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Biomedical subjects

C F Lerk

Publications and source records attributed to C F Lerk.

At least 37 records · Page 2Linked to original sources
PubMed1987

Optimization of a formulation for direct compression using a simplex lattice design.

In this paper it is demonstrated how the optimum composition of a mixture for direct compression consisting of alpha-lactose monohydrate, roller-dried beta-lactose and microcrystalline cellulose can be found using a systematic optimization technique. The experiments were chosen according to a simplex lattice design. The results of these experiments were used to fit a mathematical model, which then can predict the properties of all possible mixture compositions and enables a graphic representation of these properties in the form of contour plots. At a level of 4% the effect of three disintegrants (sodium starch glycolate, croscarmellose sodium and crospovidone) on the properties of the tablets compressed from these filler-binders, was evaluated by superimposing the contour plots of the different tablet responses. It was found that all the disintegrants used were effective in this combination of filler-binders. In order to evaluate drug dissolution rate an extra experiment with crospovidone as the disintegrant was performed, in which oxazepam was used as a test drug.

Cellulose↗
PubMed1987

Native starch in tablet formulations: properties on compaction.

Maize, potato, rice and tapioca (cassava) starch were evaluated with respect to their properties on direct compression. Rice starch showed much better compactibility as compared to maize, potato and tapioca starch. Moreover, its binding capacity proved to be almost insensitive to mixing with magnesium stearate. This in contrast to the dramatic decrease in crushing strength of potato starch tablets containing the lubricant. The compactibility of the starches was found to be strongly affected by the equilibrium moisture content of the starches, which is dependent on the relative humidity of the atmosphere under which the powders were stored. All starches showed adequate capacity for water uptake to act as a disintegrant. Rice starch exhibited worst flowability, caused by its fine particle size as compared to the other starches. Granulation of rice starch changed it into a potential filler-binder in tablets prepared by direct compression.

Chemistry, Pharmaceutical↗
PubMed1987

Release and antimicrobial activity of silver sulphadiazine from different creams.

The release and antimicrobial activity of silver sulphadiazine from five different creams were studied: unguentum emulsificans aquosum, unguentum hydrophylicum non ionogenicum, paraffin cream (15 per cent), a homemade preparation and a commercially available preparation (Flamazine). A diffusion cell was used to measure the release and the agar well diffusion technique to determine the antibacterial activity of the silver sulphadiazine released. The paraffin cream (15 per cent) preparation had the highest release rate, followed by the homemade cream and the commercially available cream. The antibacterial activity ran parallel with the release results. This study shows the silver sulphadiazine paraffin cream to be superior to the other four preparations, including the commercially available silver sulphadiazine cream, using release and antibacterial activity as criteria.

Microbial Sensitivity Tests↗
PubMed1986

Studies on tableting properties of lactose. Part III. The consolidation behaviour of sieve fractions of crystalline alpha-lactose monohydrate.

The consolidation and compaction behaviour of sieve fractions of crystalline alpha-lactose monohydrate were studied. From mercury porosimetry measurements tablet pore surface areas were derived. At a certain compaction load it appeared that tablets compressed from small particles were generally stronger and showed a larger surface area than compacts prepared from coarse sieve fractions. By plotting compact strength against pore surface area, a unique linear relationship was obtained. From these results it can be concluded that the actual tablet surface area, being a function of both the initial particle size and applied compaction pressure, is responsible for the compact strength.

Chemistry, Pharmaceutical↗
PubMed1986

Quinolones and colonization resistance in human volunteers.

The suppression of alimentary canal flora by the three quinolones nalidixic acid, ciprofloxacin and pefloxacin was investigated in fifteen volunteers. They received the three quinolone compounds in tablet form both uncoated and colon-coated. Escherichia coli suppression was poor under nalidixic acid, but complete under ciprofloxacin and pefloxacin for both administration forms. The indigenous anaerobic flora contributing to the control of aerobic Streptococcus faecalis and Candida albicans in the intestines ('colonization resistance') was not affected by nalidixic acid and pefloxacin, and only slightly by ciprofloxacin. Out of the three quinolone compounds, only colon-coated pefloxacin was associated with a considerable absorption rate at colonic level. Using these criteria of successful Escherichia coli clearing from the intestinal canal--left the indigenous flora more or less intact (in a 'selective' way)--and a good absorption rate, pefloxacin is found to be superior to ciprofloxacin and nalidixic acid. These results suggest that a colon-coated tablet with a low dose of pefloxacin is a promising administration form in the therapy of recurrent urinary tract infections and diarrhoeal diseases and in the prevention of gut colonization in immunocompromised hosts.

Adult↗
PubMed1985

Studies on tableting properties of lactose. Part 2. Consolidation and compaction of different types of crystalline lactose.

Lactose is available in several crystalline forms, which differ in binding properties. A new method of estimating the fragmentation propensity was applied to investigate the consolidation and compaction behaviour of this excipient for direct compression. Mercury porosimetry was used to demonstrate that crystalline lactose fragments during compaction. Tablet strength was found to be dependent on the degree of fragmentation only. This finding indicates that the nature of the actual binding must be the same for the different types of crystalline lactose.

Crystallization↗
PubMed1985

Effect of chlorhexidine and acetic acid on phagocytosis by polymorphonuclear leucocytes.

The effect of two disinfectants, chlorhexidine and acetic acid, on host leucocytes and bacteria was studied. At a concentration of 50 mg/l, chlorhexidine was found to be bactericidal without interfering with leucocyte function. A concentration of 500 mg/l of acetic acid was neither leucotoxic nor bactericidal. Effects equivalent to the aforementioned were achieved in serum by increasing the chlorhexidine concentration by a factor of 20 and the acetic acid concentration by a factor of 5. Acetic acid reduced leucocyte function more rapidly than it killed bacteria. On the basis of these findings, chlorhexidine is to be preferred for local application in burn wounds to prevent colonisation and infection.

Acetates↗
PubMed1985

Influence of faeces on the activity of antimicrobial agents used for decontamination of the alimentary canal.

The influence of faeces on the activity of 9 antibiotics currently used for selective decontamination of the digestive tract was studied. These in vitro findings showed that the antimicrobial activity is differently affected by the presence and concentration of faeces. Great differences in loss of activity were observed on different microorganisms. Decontaminating drugs which were found to be minimally inactivated in vitro by the presence of faeces are proven to be superior in clinical studies too.

Anti-Bacterial Agents↗
PubMed1984

Development and optimization of pharmaceutical formulations using a simplex lattice design.

The composition of pharmaceutical formulations is often subject to trial and error. This approach is time consuming and unreliable in finding the best formulation. Optimization by means of an experimental design might be helpful in shortening experimenting time. Such a design with the concomitant mathematical models, reveals effects and interactions of the variables. The independent variables are the different compositions of the mixtures of the chosen ingredients [drug(s) and excipients]. The dependent variables are the properties (responses) of the formulation. When all responses of interest have been expressed in models that describe the response as a function of the composition of the mixture, the models can be combined graphically or mathematically to find a composition satisfying all demands. In this paper an introduction to the use of mixture designs will be given by means of a theoretical part and an example: optimizing a tablet formulation consisting of excipients only.

Chemical Phenomena↗
PubMed1984

Oral controlled release dosage forms. A review.

When a drug meets the criteria which make incorporation into a controlled release dosage form rational, a proper dosage form has to be selected. Oral controlled release products, available on the Dutch market, are referred to in discussing the various methods used to control drug release by galenical means in order to achieve a prolonged therapeutic effect. The effects of some physiological variables of the alimentary tract on drug delivery from the various dosage forms, especially with regard to formulation and design, are reviewed.

Administration, Oral↗