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Biomedical subjects

N W Spurling

Publications and source records attributed to N W Spurling.

At least 19 recordsLinked to original sources
PubMed1992

Dose selection for toxicity studies: a protocol for determining the maximum repeatable dose.

1. A three-stage protocol is described for a dose-ranging study which defines the maximum repeatable dose (MRD) and provides a preview of the toxicology of new, pharmacologically active, substances before commencing the first formal regulatory toxicity studies, usually of 2 or 4 weeks duration. 2. Additionally, a range of toxicokinetic (TK) data relevant to protocol design for formal studies is generated. 3. Stage A is a dose incrementation process in which the MRD is provisionally determined and basic TK values generated. 4. In stage B the animals are dosed daily for at least 7 d, the MRD is substantiated and a wider range of TK data obtained. 5. In stage C, each of the dose levels identified for a formal study is administered once to investigate the relationship of doses to TK data. 6. This protocol can be completed using as few as 24 rats or six dogs (or primates). 7. Selection of dose levels for the first formal studies can be greatly aided by the results of a well-designed dose-ranging study including TK data. 8. For particularly toxic substances, the findings of studies based on this protocol have frequently been sufficiently clear to warrant early termination of their development.

Animals↗
PubMed1991

Phospholipase C-sensitive factor VII complexes in dog plasma.

We report the presence of a phospholipase c-sensitive activated factor VII complex in canine plasma after feeding a special diet. Low levels of complex was observed in the fasting state. The response to feeding in terms of activated factor VII varied markedly among the dogs investigated.

Animals↗
PubMed1989

An evaluation of the safety of ranitidine during seven years daily oral administration to beagle dogs.

1. Ranitidine hydrochloride was administered orally to Beagles at doses equivalent to 50 mg once daily, or 5 mg twice daily, of ranitidine base/kg for more than 7 years. 2. Apart from looseness of faeces, seen mainly after doses of 50 mg/kg and only rarely after the first year of such treatment, there were no adverse clinical effects. There were no deaths related to treatment. 3. Periodic gastroscopy revealed nothing abnormal. 4. Peak plasma levels of ranitidine occurred within 2 h of dosing; levels were proportional to the doses administered. 5. There were no major differences in fasting plasma gastrin levels between treated and untreated dogs; the expected increase occurred in response to the provision of food and, predictably, this was greater following a dose of ranitidine. 6. A normal histamine-induced gastric secretory response was demonstrated. 7. Necropsy revealed no lesions of toxicological significance. Macroscopically the stomachs appeared normal but microscopic examination showed some gastritis in both treated and control dogs. No changes in enterochromaffin-like (ECL) cells were detected. Electron microscopy showed unimpaired secretory activity of parietal cells. 8. Thus, after more than 7 years administration to beagle dogs of doses in excess of the normal daily therapeutic dose, the stomachs showed no changes attributable to treatment and their secretory capacity was unimpaired.

Administration, Oral↗
PubMed1989

Ondansetron: pre-clinical safety evaluation.

A programme of pre-clinical safety evaluation of ondansetron has been undertaken which involved a series of studies - single dose studies, repeat dose studies, reproduction studies, genotoxicity studies, oncogenicity studies, local irritancy studies, and a hypersensitivity study. Ondansetron was found to have a very good safety profile, and the only toxicity identified was associated with central nervous system activity when near lethal doses were administered. It was not genotoxic and had no reproductive or oncogenic potential.

Administration, Oral↗
PubMed1988

Hereditary blood coagulation factor-VII deficiency: a comparison of the defect in beagles from several sources.

1. Hereditary blood coagulation factor-VII deficiency has previously been identified in Beagles from a number of sources in Britain and North America. 2. A study is now reported in which the nature of the defect is compared in plasma samples from these sources. 3. When prothrombin times and Russell's Viper venom clotting times were determined on mixtures of samples, no cross-correction of the defective coagulation activity was detected. 4. Antibody neutralization assays of factor-VII related antigen and assays of factor-VII procoagulant activity revealed essentially similar levels in all samples. 5. Thus no significant genetic variants of the defect were identified.

Animals↗
PubMed1987

[The protein C inhibitory system].

The chemical and physical characteristics of the individual components of the protein-C inhibiting system, protein C, thrombomodulin, protein S and the inhibitor of the activated protein C are summarized in a survey, with their mutual relations and their physiological impact on the course of the coagulating and fibrinolytic systems being represented. Finally, the clinical implications of a hereditary and acquired protein C deficiency, of a diminished protein S level and a lowered inhibitor of the activated protein C are discussed. The complications caused by a rapid decline of protein C values after administration of coumarin derivates are referred too.

Blood Proteins↗
PubMed1986

Hereditary blood coagulation factor-VII deficiency in the beagle: immunological characterisation of the defect.

In the plasma of beagles known to be homozygotes for hereditary blood coagulation factor-VII deficiency, antibody neutralization assays indicate only slightly greater quantities of factor-VII related antigen than are detected by conventional assays of procoagulant activity. Plasma of one dog was depleted of factor-VII procoagulant activity by exposure to an immobilized antibody; the low level of activity originally present was then verified by titration with normal plasma. The plasma defect results from an incomplete deletion of synthesis.

Animals↗
PubMed1986

An evaluation of the safety of cefuroxime axetil during six months oral administration to beagle dogs.

The effects of repeated oral administration of cefuroxime axetil were assessed in Beagles. The test material, an ester, is hydrolysed following absorption from the intestine to yield the therapeutically active moiety, cefuroxime, together with acetic acid and acetaldehyde; in this study cefuroxime and unhydrolyzed cefuroxime axetil were detected in the blood. Cefuroxime axetil was administered twice daily during 27 weeks by gavage of aqueous, suspensions, total daily doses were equivalent to 100, 400 or 1600 mg cefuroxime/kg/day. Apart from three cases of intercurrent illness, unrelated to treatment, the dogs remained in good health. Effects observed in the 1600 mg/kg group included vomiting and slight suppression of body weight gain. Minor variations in haematological measurements included rather low haemoglobin levels, packed cell volumes and erythrocyte counts. Slightly smaller numbers of neutrophils were thought to reflect reduced demand on normal defensive mechanisms due to continued antibiotic treatment. Prolongation of prothrombin time and activated partial thromboplastin time is attributed to disturbance of the intestinal microbial flora and reduced synthesis of vitamin K, on which the dog is highly dependent. Cefuroxime does not have the N-methylthiotetrazole side chain thought to be responsible for inhibition by other cephalosporins of the vitamin K-dependent step in the synthesis of clotting factors. Variations in plasma chemistry included rather low levels of plasma protein. Electrophoresis showed this to be a generalised reduction; only gamma globulins were proportionally decreased and this finding, like the low neutrophil counts, is attributed to the protective action of the antibiotic. Minor metabolic adjustments to the compound are reflected in plasma levels of cholesterol and triglycerides. This spectrum of findings was seen only to a very limited extent in the 400 mg/kg group; the 100 mg/kg group was, with very few exceptions, unaffected by the treatment. Macroscopic post mortem examination and microscopic examination of tissues revealed no treatment-related features indicative of toxicity. Cefuroxime axetil was thus shown to possess very little toxicity when administered repeatedly in large doses to Beagles. The lowest dose level in this study was ten times the proposed daily clinical dose in man.

Administration, Oral↗
PubMed1985

Association of long lasting unsurmountable histamine H2 blockade and gastric carcinoid tumours in the rat.

The oral administration of loxtidine, a potent histamine H2-antagonist, to a total of 378 rats at doses of 50, 185, or 685 mg/kg/day for 116 weeks resulted in the late formation of carcinoid tumours of the gastric fundus. The first such tumour was detected after 712 days of treatment. There was no dose related response; 11 rats at the low level of treatment were affected, 12 at the intermediate and 11 at the high. Twenty seven females but only seven males were affected. No gastric tumours were found in the 228 controls. There is no evidence that loxtidine acts as a direct carcinogen and it is suggested that the tumours were the result of prolonged achlorhydria produced by a potent unsurmountable histamine H2 receptor antagonist.

Animals↗
PubMed1978

The influence of residual factor VII on the sensitivity of brain thromboplastin.

One-stage prothrombin times of normal and of factor VII-deficient beagle plasma were determined with two types of beagle brain thromboplastin, one prepared from normal beagles and the other from factor VII-deficient beagles. There was little difference between the reagents in the prothrombin times obtained for normal plasma. However, when factor VII-deficient plasma was tested, reagent prepared from factor VII-deficient beagles gave considerably longer prothrombin times than were obtained with the normal reagent and the difference increased with increasing reagent concentration to a maximum at 140 mg/ml. Prothrombin times of a series of mixtures of normal and factor VII-deficient plasma indicated that the presence of only 1/90 part of normal plasma was necessary to compensate for the difference between the two reagents. Determination of the iron content of the reagent suggested that the microcirculation of an average brain contained some 1.8 g of whole blood. The finding that brain thromboplastin prepared from factor VII-deficient beagles is more sensitive to a deficiency of factor VII in plasma, presumably a result of the smaller quantity of factor VII present in the reagent, is compatible with the known kinetics of extrinsic coagulation.

Animals↗