Direct measurement of propranolol bioavailability during accumulation to steady-state

The effect of verapamil on antipyrine pharmacokinetics and metabolism in man

The effect of verapamil pre-treatment on the pharmacokinetics and metabolism of antipyrine was studied in eight healthy male volunteers. The oral clearance of antipyrine was decreased from 2.18 to 1.95 l h-1 (P less than 0.01) by verapamil (80 mg three times daily for 2 days prior to antipyrine administration and 2 days following) while half-life was increased from 13.2 to 15.6 h (P less than 0.01). The urinary excretion of norantipyrine, 4-hydroxyantipyrine and 3-hydroxymethylantipyrine was decreased by 19.2%, 23.1% and 16.7% respectively (P less than 0.05) in the presence of verapamil. In addition, the rate constants for formation of each of these metabolites were significantly decreased by an average of approximately 30%. These results suggest that verapamil is capable of inhibiting oxidative metabolism, a finding which could be of clinical significance for drugs highly dependent upon pathways such as those inhibited in this study for elimination.

A comparison of the pharmacokinetics of propranolol in obese and normal volunteers

The pharmacokinetics of intravenous and oral propranolol have been compared in six obese and six normal subjects matched for age and sex. After intravenous administration there was no difference in plasma clearance but the volume of distribution was greater (V = 339 l vs 198 l) and the half-life was longer (t1/2 = 5.0 h vs 3.0 h) in the obese group. No important difference in the rate of oral absorption was observed. A trend towards higher systemic availability in the obese group (35% vs 27%) was not statistically significant.

Effect of propranolol on hepatic and systemic hemodynamics in dogs with chronic bile duct ligation

Propranolol has been reported to reduce portal and wedged hepatic vein pressures in man and may be useful for the prevention of variceal bleeding. However, its mechanism of action remains unclear. We have examined the effect of propranolol on the systemic and hepatic circulations in dogs with chronic bile duct ligation and secondary biliary cirrhosis. Under anesthesia, eight dogs received four increasing doses of propranolol as an i.v. bolus followed by continuous infusion. Systemic and hepatic hemodynamic parameters were measured in basal conditions and after a 30 min infusion for each dose. Portal vein and hepatic artery blood flows were measured with electromagnetic flow meters. All dogs had portal hypertension (portal venous pressure 15.3 +/- 0.8 mm Hg), a hyperdynamic circulation and severe liver disease resulting in a marked decrease of propranolol systemic clearance (8.75 ml per min per kg) and extraction (40%). The first dose of propranolol induced a decrease in heart rate (-27%) and in cardiac index (-21%), and an increase in systemic vascular resistance (+20%). With increasing doses, the systemic vascular resistance decreased with an increase in the cardiac index. Propranolol was not associated with significant modifications of hepatic hemodynamics: portal, wedged and free hepatic venous pressures and hepatic artery blood flow were stable, and portal blood flow decreased slightly at very high propranolol levels. In seven dogs studied without dissection of the hepatic vessels, there was a small decrease in portal pressure, but not in wedged and free hepatic venous pressures with increasing doses of propranolol. Thus, in dogs with intrahepatic portal hypertension, propranolol has significant effects on systemic hemodynamics, but only minimal effects on the hepatic circulation.

A modified, sensitive liquid chromatographic method for measurement of propranolol with fluorescence detection

A simple, sensitive, and rapid fluorometric-high-performance liquid chromatographic method for quantitating human and animal plasma and blood levels of propranolol has been developed. The procedure, which requires microliter volumes of triethylamine in the mobile phase mixture and microliter volumes of plasma or blood (50-100 microL), may be applied in routine clinical analysis as well as in pharmacokinetic studies using small laboratory animals. A single, selective extraction step precedes the analysis. The limiting concentration that can be detected is 1 ng/mL.

Rapid and simultaneous extraction of propranolol, its neutral and basic metabolites from plasma and assay by high-performance liquid chromatography

A high-performance liquid chromatographic method is described for the determination of propranolol, its neutral and basic metabolites from a single plasma sample. These analytes were extracted simply and efficiently by a solid-phase extraction column based on C18 modified silica (C18 Bond-Elut). Propranolol, the 4-hydroxy and N-desisopropyl metabolites were separated on a mu Bondapak C18 column with a mobile phase of acetonitrile--0.1% phosphoric acid. Propranolol glycol was selectively eluted from the C18 Bond-Elut column with acetonitrile and chromatographed separately with a mobile phase of acetonitrile--water. The recoveries of propranolol and all metabolites were greater than 78% with an intra-assay coefficient of variation between 4.9 and 7.3% at a concentration of 5-50 ng/ml. The minimum detectable levels in 1 ml of plasma were 1.0 ng/ml propranolol, 6.0 ng/ml 4-hydroxypropranolol, 1.0 ng/ml N-desisopropylpropranolol and 2.5 ng/ml propranolol glycol. Enzyme hydrolysis, Bond-Elut extraction and high-performance liquid chromatography revealed that propranolol, the neutral and basic metabolites were extensively conjugated in dog plasma (propranolol 67%, 4-hydroxypropranolol 98%, N-desisopropylpropranolol 55% and propranolol glycol 80%). With the use of pure enzymes and a selective inhibitor the nature of this conjugation appeared to involve both glucuronidation and sulfation. The conjugation of propranolol involved mainly glucuronidation (58-62%) compared to sulfation (7-12%), whilst that of 4-hydroxypropranolol mainly involved sulfation (55-65%) compared to glucuronidation (32-38%). The values for N-desisopropylpropranolol and propranolol glycol were 26-31% and 12% sulfation, 16-29% and 68-85% glucuronidation, respectively.

Clinical pharmacology of acebutolol

The clinical pharmacology and pharmacokinetics of acebutolol are summarized. Acebutolol and its longer-acting metabolite, diacetolol, are rapidly absorbed into the circulation from the gastrointestinal tract, and their bioavailability, unlike that of propranolol and metoprolol, is not significantly altered by whether the patient has recently eaten. Acebutolol is extensively metabolized by the liver, and elimination pathways involve approximately 30% to 40% through renal excretion and 50% to 60% by nonrenal mechanisms, including the bile and direct passage through the intestinal wall. The decreased hepatic metabolism and renal clearance rates seen in elderly patients may lead to the accumulation of both acebutolol and its metabolite, as has been reported with propranolol. In studies conducted to ascertain acebutolol's possible effect on common concurrently administered medications, the drug did not significantly alter either serum digoxin levels or serum insulin levels in diabetic patients treated with tolbutamide, nor did it change prothrombin time in patients treated with sodium warfarin.

Pharmacokinetics of sustained-release verapamil after a single administration and at steady state

Pharmacokinetics of conventional 80 mg tablets and two types of sustained-release (SR) tablets containing 120 and 200 mg of verapamil were compared cross-over in 12 healthy volunteers. Serum concentrations of verapamil and norverapamil were analyzed both after a single oral dose and at steady state after t.i.d. administration of conventional tablets and b.i.d. administration of SR tablets. After 120 mg SR tablets serum concentrations of verapamil usually remained below 100 ng/ml for 5 days. This inadequate bioavailability was caused by very slow absorption. The relative bioavailability of verapamil in 200 mg SR tablets was 93-96% as compared to the conventional tablets. After 200 mg X 2 and 80 mg X 3, the peak serum levels were about 300 and 190 ng/ml, respectively and the trough levels 123-153 and 52-56 ng/ml, respectively. The verapamil/norverapamil ratio varied from 0.69 to 0.84 after a single dose and from 0.8 to 0.93 at steady-state. By the 4th days of treatment, the accumulation ratios ranged between 1.75-2.07 and 1.30-1.75 for verapamil and norverapamil, respectively. For each preparation studied, the apparent Cltot of verapamil was significantly reduced at steady-state. These results show that 200 mg SR verapamil tablets fulfill the basic requirements of retard preparations allowing for twice or even once daily administration.

A multiple dose comparative study of the pharmacodynamic and pharmacokinetic behaviour of polymer-matrix and Oros dosage forms of oxprenolol in healthy volunteers

A new osmotic drug delivery system (Oros) has been evaluated in multiple-dose studies in young healthy volunteers as a sustained-release vehicle for once-daily administration of oxprenolol. Two Oros systems were examined in two separate studies, one containing 170 mg oxprenolol succinate with an initial zero-order release rate of 10 mg/h, and the other containing 260 mg oxprenolol succinate with an initial release rate of 16 mg/h. These were compared respectively with conventional oxprenolol hydrochloride (Trasicor) 80 mg twice daily and polymer-matrix oxprenolol hydrochloride (Slow Trasicor) 160 mg once daily. Variations in mean plasma levels and beta-adrenoceptor blockade (measured by inhibition of exercise tachycardia) were considerably reduced on the 10/170 Oros once-daily compared with the Trasicor 80 mg twice-daily regimen. With both formulations there was no significant change in mean plasma concentrations or areas under the curve after 8 days' treatment, and similar pre-dose plasma concentrations were obtained. There was significant inhibition of exercise tachycardia throughout 24 h after the 10/170 Oros on the eighth day. The 16/260 Oros system gave smoother pharmacokinetic and pharmacodynamic profiles, and on repeated dosing a higher mean pre-dose plasma oxprenolol concentration than Slow Trasicor. Drug availability was similar for the two dose forms, suggesting an acceptable level of absorption of oxprenolol from most of the gastrointestinal tract. On the eighth day exercise heart rate was significantly reduced throughout 24 h with 16/260 oxprenolol Oros, but only between 1 and 15 h with Slow Trasicor.

Comparison of nonlinear pharmacokinetic parameters estimated from the sinusoidal perfusion and venous equilibrium models

It is shown that the intrinsic and steady-state clearances and the values of Vm and Km of the Michaelis-Menten equation estimated via the sinusoidal perfusion model are different from the corresponding values estimated via the venous equilibration model. The liver blood flow rates estimated by two theories (from plasma data) are identical. The comparison was made using the single dose oral and intravenous and steady-state oral plasma concentration-time data for verapamil in six subjects previously published.

Stereoselective ring oxidation of propranolol in man

The objective of this study was to elucidate stereoselective mechanisms of propranolol metabolism in man. Five normal subjects were given single 80 mg oral doses of deuterium-labeled pseudoracemates of propranolol, and the stereochemical composition of propranolol and its major metabolites in urine was determined by GC/MS. The (-)/(+)-enantiomer ratios for unchanged propranolol, 1.50 +/- 0.10 (mean +/- s.e. mean), and propranolol glucuronide, 1.76 +/- 0.10, were similar to previous findings in plasma. All products of side-chain oxidation also consisted mainly of the (-)-enantiomer, with an overall (-)/(+) ratio of 1.61 +/- 0.11. A (-)/(+) ratio of 1.04 +/- 0.17 for 4-hydroxypropranolol did not indicate stereoselectivity in ring oxidation. However, the ratio for its glucuronic acid conjugate of 1.78 +/- 0.19 and for its sulphate conjugate of 0.27 +/- 0.03 suggested stereoselectivity in either the glucuronidation or sulphation of 4-hydroxypropranolol, or both. When the stereoselectivity in these secondary pathways was taken into consideration, the overall ring oxidation strongly favoured (+)-propranolol with a (-)/(+)-enantiomer ratio of 0.59 +/- 0.09. The composite observations of the stereochemistry of propranolol metabolism in man are consistent with stereoselective ring oxidation of (+)-propranolol, leading to a greater bioavailability of the pharmacologically more active (-)-propranolol and subsequent preferential side-chain oxidation and glucuronidation of this enantiomer.

Pharmacokinetics of l-propranolol during repetitive dosing in normal and uranyl nitrate-induced renal failure rats

The effect of experimental renal failure on the intravenous and oral pharmacokinetics of l-propranolol was studied in rats. Renal failure was induced by a single intravenous injection of uranyl nitrate (5 mg/kg). Pharmacokinetic studies were carried out on the fifth day after injection of the renal toxin (renal failure group) or saline (control group). Serum concentration time course of l-propranolol was characterized after a single intravenous or oral dose as well as after five consecutive doses of the drug given at 3-hr intervals. During repetitive intravenous drug administration, steady state was reached by the second dose, i.e., within 6 hr after initiation of repetitive dosing. No significant difference in the serum concentration time course of l-propranolol was observed between control and renal failure animals. In both groups the AUC over the steady-state dosing interval was on the average 21-27% higher than the AUC after a single dose, indicating a slight decrease in the systemic clearance of l-propranolol during repetitive intravenous drug administration. An approximately two- to three-fold higher serum l-propranolol concentration was observed in renal failure animals as compared to the normal controls after both single or repetitive oral dosing. The apparent reduction in oral clearance probably reflected an inhibition of the hepatic first-pass metabolism of l-propranolol in the renal failure rat. An unexpectedly high and protracted accumulation of serum l-propranolol concentration was observed during repetitive oral drug administration. Continuing accumulation was still evident after the fifth oral dose, i.e., a period of 15 hr or approximately 10 half-lives. The mean AUC over the last dosing interval was 32.0 and 17.8 times higher than the predicted steady-state estimate based on single oral dose data for control and renal failure rats, respectively. The substantial reduction in the oral clearance during repetitive drug administration may be due to an auto-inhibition of l-propranolol metabolism.

Oral and topical adrenergic beta-receptor blockers in glaucoma treatment. A multicenter study

In a long-term multicenter open randomized study of 103 patients with glaucoma or intraocular hypertension, oral propranolol combined with 2% pilocarpine was compared with 0.5% topical timolol also combined with 2% pilocarpine, with respect to the effects on intraocular pressure and other signs of glaucoma. The results showed that the hypotensive effects were highly significant and equal for both treatments. There were no significant differences between the 2 groups in the amount of cupping of the nerve head or the visual field defects developing during treatment. An additive hypotensive effect was recorded when both propranolol and timolol were combined with pilocarpine, which indicates the development of tolerance to both beta-blockers. Pulse rate and blood pressure were moderately reduced in both groups, both significantly more so in the propranolol group. The investigation indicates that when combined with pilocarpine the 2 adrenergic beta-receptor blockers are equally effective. We believe that oral propranolol can improve drug compliance in the treatment of glaucoma.

Perioperative beta blockade with propranolol: reduction in myocardial oxygen demands and incidence of atrial and ventricular arrhythmias

To determine the effect of beta blockade with propranolol on myocardial oxygen demands and postoperative arrhythmias in patients having coronary bypass operations, 50 patients with chronic stable angina undergoing operation were randomized in a double-blind fashion to receive either propranolol (60 mg every 6 hours) or a placebo. Drug administration began 24 to 48 hours prior to operation and continued through the operative period and for one month after operation. There were no deaths. Two perioperative myocardial infarctions occurred, both in patients receiving a placebo. Myocardial oxygen demand as measured by the rate-pressure product (heart rate X mean arterial pressure) was significantly reduced during induction of anesthesia (7,658 +/- 451 versus 5,786 +/- 340; p less than 0.002) and during sternotomy (8,400 +/- 550 versus 6,756 +/- 384; p less than 0.02) in propranolol-treated patients. In the first two postoperative days, nitroprusside was required for control of hypertension of 10 patients in the placebo group but in only 3 patients given propranolol (p less than 0.05). Postoperatively, 15 of the 26 patients who received a placebo had 45 episodes of arrhythmia. Seven of the 24 propranolol-treated patients had 17 episodes (p less than 0.04). We conclude that propranolol given perioperatively in doses large enough to induce beta blockade significantly reduces myocardial oxygen demands in the vulnerable period during induction of anesthesia and sternotomy, reduces the need for antihypertensive therapy in the immediate postoperative period, and causes a marked reduction in the incidence and frequency of both supraventricular and ventricular arrhythmias in the postoperative period.

Nonlinear formation of propranolol metabolites in dogs after portacaval transpositions

The formation of four major metabolites of propranolol by the liver was examined at steady state in three dogs that had undergone surgical portacaval transposition, following which injection of drug into the hindlimb delivers the total dose to the liver. Propranolol was infused directly into the liver via a hindlimb vein at dose rates ranging from 1.01 to 6.3 mg/min. In all dogs the formation of 4-hydroxypropranolol, alpha-naphthoxylactic acid, and propranolol glycol was saturable. Vmax and Km values were determined at steady state by relating the rate of excretion of each metabolite into bile and urine to the blood concentration of propranolol. The formation of propranolol glucuronide was a first order process. The use of a dog with a portacaval transposition has permitted development of a method to estimate, in vivo, the kinetic properties of enzymes responsible for hepatic first-pass metabolism of drugs.

Ethanol-induced inhibition of hepatic uptake of propranolol in perfused rat liver and in man

Studies were conducted to determine the mechanism whereby ethanol alters the hepatic disposition of propranolol. In eight isolated perfused rat livers, ethanol (mean = 40.1 mmol/l diminished the clearance of dl-propranolol (1.93 +/- 0.43 to 1.24 +/- 0.22 ml/min/g liver, p less than 0.05); increased its t1/2 (12.8 +/- 1.5 to 20.7 +/- 3.25 min, p less than 0.01); and decreased the proportion metabolized (68.7 +/- 4.7% to 34.3 +/- 10.3%, p less than 0.01). These results suggest that ethanol could substantially increase the oral bioavailability of propranolol in humans. However, in normal human volunteers administered 80 mg of propranolol orally, alone, or preceded and followed by ethanol to maintain breath ethanol concentrations of 800-1000 mg/l, increases in propranolol AUC were smaller than anticipated. Seven subjects had increases in free propranolol AUC0-8h (32%, range: 12-61%) (p less than 0.05), while total propranolol AUC0-8h increased by a mean 22% (range: -4-+49%). Propranolol free fraction varied with time and was higher after ethanol (mean = 0.090 vs 0.084) (p less than 0.077). The extent of the propranolol-induced slowing of heart rate was not influenced by ethanol (mean decrease from baseline of 13 bpm at peak propranolol effect vs 9 bpm without ethanol); mean heart rates following propranolol with ethanol were higher at all times (mean of 7.5 bpm) (p less than 0.001) than after propranolol alone. Ethanol inhibits the hepatic oxidative metabolism of propranolol in vitro; however, any effect on heart rate of higher concentrations of propranolol induced by ethanol in humans is offset by the cardio-acceleratory effect of ethanol.

Inter- and intra-subject variation in the first-pass elimination of highly cleared drugs during chronic dosing. Studies with deuterated verapamil

The pharmacokinetics of verapamil in five healthy volunteers were investigated on 4 occasions during chronic administration of deuterated verapamil. There was no statistically significant difference in oral clearance, terminal half-life, bioavailability, morning trough level and peak concentration or in the time of their occurrence on the four occasions. The plasma clearance, however, exhibited considerable inter- and intra-individual variation, ranging between 26.3% and 85.4% and 12.0% and 48.0%, respectively. Comparison of these pharmacokinetic parameters with data from previous single dose studies in the same subjects revealed a significant (p less than 0.05) decrease in the clearance and an increase in the apparent bioavailability of verapamil during chronic administration, although no difference in the half-life was found. Due to the considerable variation in the oral clearance of verapamil during chronic dosing, steady-state conditions in a strict pharmacokinetic sense may never be attained, and pharmacokinetic data obtained in single dose studies will be of limited value in predicting steady-state plasma concentrations.

Electrophysiologic actions of high plasma concentrations of propranolol in human subjects

The authors have previously shown that 40% of patients whose ventricular arrhythmias respond to propranolol require plasma concentrations in excess of those producing substantial beta-receptor blockade (greater than 150 ng/ml). However, the electrophysiologic actions of propranolol have only been examined in human beings after small intravenous doses achieving concentrations of less than 100 ng/ml. In this study, the electrophysiologic effects of a wider concentration range of propranolol was examined in nine patients. Using a series of loading and maintenance infusions, measurements were made at baseline, at low mean plasma propranolol concentrations (104 +/- 17 ng/ml) and at high concentrations (472 +/- 68 ng/ml). Significant (p less than 0.05) increases in AH interval and sinus cycle length were seen at low concentrations of propranolol, with no further prolongation at the high concentrations; these effects are typical of those produced by beta-blockade. However, progressive shortening of the endocardial monophasic action potential duration and QTc interval were seen over the entire concentration range tested (p less than 0.05). At high concentrations, there was significant (p less than 0.05) further shortening of both the QTc and monophasic action potential duration beyond that seen at low propranolol concentrations, along with a progressive increase in the ratio of the ventricular effective refractory period to monophasic action potential duration. No significant changes were seen in HV interval, QRS duration or ventricular effective refractory period. In summary, the concentration-response relations for atrioventricular conductivity and sinus node automaticity were flat above concentrations of 150 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxprenolol: clinical pharmacology, pharmacokinetics, and pharmacodynamics

Oxprenolol is clinically a well-established beta blocker that shares with other members of this group the ability to control a variety of disorders, in particular, hypertension and angina. Pharmacologically it is a nonselective beta blocker that possesses partial agonist activity (intrinsic sympathomimetic activity). Pharmacokinetically, oxprenolol behaves as a moderately lipophilic agent. This means that it is well absorbed, but then undergoes considerable first-pass loss. It penetrates well into most tissues, including the central nervous system. About 80% of oxprenolol is bound to protein in the blood, and when acute-phase proteins increase, as, for example, in patients with inflammatory disease, total plasma concentrations of oxprenolol also increase. Apart from this, the plasma concentration:time profile produced after the oral administration of oxprenolol is remarkably consistent and reproducible. Intrasubject and intersubject variability is small, and the administration of the drug after food or with many other drugs has very little effect. The beta-blocking effects of oxprenolol correlate well with the plasma concentrations, but as with other beta blockers, it has not been possible to correlate plasma concentrations directly with its therapeutic actions such as lowering blood pressure or controlling arrhythmias.

Pharmacokinetics of oxprenolol in the elderly

This paper is a brief review of the problems associated with drug therapy in the elderly. Although the elderly are more prone to suffer adverse reactions to drugs and to respond abnormally, impaired drug handling should not be blamed for these problems until other factors have been evaluated. Renal function deteriorates as people grow older, but the absorption, metabolism and distribution of most drugs may not be adversely affected by advancing age. Evidence to the contrary is sometimes based on studies of convalescent patients in whom an effect of disease or drug therapy cannot be excluded. For an assessment of the effects of aging on the pharmacokinetics of oxprenolol, 2 groups of 8 healthy females, mean age 21 and 68 years, respectively, were studied. Oxprenolol, 80 mg, was given orally in a single dose on day 1 and day 8 of a course of treatment; on the intervening days, oxprenolol, 80 mg, was given twice daily. The mean plasma concentration:time curves for both day 1 and day 8 for the 2 age groups were comparable. Thus, age alone does not affect the pharmacokinetics of oxprenolol.

Induction of propranolol metabolism by rifampicin

The effect of rifampicin on the blood concentration-time curve of propranolol at steady-state following oral administration of 120 mg every 8 h was investigated in six normal, young, male subjects. After an initial 2 week dosing period, all individuals additionally received 600 mg rifampicin daily for 3 weeks followed by a 4 week period during which again only the propranolol was given. In four of the subjects the effects of 900 and 1200 mg rifampicin daily was also studied. Changes in disposition were assessed by estimation of propranolol's oral clearance and elimination half-life during the dosage interval. Rifampicin (600 mg/day) caused a large increase in propranolol's oral clearance (35.7 +/- 16.3 vs 96.1 +/- 26.9 ml min-1 kg-1, mean +/- s.d.), but neither the elimination half-life nor extent of plasma binding were affected. Increasing the daily dosage to 900 and 1200 mg did not cause any additional changes in oral clearance. Four weeks after discontinuing rifampicin, propranolol's oral clearance had essentially returned to its pre-induction level. The oral clearance of propranolol was significantly smaller (89.5 +/- 14.4%) during the dosage interval immediately after administration of the last rifampicin dose than the value measured 24 h later. The findings are consistent with rifampicin causing induction of the drug metabolizing enzymes responsible for propranolol's biotransformation. The marked reduction in the steady-state propranolol blood concentration that results from chronic rifampicin administration would be expected to result in a significant change in clinical effectiveness of the beta-adrenoceptor blocker when the two drugs are used concurrently.

Pharmacokinetic drug interactions with propranolol

Propranolol is widely used in clinical practice and is frequently administered along with other drugs. The co-administration of propranolol and other drugs may result in either propranolol-induced changes in the disposition of other drugs or in effects of the other drugs on the pharmacokinetics of propranolol. These changes may be due to alteration in absorption, metabolism or to haemodynamic effects such as altered liver blood flow. Understanding the pharmacokinetics of propranolol is important to the rational interpretation of the effects of other drugs on propranolol's disposition. The absorption, protein binding and metabolism of propranolol may all be affected by the co-administration of other drugs. Induction of propranolol's metabolism by halofenate, phenytoin, phenobarbitone, rifampicin and alcohol have all been implicated in altering propranolol clearance, while inhibition of hepatic drug metabolising enzymes by chlorpromazine and cimetidine appear to reduce propranolol clearance. Propranolol may also affect the metabolism of other drugs such as antipyrine, chlorpromazine, theophylline and thyroid hormones. Suggestions that propranolol may alter quinidine's elimination have not been substantiated. By reducing liver blood flow propranolol may reduce the systemic clearance of other high extraction drugs such as lignocaine.

Effects of feeding on the systemic clearance of indocyanine green and propranolol blood concentrations and plasma binding

In six healthy subjects a 250 g steak significantly increased the systemic clearance of indocyanine green. During a steady-state infusion of propranolol there was a rapid decrease (mean 35%) in blood propranolol concentrations within 5 min of feeding and levels were reduced for 30 min before gradually returning towards the pre-feeding. These results suggest that the systemic clearance of high extraction drugs may be increased immediately following food.

Kinetics and cardiac effects of propranolol in humans

Six healthy volunteers received single 20-mg intravenous (IV) and 80-mg oral doses of propranolol on two occasions in random sequence. Serum propranolol concentrations were determined by gas chromatography in multiple samples drawn during 24 h after each dose. Mean (+/- SE) kinetic variables for IV propranolol were: elimination half-life (t 1/2 beta), 5.3 (+/- 0.6) h; volume of distribution, 2.3 (+/- 0.3) l/kg; total clearance, 4.9 (+/- 0.3) ml/min/kg; predicted extraction ratio, 0.23 (+/- 0.02). After single oral doses, t 1/2 beta (3.8 +/- 0.2 h) tended to be smaller than after the IV dose, and actual systemic availability (0.60 +/- 0.07) was less than that based on the predicted extraction ratio. During multiple oral dosage (80 mg every 12 h), observed steady state serum levels (47 +/- 5 ng/ml) tended to be less than those predicted based on the single oral dose (61 +/- 5 ng/ml), thus providing no evidence for reduced propranolol clearance at steady-state. Echocardiographic measurements of left ventricular performance (posterior wall velocity, diastolic dimensions) made during the single-dose oral study indicated significant impairment of function; impairment was maximal at 3 h post-dosage, and corresponded to the time of the peak serum propranolol concentration (341 ng/ml).

The effect of acebutolol and propranolol on the hypoglycaemic action of glibenclamide

1 The effect of acebutolol, a relatively selective beta-adrenoceptor blocking drug and propranolol, a non-selective one, on the hypoglycaemic action of glibenclamide after an oral glucose load has been investigated in a group of maturity-onset diabetic patients. 2 Glibenclamide significantly reduced the blood glucose levels and both acebutolol and propranolol, at therapeutic doses, were found to modify this action significantly. 3 The effect of acebutolol was slightly less than that of propranolol. The difference was not statistically significant. 4 The modes of action of sulphonylureas are reviewed and it is suggested that beta-adrenoceptor blockers may modify their effect on insulin release. This appears to be a drug interaction rather than an effect of beta-adrenoceptor blockade on glucose tolerance.

The relative bioavailability of a commercial propranolol hydrochloride tablet in man

A relative bioavailability study of conventional tablet of propranolol hydrochloride was conducted in a group of 18 healthy volunteers employing the innovator's product as the reference tablet formation. Based on plasma levels of propranolol for the 24 h following administration of 2 x 40 mg oral propranolol hydrochloride tablets, the relative extent of availability was shown to be 100.8 per cent for the test tablet formulation; no significant differences were detected between formulations with respect to any of the pharmacokinetic parameters examined. Large intersubject variations in plasma propranolol concentrations and the subsequently calculated areas under the plasma concentration/time curves were attributed to substantial presystemic biotransformation differences.

Comparison of the pharmacodynamic and pharmacokinetic profiles of single and multiple doses of a commercial slow-release metoprolol formulation with a new Oros delivery system

1 A new osmotic pressure mediated delivery system for metoprolol (Lopresor Oros) has been evaluated by measuring the haemodynamic effects and pharmacokinetics after single and multiple oral dosing in young healthy volunteers. 2 Similar studies have been carried out in the same group using equivalent single and multiple oral doses of the commercial slow-release preparation (Slow Lopresor). 3 The new osmotic delivery system produces a more uniform haemodynamic response: a plateau metoprolol concentration in plasma is reached about 6 h after dosing and is maintained for 10 h.

Exacerbation of vasotonic angina pectoris by propranolol

Using a double-blind protocol, we investigated the use of propranolol in patients with coronary artery spasm as assessed by subjective and objective variables. Both low-dose (40 mg every 6 hours) and high-dose (160 mg every 6 hours) propranolol were administered. At both doses, the duration of angina attacks was significantly prolonged but the frequency was not. We conclude that propranolol at doses up to 160 mg every 6 hours as single therapy is frequently detrimental in angina pectoris due to coronary artery spasm and should not be used as the sole treatment of this disorder.

Prediction of bioavailability for drugs with a high first-pass effect using oral clearance data

For drugs with a high hepatic clearance, bioavailability is low due to the so-called "first pass effect". Prediction of the bioavailability for these drugs has been only loosely tested. It is proposed that by plotting the reciprocal of bioavailability versus the oral clearance, a straight line with intercept of unity and slope of reciprocal of hepatic blood flow should ensue. For lignocaine and verapamil, this relationship was found to be strong and gave good predictability, whereas for propranolol this relationship was weak and gave poor predictability. The proposed method may be of value in determining whether the low bioavailability of a drug is due to hepatic first pass metabolism.

A pharmacokinetic and pharmacodynamic assessment of a combined slow-release metoprolol-chlorthalidone preparation

Beta adrenoceptor blocking drugs and diuretics are frequently given together to control hypertension and increasingly the two agents are being combined in a single preparation. Possible interactions between the two agents are therefore of interest. In this study the addition of chlorthalidone has been shown not to influence the plasma levels or beta-blocking action of a sustained release form of metoprolol. In addition, when the combination product containing sustained release metoprolol and chlorthalidone is given over 21 days, the plasma levels of each drug are similar to those reported for each drug when given alone.

Cimetidine increases steady state plasma levels of propranolol

1 The influence of cimetidine (1000 mg daily) on propranolol steady state plasma levels has been studied in seven normal volunteers. Cimetidine was used as a 200 mg normal release tablet whereas propranolol was given as a 160 mg slow release formulation once daily. 2 After 1 day of cimetidine treatment (day 9 of the study) the mean (Css) and minimal (Css min) propranolol steady state plasma levels increased significantly from 24.1 +/- 14.9 ng/ml (mean +/- s.d.) to 39.2 +/- 27.7 ng/ml (P = 0.01) and from 14.8 +/- 9.3 ng/ml to 27.1 +/- 21.2 ng/ml (P = 0.03), respectively. The apparent oral clearance (Clo) was reduced from 6.7 +/- 4.3 l/min to 4.6 +/- 3.11/min (P = 0.006). 3 A prolongation of cimetidine administration to 5 days (day 13 of the study) intensified this effect significantly (P = 0.02): Css of propranolol was elevated from 23.2 +/- 14.4 ng/ml to 44.9 +/- 26.7 ng/ml (P = 0.003); Css min was increased from 14.1 +/- 10.2 ng/ml to 28.4 +/- 17.9 ng/ml (P = 0.02) while Clo decreased from 6.9 +/- 4.1 1/min to 3.3 +/- 1.61/min (P = 0.006). 4 We conclude that the drug interaction between propranolol and cimetidine leads to significant elevations of propranolol steady state plasma concentrations which may cause a clinically relevant enhancement of the effect of a given dosage. This requires careful observation of patients under concomitant treatment with propranolol and cimetidine.

Combined high-performance liquid chromatographic procedure for measuring 4-hydroxypropranolol and propranolol in plasma: pharmacokinetic measurements following conventional and slow-release propranolol administration

An assay is described for the simultaneous determination of propranolol and its active metabolite, 4-hydroxypropranolol, in human plasma. Both compounds were separated from an ethereal extract by high-performance liquid chromatography employing a C18 bonded-phase column. Detection of the effluent was by fluorescence. Suitable fluorescent spectrometers and wavelength settings that allow optimum detection of both compounds have been described. The limit of sensitivity was 2 ng/ml for both propranolol and 4-hydroxypropranolol. Mean peak plasma levels of propranolol and 4-hydroxypropranolol in six patients receiving a single dose of a slow-release 160-mg formulation of propranolol were 28 and 6 ng/ml, respectively. These levels were about one-tenth the level obtained following a single conventionally prepared dose of propranolol (160 mg). Peak levels were delayed and plasma levels of propranolol persisted for a longer period with the slow-release formulation. Area under the curve estimates suggested that the bioavailability of the slow-release formulation following single-dose administration was about one-third that of the conventional preparation.

Regulation of human leukocyte beta receptors by endogenous catecholamines: relationship of leukocyte beta receptor density to the cardiac sensitivity to isoproterenol

High levels of beta receptor agonist have previously been shown to down-regulate beta receptor density on circulating leukocytes in man; however, the factors controlling receptor density under physiological conditions have not previously been defined. To determine whether beta receptor density is normally down-regulated by circulating, physiological levels of catecholamines we have examined the relationship between receptor density and catecholamine levels. Urinary epinephrine and norepinephrine were significantly reciprocally correlated to lymphocyte receptor density. A similar relationship existed between beta receptor density and supine plasma epinephrine, norepinephrine, upright epinephrine, and norepinephrine levels. Change in sodium intake from 10 to 400 meq/d caused a 52% increase in lymphocyte and a 48% increase in polymorphonuclear beta receptor density. The changes in receptor density were accompanied by an increase in the sensitivity to isoproterenol measured as a fall in the dose of isoproterenol required to raise the heart rate by 25 beats per minute. Beta receptor density on both lymphocyte and polymorphonuclear cells was significantly correlated to the cardiac sensitivity to isoproterenol. Propranolol administration resulted in an increase in the density of beta receptors on lymphocyte and polymorphonuclear cells that correlated with the subject's pretreatment catecholamine levels. These findings, therefore, suggest that physiological levels of catecholamines normally down-regulate beta receptors in man and that blockade of this down-regulation by propranolol allows receptor density to increase.

Reduction of liver blood flow and propranolol metabolism by cimetidine

We studied the influence of cimetidine on liver blood flow in eight normal subjects. Cimetidine acutely reduced liver blood flow during fasting by almost 25 per cent, as measured by indocyanine green clearance. Chronic cimetidine therapy (300 mg four times daily for seven days) reduced the flow by 33 per cent, as measured over eight hours by calculating the relative disposition of oral and intravenous propranolol. In addition to reducing the clearance of intravenous propranolol by decreasing live blood flow, cimetidine also inhibited the metabolism of oral propranolol and thereby further reduced elimination. The reduction in clearance of oral propranolol correlated positively (r = 0.87, P less than 0.05) with the average steady-state concentration of plasma cimetidine, suggesting that the inhibition of drug metabolism by cimetidine is dose related. Pulse rates at rest were markedly lower after propranolol plus cimetidine than after propranolol alone. The reduction in liver blood flow produced by cimetidine has important therapeutic implications for patients with alterations in liver and gastrointestinal blood flow and when drugs are used whose hepatic elimination depends on liver blood flow.

A standard approach to compiling clinical pharmacokinetic data

A standard format for a Clinical Pharmacokinetic Summary is proposed. It consists of a heading, tables, notes, and references for each drug reviewed. The table presents a unified and logical set of clinically useful population pharmacokinetic parameters. They concern four major areas: absorption, distribution, elimination, and the relationship of concentration to effect. Within each major group, parameters dealing with extents and rates of processes are given. Each such parameter is really two: a population mea value (for example, average volume of distribution) and the standard deviation of individual values about this mean. The first value allows individual predictions of dosage or drug level to be made; the second allows computation of the likely proximity of subsequently observed quantities to those predictions. The table presents single consensus values for each population parameter, rather than a list of values. A procedure for computing these consensus values, and for revising them in the light of new data, or reinterpreted old data, is given. Examples of Summaries are given. The method appears applicable to a variety of drugs. We suggest our approach as a standard one for preparing Clinical Pharmacokinetic Summaries, and urge our colleagues to consider it for that purpose.

First-pass effect: nonlinear concept comprising an explicit solution of integrated Michaelis-Menten equation

The first-pass effect results from metabolism during the first liver passage of a drug given by mouth. The metabolism is described by the Michaelis-Menten equation, but the integrated form of the Michaelis-Menten equation has no explicit solution for concentration and its handling requires a computer. However, the presented nonlinear equation of the first-pass effect is an explicit integration of the Michaelis-Menten equation and involves only general mathematics. However, the problem of evaluating the Michaelis-Menten constants Vm and Km is not resolved. Therefore, linear equations are also derived, which correspond to previous clearance models.

A propranolol radioimmunoassay and its use in the study of its pharmacokinetics following low doses

A radioimmunoassay has been developed for propranolol with a sensitivity of 2.37 nmol l-1 in unextracted plasma using a 50 microliter sample. Plasma concentration measurements were made on samples from volunteers for up to 8 h after they had been given 5, 10, or 40 mg of propranolol by mouth. Analysis of the results showed that mean elimination half-lives and total body clearances were similar following each of the doses and that the area under the curve was proportional to the dose. Steady-state propranolol concentrations in 17 patients on regular propranolol treatment were linearly related to the dose ver the range 20-640 mg d-1; the regression line extrapolated to the origin. These data indicate non-saturable kinetics for the hepatic metabolism of propranolol within the dose ranges investigated and lead us to believe that there is no 'oral-threshold' dose for propranolol. The radioimmunoassay may be useful in clinical practice for monitoring plasma propranolol concentrations and for detecting patient compliance.

Propranolol disposition in renal failure

1 Previous studies of propranolol disposition in renal failure have been conflicting. 2 Using simultaneous administration of [3H]-propranolol intravenously and unlabelled propranolol orally the principal determinants of drug distribution were calculated in normals, patients with severe renal impairment (creatinine clearance 14.5 +/- 2.8 ml/min) but not on haemodialysis and patients on haemodialysis (creatinine clearance less than 5 ml/min). 3 The effect of haemodialysis on propranolol binding and free fraction was also examined. The percentage of propranolol unbound rose from 7.1% to 9.9%. (P less than 0.001) 20 min following heparinization and beginning haemodialysis. This was accompanied by a large rise in free fatty acids from 0.567 +/- 0.059 to 3.326 +/- 0.691 mumol/ml (P less than 0.005). 4 The blood to plasma concentration ratios of propranolol were significantly higher in patients with renal failure (P less than 0.02) and on haemodialysis (P less than 0.001) and were significantly negatively correlated (P less than 0.001) with the haematocrit. 5 Although the half-life propranolol was significantly shortened in the patients with renal failure (P less than 0.02), there was no change in the apparent liver blood flow, extraction ratio or the principal determinants of steady-state drug concentrations in blood namely oral and intravenous clearance from blood. 6 There is, therefore, no pharmacokinetic basis to adjust the dosage of propranolol in patients with renal failure.

Elevated plasma free drug concentrations of propranolol and diazepam during cardiac catheterization

Patients who undergo cardiac catheterization are frequently taking propranolol and are often premedicated with diazepam. Because the intensity of a drug's action is determined by free, or non-protein-bound, levels in plasma, changes in the degree of protein binding may profoundly alter the pharmacologic effect. We examined the effects of heparin on the free levels of propranolol and diazepam in six patients who underwent cardiac catheterization. After heparinization, the free fraction of diazepam increased more than fourfold, from 1.8 +/- 0.1% to 7.9 +/- 1.2% (p < 0.002) and the free levels increased from 2.0 +/- 0.5 to 8.4 +/- 2.2 ng/ml (p < 0.025); the free fraction of propranolol increased from 7.4 +/- 0.9% to 12.5 +/- 1.4% (p < 0.001). The increase in free drug concentration was associated with elevated free fatty acid levels, which rose from 181 +/- 7 micrograms/ml to 596 +/- 119 micrograms/ml (p < 0.02). Increases in the free levels of propranolol and diazepam produced by heparinization during cardiac catheterization may result in increased pharmacolaogic effect, such as excessive sedation or respiratory depression.

Determination of propranolol and its major metabolites in plasma and urine by high-performance liquid chromatography without solvent extraction

Fast, reliable, specific and sensitive methods are reported to accurately quantitate unchanged, propranolol in plasma, and its major metabolites in plasma and urine after enzymatic hydrolysis without the need for solvent extraction. These methods enable the analyst to process a large number of propranolol samples in one working day and should prove valuable to clinical laboratories demanding both speed and specificity in an assay.

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.

Dose-dependent disposition of oral propranolol in normal subjects

The pharmacokinetics and relative systemic availability or oral propranolol were studied in three healthy volunteers following administration of 10, 40, and 80 mg of propranolol hydrochloride. Plasma concentrations of propranolol were determined using a sensitive and specific fluorometric high pressure liquid chromatographic technique. In the dosage range studied, the amount of propranolol reaching the systemic circulation increased with dose, while half-lives remained unchanged. The apparent 'threshold dose' for propranolol was much smaller than previously reported, and its contribution to the observed dose-dependent availability is doubtful. Apparent intrinsic clearance values were shown to decrease with increase in dose, with a true maximal intrinsic clearance of 5.4 l kg-1 h-1. These data suggest the saturation of a low capacity enzyme system in the liver and are consistent with theoretical characteristics of a drug that is extensively metabolized during its first pass through the liver.

A single and multiple dose pharmacokinetic and pharmacodynamic comparison of conventional and slow-release metroprolol

Pharmacokinetic and pharmacodynamic profiles for metoprolol have been measured in six healthy volunteers after single and multiple dosing with 100 mg conventional formulation twice daily and 200 mg slow-release formulation once daily. Both multidose regimes produced measurable predosing plasma concentrations of metoprolol. The plasma concentrations on the eighth day were greater than predicted by the single-dose data as indicated by the comparison of the total areas under the curve for the single dose and the dosage interval areas during multiple dosing. This increase may be associated with a change in the bioavailability and/or clearance of the drug and is currently being investigated. The peak concentrations for the two regimens were comparable but the times to peak with the slow-release regimen were significantly delayed. Both regimes produced significant beta-blocking effects over 24 h during multiple dosing, the reductions in exercise heart rate at 0 and 24 h on the eighth day corresponding to more than 20% of the maximum effect. Resting pulse rates and blood pressures were affected to a similar extent by the two regimens but neither significantly altered respiratory peak flow rates. The effects during multiple dosing were generally greater than those after a single dose and appeared to follow a more consistent trend. This observation, together with those for the plasma level data on the eighth day, illustrate the importance of performing multiple-dose studies in assessing beta-blocking drugs.