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Biomedical subjects

M J Kendall

Publications and source records attributed to M J Kendall.

At least 145 records · Page 8Linked to original sources
PubMed1989

Pharmacology of third-generation beta-blockers: greater benefits, fewer risks.

The primary goals in the management of hypertension, angina pectoris, and postinfarction cases are to prevent further damage to the cardiovascular system and to reduce the risk of subsequent myocardial infarction. Of all the drugs currently available, the beta-blockers seem the most likely to achieve this aim. The search for new beta-blockers centers around the need for agents that offer the advantages of beta 1-adrenoceptor antagonism without the unwanted beta 2 effects, which may be dangerous in asthmatic patients and may make bronchitis, diabetes, and arteriopathy worse or more difficult to control. One solution is to use a selective beta 1-adrenoceptor antagonist. Another is to develop a molecule that acts as an antagonist at beta 1-adrenoceptors and as an agonist at beta 2-adrenoceptors. celiprolol is such a "third-generation" beta-blocker in that it combines both attributes, and thereby offers a clinically relevant advance. It does not seem to disrupt glucose homeostasis or exacerbate peripheral vascular disease, the lipid profile appears to be positively altered, and the risk of bronchospasm is reduced. Celiprolol is therefore both clinically and biochemically well tolerated.

Adrenergic beta-Antagonists↗
PubMed1989

The effects of verapamil, diltiazem, nifedipine and propranolol on metabolic control in hypertensives with non-insulin dependent diabetes mellitus.

The effects of one month's treatment with each of nifedipine, verapamil, diltiazem, propranolol and placebo, given in random order, on fasting plasma glucose, haemoglobin Alc, serum fructosamine, immunoreactive insulin, cholesterol, and triglyceride were studied in a group of 19 patients with hypertension and non-insulin dependent diabetes mellitus. The metabolic effects of the active drugs were generally small but fasting plasma glucose was increased by propranolol from 9.3 +/- 3.0 to 10.4 +/- 3.4 mmol/l (P less than 0.01) (mean +/- SD) and to 10.1 +/- 3.2 mmol/l (P less than 0.05) by nifedipine. Serum fructosamine was increased from 2.75 +/- 0.53 to 2.89 +/- 0.62 mmol/l (P less than 0.05) by diltiazem and to 2.91 +/- 0.65 (P less than 0.05) by propranolol. Verapamil increased fasting serum immunoreactive insulin: diltiazem and propranolol tended to reduce it. Propranolol but not the other drugs significantly increased serum triglyceride. Calcium antagonists may be preferable to beta adrenoceptor blockers for the treatment of hypertensive diabetics. Of the three calcium antagonists we studied, verapamil may have advantages over nifedipine and diltiazem.

Aged↗
PubMed1988

The effects of ranitidine and cimetidine on the pharmacokinetics and pharmacodynamics of metoprolol.

The impact of cimetidine, ranitidine and placebo on the pharmacokinetics of metoprolol, given either as a single dose (100 mg) or for 7 days (100 mg b.d.), has been evaluated in two separate studies. The doses used were 800 mg cimetidine daily and 300 mg ranitidine daily. The subjects were all young, healthy volunteers. In the single dose study, cimetidine produced a marked increase in the peak plasma concentration of metoprolol and in the area under the plasma concentration-time curve; ranitidine had less effect, though the area under the curve was significantly greater than placebo. In the chronic dosing study, the area under the curve for metoprolol was also significantly higher on cimetidine (1796 ng h/ml; P less than 0.001) whereas the area under the curve on ranitidine (1258 ng h/ml) was comparable to that on placebo (1183 ng h/ml). Despite these drug-induced changes in plasma metoprolol concentration, neither cimetidine nor ranitidine altered the change in exercise-induced heart rate during dosing with metoprolol.

Adult↗
PubMed1988

Effects of nifedipine, verapamil and diltiazem on renal function.

Eight healthy female volunteers were given single doses of nifedipine 10 mg, verapamil 80 mg, diltiazem 120 mg or placebo on 4 different study days. Urine and sodium output increased after all four drugs, but the increase after nifedipine was significantly greater than after verapamil or placebo. Nifedipine caused a significant increase in heart rate; none of the drugs caused any change in blood pressure. Potassium excretion, creatinine clearance, free water clearance and plasma renin activity did not change with any drug. The mechanism of the natriuresis and diuresis has still to be elucidated.

Adult↗
PubMed1988

Enalapril in Raynaud's phenomenon.

The effect of enalapril in the treatment of Raynaud's phenomenon was assessed in a prospective double-blind cross-over trial in 17 patients (nine primary Raynaud's, eight Raynaud's associated with scleroderma). Each patient received 20 mg enalapril daily and placebo for 3 weeks with a 2-week washout period in between. The severity and frequency of Raynaud's attacks were measured subjectively by a diary count and objectively by measurement of finger systolic pressure changes in response to cooling (cold challenge test). Enalapril was associated with a reduction in the frequency of Raynaud's attacks, especially in patients with primary Raynaud's, compared with placebo, but there was no effect on the cold challenge test. We conclude that enalapril, like other vasodilator drugs, helps the symptoms of Raynaud's phenomenon, especially in patients with idiopathic or primary disease.

Adolescent↗
PubMed1988

Alcohol and treatment of diabetes.

The effects of alcohol on diabetic patients controlled on insulin are reviewed and the associated risks of hypoglycaemia, insulin resistance and ketosis are commented on. The impact of alcohol intake in patients with maturity onset diabetes is also considered and potential interactions with oral hypoglycaemic agents highlighted.

Alcohol Drinking↗
PubMed1988

Ranitidine versus cimetidine. A comparison of their potential to cause clinically important drug interactions.

The literature on H2-antagonist drug interactions is now extensive. The whole subject is so complicated as to make things difficult for the potential prescriber. However, it is possible to reduce most of the information contained in the literature to a few simple messages. Firstly, H2-antagonists bind to cytochrome P450 and may inhibit the metabolism of drugs eliminated by the mixed function oxygenase system. In this respect, cimetidine has a marked effect which, in most studies, has reached statistical significance. Ranitidine, on the other hand, has a much weaker effect which, even if demonstrable, is statistically non-significant. The potential benefit of ranitidine, however, has to be weighed against the relative costs of the 2 drugs. Secondly, H2-antagonists inhibit gastric acid production and may alter the rate of gastric emptying, and hence the rate of drug absorption. They may also have some effect on portal vein and hepatic artery flow. However, these effects are small and probably not clinically relevant. Thirdly, pharmacodynamic effects of H2-antagonist-drug interactions are difficult to demonstrate in planned studies, and although they are reported from time to time, adverse reactions of consequence are relatively uncommon. Fourthly, the prescriber needs to be aware that cimetidine may produce higher plasma concentrations of some drugs which have a fairly narrow therapeutic range, and this may be clinically important. Examples of drugs for which it may be undesirable to inadvertently increase plasma concentrations include warfarin, theophylline and phenytoin. Finally, for most drugs metabolised by the liver, the risk of an important interaction is small. However, if such an interaction is noted it may be helpful to refer to the other reported cases, and a number of references are included here.

Cimetidine↗
PubMed1987

Impact of beta 1 selectivity and intrinsic sympathomimetic activity on potential unwanted noncardiovascular effects of beta blockers.

Beta-adrenoceptor-blocking drugs are widely used as effective antihypertensive and antianginal agents, but treatment with these agents may be contraindicated in hypertensive patients in whom receptor blockade would interfere with noncardiovascular activities dependent on sympathetic drive. beta blockade impairs pulmonary function in asthmatic patients through antagonism of beta 2 bronchodilation. However, patients with chest problems may be treated effectively with beta 1-selective drugs, including acebutolol, atenolol and metoprolol. The metabolic response to hypoglycemia, which is mediated by beta-receptor stimulation, involves insulin release, gluconeogenesis, tachycardia and increased systolic pressure. Beta 1-selective drugs are preferred in patients who need to increase blood glucose levels because they do not interfere with glycogenolysis. Hypertension induced by pregnancy may be treated with a beta blocker with no apparent adverse effects on the fetus or neonate. Those possessing intrinsic sympathomimetic activity may be preferable.

Adrenergic beta-Antagonists↗
PubMed1987

The effect of propranolol on the rise in plasma ammonia during modest exercise.

Changes in plasma ammonia in response to exercise with and without pretreatment with propranolol have been studied. A standardised submaximal treadmill exercise test was used to assess the effects of placebo or propranolol 40 mg, 80 mg, or 160 mg twice daily given in random order for 3 days, the last dose being taken 90 min before exercise. After placebo the mean incremental rise in plasma ammonia in response to exercise was 16 mumol X 1(-1). The corresponding rise after propranolol 40 mg was 56 mumol X 1(-1) (p less than 0.01). All three doses of propranolol produced similar effects on plasma ammonia and exercise heart rates.

Adolescent↗
PubMed1987

Twelve hour (trough) plasma nifedipine concentrations during chronic treatment with nifedipine retard.

Variation in plasma nifedipine concentrations have been reported and one study has suggested the existence of a subpopulation of poor metabolisers of this drug. We have studied the variability of 12 h plasma nifedipine concentrations in 64 hypertensive patients on long-term nifedipine Retard 20 mg twice daily. A slightly skewed unimodal distribution with a modal concentration of 15 to 30 ng/ml was obtained. No relationship between 12-h plasma levels and debrisoquine hydroxylation phenotype was found.

Adult↗
PubMed1987

Inter- and intra-subject variability of nitrendipine and the effects of food.

Plasma concentrations of nitrendipine were measured, after single (20 mg) oral doses, in young healthy volunteers. On three occasions the subjects ingested the dose having fasted overnight. Data from these three occasions were used to assess variability in nitrendipine pharmacokinetics and both inter- and intra-subject variability were high. On a fourth occasion, the subjects took the tablet after a standard meal. The effects of food on nitrendipine pharmacokinetics, based on the comparison of data from the first fasting visit and the food visit, were negligible.

Adult↗
PubMed1987

Pharmacokinetic interactions between felodipine and metoprolol.

This double-blind, cross-over study in healthy male subjects evaluated the pharmacokinetics of felodipine and metoprolol given both separately and in combination. During three, five-day study periods, felodipine 10 mg b.d., metoprolol 100 mg b.d. and a combination of the two, were given in random order. There was at least a 7-day washout period between each pharmacokinetic study day. Plasma levels of unchanged felodipine and metoprolol were measured for 24 h after the last dose, on the 5th day of each treatment period. Eight subjects, aged 19-22 years, completed the study. Both felodipine and metoprolol, given alone and in combination, were well tolerated. None of the felodipine pharmacokinetic variables (tmax, Cmax, Cmin, AUC (0-12) and t1/2) changed significantly when felodipine and metoprolol were given in combination. Cmax and AUC (0-12) for metoprolol increased significantly when metoprolol and felodipine were combined, although tmax, Cmin and t1/2 for metoprolol remained unchanged. The changes in metoprolol pharmacokinetics induced by felodipine are small and unlikely to be clinically important.

Adult↗
PubMed1987

The effects of four beta-adrenoceptor antagonists during modest exercise on plasma ammonia and heart rate.

Plasma ammonia and heart rate were measured in normal volunteers before, during and after an exercise test following administration of placebo, propranolol, pindolol, metoprolol and nadolol. Small changes in plasma ammonia occurred during exercise after placebo. However, all four beta-adrenoceptor antagonists produced considerably greater rises. This effect was most marked after propranolol with the response to pindolol, metoprolol and nadolol being similar and intermediate between placebo and propranolol. Resting heart rate was reduced by all the beta-adrenoceptor antagonists except pindolol. Exercise induced changes in heart rate were significantly reduced to a similar degree by all the beta-adrenoceptor antagonists.

Adrenergic beta-Antagonists↗
PubMed1987

Ranitidine and cimetidine; drug interactions with single dose and steady-state nifedipine administration.

The effect of ranitidine 300 mg once daily and cimetidine 800 mg once daily on the disposition of nifedipine was studied in two groups of 12 volunteers. Both investigations were placebo-controlled cross-over studies. The first group received ranitidine, cimetidine or placebo for 5 days with 20 mg nifedipine given on the 5th day. Each period was separated by 1 week. The second group received nifedipine 10 mg three times daily for 5 days together with the H2-receptor antagonist or placebo. Cimetidine produced a significant increase in the AUC of both single and steady state dosing of nifedipine. Peak nifedipine levels were significantly increased only in the chronic dose study compared to placebo. Ranitidine did not produce any significant changes in either study.

Adolescent↗
PubMed1987

The pharmacokinetics of oxprenolol following oral and rectal dosing--a comparison of delivery systems and routes of administration.

Plasma oxprenolol concentrations were measured in eight healthy volunteers who received equivalent oral doses of the drug in the form of an aqueous solution and a 10/170 oxprenolol Oros drug delivery system. Absorption from the lower gastrointestinal tract was assessed by measurement of plasma concentrations after rectal administration of the pre-equilibrated Oros systems. Because three of the first four volunteers suffered local irritation, however, the other four volunteers received Slow Trasicor 160 mg orally as a comparative preparation. The rate of in vivo absorption after oral administration of the Oros system closely mirrored its in vitro release rate. Drug availability from Oros was reduced, however, and was equivalent to 77% of that from the oral solution. Oxprenolol was well absorbed from the rectum while the system was present in this segment of the gut. The reduced systemic availability in three of the volunteers could be accounted for largely by drug loss when the system was expelled. Slow Trasicor produced higher peaks but lower 24 h plasma concentrations than the orally administered Oros system. As judged from the relative areas under the plasma concentration-time curve, however, the availability of the drug from the two dosage forms was comparable.

Administration, Oral↗
PubMed1987

The influence of beta-adrenoceptor blockade on the lipolytic response to exercise.

The influence of beta-adrenoceptor blockade on the free fatty acid (FFA) response during and after submaximal exercise was studied in a group of normal volunteers. The study showed that the exercise-induced rise in serum FFA concentrations seen with placebo was reduced after pretreatment with propranolol. Furthermore, the palmitic, stearic, oleic and linoleic acid responses showed progressive attenuation with increasing doses of propranolol. Different beta blockers were studied using comparable doses: metoprolol and nadolol had little effect and produced FFA profiles that were similar to placebo whereas the changes on pindolol were comparable with those on propranolol.

Adrenergic beta-Antagonists↗