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Biomedical subjects

J R Haigh

Publications and source records attributed to J R Haigh.

At least 19 recordsLinked to original sources
PubMed1990

Effect of warfarin on plasma concentrations of vitamin K dependent coagulation factors in patients with stable control and monitored compliance.

There is a discrepancy in the results of reported studies of levels of vitamin K dependent coagulation factors in patients on warfarin therapy. This may have arisen partly because of the problem of assuring compliance with therapy in outpatients. The plasma concentrations of the vitamin K dependent clotting factors II, VII, IX and X were studied in 23 outpatients whose adherence to prescribed warfarin therapy was determined using a pharmacological indicator of compliance. In these patients, who were shown to have consistently good compliance and stable anticoagulant control over a period of 3-6 months, the activities in plasma of the four coagulation factors were not equally suppressed. Factor IX levels were significantly greater than those of factor VII (P less than 0.0001) which in turn were significantly greater than the levels of factor II (P less than 0.0001) or factor X (P less than 0.0001). There was no significant difference between the levels of factors II and X which were depressed to a similar extent. The proportion of variability of the International Normalized Ratio (INR) explained by linear regression was 51-77% and a model was derived to predict the INR from the mean of the levels of the four clotting factors. The concentrations of the coagulation factors II, VII, IX and X are likely to be highly dependent on the degree of compliance with warfarin therapy which should be taken into account when investigating the behaviour of these factors.

Aged↗
PubMed1989

Poor compliance is a major factor in unstable outpatient control of anticoagulant therapy.

Control of oral anticoagulant therapy in outpatients is often unsatisfactory. The contribution of poor compliance with prescribed warfarin to unstable anticoagulant control was investigated prospectively using low-dose phenobarbitone as an indicator of compliance in 30 out-patients, 15 with stable and 15 with unstable control. Following entry to the study, there was no significant change in anticoagulation (p = 0.36) in the group with stable control. In the group who previously had unstable control, there was a significant change in INR (p = 0.0045) and anticoagulant control greatly improved. It appears that the considerable fluctuation in INR seen in many of the latter patients before the study was due to poor compliance and that entering them into the study modified their behavior. Two patients in this group who continued to have unstable anticoagulant control were shown to be poorly compliant using the phenobarbitone indicator. The results suggest that, in outpatients, poor compliance is the major cause of unstable anticoagulation with warfarin.

Ambulatory Care↗
PubMed1989

Free concentrations of sodium, potassium and calcium in chromaffin granules.

We have measured the contents of Na+ and K+ in isolated chromaffin granules. Total contents varied between 227 and 283 nmol/mg of protein, equivalent to matrix concentrations of 53-66 mM. The value found depended on the isolation buffer used, and the ratio of the two ions reflected the composition of the buffer. We then measured the free concentration of each of these ions, and of Ca2+, in the matrix, by using a null-point method with acridine-fluorescence quenching. This monitored H+ fluxes induced by an ionophore in the presence of known concentrations of the ion in the supporting medium. In contrast with organic constituents of the matrix, which have low activity coefficients, Na+ and K+ were found to have activity coefficients around 0.8 Ca2+, however, was strongly bound: its free concentration was only 0.03% of the total.

Animals↗
PubMed1989

A sodium/proton antiporter in chromaffin-granule membranes.

Chromaffin granules, the secretory vesicles of the adrenal medulla, have a Na+/H+ exchange activity in their membranes which brings their proton gradient into equilibrium with a Na+ gradient. This explains why Na+ is mildly inhibitory to amine transport (which is driven by the H+ gradient) The activity can be demonstrated by using accumulation of 22Na+ in response to a pH gradient that is either imposed by diluting membrane 'ghosts' into alkaline media, or generated by ATP hydrolysis. It can also be monitored indirectly by fluorescence measurements in which the pH inside 'ghost' is monitored by quenching of a fluorescent weak base. This method has been used to monitor Na+ entry into acid-loaded 'ghosts' of H+ entry into methylamine accumulation. The exchanger appears to be reversible and non-electrogenic, with a stoichiometry of 1:1. Using an indirect assay we measured an apparent Km for Na+ of 4.7 mM, and a Ki for amiloride, a competitive inhibitor, of 0.26 mM. Direct assays using 22Na+ suggested a higher Km. Ethylisopropylamiloride was not inhibitory.

Adenosine Triphosphate↗
PubMed1989

Scopolamine and benzodiazepine models of dementia: cross-reversals by Ro 15-1788 and physostigmine.

The muscarinic antagonist scopolamine and the benzodiazepine lorazepam both produce transient impairments in memory and attention in normal volunteers. These impairments can be reversed by appropriate agents such as the cholinesterase inhibitor physostigmine in the case of scopolamine or the benzodiazepine antagonist Ro 15-1788 in the case of lorazepam. In this paper we investigated the pharmacological specificity of these reversals by examining the interactions of scopolamine and Ro 15-1788 and of lorazepam and physostigmine. There was no evidence that the effects of scopolamine and lorazepam on cognitive function could be attenuated by Ro 15-1788 and physostigmine, respectively. The results are discussed in terms of pharmacological models of Alzheimer's disease.

Acoustic Stimulation↗
PubMed1988

RO 16-6028, a benzodiazepine receptor partial agonist, does not exhibit anticonvulsant tolerance in mice.

The development of anticonvulsant tolerance with RO 16-6028, a benzodiazepine receptor partial agonist, was assessed in mice using an i.v. infusion of pentylenetetrazol as the convulsive stimulus. In contrast to other benzodiazepines tested previously in this seizure model the anticonvulsant protection afforded by RO 16-6028 did not change significantly during 10 days treatment (2 mg/kg b.i.d.). This result supports the hypothesis that partial agonists at the benzodiazepine receptor may induce less tolerance and/or dependence than full agonists.

Animals↗
PubMed1988

Can benzodiazepines be classified by characterising their anticonvulsant tolerance-inducing potential?

The development of anticonvulsant tolerance with three benzodiazepines was assessed in mice using a slow intravenous infusion of pentylenetetrazol as the convulsive stimulus. Chlordiazepoxide (12.5 mg/kg b.d.) and midazolam (0.75 mg/kg b.d.) induced a slowly evolving tolerance over 15 days whereas nitrazepam (0.6 mg/kg b.d.) induced a very marked rapid tolerance which developed no further during 6 days treatment. Tolerance appeared to be incomplete with all three benzodiazepines. Possible explanations for the differences in tolerance profile are discussed and an alternative basis for the classification of benzodiazepines is suggested.

Animals↗
PubMed1988

The effect of indomethacin on the psychomotor function of patients with rheumatic diseases.

We have compared the effect of single and multiple doses of indomethacin and placebo on objective measurements of psychomotor impairment in patients. Following a single 50 mg dose (n = 8), indomethacin produced psychomotor disturbance in only those patients who had no recent history of NSAID exposure. After multiple doses of indomethacin (25 and 50 mg tid for 5 days), significant psychomotor impairment was observed. We conclude that other NSAIDs may induce cross-tolerance to the psychomotor effects of indomethacin. Tachyphylaxis may develop to the psychomotor disturbance caused by indomethacin.

Arthritis, Rheumatoid↗
PubMed1988

The effect of allopurinol on the steady-state pharmacokinetics of indomethacin.

The effect of 5 days treatment with allopurinol (300 mg) on the pharmacokinetics of indomethacin at steady-state was investigated in eight patients. Allopurinol produced no significant effect on the indomethacin serum concentration-time curve. Allopurinol did not alter significantly the amounts of indomethacin excreted in the urine within 8 h. However, the urinary ratio of N-deschlorobenzoylindomethacin to indomethacin was reduced significantly by allopurinol administration (P less than 0.05).

Adult↗
PubMed1988

Lipids and platelet function in runners.

The effect of distance running on the fatty acid composition of platelet and erythrocyte membranes has been investigated, together with platelet aggregation and levels of high density lipoprotein-cholesterol (HDLc), low density lipoprotein cholesterol (LDLc), total cholesterol and triglycerides in runners (n = 11) and healthy age-matched non-running controls (n = 12). Platelet aggregation and fatty acid composition of membrane lipids in both platelets and erythrocytes are similar in both groups with the following exceptions: in platelets docosahexaenoic acid (C22:6 omega 3) is significantly higher in runners; in erythrocytes the fatty acids C20:3 omega 6/C22:1 omega 9 and C22:5 omega 3 are significantly higher in runners. There were no significant differences between the levels of HDLc, LDLc and total cholesterol in runners and controls although triglycerides were significantly lower in runners. Possible beneficial effects of running are probably mediated through effects on serum lipid and lipoprotein concentrations, and probably not due to any antithrombotic effect of platelets.

Adult↗
PubMed1987

N-desmethylclobazam: a possible alternative to clobazam in the treatment of refractory epilepsy?

The development of anticonvulsant tolerance during 10 days treatment with either clobazam or its principal metabolite, N-desmethylclobazam (NDMC), was compared in mice using an i.v. infusion of pentylenetetrazole as the convulsive stimulus. Subsequently the anticonvulsant activity of NDMC was assessed in patients with refractory epilepsy. In mice, a highly significant tolerance (P less than 0.001) developed to clobazam (10 mg kg-1 twice daily). During the same period, there was no significant change (P greater than 0.05) in the protection afforded by NDMC (40 or 80 mg kg-1 twice daily) although some reduction in anticonvulsant activity was apparent. NDMC (30 mg once daily) was given to nine patients with frequent complex partial and/or grand mal seizures who had become tolerant to the anticonvulsant effect of clobazam. Seven of the patients had been free from benzodiazepine therapy for at least 2 weeks, while the other two patients were switched directly from clobazam. Eight of the nine patients showed a favourable response to NDMC. In the seven who had been given a holiday from clobazam the response to NDMC was similar to the initial response to clobazam and was achieved at plasma NDMC concentrations in the same range as those seen during clobazam administration (1000-3000 ng ml-1). It is concluded that NDMC is active as an anticonvulsant in man and there is evidence from the animal studies to suggest that it may be preferable to clobazam.

Adult↗
PubMed1987

The effect of cimetidine on the single dose pharmacokinetics of oral clobazam and N-desmethylclobazam.

The effect of cimetidine on the single dose pharmacokinetics of orally administered clobazam and N-desmethylclobazam (NDMC) was studied in volunteers. Cimetidine inhibited the elimination of both clobazam and NDMC and inhibited the rate of formation of NDMC from clobazam. The increase in the AUC for NDMC generated from clobazam was relatively greater than that for clobazam itself. This suggests that NDMC elimination is inhibited to a relatively greater extent than clobazam elimination. The increase in AUC for NDMC generated from clobazam was also relatively greater than that for NDMC administered orally. This would suggest that cimetidine either increases the bioavailability of clobazam or reduces that of NDMC. The increases in the AUC for NDMC and for clobazam in some individuals was of a magnitude which is likely to be clinically significant.

Adult↗
PubMed1987

Pharmacokinetics of N-desmethylclobazam in healthy volunteers and patients with epilepsy.

1. The single dose pharmacokinetics of N-desmethylclobazam (NDMC) and clobazam were studied in eight healthy male volunteers. 2. Steady-state pharmacokinetic data are described from four healthy male volunteers and eight epileptic patients taking NDMC. 3. A single 30 mg dose of NDMC produced a greater Cmax (P less than 0.001) and AUC0-infinity (P less than 0.005) and a shorter tmax (P less than 0.05) and t1/2 (P less than 0.01) for NDMC than did 30 mg clobazam. 4. Mean steady-state NDMC concentrations were greater in male patients than in female patients and also in male patients compared with male volunteers. The differences between patients and volunteers might be explained by concomitant antiepileptic medication.

Adult↗