The 2013 Canadian Hypertension Education Program recommendations for blood pressure measurement, diagnosis, assessment of risk, prevention, and treatment of hypertension

We updated the evidence-based recommendations for the diagnosis, assessment, prevention, and treatment of hypertension in adults for 2013. This year's update includes 2 new recommendations. First, among nonhypertensive or stage 1 hypertensive individuals, the use of resistance or weight training exercise does not adversely influence blood pressure (BP) (Grade D). Thus, such patients need not avoid this type of exercise for fear of increasing BP. Second, and separately, for very elderly patients with isolated systolic hypertension (age 80 years or older), the target for systolic BP should be < 150 mm Hg (Grade C) rather than < 140 mm Hg as recommended for younger patients. We also discuss 2 additional topics at length (the pharmacological treatment of mild hypertension and the possibility of a diastolic J curve in hypertensive patients with coronary artery disease). In light of several methodological limitations, a recent systematic review of 4 trials in patients with stage 1 uncomplicated hypertension did not lead to changes in management recommendations. In addition, because of a lack of prospective randomized data assessing diastolic BP thresholds in patients with coronary artery disease and hypertension, no recommendation to set a selective diastolic cut point for such patients could be affirmed. However, both of these issues will be examined on an ongoing basis, in particular as new evidence emerges.

The assessment of β-adrenoceptor blocking drugs in hyperthyroidism

1 Intravenous propranolol and practolol both reduced resting supine heart rate in patients with hyperthyroidism. Propranolol produced a significantly greater reduction than practolol, which did not have a dose-dependent effect. 2 The effect of these drugs on resting heart rate was much less than their effect on the tachycardias produced both by severe exercise and by standing upright in hyperthyroid patients. Propranolol again produced a significantly greater reduction than practolol in each situation, but practolol did have a dose dependent effect on exercise heart rate. 3 The percentage reduction of standing tachycardia produced by the two drugs appeared to parallel closely the reduction in exercise tachycardia. 4 It is concluded that a simple and convenient way of assessing the activity of β-adrenoceptor blocking drugs in hyperthyroid patients would be to measure their effect on the tachycardia induced by standing. Their effect on resting heart rate should not be used. 5 Practolol may be useful in the management of hyperthyroidism in patients in whom propranolol and similar non-selective β-adrenoceptor blocking drugs are contraindicated.

Intrinsic heart rate on exercise and the measurement of beta-adrenoceptor blockade

Methods of expressing the effects of beta-adrenoceptor blocking drugs on exercise heart rate have been evaluated using a standardised exercise test. In six normal subjects given atropine (0.04 mg/kg) on two separate occasions, the mean +/- s.e. mean exercise heart rate rose by 10.3 +/- 1.8 beats/min and by 11.0 +/- 1.6 beats/min respectively. This increase was designated the 'vagal effect and was not significantly different in the two studies. After atropinsation, propranolol (0.2 mg/kg) reduced mean +/- s.e. mean exercise heart rate by 45.3 +/- 2.6 beats/min and 0.4 mg/kg by 50.8 +/- 4.5 beats/min. This mean sympathetic blockade was not altered significantly by increasing the dose of propranolol but, in four of the six subjects, the larger dose produced an increased effect of 4, 6, 12 and 16 beats/min, suggesting that maximum sympathetic blockade may not have been produced by 0.2 mg/kg. Knowledge of the vagal effect in each subject with standardised exercise enabled prediction to be made of the exercise heart rate after propranolol (0.4 mg/kg) without previous atropinisation. Propranolol (0.4 mg/kg) was then given intravenously to each subject and the actual exercise heart rate measured. There was no significant difference between the predicted and observed exercise heart rates. Propranolol (0.6 mg/kg) without atropine was then given to the four subjects who had shown increased effect with (0.4 mg/kg) and the sympathetic blockade was measured. In one subject, a further increase in sympathetic blockade of 10 beats/min was found. The intrinsic heart rate at rest and on exercise was measured for propranolol (0.2 and 0.4 mg/kg) and, for propranolol (0.6 mg/kg), the intrinsic heart rate on exercise was calculated. At rest, although no significant difference was found between the two dose levels, three subjects did not appear to have maximum autonomic blockade at 0.2 mg/kg. Similarly, several subjects had lower intrinsic heart rates on exercise after 0.4 or 0.6 mg/kg than after 0.2 mg/kg. The intrinsic heart rate on exercise was significantly greater than that obtained at rest. Using the maximum sympathetic blockade obtained in each subject as the sympathetic component of exercise, the effects of increasing oral doses of practolol on exercise heart were measured as percentage blockade of sympathetic effect and this was compared with other conventional methods of measuring beta-adrenoceptor blockade. It was found that percentage blockade of sympathetic effect correlated most closely with both percentage and absolute reduction of exercise heart rate. Correlations with exercise heart rate after drug and percentage inhibition of tachycardia, whilst also significant, did not appear as good. When the effects of practolol were expressed in terms of the potential blockade, a plateau occurred between 70 and 80% of 'maximum' sympathetic blockade. The failure to achieve higher levels with practolol may be the result of its partial agonist or intrinsic sympathomimetic activity.

The 2010 Canadian Hypertension Education Program recommendations for the management of hypertension: part 2 - therapy

OBJECTIVE

To update the evidence-based recommendations for the prevention and treatment of hypertension in adults for 2010.

OPTIONS AND OUTCOMES

For lifestyle and pharmacological interventions, randomized trials and systematic reviews of trials were preferentially reviewed. Changes in cardiovascular morbidity and mortality were the primary outcomes of interest. However, for lifestyle interventions, blood pressure lowering was accepted as a primary outcome given the general lack of long-term morbidity and mortality data in this field. Progressive renal impairment was also accepted as a clinically relevant primary outcome among patients with chronic kidney disease.

EVIDENCE

A Cochrane Collaboration librarian conducted an independent MEDLINE search from 2008 to August 2009 to update the 2009 recommendations. To identify additional studies, reference lists were reviewed and experts were contacted. All relevant articles were reviewed and appraised independently by both content and methodological experts using prespecified levels of evidence.

RECOMMENDATIONS

For lifestyle modifications to prevent and treat hypertension, restrict dietary sodium to 1500 mg (65 mmol) per day in adults 50 years of age or younger, to 1300 mg (57 mmol) per day in adults 51 to 70 years of age, and to 1200 mg (52 mmol) per day in adults older than 70 years of age; perform 30 min to 60 min of moderate aerobic exercise four to seven days per week; maintain a healthy body weight (body mass index 18.5 kg/m(2) to 24.9 kg/m(2)) and waist circumference (less than 102 cm for men and less than 88 cm for women); limit alcohol consumption to no more than 14 standard drinks per week for men or nine standard drinks per week for women; follow a diet that emphasizes fruits, vegetables and low-fat dairy products, dietary and soluble fibre, whole grains and protein from plant sources, and that is low in saturated fat and cholesterol; and consider stress management in selected individuals with hypertension. For the pharmacological management of hypertension, treatment thresholds and targets should be predicated on the patient's global atherosclerotic risk, target organ damage and comorbid conditions. Blood pressure should be decreased to less than 140/90 mmHg in all patients, and to less than 130/80 mmHg in patients with diabetes mellitus or chronic kidney disease. Most patients will require more than one agent to achieve these target blood pressures. Antihypertensive therapy should be considered in all adult patients regardless of age (caution should be exercised in elderly patients who are frail). For adults without compelling indications for other agents, considerations for initial therapy should include thiazide diuretics, angiotensin- converting enzyme (ACE) inhibitors (in patients who are not black), long-acting calcium channel blockers (CCBs), angiotensin receptor blockers (ARBs) or beta-blockers (in those younger than 60 years of age). A combination of two first-line agents may also be considered as initial treatment of hypertension if systolic blood pressure is 20 mmHg above target or if diastolic blood pressure is 10 mmHg above target. The combination of ACE inhibitors and ARBs should not be used, unless compelling indications are present to suggest consideration of dual therapy. Agents appropriate for first-line therapy for isolated systolic hypertension include thiazide diuretics, long-acting dihydropyridine CCBs or ARBs. In patients with coronary artery disease, ACE inhibitors, ARBs or betablockers are recommended as first-line therapy; in patients with cerebrovascular disease, an ACE inhibitor/diuretic combination is preferred; in patients with proteinuric nondiabetic chronic kidney disease, ACE inhibitors or ARBs (if intolerant to ACE inhibitors) are recommended; and in patients with diabetes mellitus, ACE inhibitors or ARBs (or, in patients without albuminuria, thiazides or dihydropyridine CCBs) are appropriate first-line therapies. In selected high-risk patients in whom combination therapy is being considered, an ACE inhibitor plus a long-acting dihydropyridine CCB is preferable to an ACE inhibitor plus a thiazide diuretic. All hypertensive patients with dyslipidemia should be treated using the thresholds, targets and agents outlined in the Canadian lipid treatment guidelines. Selected patients with hypertension who do not achieve thresholds for statin therapy, but who are otherwise at high risk for cardiovascular events, should nonetheless receive statin therapy. Once blood pressure is controlled, low-dose acetylsalicylic acid therapy should be considered.

VALIDATION

All recommendations were graded according to the strength of the evidence and voted on by the 63 members of the Canadian Hypertension Education Program Evidence-Based Recommendations Task Force. All recommendations reported here achieved at least 80% consensus. These guidelines will continue to be updated annually.

SPONSORS

The Canadian Hypertension Education Program process is sponsored by the Canadian Hypertension Society, Blood Pressure Canada, the Public Health Agency of Canada, the College of Family Physicians of Canada, the Canadian Pharmacists Association, the Canadian Council of Cardiovascular Nurses, and the Heart and Stroke Foundation of Canada.

Association of TCF7L2 polymorphism with diabetes mellitus, metabolic syndrome, and markers of beta cell function and insulin resistance in a population-based sample of Emirati subjects

AIMS

The prevalence of type 2 diabetes mellitus (DM) among Emirati subjects is one of the highest in the world. This has been attributed to rising prevalence of obesity acting on genetically susceptible individuals. We analyzed the associations between TCF7L2 polymorphism and DM, metabolic syndrome, and markers of beta cell function and insulin resistance in a population-based sample of Emirati subjects.

METHODS

We genotyped the two TCF7L2 single nucleotide polymorphisms (SNPs) rs12255372 and rs7903146 in 368 adult subjects. Homeostatic model assessment (HOMA) was used to assess beta cell function (HOMA2-%B) and insulin resistance (HOMA2-IR). The SNP genotypes were analyzed against disease stage [normal glucose=0 (n=188), pre-diabetes=1 (n=85), and DM=2 (n=95)] and against clinical and biochemical measures. Age and sex were included as covariates in all association analyses. Additional adjustments were made for body mass index (BMI) and waist circumference in several analyses.

RESULTS

Diabetes disease stage was marginally significantly associated with the frequency of the T variant at rs12255372 (p=0.057; adjusted p=0.017) but not at rs7903146 (p=0.5; adjusted p=0.2). Comparison between subjects with normal glucose and the combined DM/pre-diabetes showed a significant association with rs12255372 (OR 1.47, CI 1.04-2.08; p=0.03) but not with rs7903146 (OR 1.16, CI 0.81-1.64; p=0.4). We found no association with metabolic syndrome, or with insulin and glucose levels, HOMA2-%B or HOMA2-IR. The age-standardized prevalence rate for metabolic syndrome was 43.9% in men and 42.1% in women.

CONCLUSION

These data suggest that TCF7L2 variants are associated with increased risk for DM in Emirati subjects. We also demonstrate a high prevalence of the metabolic syndrome in this population.

Prevalence of diabetes mellitus and its complications in a population-based sample in Al Ain, United Arab Emirates

AIMS

To determine the prevalence of diabetes mellitus (DM) and its complications in the adult population of the United Arab Emirates (UAE) and assess the degree of metabolic control in subjects with diagnosed DM.

METHODS

A random sample of houses of Emirati citizens living in Al Ain, UAE was surveyed. Fasting blood glucose was determined by glucose meter and an oral glucose tolerance test (OGTT) was conducted if blood sugar was <7 mmol/l. DM was defined according to the WHO criteria. Pre-diabetes status was based on fasting venous blood glucose concentration of 5.6-6.9 mmol/l or 2h post-OGTT venous blood glucose level of 7.8-11.0 mmol/l.

RESULTS

There were 2455 adults (>18) living in the 452 surveyed houses of which 10.2% reported having the diagnosis of DM. A total of 373 men and non-pregnant women underwent testing, and after adjustment for factors affecting participation probability the prevalence of diagnosed DM, undiagnosed DM and pre-diabetes was 10.5, 6.6 and 20.2%, respectively. Age-standardized rates for DM (diagnosed and undiagnosed) and pre-diabetes among 30-64 years old were 29.0 and 24.2%, respectively. Logistic regression analysis showed that only age and body mass index (BMI) were significantly independently related to undiagnosed DM. In patients with diagnosed DM, the prevalence rates for retinopathy, neuropathy, nephropathy, peripheral vascular disease and coronary heart disease were 54.2, 34.7, 40.8, 11.1 and 10.5%, respectively. A significant proportion of subjects with undiagnosed DM and pre-diabetes also had micro- and macro-vascular complications. The proportion of subjects with diagnosed DM who achieved internationally recognized targets for HbA1c (<7%), LDL-C (<2.6 mmol/l) and blood pressure (<130/80 mmHg) was 33.3, 30.8 and 42.1%, respectively.

CONCLUSION

This study confirms the previously reported high prevalence of DM in the UAE. Diabetic complications were highly prevalent among subjects with diagnosed and undiagnosed DM. Metabolic control was suboptimal in most subjects with diagnosed DM. Greater efforts are urgently needed to screen early and effectively treat DM in the UAE in order to prevent long-term complications.

The diabetic hypertensive (or hypertensive diabetic)--a compelling need to optimize blood pressure

In summary, the present information on treating hypertension in the diabetic overwhelmingly indicates a compelling need to lower BP to target diastolic BP of 80 mmHg or less, to be less concerned about the types of drugs used than the blood pressures achieved and the concordance with therapy and to rely on two or more antihypertensive drugs in the majority of cases. Management of the hypertensive diabetic is very cost-effective. It is clear that we must engage in total cardiovascular risk management if we are to prevent the microvascular and macrovascular complications in the hypertensive diabetic (or the diabetic hypertensive).

Grapefruit juice--felodipine interaction in the elderly

BACKGROUND

Grapefruit juice can increase the oral bioavailability of a broad range of medications. This interaction has not been assessed in the elderly.

METHODS

Twelve healthy elderly people (70 to 83 years of age) were administered 5 mg felodipine extended release with 250 mL grapefruit juice or water in a single-dose study. Subsequently, 6 of these people received 2.5 mg felodipine for 2 days, followed by 5 mg felodipine for 6 days with 250 mL grapefruit juice or water in a steady-state study. Plasma concentrations of felodipine and dehydrofelodipine metabolite, blood pressure, and heart rate were measured over 24 hours after single and final steady-state dose.

RESULTS

Mean felodipine area under the curve and maximum concentration were 2.9-fold and 4.0-fold greater, respectively, with grapefruit juice in both studies. Interindividual variability in the extent of the interaction was high. Felodipine apparent elimination half-life was not altered. Dehydrofelodipine area under the curve and maximum concentration were increased and dehydrofelodipine/felodipine area under the curve ratio was reduced. Systolic and diastolic blood pressures were lower with grapefruit juice in the single-dose study, whereas they were not different between treatments in the steady-state study. Curvilinear relationships existed between plasma felodipine concentration and changes in systolic and diastolic blood pressures. Heart rates were higher with grapefruit juice in both studies; however, this effect was greater and more prolonged at steady state.

CONCLUSIONS

A normal dietary amount of grapefruit juice produced a pronounced, unpredictable, and sustained pharmacokinetic interaction with felodipine by reducing its presystemic metabolism in the elderly. The different blood pressure results between the studies can be explained by felodipine concentration-blood pressure response relationships. The elderly should be particularly cautioned about concomitant grapefruit juice and felodipine ingestion.

1999 Canadian recommendations for the management of hypertension. Task Force for the Development of the 1999 Canadian Recommendations for the Management of Hypertension

OBJECTIVE

To provide updated, evidence-based recommendations for health care professionals on the management of hypertension in adults.

OPTIONS

For patients with hypertension, there are both lifestyle options and pharmacological therapy options that may control blood pressure. For those patients who are using pharmacological therapy, a range of antihypertensive drugs is available. The choice of a specific antihypertensive drug is dependent upon the severity of the hypertension and the presence of other cardiovascular risk factors and concurrent diseases.

OUTCOMES

The health outcomes considered were changes in blood pressure and in morbidity and mortality rates. Because of insufficient evidence, no economic outcomes were considered.

EVIDENCE

MEDLINE searches were conducted from the period of the last revision of the Canadian Recommendations for the Management of Hypertension (January 1993 to May 1998). Reference lists were scanned, experts were polled and the personal files of the authors were used to identify other studies. All relevant articles were reviewed, classified according to study design and graded according to levels of evidence.

VALUES

A high value was placed on the avoidance of cardiovascular morbidity and premature death caused by untreated hypertension.

BENEFITS

Harms and costs: The diagnosis and treatment of hypertension with pharmacological therapy will reduce the blood pressure of patients with sustained hypertension. In certain settings, and for specific drugs, blood pressure lowering has been associated with reduced cardiovascular morbidity and mortality.

RECOMMENDATIONS

This document contains detailed recommendations pertaining to all aspects of the diagnosis and pharmacological therapy of hypertensive patients. With respect to diagnosis, the recommendations endorse the greater use of non-office-based measures of blood pressure control (i.e., using home blood pressure and automatic ambulatory blood pressure monitoring equipment) and greater emphasis on the identification of other cardiovascular risk factors, both in the assessment of prognosis in hypertension and in the choice of therapy. On the treatment side, lower targets for blood pressure control are advocated for some subgroups of hypertensive patients, in particular, those with diabetes and renal disease. Implicit in the recommendations for therapy is the principle that for the vast majority of hypertensive patients treated pharmacologically, practitioners should not follow a stepped-care approach. Instead, therapy should be individualized, based on consideration of concurrent diseases, both cardiovascular and noncardiovascular.

VALIDATION

All recommendations were graded according to the strength of the evidence and the consensus of all relevant stakeholders.

SPONSORS

The Canadian Hypertension Society and the Canadian Coalition for High Blood Pressure Prevention and Control.

Assimilating new therapeutic interventions into clinical practice: how does hypertension compare with other therapeutic areas?

Medical research has helped to clarify the benefits of some therapies for improving the treatment or outcome associated with cardiovascular disease. However, the adoption of these approaches into routine clinical practice is, in many cases, inadequate. Consequently, there are many missed opportunities to reduce the burden of morbidity and mortality from cardiovascular disease. This review summarizes the factors that may prevent modified behavior in medical practice and the effectiveness of interventions that influence change. There are many barriers that may prevent or slow the adoption of new therapeutic advances into routine clinical practice. As a result, the use of well-proven, efficacious therapy can be suboptimal. Because of this underuse, the realized benefits of treatment are below the potential benefits. Adoption of new therapies is highly dependent on the use of interventions to promote clinical change. However, the effectiveness of different types of interventions varies greatly. Nevertheless, there is a wide range of strategies available that can be used to induce real changes in practice performance and potentially improve patient outcomes. It is essential that future intervention strategies focus on improving adoption of new therapies into clinical practice. The physician must be encouraged to prescribe proven treatments to those patients who stand to benefit most. In addition, better systems of care should be developed that improve the identification of patients as suitable candidates for proven treatments and sustain their long-term commitment to therapy.

A novel formulary: collaboration between health care professionals, seniors, private sector and government in Nova Scotia

A novel formulary has been developed in Nova Scotia with the objective of providing quality treatment with needed medications at affordable cost. Creation of the formulary has involved collaboration among health care professionals, seniors, the Department of Health and pharmaceutical companies. This is the first Canadian formulary to use the Anatomic, Therapeutic, Chemical system. Drug listing is comprehensive rather than exclusive. Colour-coded recommendations on use assist physicians with drug choice. Relative costs are indicated within each therapeutic grouping. Listings indicate drugs approved for reimbursement, interchangeable medications, maximum allowable cost, drug identification number and manufacturer code. Treatment summaries provide brief overviews of therapeutic advice. Updates on new products and new or modified treatment summaries are provided every 6 months. The formulary will be the focus of coordinated educational activities on treatment for seniors and health care professionals.

Lifestyle modifications to prevent and control hypertension. 3. Recommendations on alcohol consumption. Canadian Hypertension Society, Canadian Coalition for High Blood Pressure Prevention and Control, Laboratory Centre for Disease Control at Health Canada, Heart and Stroke Foundation of Canada

OBJECTIVE

To provide updated, evidence-based recommendations concerning the effects of alcohol consumption on the prevention and control of hypertension in otherwise healthy adults (except pregnant women).

OPTIONS

There are 2 main options for those at risk for hypertension: avert the condition by limiting alcohol consumption or by using other nonpharmacologic methods, or maintain or increase the risk of hypertension by making no change in alcohol consumption. The options for those who already have hypertension include decreasing alcohol consumption or using another nonpharmacologic method to reduce hypertension; commencing, continuing or intensifying antihypertensive medication; or taking no action and remaining at increased risk of cardiovascular disease.

OUTCOMES

The health outcomes considered were changes in blood pressure and in morbidity and mortality rates. Because of insufficient evidence, no economic outcomes were considered.

EVIDENCE

A MEDLINE search was conducted for the period 1966-1996 with the terms ethyl alcohol and hypertension. Other relevant evidence was obtained from the reference lists of articles identified, from the personal files of the authors and through contacts with experts. The articles were reviewed, classified according to study design, and graded according to the level of evidence.

VALUES

A high value was placed on the avoidance of cardiovascular morbidity and premature death caused by untreated hypertension.

BENEFITS, HARMS AND COSTS

A reduction in alcohol consumption from more than 2 standard drinks per day reduces the blood pressure of both hypertensive and normotensive people. The lowest overall mortality rates in observational studies were associated with drinking habits that were within these guidelines. Side effects and costs were not measured in any of the studies.

RECOMMENDATIONS

(1) It is recommended that health care professionals determine how much alcohol their patients consume. (2) To reduce blood pressure in the population at large, it is recommended that alcohol consumption be in accordance with Canadian low-risk drinking guidelines (i.e., healthy adults who choose to drink should limit alcohol consumption to 2 or fewer standard drinks per day, with consumption not exceeding 14 standard drinks per week for men and 9 standard drinks per week for women). (3) Hypertensive patients should also be advised to limit alcohol consumption to the levels set out in the Canadian low-risk drinking guidelines.

VALIDATION

These recommendations are similar to those of the World Hypertension League, the National High Blood Pressure Education Program Working Group on Primary Prevention of Hypertension and the previous recommendations of the Canadian Coalition for High Blood Pressure Prevention and Control and the Canadian Hypertension Society. They have not been clinically tested. The low-risk drinking guidelines are those of the Addiction Research Foundation of Ontario and the Canadian Centre on Substance Abuse.

SPONSORS

The Canadian Hypertension Society, the Canadian Coalition for High Blood Pressure Prevention and Control, the Laboratory Centre for Disease Control at Health Canada, and the Heart and Stroke Foundation of Canada. The low-risk drinking guidelines have been endorsed by the College of Family Physicians of Canada and several provincial organizations.

Effects of intensive blood-pressure lowering and low-dose aspirin in patients with hypertension: principal results of the Hypertension Optimal Treatment (HOT) randomised trial. HOT Study Group

BACKGROUND

Despite treatment, there is often a higher incidence of cardiovascular complications in patients with hypertension than in normotensive individuals. Inadequate reduction of their blood pressure is a likely cause, but the optimum target blood pressure is not known. The impact of acetylsalicylic acid (aspirin) has never been investigated in patients with hypertension. We aimed to assess the optimum target diastolic blood pressure and the potential benefit of a low dose of acetylsalicylic acid in the treatment of hypertension.

METHODS

18790 patients, from 26 countries, aged 50-80 years (mean 61.5 years) with hypertension and diastolic blood pressure between 100 mm Hg and 115 mm Hg (mean 105 mm Hg) were randomly assigned a target diastolic blood pressure. 6264 patients were allocated to the target pressure < or =90 mm Hg, 6264 to < or =85 mm Hg, and 6262 to < or =80 mm Hg. Felodipine was given as baseline therapy with the addition of other agents, according to a five-step regimen. In addition, 9399 patients were randomly assigned 75 mg/day acetylsalicylic acid (Bamycor, Astra) and 9391 patients were assigned placebo.

FINDINGS

Diastolic blood pressure was reduced by 20.3 mm Hg, 22.3 mm Hg, and 24.3 mm Hg, in the < or =90 mm Hg, < or =85 mm Hg, and < or =80 mm Hg target groups, respectively. The lowest incidence of major cardiovascular events occurred at a mean achieved diastolic blood pressure of 82.6 mm Hg; the lowest risk of cardiovascular mortality occurred at 86.5 mm Hg. Further reduction below these blood pressures was safe. In patients with diabetes mellitus there was a 51% reduction in major cardiovascular events in target group < or =80 mm Hg compared with target group < or =90 mm Hg (p for trend=0.005). Acetylsalicylic acid reduced major cardiovascular events by 15% (p=0.03) and all myocardial infarction by 36% (p=0.002), with no effect on stroke. There were seven fatal bleeds in the acetylsalicylic acid group and eight in the placebo group, and 129 versus 70 non-fatal major bleeds in the two groups, respectively (p<0.001).

INTERPRETATION

Intensive lowering of blood pressure in patients with hypertension was associated with a low rate of cardiovascular events. The HOT Study shows the benefits of lowering the diastolic blood pressure down to 82.6 mm Hg. Acetylsalicylic acid significantly reduced major cardiovascular events with the greatest benefit seen in all myocardial infarction. There was no effect on the incidence of stroke or fatal bleeds, but non-fatal major bleeds were twice as common.

Familial studies of heritability of alpha1-adrenergic receptor responsiveness in superficial veins

BACKGROUND

Studies of monozygotic and dizygotic twins indicate an important genetic influence on the variability of responsiveness to norepinephrine in superficial human vein.

OBJECTIVES

Genetic aspects of variability of alpha1-adrenergic receptor responsiveness to norepinephrine in superficial veins were further investigated by studying the response to norepinephrine in the dorsal hand veins of parents and their children.

METHODS

Subjects were healthy nonsmoking adults (n = 24; age range, 40 to 52 years) and their biological children (n = 20; age range, 15 to 26 years) who were free from medications likely to modify vascular tone. Superficial vein responsiveness to norepinephrine was assessed by the linear variable differential transformer technique. The dose of norepinephrine required to constrict superficial vein diameter by 50% from baseline (ED50) was calculated for each subject. Heritability was estimated by standard techniques of regression of mid-parent/child (natural logarithm) ED50 values.

RESULTS

ED50 ranged from 5.6 to 254.6 ng/min in the parents and from 7.8 to 242.3 ng/min in the children. Heritability was calculated at 0.88.

CONCLUSIONS

These data confirm wide variability in superficial vein responsiveness to norepinephrine. The results confirm a major genetic influence in biological responsiveness of superficial vein to norepinephrine in healthy humans. Heritability of vascular alpha-adrenergic receptor responsiveness may influence vascular regulation during sympathetic stimulation and blockade.

Variability in prescription drug utilization: issues for research

The authors report the results of a literature review to identify research issues relating to physician prescribing practices and evaluate the potential for existing Canadian databases to support initiatives to improve prescribing practices. Methodologies such as small-area variation analysis and drug utilization reviews are discussed, and Canadian data sources relating to drug prescribing are assessed. The authors conclude that small-area variation analysis can be used to identify differences in drug utilization rates. A ranking method to identify drugs with the greatest variability in utilization can then be used to establish priorities for further analysis. After statistically significant factors associated with prescribing patterns are identified, intervention and policy formation will be possible. This will involve a more sophisticated integration of existing provincial information sources and the adoption of uniform guidelines to promote rational prescribing practices.

Lipids and lipoproteins during antihypertensive drug therapy. Comparison of doxazosin and atenolol in a randomized, double-blind trial: the Alpha Beta Canada Study

A randomized double-blind trial comparing the alpha-adrenergic blocker doxazosin and the beta-adrenergic blocker atenolol was completed by 131 patients with mild to moderate hypertension. Blood pressure and fasting blood lipids were determined at baseline and 4, 12, and 24 weeks of treatment. At entry, plasma lipids and lipoproteins were similar in those patients randomized to doxazosin or atenolol. After 24 weeks of treatment with atenolol, there were significant (P < .05) decreases in high-density lipoprotein cholesterol (HDL-C) and increases in triglycerides and very-low-density triglycerides (VLDL-T). In contrast, doxazosin was associated with significant (P < .05) increases in HDL-C and decreases in triglycerides and VLDL-T. There were no significant differences in HDL apolipoprotein (apo) A-I or low-density lipoprotein apoB between the drugs, but atenolol decreased the ratio of HDL-C to apoA-I, and doxazosin increased this ratio, differences that were statistically significant (P < .002). Neither apoA-I nor apoB concentration at baseline nor apoE phenotype was predictive of the lipid responses during antihypertensive treatment with either drug. Thus, there are significant favorable changes in HDL-C, total triglycerides, and VLDL-T between patients with mild to moderate hypertension and normal plasma lipids when treated with the alpha-blocker doxazosin compared with the beta-blocker atenolol. Plasma lipid or apo concentrations were not predictive of their lipid response during antihypertensive therapy with either of these agents.

Adverse effects of alpha 1-adrenergic blocking drugs

Earlier nonselective alpha 1-adrenergic blocking drugs such as phentolamine and phenoxybenzamine are now restricted to the pharmacological management of alpha 1-adrenergic crisis and phaeochromocytoma. Prazosin, the first selective alpha 1-blocker approved for the treatment of hypertension, became available in the mid-1970s. Additional alpha 1-blockers such as doxazosin and terazosin have been introduced during recent years. The undesirable effects of all members of this class are similar. Most adverse events can be attributed to reversible competitive antagonism of postsynaptic alpha 1-adrenergic receptors in tissues that sustain high levels of alpha-adrenergic sympathetic tone, e.g. resistance arteries, capacitance veins and the urinary bladder outflow tract. Orthostatic hypotension with a sensation of intense faintness and occasional syncope, can occur shortly after the initial dose. Aggravating factors include upright posture, intravascular volume depletion and concurrent administration of other medications that lower blood pressure, including all other classes of antihypertensive drugs. The problem is reduced or avoided by the choice of low starting doses, beginning treatment at bedtime and by minimising other risks. Among overall adverse effects, asthenia, dizziness, faintness and syncope predominate and occur in 10 to 20% of patients, leading to discontinuation of therapy in about half that number. Infrequent adverse events include headache, drowsiness, palpitations, urinary incontinence and priapism. Some patients experience a 1 to 2kg bodyweight gain which may be associated with secondary hyperaldosteronism. Tolerance appears to develop to the benefits of alpha 1-blockade in patients with congestive heart failure, but not in hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Early effects of cardiovascular drugs--do they predict clinical outcomes?

Indicators such as lowering of blood pressure in hypertension, alleviation of chest pain in angina pectoris, improvement in rest or exertional dyspnea from congestive heart failure (CHF) and suppression of ventricular arrhythmia are widely used in the management of cardiovascular diseases. There are often strong associations between the physiological indicators and the long-term clinical outcomes of cardiovascular disease such as stroke, myocardial infarction, sudden death and all-cause mortality. Physicians have assumed reasonably that early improvements in physiological markers will lead invariably to better long-term clinical outcomes. In recent years, a number of large clinical trials have demonstrated that short-term physiological improvements are not necessarily linked to better long-term clinical outcomes, but may be associated with less benefit than expected or even with detrimental outcomes. Management of cardiovascular diseases is complicated by the possibility that beneficial effects of a particular drug may be offset by its negative actions on the cardiovascular system. Effective antihypertensives may depress cardiac contractility; inotropes enhance left ventricular contractility in CHF, but may increase the risk of serious ventricular dysrhythmia; drugs which suppress ventricular arrhythmia may precipitate CHF or even excite pro-arrhythmic effects. Physicians must be conscious of this interplay of potentially beneficial and deleterious effects when cardiovascular drugs are prescribed. It is important in the analysis of large clinical trials of cardiovascular drugs to identify those situations in which the drug exhibits more benefit than harm and to determine, if possible, those aspects of drug action, drug dosage and population characteristics which contribute to the beneficial and detrimental actions.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive effect and tolerability of felodipine extended release (ER) tablets in comparison with felodipine plain tablets (PT) and placebo in hypertensives on a diuretic. Canadian Study Group

Antihypertensive efficacy and tolerability of felodipine extended release (ER) (o.d.), felodipine plain tablet (PT) (b.i.d.), and placebo were compared in mild to moderate hypertensives whose seated diastolic blood pressure (DBP) was > or = 95 mm Hg while on hydrochlorothiazide 25 mg od. In addition to the diuretic, patients were randomised to felodipine ER 5 mg od (n = 50), PT 2.5 mg bid (n = 50), or placebo (n = 48) for 6 weeks, with clinic visits every 2 weeks. If seated DBP was > or = 90 mm Hg at any visit, daily dosage of felodipine was doubled to a maximum of 20 mg. The mean difference between ER and placebo was 5.1 mm Hg (p = 0.003); for PT vs. placebo the difference was 5.3 mm Hg (p = 0.002). Seated systolic blood pressure (SBP) was reduced by a mean difference of 6.8 mm Hg in the felodipine PT group compared with placebo (p = 0.03). Fourteen patients were withdrawn: 4 from the placebo group, 4 from the felodipine ER group, and 6 from the felodipine PT group. The most commonly reported adverse event was peripheral edema. In patients not adequately controlled on diuretic alone, felodipine ER o.d. and felodipine PT b.i.d. were superior to placebo in reducing seated DBP.

Creatinine elevation in patients receiving amiodarone correlates with serum amiodarone concentration

Serum creatinine and drug concentrations were measured at 0, 1, 2, 3, 6, 9 and 12 months in 30 consecutive patients started on amiodarone. In 28 of these patients with no obvious cause for altered renal function, mean serum creatinine increased to 11% above baseline (P < 0.005). Rising creatinine concentrations correlated with amiodarone concentrations (y = 93.9 + 8.6x, r = 0.51, P < 0.0001). When assessing elevation of serum creatinine in a patient receiving amiodarone, physicians should be aware that it may be related to this drug.

Quinidine interaction with nifedipine and felodipine: pharmacokinetic and pharmacodynamic evaluation

Conflicting findings suggest that serum quinidine concentrations may be decreased or increased by nifedipine. We performed a double-blind, placebo-controlled trial of Latin-square design. Twelve healthy men received 3 days of pretreatment with nifedipine prolonged action (20 mg twice a day) or felodipine extended release (10 mg every day), another dihydropyridine calcium antagonist, followed by coadministration of quinidine (400 mg). Quinidine pharmacokinetics were not changed by either dihydropyridine. However, 3-hydroxyquinidine area under the concentration-time curve (AUC) and 3-hydroxyquinidine/quinidine AUC ratio were decreased by felodipine, consistent with reduced metabolite formation. Heart rates and adverse events were higher with felodipine, demonstrating lack of bioequivalence with nifedipine. The QTc interval did not deviate from that expected for the observed quinidine concentration, suggesting the pharmacokinetics of active quinidine metabolites were not markedly altered among treatments. Quinidine disposition did not appear to be changed sufficiently to be clinically important by sustained-release nifedipine and felodipine.

The place of alpha blockers in the antihypertensive armamentarium

Although beta-blockers and diuretics are presently the only medications shown to reduce morbidity and mortality in hypertensives in large clinical trials, these drugs have not exerted optimal expected benefits in reducing cardiac events. Alpha-1 selective blockers exhibit a favorable impact on lipids, particularly on HDL-cholesterol. Unlike beta-blockers, they do not increase triglycerides and they do not produce the increase in LDL-cholesterol observed with traditional doses of diuretics. Alpha-blockers should be considered in the treatment of hypertensives with lipid disorders or diabetes and in those who have contraindications, failure to respond or toxicity associated with diuretics and/or beta-blockade.

Cardiovascular risk factors in perspective

Coronary heart disease and other manifestations of atherosclerosis are leading causes of morbidity and mortality in Canada. Despite favourable trends in recent years, we should try to reduce cardiovascular events further. Physicians must translate current knowledge into public health policies and management strategems for individual patients. Patients are best served by a comprehensive risk management approach, involving nonpharmacological (mainly lifestyle) changes and drug therapy.

The cyclosporin-erythromycin interaction: impaired first pass metabolism in the pig

1. The pharmacokinetic interaction between cyclosporin (CsA) and erythromycin has been studied in the weanling pig model. 2. Blood CsA and metabolite-1 (M1) concentrations were monitored by high performance liquid chromatography in portal, hepatic and jugular venus blood before and after treatment with erythromycin stearate for 7 days. 3. Erythromycin significantly increased maximum concentration (Cmax) and area under the concentration-time curve from 0 to 24 h (AUC) of CsA in the peripheral circulation. This was accompanied by a significant reduction in the hepatic extraction ratio calculated from portal and hepatic Cmax and AUC data. 4. The extraction ratio appears to be concentration-dependent in that values derived from Cmax (high concentrations) were greater than those from AUC (average concentrations). 5. Time to Cmax (tmax) and t1/2 of CsA were essentially unchanged and no significant changes were observed in peripheral M1 kinetics apart from a small increase in tmax. 6. The pharmacokinetic changes observed in the pig suggest that the CsA-erythromycin interaction is caused by inhibition of hepatic metabolism and the impact of inhibition is greatest during first-pass when CsA concentrations are at their highest.

Interaction between oral verapamil and beta-blockers during submaximal exercise: relevance of ancillary properties

The interaction between verapamil and beta-blockers may involve negative chronotropic, inotropic, and dromotropic effects. Three randomized, double-blind, crossover trials evaluated standardized submaximal exercise hemodynamics after oral verapamil (120 mg) and beta-blocker, alone and in combination, in groups of eight healthy men. The beta-blockers were propranolol (80 mg), metoprolol (100 mg), and pindolol (5 mg). During submaximal exercise, each beta-blocker produced similar reductions in heart rate. Likewise, each verapamil and beta-blocker combination caused greater decreases in heart rate and prolongation of PR interval than did either drug alone. Only the verapamil and propranolol combination produced greater reduction of systolic blood pressure and prolongation of rate-adjusted PR interval. All verapamil and beta-blocker combinations caused frequent adverse events, predominantly exercise fatigue and resting first-degree heart block. Although the verapamil and metoprolol or pindolol combinations produced lesser negative dromotropic or inotropic effects compared with verapamil and propranolol, coadministration of verapamil and any beta-blocker should be performed cautiously.

Genetic aspects of variability in superficial vein responsiveness to norepinephrine

Venoconstriction of the dorsal hand vein by local norepinephrine infusion was measured by the linear variable differential transformer method in 15 healthy unrelated subjects and eight pairs of monozygotic and six pairs of dizygotic twins. Incremental norepinephrine infusion produced dose-related venoconstriction. In unrelated subjects the doses of norepinephrine constricting basal vein diameter by 50% (ED50) ranged from 3.9 to 120.5 ng/min. There was a positive linear relationship between doses of norepinephrine infused and local steady-state plasma concentrations of norepinephrine achieved in each subject. The reciprocals of the slopes of these dose-concentration relationships, which reflect local norepinephrine clearance (disposition) in the vein, ranged from 0.47 to 1.86 ml/min. Plasma concentrations of norepinephrine associated with reduction of basal vein diameter by 50% (EC50) ranged from 1.4 to 110.2 ng/ml, with variability similar to that of ED50. There was a very high level of concordance in ED50, EC50, and clearance of norepinephrine within pairs of monozygotic twins but not within dizygotic twins. Differences in pharmacokinetics of infused norepinephrine exert a minor impact on overall intersubject variability. Genetic aspects of "tissue responsiveness" (i.e., vascular alpha-adrenoceptor response, smooth muscle contractility, and endothelial function) appear to be largely responsible for the wide intersubject variability in venoconstrictor responsiveness to norepinephrine.

The heart rate-PR interval relationship: a model for evaluating drug actions on SA and AV nodal function

The relationship between heart rate (HR) and PR interval (PR) has been investigated to determine inter-subject variability, within-subject variability and potential reference standards. Eight healthy male volunteers underwent upright graded submaximal treadmill exercise during eight separate study sessions. All subjects exhibited statistically significant negative linear relationships between PR and HR. Although there was considerable inter-subject variability, there was little within-subject variability in the interpolated PR at HR between 80 and 120 beats min-1. The HR-PR regression model has greatest validity within this HR range and for individual subjects rather than pooled or group data.

Relation of amiodarone hepatic and pulmonary toxicity to serum drug concentrations and superoxide dismutase activity

Hepatic enzymes, pulmonary function, serum amiodarone and desethylamiodarone (DEA) concentrations and erythrocyte superoxide dismutase (SOD) activity were monitored at regular intervals for 1 year in 30 patients receiving amiodarone. Subclinical hepatotoxicity developed in 5 patients. These patients had higher baseline alanine transaminase values (42.6 +/- 6.8 vs 22.9 +/- 1.8 U/liter) and had an increase in serum aspartate transaminase from 27 +/- 4.1 at baseline to 147 +/- 77.3 U/liter at 12 months. The other patients had little variation in aspartate transaminase. Six patients with normal baseline carbon monoxide diffusing capacity had subclinical pulmonary toxicity develop with a mean decrease in diffusing capacity to 0.7 +/- 0.05 of the baseline value, which correlated with decreasing erythrocyte SOD activity. Mean carbon monoxide diffusing capacity and SOD activity remained unchanged in the other patients. The mechanisms of hepatic and pulmonary injury remain unknown, but appear to be associated with exposure to higher total serum concentrations of amiodarone plus DEA. Patients who had hepatic and/or pulmonary abnormalities develop received higher doses of amiodarone (440 +/- 27 vs 340 +/- 18 mg/day), but also had a higher amiodarone:DEA ratio suggesting that dose-dependent kinetics contributed to the higher concentrations. Elevated baseline alanine transaminase may indicate increased risk for hepatotoxicity while a progressive decrease in erythrocyte SOD may be an early indication of pulmonary toxicity. The latter finding indicates a need to investigate the role of free radicals in the pathogenesis of amiodarone pulmonary toxicity.

Correlation of amiodarone dosage, heart rate, QT interval and corneal microdeposits with serum amiodarone and desethylamiodarone concentrations

Pharmacokinetic-dynamic relations for amiodarone have been difficult to define. Few studies have successfully correlated serum amiodarone concentration with either dose or pharmacodynamic effects. Reduction in heart rate, prolongation of corrected QT interval and accumulation of corneal microdeposits are 3 clinical effects well suited for making kinetic-dynamic comparisons because they occur in virtually all patients receiving amiodarone. Data on heart rate, corrected QT interval, corneal microdeposits, cumulative dose and serum concentrations of amiodarone and desethylamiodarone (DEA) were collected over the course of 1 year after initiation of therapy in 27 patients (mean age 55.4 +/- 2.35 years). Mean elimination half-lives in this study population were 56 days for amiodarone and 129 days for DEA, as estimated from cumulation kinetics without drug withdrawal. The extremely long half-lives of amiodarone and DEA make demonstration of steady-state concentration-response relations difficult. A new approach using analysis of sequential data before steady-state reveals general relations between dose, DEA concentration and 3 clinically observable effects of amiodarone. A linear relation was evident between DEA concentration and log mean cumulative amiodarone dose (mg/kg) for the population. The steep segments of the concentration-response curves for heart rate, microdeposits and corrected QT interval occurred at low, medium and high serum amiodarone and DEA concentrations, respectively. Patients not developing a decrease in heart rate or corneal microdeposits likely have very low serum drug concentrations and may not be adequately treated. The monitoring of heart rate, corrected QT interval and corneal microdeposits as an aid to assessing adequacy of amiodarone therapy requires further study.

Synergistic adverse hemodynamic interaction between oral verapamil and propranolol

The interaction between oral verapamil and propranolol may involve negative chronotropic, inotropic or dromotropic effects. The immediate effects of orally administered verapamil (120 mg) and propranolol (80 mg), alone and combined, on submaximal exercise hemodynamics and on pharmacokinetics were studied in eight healthy male volunteers in a randomized, double-blind, crossover manner. Maximum effects on heart rate, systolic blood pressure, PR interval and rate-adjusted PR prolongation were greatest with the combined administration of verapamil and propranolol. The combination caused a high frequency of adverse drug events, predominantly exercise fatigue. Verapamil increased the AUC and Cmax and shortened the tmax of propranolol. Propranolol decreased the AUC and Cmax of verapamil. The greater reduction of heart rate with the combination of verapamil and propranolol was only partially explained by higher plasma concentrations of propranolol. The combination of propranolol and verapamil produced clinically important synergistic adverse effects during exercise. Negative dromotropic effects occurred primarily by direct AV node inhibition and were more important than previously recognized.

A double-blind, randomized trial of PY108-068 in acute ischemic cerebral infarction

A double-blind, randomized, pilot trial of the calcium channel antagonist PY108-068 was completed in patients with acute ischemic cerebral infarction. Nine treated patients received PY108-068 orally (150 mg/day in divided doses) and 10 control patients received placebo within 48 hours of stroke onset for 21 days. The mean age of the treated patients (four men, five women) was 63.7 years and of the control patients (seven men, three women) 64.4 years. Most infarctions were in the territory of the middle cerebral artery. One treated patient died of sudden cardiac death on Day 12; one control patient died of cerebral herniation. Two treated patients had episodes of clinically insignificant hypotension during Day 1 of treatment. Two control patients had myocardial infarctions during the trial. The mean Toronto Stroke Scale scores at stroke onset were 67 and 90 and at Week 12 were 22.5 and 34.7 in the treated and control groups, respectively. There was parallel improvement in the two groups, with no significant difference between groups (p = 0.12). The mean Barthel Index functional scores at stroke onset were 32.8 and 33 and at Week 12 were 90 and 78.8 in the treated and control groups, respectively. There was a trend in favor of the treated group, but differences between groups did not reach significance. In this pilot trial, PY108-068 was found to be safe but not effective in patients with acute ischemic cerebral infarction.

Elevation of serum total cholesterol and triglyceride levels during amiodarone therapy

Over the last decade there has been increasing awareness that some cardiovascular medications may adversely affect serum cholesterol concentrations. It has been suggested previously that amiodarone may alter serum cholesterol, triglyceride and glucose concentrations, but no substantive data support this observation. During the course of a 1-year study of adverse effects in patients taking amiodarone, 21 patients with normal total serum cholesterol before entry in the study were prospectively investigated for changes in lipid metabolism. A statistically significant sustained rise of 17% in total serum cholesterol occurred from a baseline of 178 +/- 7 mg/dl (4.6 +/- 0.2 mmol/liter) to 208 +/- 9 mg/dl (5.4 +/- 0.2 mmol/liter). Ten of the patients developed elevations of cholesterol above the 75th percentile for their age and sex. This group experienced a sustained rise of 20% in mean cholesterol concentration from baseline, had statistically significant elevations of triglyceride concentrations and had higher glucose and desethylamiodarone concentrations than patients who did not develop elevations in cholesterol greater than the 75th percentile. It may be possible to predict these differences in response as early as 4 to 8 weeks after starting therapy. Because amiodarone is increasingly used in patients without ischemic heart disease or life-threatening arrhythmias, the potential atherogenic risk of these metabolic abnormalities merits further investigation.

Mean apical concentration and duration in the comparative bioavailability of slowly absorbed and eliminated drug preparations

Present criteria for comparing bioavailability are inadequate when the Cmax and tmax cannot be reliably identified in individual subjects. Drug formulations which are slowly absorbed and eliminated have concentration-time profiles with a broad apex, increasing the likelihood that samples taken at the apical region of the curve will have statistically indistinguishable concentrations. Using data from a study of three dosage forms of piroxicam, we propose an alternative approach which decreases the influence of sampling bias and analytical error on the identification of the apex of the concentration-time curve and provides a simple tool for describing the shape of the curve around the apex. An adequate frequency of sampling around the expected apex of the concentration-time curve and consideration of the coefficient of variation (CV) of the analytical assay when assessing the observed Cmax are used in defining new parameters. This approach may be useful for studying the relationship of onset and duration of maximal plasma concentration to the efficacy and toxicity of drugs and in developing standards for comparing the bioavailability of slow-release preparations, which is of increasing interest to pharmaceutical companies and regulatory agencies.

Treatment of pruritus in primary biliary cirrhosis with rifampin. Results of a double-blind, crossover, randomized trial

The cause of pruritus of cholestasis is unknown. We have hypothesized that pruritus may be caused by an indirect effect of high hepatic concentrations of toxic bile acids. To test this hypothesis, we have conducted a double-blind, controlled, crossover clinical trial of rifampin, an agent that inhibits hepatic bile acid uptake and may detoxify hepatic bile acids by stimulation of mixed-function oxidases. Nine patients with primary biliary cirrhosis received 300-450 mg/day of rifampin and placebo sequentially, in random order. Each treatment was administered for 14 days, with a 14-day washout between treatments. Endpoints included patient preference, changes in a daily visual analogue scale pruritus score, and amount of cholestyramine ingested. Antipyrine elimination rates and serum bile acids were tested at the end of each treatment period. All 9 patients completed the trial and 8 of them preferred rifampin to placebo (p = 0.03). There were no adverse reactions. Visual analogue scale pruritus scores showed no significant placebo response or any effect from the order of treatment, but did show a highly significant reduction in pruritus in response to rifampin (p less than 0.002). This effect was evident within the first week of rifampin treatment. Rifampin produced a 33% reduction in antipyrine plasma half-life, but no change in fasting total serum bile acids. Cholestyramine usage did not change significantly. We conclude that rifampin is useful for short-term relief of pruritus in primary biliary cirrhosis; however, the mechanism of this effect is unknown. Longer trials are needed, as are trials in other cholestatic disorders.

Cyclosporin-erythromycin interaction in normal subjects

We studied the pharmacokinetic interaction between cyclosporin (CYA) and erythromycin in normal subjects. Plasma CYA concentrations were measured by high performance liquid chromatography (h.p.l.c.) and radioimmunoassay (RIA) and estimates of metabolite formation were obtained from inter-assay differences between these measurements. Erythromycin significantly increased the maximum concentration and the area under concentration-time curve. Time to maximum concentration and apparent oral clearance of CYA were significantly decreased. The half-life, however, was not altered. Significant reductions in the proportion of apparent metabolite were observed at times of maximum CYA concentrations but not at later time periods (12 and 24 h). The mechanism of the drug interaction appears to be decreased hepatic first-pass metabolism but an effect on CYA absorption cannot be excluded. These results on normal subjects confirm that patients administered CYA and erythromycin risk CYA toxicity. However, the risk can be reduced by dose reduction based on more frequent CYA monitoring or by using a different antibiotic.

Relationships between heart rate and PR interval during physiological and pharmacological interventions

The relationships between heart rates (HR) and corresponding PR intervals (PR) were studied in 12 healthy young subjects during rest, standing and graduated treadmill exercise to heart rates of 160 to 170 beats min-1 and during the infusion of isoprenaline to heart rates of 100 to 110 beats min-1. During exercise, PR diminished with increasing HR. Over the range of HR from 60 to 160 beats min-1 all 12 individual subjects exhibited negative linear correlations between HR and PR described by the equation: PR (ms) = -0.351 HR (beats min-1) + 176.7 for composite data. During isoprenaline infusion the PR interval also diminished with increasing heart rate. Over the range of HR from 60 to 110 beats min-1, 11 of the 12 subjects exhibited negative linear correlations between HR and PR described by the equation: PR (ms) = -0.582 HR (beats min-1) + 186.5 for composite data. The exercise model was used to study the indirect (or rate-dependent) effects and the direct actions on atrioventricular conduction of beta-adrenoceptor blocking drugs and calcium channel antagonists, alone and in combination, in three groups of healthy subjects. Control and placebo observations on HR and PR at rest, standing and during exercise in these additional subjects also exhibited individual inverse linear relationships between HR and PR. Following the administration of beta-adrenoceptor blockers, PR were prolonged more than expected at the HR observed. Rate-adjusted PR prolongation during exercise exceeded standing which exceeded resting, indicating greater beta-adrenoceptor blockade in atrioventricular nodal tissue than in sinoatrial nodal tissue at each level of activity.(ABSTRACT TRUNCATED AT 250 WORDS)