Enrico Ragazzi

Quantitative analysis of phenolic compounds after thin-layer chromatographic separation.

Abstract A method has been developed for the quantitative analysis of phenolic substances having non-substituted phenolic groups after their separation by thin-layer chromatography on silica gel or cellulose. After the clear detection of the phenolic substance on the chromatoplate by means of Folin-Ciocalteu reagent, the quantitative spectrophotometric determination of the substance is carried out by transferring the sorbent area containing the spot into a test-tube and using the Folin-Ciocalteu reagent, without the necessity for carrying out a prior elution for the recovery of the substance. The method appears to have good accuracy and to be suitable for general application.

Simple method for the quantitative analysis of tetracyclines by direct fluorimetry after thin-layer chromatography on cellulose plates.

A thin-layer chromatographic method is described in which tetracyclines are separated on a cellulose layer by development with aqueous solutions of certain salts (magnesium, calcium, barium and zinc chloride). The spots exhibit good fluorescence in UV light, allowing ready detection without the necessity for treatment with any reagents. This fluorescence can be used for the direct photometric determination of the tetracyclines with good accuracy.

Possibilities of conveying a cationic drug in Carbomer hydrogels.

A drug with cationic characteristics such as procaine can be conveyed in a Carbomer hydrogel in two different ways: (i) in the form of salt in solution in the aqueous phase, and (ii) in the base form salified with the same polymer. Introduction of the drug into the hydrogel with different concentrations of polymer produced, in both cases, a reduction in viscosity in relation to drug concentration. The gels with procaine salified with the polymer showed greater viscosity. The drug release rate, in general, diminished with the increase in polymer concentration. Nevertheless, when this concentration was maintained, there was no variation in release rate when the viscosity produced as a consequence of drug concentration was changed. Gels with procaine salified with the carboxyvinylic polymer had a faster release rate than those with procaine in the hydrochloride form dissolved in the aqueous phase. These results have also been confirmed by a simulated absorption test.

Characterization of in vitro relaxant mechanisms in erectile tissue from rabbits of different ages

In the present study we investigated the in vitro relaxant response of erectile tissue obtained from rabbits of different ages (3, 7 and 24 months) in order to detect the progression with age of cavernosal activity in response to substances acting via endothelium-dependent or-independent mechanisms. Noradrenaline induced a concentration-dependent contraction (0.1 μM–3 mM), with an increase in the contractility in the 24-month-old group. Acetylcholine produced a concentration-dependent relaxant effect in the three age groups, with a reduction of the maximal relaxant effect in older animals. ATP (10 μM–1 mM) and adenosine (10 μM–1 mM) induced a concentration-dependent relaxant effect that was higher in the older group. The presence of the NO-synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) (0.1 mM) or of the P2-purinoceptor antagonist suramin did not affect ATP relaxation. Relaxation induced by sodium nitrite and nifedipine was reduced in older animals. In conclusion, aging selectively alters the in vitro responsiveness of rabbit erectile tissue. Purinergic system remains more active despite a decrease in the maximal endothelial cholinergic activity and the direct smooth muscle relaxant component.

Drug Release from Lipogels According to Gelling Conditions and Mechanical Treatment

The release rate of a drug dissolved in the liquid phase of lipogels may be greatly affected by the type and concentration of gelling agent and by processing conditions and mechanical treatment of the ointment. These differences in release rate are reduced after application of mechanical stress comparable with the strain exerted on the ointment during application to the skin. Therefore, changes in the concentration of gelling agents used to achieve suitable consistency and manufacturing and packing processes that meet industrial and marketing requirements do not appear to exert a practical influence on drug availability after application to the skin.

Correlation of in vitro and in vivo paracetamol availability from layered excipient suppositories

An in vivo investigation of paracetamol availability was carried out on eight healthy volunteers, comparing two paracetamol suppository formulations prepared using two different gliceride bases, a fast drug-releasing one and a slow drug-releasing one, i.e. Witepsol H15 and W35, respectively. The formulations were selected on the basis of a previous in vitro drug release study, which showed that, by superimposing the excipients in two layers within the same suppository, the drug release kinetics could be modulated using different ratios between the two layers. The comparison between the two different formulations in terms of plasma profiles and total amounts of drug excreted in urine revealed an increase in the extent of drug absorption from the layered excipient suppository. As the W35 has a higher monoglyceride content than the H15, this improved paracetamol availability could be ascribed to the absorption-enhancing effect of the monoglycerides. Moreover, the W35 has also a higher viscosity, which could possibly cause the suppository to be retained for a longer time in the lower part of the rectum, where the blood is drained directly to the systemic circulation. It was therefore hypothesized that the enhanced paracetamol availability could be also due to a liver bypass mechanism. For a further examination of the paracetamol absorption kinetics after rectal administration, a one-compartment model was fitted to the drug plasma concentration data. This approach allowed to draw absorption versus time profiles, which showed that a retardation actually occurred in paracetamol absorption when using suppositories containing the slow drug releasing excipient W35. These absorption data were then employed for an A level in vitro-in vivo correlation testing, and a linear relationship was found between in vitro release rate and in vivo absorption rate, both for fast releasing and for the layered excipient suppositories.

Effect of gelling conditions and mechanical treatment on drug availability from a lipogel

This study has been conducted to determine whether the rheological differences depending on gelling and treatment conditions could have an influence on drug availability. Lipogels with constant composition were obtained by gelling olive oil with monodiglycerides at rest, under stirring, and milled after gelling. The considerable differences in rheological characteristics produced significant differences on in vitro drug release tests, whereas a lesser influence was observed on in vitro simulated absorption test. The rheological differences appeared not to influence in vivo drug availability. Also, rheological differences owing to the concentration of the gelling agent showed no significant influence on in vivo availability.

Functional response of cavernosal tissue to distension

We studied rabbit isolated erectile tissue responses to changes in preload and to active tension development with norepinephrine. The effects of antagonists of endothelin-1, prostaglandins E2 and F2αand of nitric oxide were also tested on normal and de-endothelialized preparations. Tissue distension was found to elicit spontaneous rhythmic contractions. Increase in preload diminished the latency of the spontaneous activity and augmented the developed force. Active tension development and the inhibitor of the Na+,K+ pump, ouabain, opposed the spontaneous activity. A marked reduction in the resting tension with abolition of the spontaneous activity was observed on normal, but not on de-endothelialized tissues, following the addition of the specific prostaglandin E2 and F2α receptor antagonist, SC-19220. At 3 × 10−4 M, the highest concentration used, the endothelin-A receptor antagonist BQ-123 failed to change the pattern of the spontaneous activity and the resting tension of normal tissues. The nitric oxide synthesis inhibitor, l-NAME, did not produce reliable effects. These findings point to a causal relation between cavernosal tissue distension and phasic and tonic contractions. Phasic contractions appear to be elicited by smooth muscle cells through the enzyme Na+,K+-ATPase. Increase in the resting tone could be mediated, at least in part, by the endothelium, through the release of prostaglandins E2 and/or F2αbut not of endothelins. We discuss the hypothesis that, in cavernosal tissue, mechanotransduction of distension to contractile responses is an important determinant of detumescence.

Layered excipient suppositories: The possibility of modulating drug availability

The release rate of a drug dose from suppositories is affected by characteristics of the excipient (melting temperature and rate, viscosity at rectal temperature, hydro-lipophilic characteristics). Release kinetics from excipients commonly available do not always respond to clinical requirements, even after the introduction of auxiliary agents. Release curves which were differentiated and adaptable to therapeutic conditions were obtained by vehicling a drug in suppositories of two superimposed layers of lipophilic excipients with different characteristics and hence with a difference in drug availability. The two distinct excipient layers release the drug from these suppositories contemporaneously but independently. The amount of drug released in the time course is the sum of the single amounts individually released by the two suppository layers. By previously mixing the two excipients, release rate becomes uniform in the suppository body overall and is conditioned only by the assumed characteristics of the mixture. The release mechanism for superimposed layer suppositories is confirmed by the good agreement between experimental and calculated curves. By using a pair of excipients with different characteristics in superimposed layers between which the drug is distributed, it is possible to modulate drug release kinetics by regulating the reciprocal ratio between the two suppository fractions.

Influence of processing conditions in the manufacture of O/W creams: I. Effect on dispersion grade and rheological characteristics

Two series of O/W creams having the same general formulation were prepared in three different mechanical conditions (F with an hand blender; S with a turbomixer; T with a vacuum turbo emulsor) using two types of surfactants, polyoxyethylene-cetostearyl alcohols and polyglyceryl-3-methylglucose-distearate. By means of microscopic image analysis it was possible to point out the dispersion grade of the oil internal phase increasing with the energy applied under the conditions of manufacture (F < S < T). The level of dispersion influenced significantly on the rheological characteristics of the creams. With polyoxyethylene-cetostearyl alcohols, the viscosity of creams increased as the energy applied in manufacturing increased, with polyglyceryl-3-methylglucose-distearate on the contrary decreased. Moreover, indifferently to the manufacturing conditions, even in the same concentration of surfactant, the creams obtained with the last produced a much greater viscosity. At a parity of manufacturing conditions the differences between the batches of productions were not significant.