An evaluation of the alpha-adrenoceptor antagonism produced by SK&F 86466 in healthy normotensive males

SK&F 86466 is a novel, potent alpha-adrenoceptor antagonist which, in animal experiments, is reported to show a high selectivity for alpha 2-adrenoceptors at both pre- and post-junctional sites. The effects of two intravenous doses of 80 and 200 micrograms kg-1 of SK&F 86466 were assessed in a placebo-controlled, double-blind, randomised study in eight young, healthy, normotensive males. Two indices of alpha-adrenoceptor activity were investigated: i) Pressor responsiveness to the relatively selective alpha 1-adrenoceptor agonist phenylephrine and to the preferential alpha 2-adrenoceptor agonist alpha-methylnoradrenaline. ii) Circulating levels of noradrenaline. SK&F 86466 at a dose of 200 micrograms kg-1 produced rightward shifts of the pressor dose-response curves to both agonists: a 1.4 fold shift for phenylephrine (P = 0.023) and a 1.6 fold shift for alpha-methylnoradrenaline (P = 0.051). Erect plasma noradrenaline sampled at 105 min into the infusion was significantly increased from 2.9 to 5.0 nmol l-1 by SK&F 86466 200 micrograms kg-1 (P = 0.002). The change in the phenylephrine responses indicates post-junctional alpha 1-adrenoceptor blockade and the rise in noradrenaline is consistent with pre-junctional alpha 2-adrenoceptor antagonist activity. Overall the results of this study suggest that SK&F 86466, at a dose of 200 micrograms kg-1, causes both alpha 1- and alpha 2-adrenoceptor antagonism in human subjects.

Prediction of the antihypertensive response to enalapril

This study investigates the potential utility of a drug concentration-effect modelling approach to predict the long-term response to antihypertensive treatment with enalapril. Concentration-effect relationships were characterized in 13 subjects following a single dose of enalapril (20 mg) and for each individual the derived parameters were used to predict the steady-state blood pressure profile. The predicted responses (before dosing and 4 h after dosing) were in close agreement with the responses observed after 6 weeks. In individual patients, the observed and predicted blood pressure profiles over a 12 h period were compared. In six of the 13 subjects, there were statistically significant (P less than 0.05) prediction errors. However, in all but one of these patients the error was less than 10%, and for the group as a whole the mean prediction error was small and not statistically significant (-0.6 +/- 2.1 mmHg). The kinetic-dynamic parameters derived from observations of the first dose were used to simulate steady-state responses to several alternative doses and dose frequencies. A regimen of 10 mg twice daily increased the ratio of blood pressure at trough-to-peak response to 75 +/- 5% compared to 33 +/- 16% when 20 mg was given once daily. In addition, a twice-daily regimen reduced the coefficient of variation of the hourly average blood pressure. Thus, concentration-effect parameters derived from the first dose response to enalapril have potential not only for predicting long-term antihypertensive response, but also for optimizing dosage regimens for individual patients.

Clinical studies with the potassium channel activator cromakalim in normotensive and hypertensive subjects

Eight normotensive subjects received single and multiple doses of cromakalim (1 mg) and placebo in a randomised double-blind cross-over study to examine general tolerance to cromakalim and its effects on blood pressure (BP), heart rate (HR), and pressor responses to norepinephrine (NE) and angiotensin II (AII). In a second study, 10 hypertensive patients whose BP control was unsatisfactory with atenolol 50-100 mg received additional treatment with placebo followed by cromakalim 1 mg daily for 4 weeks. Assessments were made of BP, HR, apparent hepatic blood flow and renal blood flow (RBF), pulmonary function, and the pharmacokinetics of atenolol. Cromakalim was generally well tolerated in both normotensive and hypertensive subjects. In the normotensive group, cromakalim produced a reflex increase in HR without any detectable decrease in BP: average (placebo-subtracted) increases in HR at 4 h were 16 beats/min with subjects in an erect position after the single dose and 14 beats/min after 7 days. Cromakalim had no effect on pressor responses to NE and AII. Addition of cromakalim to atenolol was associated with modest further reductions in BP between 0.5 and 3 h after drug administration, with maximal reductions of 21/14 mm Hg (subjects in supine position) 2 h after the first dose. Cromakalim had no effect on apparent liver blood flow and RBF, pulmonary function, and the steady-state pharmacokinetics of atenolol. Single and multiple 1-mg doses of cromakalim are well tolerated but are associated with only modest vasodilator activity.

Antihypertensive drugs and blood lipids

Hypertension frequently coexists with hyperlipidaemia and it has been suggested that the potential benefits of blood pressure reduction may be compromised if lipid levels are not concurrently reduced. In addition, conventional first line antihypertensive drugs (thiazide diuretics and beta-blockers) produce adverse changes in blood lipids which are most apparent in the short-term but do not entirely disappear during chronic treatment. Of the alternative first-line antihypertensive agents, the calcium antagonist and ACE inhibitor drugs are lipid 'neutral' but only the alpha 1-blockers have been associated with favourable effects on the lipid profile.

Concentration-effect relationships and antihypertensive mechanisms: ketanserin in the treatment of essential hypertension

Concentration-effect relationships were characterized in individual hypertensive patients treated with single and multiple doses of ketanserin. There were significant changes in the concentration-effect parameters during continued treatment, and overall there was a reduction in antihypertensive responsiveness, from -0.47 to -0.25 mmHg/ng per ml. The nature of the changes, however, raises the possibility that there were associated changes in the site and mechanism of the underlying antihypertensive action. It is possible that a peripheral mechanism, perhaps alpha 1-adrenoceptor antagonism, is relatively more pronounced after the first dose whereas a central mechanism, perhaps related to serotonergic antagonism, is relatively more important during chronic treatment. We conclude that this technique of concentration-effect analysis may be useful in exploring mechanisms of action and identifying issues which require further clarification.

Vascular pressor responses in treated and untreated essential hypertension

Thirty-seven essential hypertensives received placebo for 3 weeks followed by nifedipine retard (n = 14) or enalapril (n = 13) or doxazosin (n = 10) as monotherapy for 6 weeks and attended study days to evaluate the effects of placebo, first dose, and chronic (1-6 weeks) treatment. On each study day, pressor responses to i.v. infusions of phenylephrine (PE) and angiotensin II (AII) were measured 1.5-3 h after drug administration and the derived PD20 values (dose required to increase mean blood pressure by 20 mm Hg) compared. Each treatment produced comparable reductions in BP. Nifedipine significantly attenuated the pressor responses to AII and PE: for AII, the mean PD20 (ng/kg/min) increased from 8.2 (placebo) to 9.9 (first dose), 13.9 (1 week), and 17.4 (6 weeks). Pressor responsiveness to both AII and PE was unchanged following enalapril: for PE, the mean PD20 (micrograms/kg/min) was 2.1 (placebo), 1.5 (first dose), and 1.5 (6 weeks). Doxazosin produced rightward shifts of the PE pressor dose-response curves but had no effect on responses to AII. The relationship between the simultaneous BP and HR changes during the infusion of PE was used as an index of cardiac baroreflex activity. In contrast to enalapril and doxazosin, which had no effect, nifedipine reduced the slope of the HR/BP relationship from -0.62 (placebo) to -0.38 (first dose) and -0.31 beats/min/mm Hg (6 weeks). For comparable reductions in BP, doxazosin only affects adrenergic mechanisms whereas nifedipine affects both adrenergic and non-adrenergically mediated vasoconstriction. The ACE inhibitor enalapril had no effect on pressor responses to AII and PE.

The influence of age on the pharmacokinetics and antihypertensive responses to dilevalol

Age may influence the response to antihypertensive drug treatment either indirectly, by altering the plasma drug concentrations, or directly, by altering the nature and magnitude of the blood pressure reduction. This study investigates the effect of age on the pharmacokinetics and antihypertensive responses following acute and chronic treatment with dilevalol in 18 patients (age range 28-73 years) with essential hypertension. There were no significant age-related changes in pharmacokinetics for either acute or chronic treatment with dilevalol. Correspondingly, there was no evidence of any age-related difference in the antihypertensive response and, in absolute terms, this was slightly greater in the six oldest patients in whom blood pressure fell by 18/10 mmHg, supine, and 16/8 mmHg, erect, after the first dose of dilevalol, compared to 4/3 and 6/3 mmHg, respectively, in the six youngest patients. When allowance was made for the differences in starting (pretreatment) blood pressure, there was no significant difference in the antihypertensive response of the elderly compared to the young patients. This study has shown that the antihypertensive efficacy of dilevalol is not attenuated in the elderly and that there are no age-related differences either in pharmacokinetics or in antihypertensive responsiveness.

Kinetic-dynamic relations and individual responses to enalapril

Pharmacokinetic and pharmacodynamic variability largely account for interindividual differences in the response to antihypertensive drugs including angiotensin converting enzyme inhibitors. The factors determining the response to enalapril have been investigated in a placebo-controlled study in essential hypertension. The effects of placebo, the initial dose of enalapril, and long-term (1 and 6 weeks) treatment with enalapril were studied in 13 subjects. By using an integrated kinetic-dynamic model that incorporates a parameter for saturable protein binding, individual responses for blood pressure reduction and angiotensin converting enzyme inhibition were characterized in terms of the maximum effect (Emax) and the drug concentration required to produce 50% of Emax (Ce50). In individual subjects, plasma enalaprilat concentrations could be correlated with falls in blood pressure and changes in plasma angiotensin converting enzyme activity. For the group, Emax was -46.1 +/- 16.5 and -19.7 +/- 3.8 mm Hg for systolic and diastolic blood pressure, respectively, and the corresponding Ce50 values were 66.1 +/- 20.2 and 61.6 +/- 22.5 ng/ml. For angiotensin converting enzyme inhibition, Emax (%) and Ce50 (ng/ml) were, respectively, 102.4 +/- 5 and 19.8 +/- 13 after the first dose, 103 +/- 5 and 33.4 +/- 20.3 after 1 week, and 101.3 +/- 2.2 and 31.3 +/- 18.9 after 6 weeks. There was no relation between the responsiveness to enalapril (Emax or Ce50) and patient age or plasma renin activity, but there was a significant positive correlation between Emax and the pretreatment blood pressure. In individual subjects, Emax (first dose) was directly correlated with Emax after 1 and 6 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors influencing the responses to calcium antagonists in elderly patients with hypertension and ischaemic heart disease

The results of a variety of studies that have investigated the effect of age on the pharmacokinetics and pharmacodynamics of calcium antagonist drugs have produced the following conclusions. Primarily, as a result of an age-dependent decline in plasma drug clearance, there is a tendency for elderly patients to have higher plasma drug concentrations than young patients. In terms of pharmacological response, there is good evidence of therapeutic efficacy in both hypertension and ischaemic heart disease, but there is no convincing evidence of any preferential age-related effect, particularly in relation to blood pressure reduction. Similarly and conversely, there is no convincing evidence that the elderly are at greater risk from the adverse effects of calcium antagonist drugs, particularly those which reflect the negative effects on cardiac conduction. An integrated mathematical method for describing antihypertensive response, which incorporates both pharmacokinetic and pharmacodynamic information, has been used to investigate the variability in antihypertensive effect with nifedipine and verapamil. There was no relationship between responsiveness (in mmHg/ng/mL) and patient age and plasma renin activity; however, responsiveness during chronic treatment was directly correlated with the height of the starting blood pressure and the response to the first dose.

Treatment of high blood pressure--the effect on coronary morbidity and mortality

Established drugs used in the treatment of hypertension have reduced stroke but have had disappointingly little impact on coronary artery disease and its complications. This could be due to inadequate falls in blood pressure (or excessive falls). It is possible that the role of blood pressure in ischaemic heart disease has been over-estimated compared to other risk factors. Alternatively, the drugs used previously may have adversely affected other factors. Mortality in treated hypertensives remains higher than normotensives but so does their blood pressure. The blood pressure on treatment is a much better predictor of outcome than initial blood pressure. This suggests that improved blood pressure control may be desirable. In our hospital-based hypertension clinic many patients have more than one risk factor. In spite of intensive efforts between 1980 and 1988, smoking habits changed little and serum cholesterol and random blood glucose actually rose. Cholesterol is high in our population of hypertensive patients and the mean (+/- SD) rose from 6.4 +/- 1.3 to 6.6 +/- 1.3 (n = 127; P less than 0.01). These observations highlight the importance of a multiple risk factor approach. The benefits of alternative drugs which can lower total cholesterol and/or low-density lipoprotein (LDL) and/or raise high-density lipoprotein (HDL) deserve study in this population. A final possibility is that the widely observed association between hypertension and ischaemic heart disease is not causal (or is weak compared to other risk factors). If a common underlying mechanism caused both atheroma and hypertension then reduction of blood pressure would not be expected to reverse atheroma and its complications. At present this possibility cannot be excluded.

Prediction of response to antihypertensive therapy with enalapril and nifedipine

We evaluated the usefulness of an integrated concentration-effect modelling technique in predicting the long-term response to antihypertensive therapy with enalapril and nifedipine. Two groups of essential hypertensives were given monotherapy with 20 mg nifedipine twice a day (n = 14) or 20 mg enalapril once a day (n = 13), and were studied following the administration of the drugs and after at least 6 weeks' treatment. For both drugs the predicted responses (predose and 4 h postdose) were in close agreement with the observed responses. With enalapril the observed and predicted profiles over a 12-h study period were well correlated in all subjects. In contrast, with nifedipine, although there was generally good agreement, the model over-predicted the profile of response in one patient and under-predicted the profile in one patient. Thus, there is evidence that application of concentration-effect analysis is useful in predicting the steady-state antihypertensive effect from the first dose-response to the drug.

Hypercholesterolaemia in treated hypertensives: a controlled trial of intensive dietary advice

We evaluated dietary counselling by dietitians in hypercholesterolaemic hypertensives over 6 months. A total of 141 patients were randomly assigned to intensive advice or usual care. Body weight fell significantly in the intervention group, but did not in the controls. There was a modest but significant fall in total cholesterol from 7.1 to 6.8 and 7.1 to 6.9 mmol/l in the diet and the control groups, respectively (4 and 3%). A similar pattern emerged from the triglyceride measurements. Low-density lipoprotein fell in both groups, but only achieved significance (P less than 0.05) in the intervention group. High-density lipoprotein did not change. There was a more marked change in cholesterol when serum levels during the study were compared with the previous annual review. These falls occurred after selection for the study but before random allocation to groups. They are unlikely to reflect regression to the mean as the lipids were stable for 2 or more years before the study, but may reflect spontaneous changes in diet after the patients were labelled hypercholesterolaemic. Dietary advice can lower total cholesterol but the magnitude of this decrease is small. Additional approaches are likely to be required to reduce plasma cholesterol to a normal range.

Pressor responsiveness, age and hypertension

It has long been accepted that enhanced vascular reactivity is an integral part of the hypertensive state. This study investigates pressor responsiveness to the selective alpha 1-adrenoceptor agonist, phenylephrine, in 62 normotensive and hypertensive subjects aged 20-70 years. Since blood pressure increases with age, it is possible that effects attributed specifically to blood pressure will be confounded by age. The present study showed no correlation between responsiveness and starting blood pressure. However, responsiveness was positively correlated with age. These results suggest that it may be an oversimplification to attribute increased vascular responsiveness to the hypertensive state.

Concentration-effect relationships and individual responses to doxazosin in essential hypertension

1. This study investigates aspects of the pharmacokinetics, pharmacodynamics and concentration-effect relationships in 10 patients with essential hypertension during acute and chronic treatment with doxazosin, an alpha 1-adrenoceptor antagonist. 2. Following the first dose of doxazosin (2 mg) there were significant reductions in blood pressure, increases in heart rate and in plasma noradrenaline, and parallel rightward shifts of the phenylephrine pressor response curves, consistent with alpha-adrenoceptor antagonism. There was no significant change in the pressor response to angiotensin II. 3. Using an integrated kinetic-dynamic model, individual blood pressure responsiveness was characterised as the fall in blood pressure (mm Hg) per unit drug concentration. Responsiveness to the first dose of doxazosin was directly correlated with the responsiveness after 1 and 6 weeks treatment although there was a systemic reduction (of approximately 30%) which occurred during the first week of treatment. 4. Neither the acute nor long-term responsiveness to doxazosin was related to age, plasma renin activity, plasma noradrenaline or the pretreatment sensitivity to phenylephrine. There was a significant relationship between responsiveness and the height of the initial (pretreatment) blood pressure. 5. Integration of pharmacokinetic and pharmacodynamic data provides a reproducible index of responsiveness which can be used to investigate the consistency of the long-term anti-hypertensive response, to identify factors which influence the magnitude of the response, and to optimise the choice of dose and dose interval.

Predictability of antihypertensive responsiveness and alpha-adrenoceptor antagonism during prazosin treatment

This study investigates concentration-effect relationships in nine patients who had essential hypertension treated with prazosin. Antihypertensive responsiveness was determined for each individual patient in terms of millimeters of mercury of blood pressure reduction per nanogram per milliliter of plasma prazosin concentration. The principal findings were that there was significant attenuation of antihypertensive responsiveness, from 11.5 mm Hg per nanogram per milliter after the first dose to 8.7 mm Hg per ng/ml after 1 week of treatment with prazosin. Correspondingly, there was significant attenuation of the degree of alpha 1-antagonism as assessed by the pressor response to intravenous phenylephrine. However, there was no significant further attenuation of either assessment during continued treatment for up to 3 months. These findings suggest that after an early adaptation, which occurs within the first week of treatment, there is no long-term attenuation of the antihypertensive effect of prazosin. Despite this initial adaptive change, the magnitude of the long-term antihypertensive effect of prazosin was predictable from the first dose response in individual patients.

Pharmacokinetic-pharmacodynamic relationships of alpha-adrenoceptor antagonists

Competitive alpha1-adrenoceptor antagonists are effective in the treatment of both hypertension and cardiac failure. Prazosin has both a short half-life and a short duration of action, but other related quinazoline derivatives, such as doxazosin and terazosin, have pharmacokinetic and pharmacodynamic profiles which make them potentially suitable for once-daily administration. Acute reductions in blood pressure have been correlated with plasma concentrations of prazosin but in most instances, particularly during long term therapy, there is no simple, direct relationship between drug concentration and the fall in blood pressure. Using integrated pharmacokinetic-pharmacodynamic analysis, correlations have been described not only for reductions in blood pressure during short and long term treatment but also for alpha1-adrenoceptor antagonist activity. Furthermore, this integrated approach defines the drug concentration-effect relationship in individual subjects and provides a mathematical description of response that is potentially useful for investigating the factors (both kinetic and dynamic) which influence the inter- and intrasubject variability in antihypertensive effect of alpha-adrenergic blockers. Preliminary data suggest that the long term response to treatment with prazosin and doxazosin is mainly dependent upon the height of the pretreatment blood pressure and the response to the first dose.

Clinical pharmacological evaluation of calcium antagonists and other drugs modifying myogenic tone in essential hypertension

The factors determining the acute and long-term response to calcium antagonists have been studied in controlled trials in essential hypertension. The importance of dose and plasma level in determining the response has been confirmed. The blood pressure response has been modelled and mathematically described, with drug concentrations related to blood pressure falls by linear or Emax (maximum fall in blood pressure) models. The acute response predicted the response after 6 weeks of treatment. Neither age nor plasma renin activity independently influenced the response to calcium antagonists. The level of pretreatment blood pressure (starting blood pressure) was positively related to indices of response. In similar studies with other drugs modifying myogenic tone, while vascular reactivity to selective agonists was reduced, enhanced or unchanged, blood pressure falls were related to plasma levels in all cases.

Angiotensin-converting enzyme inhibitors in the elderly

Although early studies suggested little role for angiotensin-converting enzyme (ACE) inhibitors in older hypertensive patients, more careful evaluation has confirmed their efficacy and good tolerability. Although the elderly tend to have low plasma renin levels, the fall in blood pressure after ACE inhibitors is at least as great (and in several studies greater) than in younger age groups. Because several ACE inhibitors, including captopril and enalaprilat, are eliminated by the kidneys, there are predictable age-related effects on pharmacokinetics. Reduced renal clearance will contribute, at least in part, to the enhanced intensity and duration of action seen in elderly patients. However, not all the effects of age on the kinetics and dynamics of ACE inhibitors are predictable. Studies with perindopril and benazepril in the elderly confirm the efficacy of this group of drugs but highlight other pharmacokinetic differences. ACE inhibitors are effective in reducing blood pressure and can be considered for wider use in elderly hypertensives.

Pressor responsiveness in essential hypertension and the effects of treatment with an alpha blocker, calcium antagonist or ACE inhibitor

We have studied the contribution of neurohumoral and structural factors to pressor responsiveness and peripheral resistance in mild/moderate hypertension. Pressor responses to intravenous infusions of phenylephrine (an alpha1 agonist) and angiotensin II were studied in groups of patients with essential hypertension before and after treatment, for 6 weeks with either nifedipine (20 mg bid), enalapril (20 mg daily) or doxazosin (2 mg daily). All drugs lowered blood pressure to a similar extent. Pressor responsiveness to both phenylephrine and angiotensin II showed wide intersubject variation when expressed as the dose of agonist required to raise mean arterial pressure by 20 mmHg (PD20). A group of age-matched normotensive controls showed a similar PD20 for phenylephrine to hypertensives. Angiotensin 11 sensitivity was greater in hypertensives. Drug treatment had different effects in hypertensive patients. Doxazosin, an alpha blocker, reduced the responsiveness to phenylephrine but had no effect on responses to angiotensin II. Nifedipine attenuated responses to both agonists while treatment with enalapril increased responsiveness to both phenylephrine and angiotensin II. We have not found evidence of systematic differences in alpha 1 receptor responses in hypertensives and different "vasodilator" drugs can lower blood pressure with widely different effects on adrenergic and non-adrenergic vascular responses.

The influence of cilazapril on indices of autonomic function in normotensives and hypertensives

1. In two single dose studies, acute blood pressure reduction with cilazapril was not associated with any significant change in supine or erect heart rate in either normotensives or hypertensives. 2. To investigate the lack of reflex cardioacceleration, a series of autonomic function tests was undertaken when there was maximum ACE inhibition, maximum evidence of angiotensin II withdrawal and the lowest blood pressure. 3. There was no evidence that cilazapril had any significant impact on indices of sympathetic nervous activity or the integrity of baroreflex mechanisms. 4. The results for the bradycardic response to apnoeic facial immersion, suggested enhanced parasympathetic activity, consistent with the withdrawal of the vagolytic actions of angiotensin II. 5. These results suggest that the absence of a heart rate response to ACE inhibition is not related to a profound sympatho-inhibitory effect or an impairment of baroreflex function. While there is some evidence of enhanced cardiac parasympathetic tone it seems unlikely that this is the sole explanation for the lack of cardioacceleration.

The pharmacokinetics and angiotensin converting enzyme inhibition dynamics of cilazapril in essential hypertension

1. In a double-blind, placebo controlled, crossover study 12 patients with essential hypertension received single doses of 5, 10 and 20 mg of cilazapril. 2. Peak plasma levels of cilazaprilat and the 24 h areas under curve were directly proportional to dose. 3. The elimination half-life during the first 8 h was about 1.7 h. 4. From 24 h onwards there was a prolonged terminal elimination phase with a half-life of about 40 h, and strict dose proportionality of plasma concentrations was not maintained. 5. The pharmacokinetics of cilazaprilat and the pharmacodynamics of plasma ACE inhibition were well described by a one compartment model with saturable binding to ACE. 6. The coefficients of the model which related to plasma ACE and its interaction with cilazaprilat were in good agreement with model independent observations. 7. The values for kinetic and dynamic parameters in hypertensive patients were comparable with those reported for healthy volunteers.

Calcium antagonists in the treatment of hypertension and angina pectoris in the elderly

Calcium antagonist drugs are widely used in the treatment of hypertension and ischemic heart disease in middle-aged and elderly patients. There are reports that both the pharmacokinetics and pharmacodynamics of these drugs may be affected by increasing age, but the clinical relevance of any age-related changes remains unclear. There is evidence of significant age-related differences in pharmacokinetics that mainly reflect reduced drug clearance in the elderly, leading to higher plasma drug levels. However, calcium antagonist drugs demonstrate wide intersubject variability in pharmacokinetics, particularly in the elderly, and this often obscures any age-related differences. Increased antihypertensive responsiveness has been reported in the elderly, but there is other evidence to suggest that this may not be an independent age-related effect. If allowance is made for differences in pretreatment blood pressure and plasma drug concentrations, there is no confirmatory evidence of an age-related preferential antihypertensive action. Similarly, there is no evidence that the elderly are more susceptible to the adverse pharmacological effects of calcium antagonist drugs. For example, studies of the cardiac conduction effects of verapamil have failed to show an increased effect in the elderly. In fact, young subjects appear to be more likely to develop significant prolongations of atrioventricular conduction. Thus, although there are age-related differences in the clinical pharmacology of calcium antagonist drugs, there is no evidence to suggest that this affords any specific additional beneficial or adverse impact on their therapeutic usefulness.

Initial blood pressure as a predictor of the response to antihypertensive therapy

1. The relationship between fall in systolic blood pressure and initial systolic blood pressure has been investigated in 255 mixed normotensive and hypertensive subjects given placebo or one of five types of antihypertensive drug (ACE inhibitors, calcium antagonists, direct vasodilators, alpha-adrenoceptor blocker, beta-adrenoceptor blocker). 2. In all cases there was a significant correlation between the change in blood pressure and initial blood pressure. When Oldham's transformation was used (replacing the initial blood pressure by the mean of the initial and minimum pressures) the correlation coefficients were all reduced, although five out of six were still statistically significant. 3. In a subset of 43 hypertensive subjects given four antihypertensive agents, concentration-effect analysis was carried out. For three of the agents a linear model was used to relate effect to concentration; for the remaining agent a Langmuir type model was used. 4. For all four sets of data for which concentration-effect analysis was carried out, there was a significant correlation between the sensitivity of response and the initial blood pressure. 5. The observed relationships between initial blood pressure, change in blood pressure and sensitivity of response can be qualitatively explained by postulating a general form of dose-response relationship for all antihypertensive agents.

Kinetic-dynamic relationships and antihypertensive mechanisms of ketanserin in essential hypertension

This study of ketanserin illustrates the use of concentration-effect analysis in clinical investigations of antihypertensive mechanisms and the factors responsible for interindividual differences in blood pressure response. Using an integrated kinetic-dynamic model the acute and chronic responses to ketanserin were characterized for each individual patient in terms of blood pressure fall per unit drug concentration. Two principal findings were obtained from this approach. (1) There was a significant reduction in responsiveness to ketanserin during chronic treatment: on average, -0.47 after the first dose compared with -0.25 mmHg/ng per ml after 1 month. (2) There was a significant change in the parameter keq, which characterizes the temporal discrepancy between the time profiles for plasma drug concentration and effect: from a mean value of 0.49 (first dose) to 1.86/h (1 month). There was no significant relationship between the responsiveness to ketanserin and patient age, peripheral alpha 1-adrenoceptor blockade or initial blood pressure. These results suggest that there is a change in the relative contributions of the component antihypertensive mechanisms during continued treatment with ketanserin. Furthermore, there is no clear relationship between patient age and responsiveness to ketanserin.

Nifedipine: individual responses and concentration-effect relationships

Dynamic and kinetic variability account for the large intersubject differences in the antihypertensive response to nifedipine, and a clear concentration-effect relationship has not been established. The effects of placebo, first dose, and chronic (1 and 6 weeks) treatment with nifedipine were studied in 14 subjects with essential hypertension using an integrated kinetic-dynamic model to calculate individual subject responsiveness in terms of fall in blood pressure per unit change in drug concentration. Nifedipine concentrations were well correlated with the fall in systolic blood pressure in individual subjects, and the mean responsiveness was -0.48 mm Hg/ng/ml after the first dose, -0.45 mm Hg/ng/ml after 1 week, and -0.49 mm Hg/ng/ml after 6 weeks. The responsiveness to the first dose of nifedipine was significantly correlated with the responsiveness after 1 (r = 0.83) and 6 weeks (r = 0.78) of therapy and with the height of the pretreatment blood pressure (r = 0.6). This study incorporated kinetic as well as dynamic information to characterize the antihypertensive response to nifedipine and identify nifedipine concentration-effect relationships in individual hypertensive subjects.