulsifier(s) in a range of HLB values of 7.5 to 9.5. The emulsions were prepared by paddle mixing as a method of low-shear emulsification. After centrifugation of the resulting O/W emulsions, the volume of FC-75 which separated was utilized as a measure of the emulsification efficiency. In general, emulsions prepared at temperatures where the surfactant was in a lamellar-to-isotropic surfactant solution transition, L alpha----L3, displayed a better emulsification efficiency than those prepared with other surfactant phases.

Drug Stability↗
PubMed1991

Bead coating. I. Change in release kinetics (and mechanism) due to coating levels.

Beads containing 50% acetaminophen (APAP) and 50% microcrystalline cellulose (Avicel PH 101) were prepared and then coated using an aqueous ethylcellulose based dispersion (Aquacoat) to evaluate the effect of the coating level on drug release. The APAP release was shown to be dependent on levels of the coating and a change in mechanism was suggested. Drug release from incompletely coated beads at low levels of coating can be described with the square root of time model, while drug release from beads with a high level of coating appears to be best described by zero-order release. At low coating levels, the drug release rate constant based on the square root relationship seems to be linear with the coating level. At high coating levels, drug release rate in terms of a zero-order model appears to be proportional to the reciprocal of the coating level.

Cellulose↗
PubMed1988

Predicting coordinated lipid biosynthesis: application to the surfactant-accommodated epidermis.

Factorialized correlation analysis is proposed as a method for predicting the coordination of multiple enzyme pathways. The approach can be used potentially to find new relationships and to predict relationships that have been established in other tissues. However, careful tracer studies are needed to verify the cause-and-effect relationships between precursor and products. In this study, guinea pigs that were chronically treated with an anionic, a nonionic and a cationic surfactant passed through an irritation stage to a clinical state that appeared normal. The method was used to examine binary coordination of lipid biosynthesis in the epidermis by using a factorialized table of regression coefficients. Coordinated lipid relationships that have been reported in other tissues were predicted between sphingomyelin and cholesterol, as well as between phosphatidylcholine, phosphatidylserine and phosphatidylethanolamine. A new inverse relationship was found between triglycerides and both sphingomyelin and cholesterol, using this method. These data are discussed with respect to a membrane fluidization model for the accommodated state.

Animals↗
PubMed1986

The pharmacodynamic response of the basal skin potential to quinidine gluconate.

The basal skin potential (BSP) was explored as an indirect means of continuously monitoring the cardiac response of quinidine gluconate. A method was developed to follow the BSP using a high impedance, recording polygraph and nonpolarizing calomel electrodes. Intravenous administration of quinidine gluconate caused time dependent changes in the BSP. Further studies showed that blood levels during the elimination phase and the QT interval of the electrocardiogram (ECG) over their entire time period were highly correlated with the BSP. Optimal correlation with the QT interval occurred when the BSP curve was shifted to earlier times by approximately 10 minutes, reflecting possible differences in the accessibility or mechanism of the respective pharmacologic compartments. Further application of the BSP for pharmacodynamic monitoring will require electrode refinements and an increased understanding of its mechanism of action.

Animals↗
PubMed1984

Percutaneous absorption: a new physicochemical predictive model for maximum human in vivo penetration rates.

A diffusion model for stratum corneum-limited percutaneous absorption based on the interaction of the diffusate with the stratum corneum was derived. Two types of interactions were proposed, ion-dipole and lipid-lipid, based on current knowledge of the stratum corneum and on irreversible thermodynamic arguments. The resulting flux equations predict a linear dependence of flux on the dipole moment and ln X of the diffusates , where X is the mole fraction solubility. These flux equations were tested on 21 different diffusates whose human percutaneous absorption rates in vivo had been previously determined. A solubility method was used to classify the interaction pathway for each diffusate . Correlation of the maximum absorption rate for the lipid and polar pathways give correlation coefficients of 0.946 and 0.998, respectively. It is believed that these studies provide a starting point for the ultimate goal of percutaneous absorption research: to be able to bypass in vivo and in vitro studies and to predict absorption solely on the basis of the physicochemical properties of the diffusates .

Chemical Phenomena↗
PubMed1979

Kinetics of absorption and elimination of pralidoxime chloride in dogs.

The kinetics of the absorption and elimination of pralidoxime chloride were investigated in the dog. Similar apparent elimination rate constants were obtained after intravenous, intramuscular, and oral administration. Although oral absorption occurred slowly, intramuscular absorption proceeded rapidly. With in situ techniques, it was found that no absorption occurred from the isolated stomach and duodenum but that absorption did take place from the jejunum and ileum.

Absorption↗
PubMed1975

Rapid methods for bioavailability determination utilizing urinary excretion data.

Two equations were developed which enable urinary excretion data to be utilized for estimating drug bioavailability within 12 hr-starting between one and two half-lives of the drug, depending upon the relative rates of absorption, distribution, and elimination. Both equations were examined using simulated data for both the one- and two-compartment open models. One equation was tested using literature data with excellent results.

Absorption↗