Biomedical subjects

R S Müller

Publications and source records attributed to R S Müller.

7 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↗

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↗

PubMed1992

[An unusual tumor of the nictitating membrane gland of dogs-- a case report].

A tumor of the third eyelid gland was diagnosed in a 13 year old female Chihuahua. Histopathology of the excised tissue revealed an apocrine adnexoma with squamous metaplasia. The literature regarding prolapse and tumors of the third eyelid gland was reviewed. No case with similar morphology to this tumor was described to our knowledge.

Animals↗

PubMed1992

[The uveodermatologic syndrome in dogs].

A review of the literature pertaining to the uveodermatological syndrome of dogs is presented. This syndrome is marked by depigmentation of the periocular region, lips and nose in association with severe uveitis. Early diagnosis and therapy can prevent serious vision loss. Symptoms and therapy of the cases described in the literature as well as cases seen at the Veterinary Medical Teaching Hospital in Davis/California are discussed.

Animals↗