Biomedical subjects

Dorottya Kiss

Publications and source records attributed to Dorottya Kiss.

5 recordsLinked to original sources

PubMed2006

[Physical ageing of amorphous polymeric excipients III. The possible consequences of ageing].

Polymeric excipients are widely used in pharmaceutical technology, and most of them are amorphous or partly amorphous. A well-known property of such materials is that they undergo physical ageing, which is accompanied by volume and enthalpy relaxation and thus might result in severe structural changes in the polymer. This latter phenomenon can influence the properties of excipients and dosage forms, such as processability, mechanical strength and drug release. These alterations are of great significance in the case of solid dosage forms, as physical ageing occurs in the solid state of the polymer. Considering conventional tablets, the structural changes of fillers or binders along with storage can influence the above mentioned properties, while in the case of modified release tablets, matrix-forming and film-forming agents are to be taken into account, as well. In addition to this, by the examination of films, the presence of plasticizers is of great importance, as these materials can facilitate physical ageing via increasing the molecular mobility of the polymer. In the case of certain therapeutic systems (e.g. intrauterine devices), where the base of the dosage form is polymeric, significant changes are to be noted considering the drug release and physiological tolerability of the system.

Dosage Forms↗

PubMed2006

[Pphysical ageing of amorphous polymeric excipients II. Tracking possibilities].

In the course of physical ageing of amorphous polymers, both macro- and microstructural changes occur in the materials. Volume and enthalpy relaxation can be considered as macrostructural aspects of ageing, and can be tracked by dilatometry and calorimetry, respectively. In dilatometric measurements, volume changes are usually traced back to the changes in the length of the examined materials. Among calorimetric methods, differential scanning calorimetry (DSC) is the most widely used technique for monitoring enthalpy changes. Considering microstructural aspects of polymer ageing, free volume plays a critical role in the interpretation of the experimental results. Changes in the size and distribution of the free volume holes can be tracked by spectroscopic methods like positron annihilation lifetime spectroscopy (PALS), electron spin resonance spectroscopy (ESR) and fluorescence spectroscopy. Other techniques, as the use of photochromic probes and labels or small angle X-ray scattering (SAXS) can be informative, as well. The morphological aspects of ageing, on the other hand, can be studied by scanning electron microscopy (SEM).

Calorimetry, Differential Scanning↗

PubMed2005

The effect of structured triglycerides on the kinetic stability of total nutrient admixtures.

PURPOSE: The physical stability of two types of total parenteral nutrient (TPN) admixtures was studied as a function of storage time and temperature. One of them contained only structured triglycerides and the other exclusively long-chain triglycerides as lipid components. METHODS: Droplet size of the mixtures was followed by photon correlation spectroscopy for 10 days. Zeta potential and dynamic surface tension measurements were carried out to evaluate the possible changes in the charge and interfacial surface tension of the emulsion droplets during the storage. pH values were monitored in order to follow the possible decomposition processes in the course of storage. RESULTS: Droplet size of emulsions prepared with lipids containing exclusively long-chain triglycerides showed remarkable increase after 4 days of storage in contrast with that of the mixtures containing structured lipids. CONCLUSIONS: The obtained results indicate that besides the advantageous metabolic effects of structured triglycerides, their application is recommended to improve the physical stability of TPN admixtures.

Drug Stability↗

PubMed2005

[Gastroretentive dosage forms].

Gastroretentive dosage forms are drug delivery systems which remain in the stomach for an extended period of time, and allow both spacial and time control of drug liberation. Their application can be advantageous in the case of drugs that are absorbed mainly from the upper part of the gastrointestinal tract or are unstable in the medium of distal intestinal regions. They can also be used beneficially in the local therapy of the stomach. Because of the complicated and by many factors influenced physiology of this organ, the design of such delivery systems is a task requiring due foresight and knowledge. Gastroretentive dosage forms can be floating, expandable, bioadhesive, modified shape and high density systems according to the physical property leading to prolongation of gastric residence time. Combinations of the listed categories can occur as well. Several spirited ideas and solutions have come up in the literature for the preparation of such delivery systems, but there is still need for development in the field of implementation and prediction of in vivo behaviour before these dosage forms can be elemental part of clinical practice.

Administration, Oral↗

PubMed2005

[Physical ageing of amorphous polymeric excipients I. physicochemical principles].

Most of the polymeric excipients applied in pharmaceutical technology are amorphous, which, as a result of physical ageing, can lead to changes in the stability of these materials and dosage forms prepared from them. For the tracking of physical aging and understanding its consequences, a complex knowledge of the physicochemical properties and behaviour of amorphous polymers is necessary. In the case of these materials, three single-phase physical states can be distinguished: glassy, rubbery and viscous. The transition from glassy to rubbery state occurs at the glass transition temperature, the change of which as a function of the storage conditions provides information about the physical ageing of the material. The ageing process is usually accompanied by enthalpy and volume relaxation, which are considerably influenced by the presence of different plasticizers, e.g. water. These materials usually change the glass transition temperature of the polymer, which is a result of their effect on the free volume of the system. In view of the hygroscopic behaviour and water-uptake mechanisms of polymers, the probability and extent of structural changes caused by physical aging can be predicted.

Cellulose↗