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Biomedical subjects

A H Thomas

Publications and source records attributed to A H Thomas.

At least 37 records · Page 2Linked to original sources
PubMed1978

Control of the composition of gentamicin sulphate by proton magnetic resonance spectrometry.

The proportions of the main components present in gentamicin sulphate complex, gentamicins C1, C1a and C2, can be monitored by 1H nuclear magnetic resonance (nmr) spectrometry. The method depends on measurement of the peak heights of signals for N-methyl and C-methyl groups present in all three components and of those present in C1 and C2 only, followed by calculation of peak height ratios to control composition within acceptable limits. The precision and reproducibility of the method have been established through two collaborative studies each involving seven laboratories. In the second study, with an improved procedure, the mean variance between laboratories with 10 samples was 3.4 X 10(-4) for the N-methyl ratio of the peak at delta 2.75 to that at delta 2.95, and 1.25 X 10(-3) for the C-methyl ratio of the peak at delta 1.25 to that at delta 1.35. Within laboratories the mean variance for triplicate determinations was 7.4 X 10(-5) and 8.9 X 10(-5) respectively. The data presented here form the experimental basis for the test controlling the composition of gentamicin sulphate in the British Pharmacopoeia 1973: Addendum 1975, and for the introduction into the British Pharmacopoeia of nmr spectrometry as an analytical technique. The reference standards and all batches of gentamicin sulphate intended for therapeutic use in the United Kingdom examined by this procedure comply with the limits laid down.

Gentamicins↗
PubMed1977

No-touch technique for intraocular malignant melanomas.

Large variations in intraocular pressure occur during enucleation, scleral depression, 32P testing, and vigorous rubbing of an eye. Data from animal studies show that during a critical phase of an intraocular malignant melanoma, ocular massage significantly decreased longevity due to increased metastastic disease. We report "no-touch" technique to prevent tumor spread from occurring secondary to ocular manipulation during enucleation. This technique avoids IOP elevations above 50 mm Hg before freezing completely around the tumor, thereby preventing flow of fluid and blood to or from the tumor prior to the manipulation necessary for enucleation. Theoretically, the patient with an ocular tumor should be warned against vigorous rubbing of his eyes and hard lid squeezes or diagnostic techniques that elevate IOP. The ophthalmologist should perform enucleation with gentieness and avoid pressure on the globe. Patients who are being followed up with a suspected ocular tumor should be warned not to rub or vigorously squeeze their eyelids.

Animals↗
PubMed1973

The second international standard for polymyxin B.

Since supplies of the first International Standard for Polymyxin B were exhausted, it was replaced by a second international standard the potency of which was estimated from the results of a collaborative assay carried out by 5 laboratories in 4 countries. The wide variations in the results probably resulted from difficulties experienced in handling the first international standard. The potency finally agreed upon by the collaborating laboratories, on the basis of the overall mean values obtained after rejection of the most discrepant assays, was 8 403 IU/mg. That value was accepted by the WHO Expert Committee on Biological Standardization (1970), which consequently defined the International Unit of polymyxin B as the activity contained in 0.000119 mg of the second international standard.

International Cooperation↗
PubMed1973

The second international reference preparation of lymecycline.

The second International Reference Preparation of Lymecycline was established. Nine laboratories in 8 countries collaborated in assaying its potency in terms of the first International Reference Preparation, of which stocks had become exhausted. The best estimate of potency was taken to be 948 IU/mg, which was the unweighted geometric mean of a total of 124 assays. On this basis, the International Unit of lymecycline was defined as the activity contained in 0.0010548 mg of the second International Reference Preparation.

International Cooperation↗
PubMed1973

The second international standard for tetracycline.

A second international standard has been established to replace the first International Standard for Tetracycline, stocks of which were depleted. The International Unit of tetracycline is defined as the activity contained in 0.00101833 mg of the second International Standard, corresponding to a potency of 982 IU/mg. These values were assigned on the basis of the results of an international collaborative assay carried out by laboratories in 19 countries. Most of the assays were by diffusion techniques; a few were by turbidimetric methods. Both procedures gave statistically valid assays but there was some heterogeneity of repeated estimations within a laboratory and also some heterogeneity of the mean estimates from each laboratory. The agreed defined potency was the unweighted mean of 281 individual assays; the confidence limits were 978-986 IU/mg.

International Cooperation↗