Effects of dilevalol, an R, R-isomer of labetalol, on blood pressure and renal function in patients with mild-to-moderate essential hypertension

Effects of dilevalol (R,R-labetalol) compared with nifedipine on heart rate, blood pressure and muscle blood flow at rest and on exercise in hypertensive patients

1. Dilevalol (R,R-labetalol) is a non-selective beta-adrenoceptor antagonist with beta 2-adrenoceptor agonist activity. Its effects after 1 month's administration on heart rate, blood pressure and muscle blood flow were studied in a double-blind crossover comparison with nifedipine in 16 hypertensive patients. 2. Dilevalol and nifedipine were similarly effective in lowering systolic and diastolic blood pressure at rest, but dilevalol limited the rise in systolic blood pressure induced by exercise more than nifedipine (rise of 27 vs 53 mm Hg respectively, P < 0.01). 3. Dilevalol decreased resting heart rate compared with nifedipine (73 vs 92 beats min-1 respectively, P < 0.01). Dilevalol limited the exercise induced rise in heart rate more than nifedipine (36 vs 48 beats min-1 respectively, P < 0.01). 4. Muscle blood flow (measured by strain gauge plethysmography) was not affected by either dilevalol or nifedipine at rest. After exercise, dilevalol caused an increase in excess blood flow compared with placebo (10.8 vs 5.1 ml min-1 dl-1 respectively, P < 0.01). The difference between dilevalol and nifedipine did not reach statistical significance (10.8 vs 6.5 ml min-1 dl-1 respectively, P > 0.05). 5. On blood pressure and heart rate, dilevalol demonstrated beta-adrenoceptor blocker activity at rest and on exercise. On muscle blood flow, dilevalol appeared to have no effect at rest, but may have acted as a beta-adrenoceptor blocker rather than as a beta 2-adrenoceptor agonist during exercise.

Renal hemodynamics and reduction of proteinuria by a vasodilating beta blocker versus an ACE inhibitor

The effects of a nonselective beta-adrenergic blocking drug with beta-2 agonist activity (dilevalol 200 mg) on proteinuria and renal hemodynamics were evaluated in a double-blind crossover study versus an ACE inhibitor (enalapril 5 mg) in eight patients with glomerulonephritis, moderate renal function impairment and proteinuria greater than 1 g/24 hr. Patients were studied after a one week placebo phase while off all other medications, except steroids in a few cases, and after three weeks of treatment. A 10-day placebo washout perod was included between the various drug treatments. During each period renal hemodynamics were measured by clearance techniques, and urinary protein excretion as well as fractional clearance of albumin and IgG were determined. Both drugs reduced mean arterial pressure and proteinuria to a similar extent [mean arterial pressure: placebo 108 +/- 13 mm Hg; dilevalol 103 +/- 11 mm Hg (P less than 0.05); enalapril 103 +/- 12 mm Hg (P less than 0.05); protein excretion: placebo 5.1 +/- 4.2 g/day; dilevalol 3.3 +/- 3.0 g/day (P less than 0.05); enalapril 2.8 +/- 2.8 g/day (P less than 0.05)]. The antiproteinuric effect was greater with enalapril than dilevalol. Dilevalol reduced GFR [baseline inulin clearance: 73.3 +/- 38 ml/min/1.73 m2; after dilevalol: 63.3 +/- 28 ml/min/1.73 m2 (P less than 0.05)] and the decrease of proteinuria correlated positively with the reduction of GFR. Enalapril did not significantly lower the GFR (inulin clearance during enalapril 66.8 +/- 23 ml/min/1.73 m2) and the reduction of proteinuria did not correlate with the lowering of the GFR.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical pharmacokinetics and kinetic-dynamic relationships of dilevalol and labetalol

Dilevalol and labetalol are examples of a growing number of new beta-blockers which combine nonselective beta-adrenoceptor antagonism with vasodilator activity. Dilevalol is one of the 4 stereoisomers of labetalol, and is estimated to form approximately 25% of the racemic drug. Labetalol itself is an alpha 1-antagonist but dilevalol, which has negligible affinity for alpha-receptors, exerts its vasodilator effect via beta 2-agonism. Both drugs are rapidly and completely absorbed in 60 to 90 min and subject to extensive first-pass hepatic metabolism; the average bioavailability after oral administration is around 20 to 35%, and there is wide interindividual variability in plasma drug concentrations and dosage requirements. The volume of distribution of dilevalol (17 to 25 L/kg) is higher than that reported for labetalol (3 to 16 L/kg), although both drugs are concentrated in the extravascular compartment. Correspondingly, the elimination half-life of dilevalol at steady-state is around 15h compared with 8h for labetalol. There is evidence that the pharmacokinetics of dilevalol change (a reduction in clearance) in translation from single-dose to long term therapy. There is no clinically significant effect of age on the steady-state disposition of either drug and the pharmacokinetics of labetalol appear to be unchanged during pregnancy. Although there is a linear relationship between dose and area under the concentration-time curve, early studies found no evidence of a simple relationship between dose or plasma drug concentration and the fall in blood pressure. However, an integrated pharmacokinetic-pharmacodynamic model has been used to correlate concentrations of both drugs with reductions in systolic and diastolic blood pressure in individuals. This approach derives a mathematical description of antihypertensive response which integrates pharmacokinetic and pharmacodynamic information and also takes account of placebo effects and changes in drug concentration and blood pressure during the dosage interval. The pharmacokinetic-pharmacodynamic relationships of labetalol are characterised by a linear model. For example, in a group of healthy volunteers, the 'responsiveness' to labetalol was -0.19mm Hg/micrograms/L. In contrast, the relationships of dilevalol are best described by a Langmuir maximum effect model, and so individual responses to short and long term treatment have been quantified by the concentration-effect parameters of maximum effect and drug concentration required to produce 50% of this.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of dilevalol and placebo in the management of isolated systolic hypertension using ambulatory monitoring

1. The antihypertensive effect of dilevalol, a compound which combines beta-adrenoceptor blocking and vasodilating properties due to beta 2-adrenoceptor agonism, was studied in nineteen patients with isolated systolic hypertension (ISH). A randomized, double-blind, placebo-controlled, cross-over trial with two 4 week treatment periods was used to compare the efficacy of once daily dosing with dilevalol (in the range of 100-400 mg daily) against placebo. Assessment of response involved both casual blood pressure readings (amongst all patients) and 24 h ambulatory blood pressure monitoring (in ten of the nineteen patients). 2. A mean fall of 12/5 mm Hg (s.e. mean 3/2, P less than 0.05) and 9/3 mm Hg (s.e. mean 3/2, P less than 0.05) in supine and standing blood pressure respectively was observed with dilevalol. Mean heart rate was unchanged. The ambulatory monitoring profile demonstrated a smaller reduction in mean blood pressure (7/8 mm Hg) over the 24 h period and a reduction of 10/11 mm Hg over the daytime period. A blunting of the early morning increase in systolic pressure was observed with dilevalol. 3. The drug was well tolerated with light headedness and lethargy being reported more commonly than with placebo. Biochemical parameters were unaffected. 4. It is concluded that dilevalol in the doses used has a small but measurable antihypertensive effect as monotherapy in the treatment of ISH.

Comparison of the renal effects of dilevalol and carteolol in patients with mild to moderate essential hypertension

The effects of 6 weeks of treatment with dilevalol 100 mg once daily, or carteolol 10 mg once daily, on renal blood flow (RBF), glomerular filtration rate (GFR) and total renal vascular resistance (TRR) were studied in 10 patients with mild-to-moderate essential hypertension in a randomised cross-over experiment. Both drugs lowered the systolic and diastolic blood pressures to a similar extent without altering the heart rate. Carteolol non-significantly decreased RBF by 9.2% and GFR by 12.3% without altering. TRR, whereas dilevalol produced a significant reduction in TRR by 13.2% (p less than 0.05), a non-significant decrease in RBF by 4.6% and no change in GFR. Neither drug changed plasma osmotic pressure, serum total protein concentration, electrolytes or plasma aldosterone concentration. Plasma renin activity tended to be lower in the dilevalol phase as compared to the carteolol phase. The results suggest that dilevalol may cause a greater decrease in TRR and less reduction in GFR when compared to carteolol in patients with mild-to-moderate essential hypertension. The difference in the renal effects might be due to the difference in the potency of vasodilatory properties of both drugs at the doses applied.

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical pharmacokinetic considerations in the elderly. An update

There are numerous studies of drug handling in the elderly, but it is difficult to assess the significance of changes seen in vitro, or after single-dose administration, because they are often compensated by other mechanisms at steady-state. However, a knowledge of these studies is important as the results alert the investigator to possible treatment problems. The high incidence of adverse drug reaction in the elderly population leaves no doubt that improvements in therapy are needed. Research has been directed at seeking patterns of abnormality in the elderly on which to base recommendations for alterations in dosage regimens. The major shortcoming of this approach has been the failure to distinguish between the effect of chronological age on drug pharmacokinetics, and drug kinetics in elderly people with multiple pathology. The latter concern appreciates the variety of factors involved and the importance of treating each patient as an individual: presentation of mean data is confusing and misleading. The objective of drug treatment in any age group, but particularly in the elderly, is to administer the smallest possible dose which gives adequate therapeutic benefit throughout the entire dosage interval with the minimum of side effects. For most drugs the safe starting dose in the elderly is one-third to half that recommended in the young. Vigilance for potential side effects with plasma concentration monitoring, if available, should help keep toxicity to a minimum. When other medications are added or changed, the possibility of interaction should be anticipated. Methods for individualisation of dosage regimens and the use of sustained-release formulations in the elderly are discussed. Dosage alteration in the elderly in terms of reduced dose frequency, rather than dose size, may help improve compliance. A knowledge of the pharmacokinetics of a drug helps determine which approach will be most beneficial.