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Biomedical subjects

R Gröning

Publications and source records attributed to R Gröning.

18 recordsLinked to original sources
PubMed2006

Development and in vitro evaluation of expandable gastroretentive dosage forms based on compressed collagen sponges.

The objective of this study was to develop and evaluate new collagen gastroretentive dosage forms (GRDFs) which expand in the stomach after contact with gastric fluids. The GRDFs should remain in the stomach for a prolonged period of time due to their size. The dosage forms were prepared from collagen sponges. The sponges were manufactured by freeze-drying a riboflavin-containing collagen solution. A computer controlled material supply was constructed to transport precompressed collagen into a tablet machine. A second type of tablet was manufactured by combining compressed collagen sponges with hydrophilic matrix layers of hydroxypropylmethylcellulose. Matrix layers containing captopril or aciclovir were developed. In vitro experiments were performed with both types of dosage forms. The collagen tablets expand within a few minutes after contact with artificial gastric juice and form a drug delivery system with a size of 8 mm x 18 mm x 60 mm. Riboflavin is released over 16 h. If two layer tablets are used, the release of aciclovir or captopril can be controlled by the composition of the sustained release layer.

Acyclovir↗
PubMed2004

Interactions between aqueous Hypericum perforatum extracts and drugs: in vitro studies.

Physico-chemical interactions between drugs and plant extracts can result in the formation of nanoparticles, microparticles and precipitates. The extraction method may have an influence on the components of the plant preparations and the interactions between drugs and plant extracts. In this study the particle formation in different drug-containing preparations of Hypericum perforatum L. was compared. The formation of nanoparticles was investigated by PCS and scanning electron microscopy. Precipitates were separated from nanoparticles by centrifugation or filtration. The particle formation in drug-containing infusions and reconstituted methanolic extracts of Hypericum perforatum L. was different. In reconstituted dry extracts 21.5% 17alpha-ethinylestradiol and 36.6% levonorgestrel was bound to precipitates, in aqueous Hypericum infusions less than 4% of the hormones was bound. In infusions containing desipramine nanoparticles were formed while the formation of nanoparticles in desipramine-containing reconstituted extracts was negligible. Up to 10% of desipramine was bound to precipitates in reconstituted extracts, but only 4% was associated with the precipitate of infusions. The interactions between extracts of Hypericum perforatum L. and drugs depended on the extraction method. Reconstituted methanolic extracts showed a more intensive binding with oral contraceptives than aqueous infusions.

Chromatography, High Pressure Liquid↗
PubMed2004

Formation of particles in aqueous infusions of the medical plant Harungana madagascariensis.

In some aqueous plant extracts the formation of nanoparticles, microparticles and macroparticles has been observed. In the present investigation the particle formation in aqueous infusions of Harungana madagascariensis LAM. EX. POIR., a medicinal plant, was investigated using photon correlation spectroscopy (PCS) and scanning electron microscopy (SEM). The results show that nanoparticles with mean diameters of 220 nm are formed in aqueous infusions of the dried leaves of Harungana. The particles have an almost spherical shape. In aqueous infusions of the dried stem bark nanoparticles with a mean diameter of 242 nm (PCS) are observed at 25 degrees C. The particle size distribution has a maximum in the range of 200 nm to 300 nm. Nanoparticles can be detected in infusions of the leaves and the bark in the range of 25 degrees C to 55 C. The mean diameter of the nanoparticles in preparations of the bark is temperature dependent: At 55 degrees C the mean diameter is 144 nm, at 30 degrees C 197 nm and at 25 degrees C 242 nm. Lower temperatures result in higher count rates. In infusions of the leaves the mean diameters vary between 220 (25 degrees C) and 139 nm (55 degrees C). The particle formation was investigated at pH 2.2, 4.0 and 7.4 at 37 degrees C. Nanoparticles are detected in infusions of the leaves and the stem bark at each pH. The pH value has an influence on the mean diameter and the count rate.

Chemistry, Pharmaceutical↗
PubMed2003

Physico-chemical interactions between extracts of Hypericum perforatum L. and drugs.

The aim of the present study was to investigate physico-chemical interactions between extracts of Hypericum perforatum L. and drugs. The formation of nanoparticles, microparticles and precipitates in aqueous drug-free and drug-containing preparations of H. perforatum L. was investigated. In aqueous infusions of Hyperici herba only small amounts of nano- and microparticles were observed using photon correlation spectroscopy and scanning electron microscopy. In the presence of promethazine nanoparticles are formed. Between 20.3 and 5.3% of the drug is bound to nanoparticles. Maximally 4.3% of the drug is associated with precipitates. Warfarin has a negligible effect on the particle formation in aqueous infusions of Hyperici herba. In further studies dry extracts of H. perforatum were reconstituted in water. Nanoparticles and precipitates are formed in the drug-free preparations. Scanning electron micrographs show almost spherical nanoparticles with a mean diameter between 100 and 300 nm. After addition of promethazine a precipitate is formed. Maximally 12.8% of the drug is associated with the precipitate. In warfarin-containing reconstituted extracts, nano- and microparticles as well as precipitates are observed. The amount of free warfarin in solution is reduced by 36.6% maximally. A loss of the anticoagulant effect which is described in the literature may partly be caused by particle formation.

Chemical Phenomena↗
PubMed2003

New constituents of Piper guineense fruit and leaf.

Fourteen compounds were isolated from the fruits and leaves of Piper guineense Schum and Thonn (Piperaceae). Two of those were regarded to be new natural compounds, N-pyrrolidyl-2,4-octadecadienamide and N-piperidyl-2,4-octadecadienamide.

Fruit↗
PubMed2002

GC/MS investigations of the minor constituents of Piper guineense stem.

Chemical investigations by GC/MS-analysis of stem extracts of Piper guineense resulted in the detection and identification of thirty-nine new constituents of the stem, apart from previously isolated constituents. These are isobutyl, pyrrolidyl and piperidyl amide alkaloids. Fifteen new natural products have been identified. Four of these natural products have been designated iyeremide A and B (these are pyrrolidine and piperidine analogues of pellitorine) and cycloguineense A and B, which are also piperidine analogues of cyclostachine A and B. There is a need to confirm the structures of some of these new constituents by synthesis. Apart from these amide alkaloids, many volatile oil components-monoterpenes, sesquiterpenes, terpenoids, lignans and sterols--were detected.

Alkaloids↗
PubMed2001

Nanoparticles in plant extracts--factors which influence the formation of nanoparticles in black tea infusions.

The influence of different factors on the formation of nanoparticles in freshly brewed tea extracts was investigated. A black tea infusion was observed during cooling using photon correlation spectroscopy (PCS). The mean particle size and the number of the nanoparticles increase with decreasing temperature. In the presence of caffeine more particles are formed within the infusion. To study the influence of slight structural differences between methylxanthines, the effect of the addition of caffeine to solutions of freshly prepared decaffeinated tea was compared to that of theophylline and theobromine. In the case of theophylline fewer nanoparticles were formed. Molecular modelling calculations were performed to evaluate the most probable geometries for caffeine-polyphenol complexes. A parallel position and a congruent orientation of the 6-membered ring of caffeine and the aromatic galloyl group is the most probable geometry.

Absorptiometry, Photon↗
PubMed1999

Pulsed release of nitroglycerin from transdermal drug delivery systems.

To achieve a discontinuous drug delivery to the skin a new actively controlled transdermal system has been developed. The system consists of a tube shaped drug reservoir in combination with an electronic circuit and a gas producing cell. A magnetic switch was used to control the onset of the production of hydrogen gas. The gas was generated with a constant rate. The tube reservoir was filled with a solution of nitroglycerin in propylene glycol. A discontinuous distribution of nitroglycerin in the reservoir is responsible for the pulsed release. 2, 3, 4, or 6 fractions of nitroglycerin solution, which were separated from each other by sections with air, were filled into the tube reservoir. The release studies show that the release patterns directly reflect the number of doses, which were filled into the tube. A lag time of about 60 min was obtained, if the gas production is regulated by a 2.7 kOmega resistor. The drug is released during the pre-programmed time intervals within 6-7 h. Between the time intervals no drug release occurs.

Administration, Cutaneous↗
PubMed1998

Acyclovir serum concentrations following peroral administration of magnetic depot tablets and the influence of extracorporal magnets to control gastrointestinal transit.

In the present investigations peroral acyclovir depot tablets with internal magnets were developed. An extracorporal magnet was used to prolong the gastric residence times of the dosage forms and to influence the duration of absorption of acyclovir. The magnetic depot tablets contained 200 mg acyclovir. In a three-way cross-over in vivo study with five healthy male subjects, the plasma concentration-time profiles of acyclovir were determined. The acyclovir plasma concentrations following peroral administration of magnetic depot tablets in the presence and absence of an extracorporal magnet were determined. A commercially available immediate release preparation was used as a reference preparation. In the presence of an extracorporal magnet which was placed in the stomach region, the plasma concentrations of acyclovir were significantly higher after 7, 8, 10 and 12 h (P<0.05, U-test, Wilcoxon, Mann-Whitney). The mean area under the plasma concentration-time-curve (AUC0-24h), in the presence of the extracorporal magnet was 2802.7 ngh/ml. Without the extracorporal magnet a mean AUC0-24h of 1598.8 ngh/ml was achieved. Computer simulations were carried out to show the influence of the gastric residence time of acyclovir depot preparations on the plasma concentration-time profiles of acyclovir.

Acyclovir↗
PubMed1995

Development of biologically-controlled insulin pumps with glucose-dependent release.

An experimental insulin pump has been developed in which living microorganisms are used to measure glucose concentration and to produce the energy required to control the release of insulin. The insulin pump consists of a miniaturised bioreactor containing 50 mg freeze-dried yeast. 300 microL of glucose-containing liquid are injected into the bioreactor through a septum. When solutions containing 100 mg or 400 mg glucose in 100 mL are used, the amounts of insulin released differ significantly even within the first measuring interval of 15 min (t-test, p < 0.05). Within 120 min, 4 I.U. and 17 I.U. insulin respectively are released from the two glucose solutions.

Biosensing Techniques↗
PubMed1993

Encapsulation of drugs and excipients in liposomes--measurements with drug-specific electrodes.

In this study, the degree of encapsulation of benzalkonium chloride in liposomes was quantitatively measured using a potentiometric membrane electrode specific for benzalkonium chloride. The encapsulation of lidocaine hydrochloride was examined with another ion-selective electrode for comparison. Liposomes were prepared from a commercially available liposome concentrate (Phosal 75 SA). Photon correlation spectroscopy was used to detect the formation of liposomes in the size range of 200 nm. The measurements with the membrane electrode enabled the activity of the free drug to be quantitatively determined in the presence of liposomes. The investigations showed that, in the concentration range examined, up to 97% of the amphiphilic benzalkonium chloride is encapsulated in the liposomes. In the case of the hydrophilic lidocaine hydrochloride, virtually no liposomal encapsulation occurs.

Benzalkonium Compounds↗
PubMed1989

[Characterization of drug absorption from the gastrointestinal tract with the use of numeric deconvolution].

The present investigation is concerned with the absorption of drugs from the gastrointestinal tract. The duration of absorption of drugs was calculated using numerical deconvolution. Clinical data were obtained from the literature. The absorption of 36 different drugs is characterized. The results show that the duration of absorption is not uniform. Penicillins and tetracyclines are absorbed for about 3 hours after application. Most drugs are absorbed during 4 to 6 hours. A few drugs, e.g. theophylline or metoprolol, are absorbed for more than 12 hours from the gastrointestinal tract.

Humans↗
PubMed1987

[Germ reduction by microwaves--microwave specific effects].

A commercial 2450-MHz microwave oven has been used to inactivate microorganisms in pharmaceutical solutions and auxiliary materials. The present investigation is concerned with the possible existence of a specific microwave effect, potentiating the thermal effect of microwave irradiation. Bacillus subtilis suspensions in polyethylenglycol 300, distilled water and peanut oil were used. It is shown that microwave heating is significantly more lethal to Bacillus subtilis microorganisms than equivalent conventional heating.

Bacillus subtilis↗
PubMed1987

Microencapsulation of potassium chloride with mastic.

The present investigation deals with the microencapsulation of potassium chloride with mastic. Spherical potassium chloride crystals with a mean particle diameter of approximately 450 microns were used. It could be shown that with a layer of mastic wall material thicker than 21 microns the release of potassium chloride in the in vitro test can be controlled for more than 6 h. The thickness of the wall material over the tested range of 21 to 33 microns has only a limited effect on the kinetics of release of potassium chloride. Increasing the thickness of the layer from 21 to 33 microns merely leads to a reduction of about another 10% in the amount of drug released in 6 h.

Capsules↗