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Biomedical subjects

R Thibert

Publications and source records attributed to R Thibert.

15 recordsLinked to original sources
PubMed2003

Polymorphic properties of micronized carbamazepine produced by RESS.

Carbamazepine microparticles were produced by the rapid expansion of supercritical carbon dioxide solutions (RESS) method. The characteristics of the resulting particles were studied by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and image analysis. X-ray diffractograms and SEM photomicrographs revealed that the crystalline nature of the produced carbamazepine microparticles depended on operating pressure and temperature conditions. Different polymorphs were obtained under various operating conditions. Under certain temperature (below 40 degrees C) and pressure (below 240 bar) conditions, it was possible to form primarily the carbamazepine polymorph stipulated by US Pharmacopeia. A significant reduction was observed in the particle size and size distribution range of carbamazepine produced by RESS. The processed particles had a mean diameter smaller than 3 microm and a size distribution range between 0.5 and 2.5 microm compared to unprocessed starting material with a mean diameter of approximately 85 microm and a size distribution range between 15 and 336 microm. Thus, this study demonstrates that the polymorphic characteristics of carbamazepine microparticles produced by the RESS method can be controlled by varying operating pressure and temperature parameters.

Calorimetry, Differential Scanning↗
PubMed1999

Influence of the Fractal Character of Model Substances on their Reactivity at Solid-Liquid Interfaces.

The fractal theory has been applied to study surface complexity where surface aspects influence physical properties and play a role in controlling heterogeneous reactions at interfaces. In this work, the influence of the fractal character of some selected antacids was investigated in regard to their neutralizing activity. The materials used were magnesium trisilicate, magnesium hydroxide, and heavy and light magnesium oxide, each from three different manufacturers. Surface area, total pore volume, and particle size were measured. Fractal dimension was determined from gas adsorption data according to pore size distribution, the Frenkel-Halsey-Hill, and thermodynamic methods. The results obtained show a correlation between neutralization activity and fractal character rather than total surface area or particle size. Also, the effect of porosity in terms of total pore volume was modified by the structure of the porous network. The complexity of the pore network played a major role in controlling reactivity. However, the effect of surface roughness was only demonstrated when adsorption on the surface was a rate-limiting step in the reaction. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Determination of the viscosity of an amorphous drug using thermomechanical analysis (TMA).

PURPOSE: To evaluate thermomechanical analysis (TMA) as a technique for determining the viscosity of amorphous pharmaceutical materials. This property of amorphous drugs and excipients is related to their average rate of molecular mobility and thus to their physical and chemical stability. METHODS: Indomethacin was selected as a model amorphous drug whose viscosity has previously been reported in the literature. A Seiko TMA 120C thermomechanical analyzer was utilized in isothermal penetration mode to determine the viscosity of the amorphous drug over the maximum possible range of temperatures. RESULTS: Using a cylindrical penetration geometry it was possible to accurately determine the viscosity of amorphous indomethacin samples by TMA over the temperature range from 35 to 75 degrees C. The results were consistent with those reported in the literature using a controlled strain rheometer over the range 44-75 degrees C. The limiting lower experimental temperature for the TMA technique was extended to significantly below the calorimetric glass transition temperature (Tg approximately 42 degrees C), thus allowing a direct experimental determination of the viscosity at Tg to be made. CONCLUSIONS: Thermomechanical analysis can be used to accurately determine the viscosity of amorphous pharmaceutical materials at temperatures near and above their calorimetric glass transition temperatures.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1997

A comparison of pulmonary availability between Ventolin (albuterol) nebules and Ventolin (albuterol) Respirator Solution.

The two most common albuterol preparations used for nebulization are: (1) Ventolin (albuterol) respirator solution (Glaxo Canada Inc; Montreal, Canada) of which 2.5 mg (0.5 mL) is diluted with 2 mL of normal saline solution, and (2) the preservative-free, prediluted Ventolin (albuterol) Nebules PF (Glaxo) (2.5 mg/2.5 mL). The two preparations were compared using both a Hudson 1720 "T" up-draft Neb-U-Mist jet nebulizer and a Hudson 1730 "T" up-draft Neb-U-Mist II jet nebulizer (Hudson; Temecula, Calif), which were driven by a compressor (Pulmo-Aide; Devilbiss; Somerset, Pa) and by dry compressed air at 6 and 8 L/min. Particle size distribution was measured with a particle sizer (Malvern 2600; Malvern Instruments; Malvern, UK) and drug output for the nebulizer was calculated from the differences in predrug and postdrug volume and concentration. Drug availability was defined as the amount of drug carried in particles less than 5 microns in diameter. Drug availability was greater with the albuterol respiratory solution, due to the surface activity of the preservative benzalkonium chloride, for both nebulizers but particularly for the 1720. Differences in drug availability between nebulizers exceeded fourfold depending on the preparation, the nebulizer, and the nebulizing flow. These differences could not have been predicted from the manufacturer's specifications. The results suggest that prediction of drug availability must be based on measurements with the specific preparation and the specific nebulizer used.

Aerosols↗
PubMed1997

The choice of jet nebulizer, nebulizing flow, and addition of albuterol affects the output of tobramycin aerosols.

The use of inhaled antibiotics in the treatment of cystic fibrosis has become widespread despite controversy in the literature as to the appropriate dosing regimen and its effectiveness. This study compared two tobramycin (T) preparations (one with and one without the addition of albuterol) using two different jet nebulizers in order to determine if drug output would be affected. Using calibrated flows from a dry compressed gas source of 6 and 8 L/min as well as a specific compressor (Pulmo-Aide), the Hudson 1720 nebulizer was compared with the newer disposable Hudson 1730. The albuterol preparation used in this study was the Ventolin (albuterol) Respirator Solution (VRS). The nebulizers were charged with (1) 2 mL T (80 mg/2 mL) with 0.5 mL VRS (5 mg/mL) and normal saline solution to make the total nebulizer charge of 3 or 4 mL, or (2) 2 mL T and either 1 or 2 mL normal saline solution. A laser diffraction analyzer (Malvern 2600) was used to determine the aerosol particle size distribution. From the distribution, the respirable fraction, which is the fraction of aerosol that could enter and remain in the lungs, was calculated. For all solutions and each particular flow, the Hudson 1730 had a larger respirable fraction of T. The addition of VRS lowered the surface tension of the solution in the nebulizer and resulted in a greater output of T. This effect was most apparent for the 3-mL volume fills of the Hudson 1720. The greatest differences were between the 3-mL nebulizer charges of T using the Hudson 1720 driven by a flow of 6 L/min, which produced 8 mg of T in the respirable fraction, compared with 35 mg produced by the Hudson 1730 driven by a flow of 8 L/min. These results suggest that different nebulizers, different nebulizer solutions, and different techniques of nebulization may result in very different amounts of T aerosol output in the respirable fraction.

Administration, Inhalation↗
PubMed1993

Use of fractal dimension in the study of fractured surfaces of insulin zinc crystals.

The micromorphology of two types of insulin zinc crystals was characterized by computerized image analysis. It was demonstrated that one can identify the recombinant DNA crystals from those of animal origin in a blinded sample by perimeter fractal dimension analysis. Fractal dimension analysis was also applied in the study of irregularly fractured surfaces produced by thermal and mechanical stress. The results obtained suggest that the fractal dimension is related to the intensity of applied stress. The characterization of newly formed boundaries of insulin zinc crystals produced by mechanical or thermal stress could determine various surface-related kinetic processes.

Animals↗
PubMed1993

Evaluation of the surface roughness of cystine stones using a visible laser diode scattering approach.

To understand the processes of fragmentation and the chemical reactivity of solids, proper characterization of surface topography is crucial. This paper describes a non-destructive technique of quantifying the surface roughness of cystine renal stones, using visible laser diode scattering and fractal geometry. Fragments of cystine stones were mounted on microscope slides and coated by a carbon-sputtering apparatus. The slides were placed under a dynamic active-vision system, using a visible laser diode to measure three-dimensional surface coordinates. The data obtained were analyzed by fractal geometry. Surface fractal dimensions were determined by the variation method. The results showed that the surface of a compact-size sample can be evaluated quantitatively. The technique is valuable for the accurate presentation of surfaces in three dimensions.

Cystine↗
PubMed1991

The study of the surface geometry of renal stone fragments after shock wave and ultrasound disintegration.

Computerized image analysis was used for characterizing the irregular boundaries of calcium oxalate stone fragments resulting from shock wave and ultrasound disintegration. The complexity of the contour of the fragments was determined to evaluate the surface roughness of the rugged profile of the samples. Crack propagation on the crystal surface of the mineral phase was studied using fractal geometry. A significant difference was observed in the boundary variation of the calcium oxalate stone fragments treated by shock wave and ultrasound. Crack propagation in the mineral phase crystal was found to depend on the method of fragmentation used. There is also an experimental evidence that the surface topography of the stone fragments produced by shock wave depends on the microhardness of the stone material.

Calcium Oxalate↗
PubMed1988

Application of fractal dimension to the study of the surface ruggedness of granular solids and excipients.

This report describes the use of fractal analysis in the study of the surface ruggedness of pharmaceutical solids. A comparison of the fractal dimension of granules and excipients prepared by different techniques revealed a possible correlation between the physical behavior of these granules and their surface geometry. The applications of the proposed tool in the study of the surface geometry of pharmaceutical bulk solids are discussed.

Chemical Phenomena↗
PubMed1976

[Diabetes and diseases of the internal ear].

The authors present a series of 30 cases of vertigo where diabetes and hyperlipidemia were found. The literature on the subject is reviewed, and evidence points to a diabetic lesion of the inner ear. Our cases illustrate that lesion and its clinical presentation.

Adolescent↗
PubMedDate not supplied

End-organ and drug-induced vestibular nystagmus.

The occurrence of spontaneous, positional and paroxysmal positional nystagmus was studied in patients with end-organ lesions, and in subjects with drug-induced central vestibular nystagmus. Repeated vestibular examination using electronystagmography for assessment of spontaneous and positional nystagmus in the standard head positions was carried out. The findings indicate that the paroxysmal positional nystagmus is the most frequently seen nystagmus prior to its disappearance in end-organ induced nystagmus and also the most frequently seen in drug-induced nystagmus. The direction changing type of nystagmus was very frequently encountered in end-organ lesions. These findings indicate that the type of horizontal vestibular nystagmus by itself is of no diagnostic value in localizing the site of the lesion and that the various types reflect different degrees of vestibular compensation that occur prior to their disappearance. The value of various classifications of positional nystagmus lies mainly in that they help describe the nystagmus clinically.

Adult↗
PubMedDate not supplied

[Two cases of benign polypes of the ureter (author's transl)].

The polyp of the ureter is a tumour which originates in the connective tissue and is covered by normal urothelium. Radical surgery is justified in some of these urothelial tumours but one should also consider a more conservative attitude when one deals with a benign fibro-epithelial polyp of the ureter especially when they are located in the lower or upper third of the ureter. We present two cases, one which represents the eleventh case of benign fibro-epithelial polyp described in children in the literature.

Child↗