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G Di Colo

Publications and source records attributed to G Di Colo.

30 records · Page 2Linked to original sources
PubMed1981

Outcome of the in vitro studies on drug absorption employing the isolated rat small intestine.

The in vitro methods for studying the intestinal absorption of drugs involving the use of the isolated rat small intestine are reviewed in order to provide indications on their actual usefulness and limitations. The most significant works dealing with the structural integrity of the intestinal mucosa, the functional integrity of the isolated intestine, the factors influencing passive transport such as pH, sugars, ions, physiological and synthetic surface-active agents, and complexation, are reviewed.

Animals↗
PubMed1981

Effect of tissue degeneration on drug transfer across in vitro rat intestine.

A modified rat intestinal sac technique involving a closed circulation of the mucosal drug solution through the lumen was developed with the aim of clarifying the influence of tissue degeneration on drug transfer in the current in vitro methods for studying intestinal absorption. Data on salicylate transfer in agreement with the literature reports on the everted rat intestinal sac technique were obtained with the physiological Tyrode or Krebs-Henseleit buffers. In neither case was the transfer rate influenced by a progressive disruption of the mucosa which resulted upon histological examination of the perfused sacs. The rate-controlling barrier to drug transport, probably located in the inner tissues, maintained a constant permeability to salicylate in the said physiological solutions over a period of 80 min. On the other hand, the gut permeability underwent a nonreversible alteration by each of two phosphate buffers employed in the past for studies with the everted rat intestine. The liability of such an alteration to occur at nonphysiological pH was found to be a major obstacle to the study of the effects of pH on drug transport. A case where the reversibility of these effects could be verified allowed us to state that unionized salicylic acid was transported at a 8.6-fold faster rate than salicylate. Apart from the inherent limitations of the in vitro preparation, the technique presented here provides the following advantages over the classical everted intestinal sac technique: 1) eversion of intestine is avoided; 2) constancy of the mucosal drug concentration is guaranteed throughout the experiment; 3) volume variations of the serosal solution due to water absorption by the intestinal tissues and/or to osmotic phenomena are negligible.

Animals↗
PubMed1980

Vehicle effects in percutaneous absorption: in vitro study of influence of solvent power and microscopic viscosity of vehicle on benzocaine release from suspension hydrogels.

The release through silicone rubber membranes of benzocaine suspended in carbomer hydrogels containing different concentrations of low molecular weight polysols (ethylene glycol, propylene glycol, glycerol, and sorbitol) was studied to establish general principles and procedures for control of the effects on percutaneous absorption caused by changes in drug solubility and/or diffusivity in the vehicle. The effect of the additives on the release is expressed in terms of the relative released amount, i.e., the ratio, Q/Qw, of the amount of drug released from each additive-containing gel to the amount released at the same time from the additive-free gel. The experimental Q/Qw values are correlated with values calculated by a simple equation involving known or readily measurable parameters such as the drug concentration in the gel, the drug solubility in the pure liquid phase, and the viscosity of this phase. Derivation of such a relationship from a known equation describing the vehicle-controlled relase of suspended drugs was possible because an inverse proportionality was observed between drug diffusivity in the gels and the viscosity of the respective solvents. This relationship is interpreted with respect to current theories on drug diffusion in diluted gels.

Benzocaine↗
PubMed1977

Release of drugs from ointment bases II: In vitro release of benzocaine from suspension-type aqueous gels.

The in vitro release of benzocaine, suspended in an aqueous gel, through silicone rubber membranes was studied to test an extension of existing mathematical models. The theoretical treatment proposed is intended for experimental systems involving release, through a non-porous membrane, of a drug whose concentration is a few times (larger than or equal to 3) greater than its solubility in the vehicle. For either micronized (2micrometer) or macrosize (125 micrometer) drug, the Q (amount released) versus t1/2 (time1/2) plots were not linear until substantial time had elapsed. Excellent agreement was found between the experimental points and theoretical plots, generated by a computer fit to experimental data of an equation derived from a reported vehicle-boundary diffusion layer model. The values of the solubility and of the diffusion layer model. The values of the solubility and of the diffusion coefficient of benzocaine in the gel, calculated by the present mathematical treatment from release data, were in agreement with literature data. The particle size of released benzocaine did not influence the release pattern, thus confirming release in the present conditions to be diffusion rather than dissolution controlled. The present method is applicable for determining the solubility and diffusion coefficient of drugs in vehicles in cases not contemplated in current release theories.

Benzocaine↗