Clinical pharmacokinetics of beta-adrenoreceptor blocking drugs

Pharmacokinetics and bioavailability of diacetolol, the main metabolite of acebutolol

The pharmacokinetics and bioavailability of diacetolol, the principal metabolite of acebutolol, were studied in 6 healthy subjects. Plasma concentrations were determined following a single intravenous injection of diacetolol 100 mg and three oral doses of diacetolol 100, 400 and 800 mg, in random order. The average oral bioavailability of diacetolol was F: 0.302 +/- 0.052 (100 mg), 0.363 +/- 0.052 (400 mg) and 0.426 +/- 0.068 (800 mg); the differences are not significant. The mean plasma half-life of the terminal phase, 7.94 +/- 0.26 h after intravenous administration, was significantly higher than after oral administration 12.27 +/- 1.00 h (100 mg), 12.82 +/- 1.59 h (400 mg) and 13.05 +/- 13.05 +/- 1.22 h (800 mg) (p less than 0.02 to 0.05); the mean urine half-lives of the terminal phase were not significantly different. Renal clearance of diacetolol 10.2 +/- 0.81 . h-1 represented about wo-thirds of total body clearance 15.9 +/- 1.21 . h-1. The results suggest either a first-pass effect or incomplete absorption of diacetolol after oral administration.

Circulatory effects of sublingual and oral sustained-release nitroglycerin in healthy young men

The effects on heart rate and blood pressure during standing, and on plethysmographic arterial pulsation in the calf, of nitroglycerin 0.5 mg sublingually, 6.5 mg orally and a placebo tablet were studied for up to 8 h. Sublingual nitroglycerin increased heart rate and arterial pulsation; the peak height and duration of these effects occurred at slightly different times. Oral nitroglycerin had no effect on heart rate but did increase pulsations as compared to placebo. In the orthostatic test, heart rate and pulse amplitude were affected by both forms of administration. Comparing the areas-under-curve for these variables for the two forms suggested that, in comparison with sublingual nitroglycerin, about 1/3 of the oral nitroglycerin was biologically effective over 8 h. Pulse plethysmography appeared to be the most sensitive method for "bioassay" of nitroglycerin.

Sotalol and metoprolol comparison of their anti-hypertensive effect

28 patients, aged 35-62 years, with uncomplicated hypertension, entered a double-blind, crossover study, in which the effects of single daily doses of sotalol and metoprolol were compared. Both drugs exerted a clinically useful anti-hypertensive effect as monotherapy, or in combination with a thiazide diuretic. No significant difference in hypotensive effects was noted between the two beta-blocking agents, when the dose was titrated to an optimal clinical effect. Treatment with sotalol and metoprolol was associated with a clinically insignificant increase in serum uric acid concentration. The side-effects observed were few, and in only two cases was therapy discontinued. We regard both sotalol and metoprolol as useful anti-hypertensive drugs.

Influence of renal failure on the hepatic clearance of bufuralol in man

The beta-blocking agent bufuralol is subject to first-pass metabolism and is eliminated from the body almost entirely by biotransformation. Its major metabolite in plasma (1'-hydroxy-bufuralol) is biologically active and may contribute to the pharmacological effect of the drug. The effect of renal failure on the behavior of the parent compound and three of its metabolites was studied by comparing their kinetics in normal volunteers and in patients with severe renal insufficiency. Bufuralol was given orally to all subjects (20 mg); some of the healthy volunteers also received the drug intravenously (5 mg). Renal failure was found to be associated with a marked increase of the areas under the plasma concentration-time curves of the parent compound, whereas its halflife of elimination was not markedly influenced. The behavior of 1'-hydroxy-bufuralol was consistent with a decreased renal clearance. The behavior of bufuralol in patients with renal failure was analyzed using the clearance approach. From this analysis it appears that the presystemic biotransformation of bufuralol is decreased in renal failure and that changes in systemic clearance are compensated in our patients by modifications of the volume of distribution, resulting in little net change in the halflife of elimination.

Comparative pharmacodynamics and plasma levels of beta-adrenoceptor blocking drugs

1. Metoprolol (ME), pindolol (PI) and propranolol (PR) were studied in nine subjects at different doses and at 'maximum beta-adrenoceptor blockade' at a defined exercise load. Exercise tests were performed after each dosing period; isoprenaline stimulation was studied at the highest dose level. 2. ME and PR reduced heart rate at rest with most doses tested, while PI had no effect on resting heart rate. 3. Exercise heart rate was reduced with the smallest daily doses (ME 75 mg; PI 7.5 mg; PR 60 mg), and maximum reduction was from 163 to 116 beats/min (ME), 124 (PT) and 115 (PR) beats/min with daily doses of 242, 23 and 233 mg, respectively. 4. Resting blood pressure was not significantly affected by any beta-adrenoceptor blocker dose, but exercise induced blood pressure decreased from 166 to 130 (ME), 138 (PI) and 131 (PR) mm Hg, respectively. 5. Mean plasma concentrations at 'maximum beta-adrenoceptor blockade' were 158 (ME), 24 (PI) and 159 (PR) ng/ml without significant differences in the plasma level variation between beta-adrenoceptor blockers. 6. Isoprenaline doses required to increase heart rate by 30 beats/min were 3.8 microgram (control), 22 microgram (ME), 458 microgram (PI) and 200 microgram (PR), respectively. The differences may be due to different ratios of beta 1, beta 2 activity of the beta-adrenoceptor blockers tested.

Disposition and activity of beta-adrenoceptor antagonists in the rat using an ex vivo receptor binding assay

The disposition and activity of some beta-adrenoceptor antagonists in the rats was determined using an ex vivo receptor binding assay. Rats were injected with different doses of beta-adrenoceptor antagonists and the extent of receptor occupation was assessed in various tissues under in vitro conditions. Rats treated with (-)-propranolol (0.1 mumol. kg-1) displayed peak plasma levels of biologically active drug assayed by radioreceptor assay 15 min after administration. On the other hand, the highest concentration of bioactive drug, assessed by ex vivo assays, was observed at 30 min in all tissues examined. Dose-response curves revealed that (-)-propranolol was about 100 fold more potent than (+)-propranolol in all tissues examined, and that there was a small (3 fold) degree of selectivity for both isomers towards lung and spleen over heart, cortex and cerebellum. The affinity of (-)-propranolol in heart and lung using the ex vivo binding assay was similar to the affinity of this agent to inhibit in vivo isoprenaline-stimulated cyclic AMP formation in these tissues. The beta 1-selective antagonist (+/-)-atenolol demonstrated selectivity towards those tissues that have been previously shown to possess a predominance of beta 1-adrenoceptors, though penetration to the central nervous system was substantially less than propranolol. The inherent advantages of this ex vivo assay are discussed.

Evaluation of a radioreceptor assay for beta-adrenoceptor antagonists in plasma

A radioreceptor assay (RRA) recently developed in this laboratory for beta-adrenoceptor antagonists in plasma was evaluated in normal volunteers and compared with a radioimmunoassay (RIA) for propranolol. The RRA depends upon the ability of beta-adrenoceptor antagonists to complete with a radiolabelled ligand for beta-adrenoceptor binding sites on lung membranes. Unlike other assays, it measures biologically active drugs including active metabolites of the parent compound. In volunteers given a single oral dose of (+/-)-propranolol, considerable differences between the two assay methods were demonstrated. In other experiments this difference was shown to relate to the RIA's sensitivity to the inactive (+)-isomer of propranolol and possibly to inactive metabolites. The facility of the RRA in measuring plasma levels of several other non-selective beta-adrenoceptor antagonists was also demonstrated. By employing (-)-propranolol as the standard in the RRA, all of these drugs can be directly compared with a single and relatively simple assay technique.

Pharmacokinetic and pharmacodynamic properties of metoprolol in patients with impaired renal function

The pharmacokinetics of metoprolol have been studied in a group of patients with varying degrees of renal impairment and in healthy subjects after administration of 20 mg of metoprolol tartrate intravenously and 50 mg orally in a single dose and during steady-state conditions. There were no significant differences in the extent of bioavailability or rate of elimination of the drug between the 2 groups. The fraction of the oral dose systemically available during steady-state was 59 +/- 9% in the renal patients and 55 +/- 7% in the control group. Total body clearance in the patients with renal failure was 1.0 +/- 0.1 L/min and in the healthy subjects it was 0.8 +/- 0.1 L/min. The corresponding values for the elimination half-life were 4.6 +/- 1.2h and 4.1 +/- 1.0h, respectively. The beta-adrenoceptor blocking effect of metoprolol (determined as percent reduction of exercise heart rate) did not differ significantly between the 2 groups during steady-state conditions. The effect on exercise heart rate was linearly related to the log of the plasma concentration of metoprolol. The relationship was identical for the single dose and during steady-state conditions, indicating that accumulation of metabolites in patients with renal failure does not influence the beta-blocking properties of metoprolol.

Serum glibenclamide in diabetic patients, and influence of food on the kinetics and effects of glibenclamide

The steady state concentrations of glibenclamide in serum were measured radioimmunologically in 37 diabetic patients after administration for at least a year. No other antidiabetic drugs had been given. The interindividual variation in glibenclamide concentrations was extremely large (0 to 1520 nmol/l), greatly exceeding the variation in dosage (2.5--25 mg daily). There was no relation between dose and serum concentration of glibenclamide. Only four (9%) patients had fasting blood glucose concentrations below 5.5 mmol/l, and fewer than half had values below 8 mmol/l. In most cases, therefore, the therapy was inadequate. Single-dose kinetics of glibenclamide was assessed in healthy volunteers. Food intake did not influence the bioavailability of a 5 mg dose of glibenclamide. There was no insulin increase in response to glibenclamide unless a meal was also given, and this increase was not significant until 1 h after administration of drug and meal, when the mean serum concentration of glibenclamide had reached 100 nmol/l. Even in the fasting state, however, there was a progressive fall in blood glucose after glibenclamide administration, significant within 45 min and with a nadir at 2--2 1/2 h.

Accumulation of drugs by resting or beating cardiac tissue

The rate and degree of accumulation of 12 neutral, anionic and cationic drugs were studied in resting and 2 Hz-stimulated isolated left auricles of the guinea pig. The uptake process was accelerated in muscles driven electrically. The time needed to reach equilibrium was related to the extent of accumulation which in turn corresponded with the lipophilicity of the drug. The frequency-induced changes in the kinetics of the accumulation disappeared under reduced mechanical activity of the muscle. It is suggested that the increased mechanical activity enhances drug disposition within the extracellular space, so that more drug is available for transmembrane penetration.

beta-Blockade therapy for supraventricular tachyarrhythmias after coronary surgery: a propranolol withdrawal syndrome?

A high incidence of cardiac arrhythmias and hypertension has been noted after coronary artery bypass surgery in patients previously treated with oral propranolol. Forty-two patients undergoing coronary bypass surgery had propranolol withdrawal 10 hours before surgery and were randomized into a group treated with propranolol immediately postoperatively, and a nontreatment group. Patients treated with prophylactic propranolol had a significantly lower incidence of postoperative supraventricular arrhythmias compared to patints who received no prophylaxis. All the arrhythmias responded rapidly to 1 mg of intravenous propranolol therapy, whether it was used as a primary treatment or as a supplement to prophylactic propranolol. The findings suggest that (1) there is a high incidence of supraventricular arrhythmias and sinus tachycardia after coronary artery bypass which might reflect an abrupt propranolol withdrawal, and (2) that perioperative prophylactic or supplementary propranolol therapy will successfully prevent or treat most of these arrhythmias.

Food-induced reduction in bioavailability of atenolol

The influence of food intake on the bioavailability of the beta-adrenoceptor blocker atenolol was assessed by measurement of its single-dose kinetics in ten healthy volunteers, who took 100 mg both in the fasting state and together with a standardized breakfast. Food intake significantly shortened the time to reach peak concentration (2.7 h vs 1.5 h), but caused a significant reduction in AUC values, the mean decrease being 20%. The elimination half-life was unaffected. Atenolol, which is relatively hydrophilic, is incompletely absorbed in the fasting state, and escapes first-pass metabolism. The present findings indicate that food intake causes further impairment of its absorption, even though the absorption rate may initially be enhanced. This contrasts with previous observations on the more lipophilic beta-adrenoceptor blockers propranolol and metoprolol.

Pharmacodynamic studies in man of the beta-adrenoceptor antagonist DL 071 IT

DL 071 IT, a new potent non-selective beta-adrenergic blocking drug with intrinsic sympathomimetic activity and weak membrane stabilizing activity, was evaluated alone and in comparison with oxprenolol, in six volunteers, at rest and during an exercise test. Heart rate and systolic pressure were monitored for up to 7 h after oral administration of the drugs. Exercise heart rate and systolic pressure were significantly reduced by both drugs, but only DL 071 IT caused a significant reduction in resting heart rate. As compared to oxprenolol, DL 071 IT has a longer duration of action and is from 5.0 to 13.5 times more potent.

Plasma concentrations of propranolol and 4-hydroxypropranolol during chronic oral propranolol therapy

1 The plasma levels of propranolol and 4-hydroxypropranolol have been measured in 17 hypertensive patients receiving chronic oral therapy with propranolol. 2 The range of plasma propranolol concentrations was from 5.3 to 300 ng/ml, and that of 4-hydroxypropranolol was from 2.1 to 36.0 ng/ml. 3 The mean (+/- s.d.) plasma concentration ratio of 4-hydroxypropranolol to propranolol was 0.130 (+/- 0.005); however, a very wide range was observed with individual values ranging from 0.057 to 0.241. 4 A statistically significant correlation was observed between the plasma concentration of 4-hydroxypropranolol and that of propranolol. 5 Propranolol and 4-hydroxypropranolol plasma concentrations were each significantly, but poorly, correlated with daily propranolol dose. 6 The clinical significance of the results has been discussed.

beta-Adrenoceptor blocking effects and pharmacokinetics of pindolol. A study in hypertensive Africans

The beta-adrenoceptor blocking effects of pindolol were compared with those of a placebo in a double-blind trial in twelve hypertensive Africans. Heart rate and arterial blood pressure were measured at rest and immediately after exercise, before and at intervals up to 8 h after oral administration of the drugs. Plasma levels of pindolol were also determined. Pindolol reduced systolic blood pressure and antagonised exercised-induced tachycardia. The mean time to peak level of pindolol was 1.9 h and the mean half-life was 4.2 h. Comparison of plasma levels of pindolol and beta-adrenoceptor blocking activity showed good correlation between them. It is concluded that the pharmacokinetics and beta-blocking effects of pindolol in Africans are not dissimilar from published data for other races.

Pindolol pharmacokinetics in relation to time course of inhibition of exercise tachycardia

1 Pharmacokinetics of pindolol were studied in normal subjects given 5, 10 and 20 mg orally and 3 mg i.v. Plasma half time was 2.9 +/- 0.3 (s.e. mean) h for both routes; peak drug levels occurred 1--2 h after ingestion and bioavailability was 53%. Plasma protein binding was 38% and was independent of plasma concentration; the drug was not concentrated in the red cell. 2 Work-heart rate regression lines were calculated from resting heart rate and three grades of 'steady-state' exercise standardized for the maximum work capacity (Wmax) of each subject. The equation was characterized by slope and HR50 (calculated heart rate at 0.5 Wmax). 3 After giving 5 mg i.v. pindolol to produce maximum cardiac beta-adrenoceptor blockade there were differences in inhibition of resting heart rate, slope, HR50 and maximum heart rate suggesting differences in sympathetic components. However, estimates of the degree of inhibition were closely similar for each variable when determined before and after atropinization indicating that the accuracy of estimation was independent of the level of vagal activity. 4 After oral pindolol peak inhibition of resting heart rate, slope and HR50 coincided with peak plasma concentration. Peak reduction of resting heart rate was greatest at the lowest dose, but inhibition of slope and HR50 were similar at all doses. 5 The different heart rate parameters recovered at different rates. After 24 h slope had returned to control, and the residual inhibition of HR50 reflected residual beta-adrenoceptor blockade of resting heart rate, as demonstrated by a shift in isoprenaline-heart rate relationship. 6 Inhibition of HR50 and other exercise parameters were 20% less in the concentration range 5--20 ng/ml than peak inhibition obtained in the range 21--160 ng/ml. The higher potency of pindolol compared with propranolol can be accounted for by the difference in protein binding.

Pharmacokinetics of pindolol in Africans

The pharmacokinetics of pindolol were determined in 12 hypertensive African subjects after a single oral dose of the drug. The estimated pharmacokinetic parameters do not differ significantly in Africans from the values which have been obtained in other races.

Measurement of beta-adrenoceptor antagonists in biological fluids using a radioreceptor assay

A new assay for plasma levels of beta-adrenoceptor antagonists is described. The assay depends upon the ability of the drug to compete with a labelled beta-adrenoceptor antagonist (-)-[3H]dihydroalprenolol for beta-adrenoceptor binding sites on lung membranes. The assay is simple to perform, very sensitive and does not require prior extraction of plasma. The assay can also detect bioactive metabolites of these agents and is clearly not limited to a single beta-adrenoceptor antagonist.

Transplacental passage of atenolol in man

Maternal and umbilical serum concentrations of atenolol, a hydrophilic, cardioselective beta-adrenoceptor antagonist, were studied at delivery in seven cases of pregnancy hypertension. The drug had been administered to each patient for at least one week. Atenolol was detected in both maternal and umbilical serum in six cases, showing that there is transplacental passage of the drug. In the seventh case, who had stopped taking atenolol more than one day before delivery, neither maternal nor umbilical serum contained a measurable quantity of the drug. Atenolol concentration varied 3- to 6-fold between individuals, but there was no systematic difference between maternal and umbilical levels. It seems reasonable to assume that during steady state conditions the blood level of atenolol in mother and fetus is approximately equal, and that fetal accumulation of the drug does not occur.

Comparison of disposition and effect of timolol and propranolol on exercise tachycardia

The kinetic disposition and beta-adrenergic blocking action in relation to plasma level of a single oral dose of either timolol or propranolol has been compared in healthy male volunteers. The disposition profiles clearly disclosed different properties of the two drugs, although their half-lives were similar. The available fraction of timolol in the systemic circulation was estimated to be approximately 60% of the dose, and 17.4% was exereted unchanged in urine. The logarithm of plasma concentration showed a significant correlation with the beta-blocking activity assessed by an exercise test. The mean potency ratios of timolol to propranolol as an antagonist of chronotropic effects on exercise tachycardia were 11 to 17 and 3.6 to 5.5 in dose- and concentration-effect relationships, respectively. The absolute reduction of exercise heart rate gave the best coefficient of all measures of beta-blockade. When drug action was measured as beta-blockade assessed by a given response to exercise tachycardia, the effect declined linearly with time, even though plasma levels fell exponentially. This results suggest that the pharmacokinetic t1/2 is much shorter than the pharmacological t1/2.

Clinical pharmacologic observations on timolol. I. Disposition and effect in relation to plasma level in normal individuals

The disposition profiles of a new beta-adrenergic blocking drug, timolol, were investigated at 11 different times in normal individuals after a single oral dose. The disposition of timolol follows first-order kinetics and may be adequately described by a one-compartment model. The pharmacokinetic data were not significantly different among the three dose levels examined. After the single oral doses, overall elimination half-life was 3.2 +/- 0.2 hours (mean +/- S.E.M.), with an observed peak time of 2.0 +/- 0.2 hours; extrapolated volume of distribution was 1.81 +/- 0.15 liter/kg; and the total plasma clearance was 557 +/- 61 ml/min. Approximately 20 per cent of elimination from the human body was dependent on the kidney. The area under the curve from zero to infinity and the peak concentration observed were dose dependent. A linear relationship was found between timolol plasma concentrations and beta-adrenergic blocking effects (per cent inhibition), as estimated from exercise-induced tachycardia. Timolol is a beta blocker which must await further clinical trials for the assessment of therapeutic implications in relation to plasma levels.

Clinical pharmacologic observations on timolol. II. Antihypertensive effect and kinetic disposition on twice-daily dosing in patients with mild or moderate hypertension

Timolol given on a twice-daily schedule has shown both antihypertensive effectiveness and plasma renin-suppressing action in eight patients with mild or moderate hypertension. However, the causal relationship between the drug plasma level, blood pressure fall, and change in plasma renin activity was not so clearly demonstrated in the present study. The disposition profiles of timolol at the steady state show an elimination half-life of 4.7 +/- 0.7 hours and a total plasma clearance of 225 +/- 21 ml/min. These values are found to be different from those of our previous observations obtained in normal individuals. Although the range of mean timolol concentrations at steady state varies to a certain extent among different patients, the dosage regimens for patients who will receive treatment for certain chronic disease states (e.g., arrythmias, obstructive cardiomyopathy, and angina pectoris, but not hypertension) in relation to plasma levels should be based on the disposition data obtained under steady state conditions. Bronchospasm developed in one of eight patients whose timolol level was found to be higher than the average of other patients given the same dosage.

Single and multiple dose pharmacokinetics of pindolol

The pharmacokinetics of pindolol were studied in six healthy individuals following a single 10 mg dose (SD) and multiple (5 mg tid over 6 days) dose (MD). The plasma elimination half-life was identical after SD (4.7 +/- 0,8h) and MD (4.1 +/- 1.1h). Steady state plasma concentrations were reached after 36 h and remained stable thereafter. The variation in steady state concentrations was small in each individual and also between individuals. The steady state concentration of pindolol can be predicted from the pharmacokinetic data obtained after a single dose. The results of the present study suggest that the disposition of pindolol is linear over the concentration range studied.

Results from a multicentre trial of metoprolol and a study of hypertensive patients with chronic obstructive lung disease

Ninety-nine patients took part in a multicentre, long-term study of metoprolol in the treatment of hypertension. Significant reductions in blood pressure and heart rate were achieved by the use of metoprolol alone, or in combination with other antihypertensive agents. Side effects were similar to those seen with other beta-adrenergic blocking agents, except that bronchospasm and cold extremities were rarely encountered. Results of monitoring for the abnormal eye symptoms and antinuclear factor titre are discussed. In a second study, 14 hypertensive patients with asthma (11 patients) or history thereof (three patients), received metoprolol for their hypertension. In general, no significant change in forced expiratory volume in one second (FEV1) was found, despite significant reduction in blood pressure and heart rate. The concomitant use of a beta2-agonist is discussed.

Serum tolbutamide and chlorpropamide concentrations in patients with diabetes mellitus

A selective and sensitive gas chromatographic technique was used to measure the steady-state serum concentrations of tolbutamide and chlorpropamide in 97 patients with maturity-onset diabetes mellitus who had been taking these drugs (37 tolbutamide, 60 chlorpropamide) for at least a year. No other antidiabetic agents had been given. The serum tolbutamide concentrations varied widely between the patients (from close to zero to 370 mumol/l (100 mug/ml)), yet the variation in dosage was only sixfold (0.5-3.9 g daily). The serum chlorpropamide concentrations varied even more widely (from close to zero to 882 mumol/l (244 mug/ml)), though the dosage variation was fourfold (125-500 mg daily). There was no systematic relation between dosage and serum concentrations of the drugs.Only 2 (5.4%) of the tolbutamide-treated patients and 10 (16.7%) of the chlorpropamide-treated patients had normal fasting blood glucose concentrations (below 5.5 mmol/l (99 mg/100 ml)), and fewer than half had values below 8.0 mmol/l (144 mg/100 ml). In most cases, therefore, the treatment was insufficient.There was no significant difference in mean fasting blood glucose concentrations between the two treatment groups. The mean steady-state concentration of chlorpropamide, however, was significantly higher than that of tolbutamide. Thus, contrary to common belief, the intrinsic activity of chlorpropamide is apparently not greater than that of tolbutamide. The alleged greater potency of chlorpropamide seems to be related wholly to kinetic differences, such as the less extensive metabolic degradation and slower elimination of the drug.We conclude that treatment with sulphonylureas in conventional dosage is far from optimal and that monitoring the concentrations of these drugs in the blood may help to improve their efficacy.

Long term effect of timolol and hydrochlorothiazide, or hydrochlorothiazide and amiloride, in essential hypertension

Twenty-four patients with mild to moderate hypertension were treated for up to 60 weeks with hydrochlorothiazide and either placebo, timolol, or timolol and amiloride. The effect of adding timolol and amiloride to hydrochlorothiazide was evaluated in a double blind trial. In 22 of the 24 patients a supine diastolic blood pressure below or equal to 95 mm Hg was produced by hydrochlorothiazide and timolol. Replacing a potassium supplement with amiloride increased the antihypertensive effect.