Direct measurement of propranolol bioavailability during accumulation to steady-state

Trigeminovascular effects of propranolol in men and women, role for sex steroids

Objective

Assess whether propranolol modulates the trigeminovascular system in both men and women.

Methods

We investigated the effect of propranolol (80 mg, 90 min after oral administration, corresponding to T_max) on the increase in dermal blood flow of the forehead skin (innervated by the trigeminal nerve) by capsaicin application (0.6 mg/mL) and electrical stimulation (0.2–1.0 mA) before and after placebo (grapefruit juice) or propranolol (oral solution diluted in grapefruit juice) in a randomized, double‐blind, placebo‐controlled cross‐over study, including healthy males (n = 10) and females on contraceptives (n = 11). Additionally, we compared our results with data from the Dutch IADB.nl prescription database by analyzing the change in triptan use after propranolol prescription in a population similar to our dermal blood flow study subjects (males and females, 20–39 years old).

Results

Dermal blood flow responses to capsaicin were significantly attenuated after propranolol, but not after placebo. When stratifying by sex, no significant changes in the capsaicin‐induced dermal blood flow were observed in females after propranolol, whereas they remained significant in males. Dermal blood flow responses to electrical stimulation were not modified in any case. In our prescription database study, after propranolol, a more pronounced decrease in triptan use was observed in male patients than in female patients.

Interpretation

Propranolol (80 mg) inhibits capsaicin‐induced increases in dermal blood flow in a sex‐dependent manner. In patients, a more pronounced decrease in triptan use is observed in males when compared with females, suggesting an interaction between propranolol and sex steroids in the modulation of the trigeminovascular system.

Extracorporeal treatment for poisoning to beta-adrenergic antagonists: systematic review and recommendations from the EXTRIP workgroup

BACKGROUND

β-adrenergic antagonists (BAAs) are used to treat cardiovascular disease such as ischemic heart disease, congestive heart failure, dysrhythmias, and hypertension. Poisoning from BAAs can lead to severe morbidity and mortality. We aimed to determine the utility of extracorporeal treatments (ECTRs) in BAAs poisoning.

METHODS

We conducted systematic reviews of the literature, screened studies, extracted data, and summarized findings following published EXTRIP methods.

RESULTS

A total of 76 studies (4 in vitro and 2 animal experiments, 1 pharmacokinetic simulation study, 37 pharmacokinetic studies on patients with end-stage kidney disease, and 32 case reports or case series) met inclusion criteria. Toxicokinetic or pharmacokinetic data were available on 334 patients (including 73 for atenolol, 54 for propranolol, and 17 for sotalol). For intermittent hemodialysis, atenolol, nadolol, practolol, and sotalol were assessed as dialyzable; acebutolol, bisoprolol, and metipranolol were assessed as moderately dialyzable; metoprolol and talinolol were considered slightly dialyzable; and betaxolol, carvedilol, labetalol, mepindolol, propranolol, and timolol were considered not dialyzable. Data were available for clinical analysis on 37 BAA poisoned patients (including 9 patients for atenolol, 9 for propranolol, and 9 for sotalol), and no reliable comparison between the ECTR cohort and historical controls treated with standard care alone could be performed. The EXTRIP workgroup recommends against using ECTR for patients severely poisoned with propranolol (strong recommendation, very low quality evidence). The workgroup offered no recommendation for ECTR in patients severely poisoned with atenolol or sotalol because of apparent balance of risks and benefits, except for impaired kidney function in which ECTR is suggested (weak recommendation, very low quality of evidence). Indications for ECTR in patients with impaired kidney function include refractory bradycardia and hypotension for atenolol or sotalol poisoning, and recurrent torsade de pointes for sotalol. Although other BAAs were considered dialyzable, clinical data were too limited to develop recommendations.

CONCLUSIONS

BAAs have different properties affecting their removal by ECTR. The EXTRIP workgroup assessed propranolol as non-dialyzable. Atenolol and sotalol were assessed as dialyzable in patients with kidney impairment, and the workgroup suggests ECTR in patients severely poisoned with these drugs when aforementioned indications are present.

Effects of Propranolol on Neurodevelopmental Outcomes in Patients with Infantile Hemangioma: A Case-Control Study

Background

The aim of this study was to examine whether oral propranolol has any effect on neurodevelopment outcomes in young children with problematic infantile hemangiomas (IHs).

Methods

Thirty-six children with a diagnosis of problematic IH who were treated with oral propranolol were compared with 34 healthy children with no history of propranolol therapy. Patients received propranolol therapy for at least 3 months. Gesell developmental schedules (GDS) were used to evaluate neurodevelopment outcomes in the two groups. The scores of each GDS domain were compared between the two groups.

Results

There were no significant differences in developmental quotient (DQ) values for any of the five domains between the patients and healthy controls (P < 0.05). Multiple stepwise regression analyses showed that none of the domains in the control group were influenced by the children's gender or age (P < 0.05). In addition, we found that gender, age at the initiation of therapy, age at the time of the neurodevelopment test, and treatment duration had no effect on any domain of the GDS in the patient group (P > 0.05).

Conclusion

Propranolol has no obvious effect on neurodevelopmental outcomes in children. Early treatment and treatment duration had no negative effect on central nervous system (CNS) development.

Compilation of Pharmacokinetic Parameters of Beta-Adrenergic Blocking Agents

After defining the drug class of β-adrenergic blocking agents, general aspects for clinical use of β-blockers are discussed, namely absorption, distribution, metabolism, elimination, correlation between clinical response and drug disposition, drug interactions, and influence of disease on drug response and disposition. Pharmacokinetic data for the following β-blockers were retrieved from the literature: acebutolol, alprenolol, atenolol, labetalol, metoprolol, nadolol oxprenolol, penbutolol, pindolol, practolol, propranolol sotalol, talinolol, timolol, and tolamalol. Those pharmacokinetic parameters which were not listed in the original literature were calculated. The use of pharmacokinetic parameters of β-blockers for clinical application is discussed.

Propranolol and central nervous system function: potential implications for paediatric patients with infantile haemangiomas

Given its improved safety profile compared with systemic corticosteroids, propranolol has become the mainstay treatment of infantile haemangioma (IH) worldwide. There is evidence, mainly from adult volunteer studies, that propranolol use is associated with central nervous system (CNS) effects. Impairment to short- and long-term memory, psychomotor function, sleep quality and mood with relatively low doses and durations of treatment have been reported. The exact magnitude of CNS effects resulting from propranolol use, especially in the early developmental stages and for prolonged periods of use, is not currently known. These effects may not be readily recognizable and require specialized assessment of cognitive function not routinely performed. Furthermore, there may be a delay between exposure and cognitive defects. The evidence to date provides a strong rationale to proceed with caution when prescribing propranolol for IH: treatment should be used only when indicated (in the presence of ulceration, impairment of a vital function or risk of permanent disfigurement) and for a limited duration, and the benefits of treatment should be weighed carefully against potential adverse events before treatment is initiated. This narrative review describes the evidence for an effect of propranolol use on CNS function from volunteer and patient studies, including IH.

Inferior frontal gyrus preserves working memory and emotional learning under conditions of impaired noradrenergic signaling

Compensation has been widely applied to explain neuroimaging findings in neuropsychiatric patients. Functional compensation is often invoked when patients display equal performance and increased neural activity in comparison to healthy controls. According to the compensatory hypothesis increased activity allows the brain to maintain cognitive performance despite underlying neuropathological changes. Due to methodological and pathology-related issues, however, the functional relevance of the increased activity and the specific brain regions involved in the compensatory response remain unclear. An experimental approach that allows a transient induction of compensatory responses in the healthy brain could help to overcome these issues. To this end we used the non-selective beta-blocker propranolol to pharmacologically induce sub-optimal noradrenergic signaling in healthy participants. In two independent functional MRI (fMRI) experiments participants received either placebo or propranolol before they underwent a cognitive challenge (Experiment 1: working memory; Experiment 2: emotional learning: Pavlovian fear conditioning). In Experiment 1 propranolol had no effects on working memory performance, but evoked stronger activity in the left inferior frontal gyrus (IFG). In Experiment 2 propranolol produced no effects on emotional memory formation, but evoked stronger activity in the right IFG. The present finding that sub-optimal beta-adrenergic signaling did not disrupt performance and concomitantly increased IFG activity is consistent with, and extends, current perspectives on functional compensation. Together, our findings suggest that under conditions of impaired noradrenergic signaling, heightened activity in brain regions located within the cognitive control network, particularly the IFG, may reflect compensatory operations subserving the maintenance of behavioral performance.

Understanding the pharmacokinetics of anxiolytic drugs

INTRODUCTION

Anxiety disorders are considered the most common mental disorders and they can increase the risk for comorbid mood and substance use disorders, significantly contributing to the global burden of disease. For this reason, anxiolytics are the most prescribed psychoactive drugs, particularly in the Western world.

AREAS COVERED

This review aims to analyze pharmacokinetic profile, plasma level variations so as the metabolism, interactions and possible relation to clinical effect of several drugs which are used primarily as anxiolytics. The drugs analyzed include benzodiazepines, anticonvulsants (pregabalin, gabapentin), buspirone, β-blockers and antihistamines (hydroxyzine). Regarding the most frequently used anxiolytic benzodiazepines, data on alprazolam, bromazepam, chlordesmethyldiazepam, chlordiazepoxide, clotiazepam, diazepam, etizolam, lorazepam, oxazepam, prazepam and clonazepam have been detailed.

EXPERT OPINION

There is a need for a more balanced assessment of the benefits and risks associated with benzodiazepine use, particularly considering pharmacokinetic profile of the drugs to ensure that patients, who would truly benefit from these agents, are not denied appropriate treatment. An optimal pharmacological approach involving an integrative pharmacokinetic and pharmacodynamic optimization strategy would ensure better treatment and personalization of anxiety disorders. So it would be desirable for the development of new anxiolytic drug(s) that are more selective, fast acting and free from the unwanted effects associated with the traditional benzodiazepines as tolerance or dependence.

Human amygdala reactivity is diminished by the β-noradrenergic antagonist propranolol

BACKGROUND

Animal models of anxiety disorders emphasize the crucial role of locus ceruleus-noradrenergic (norepinephrine, NE) signaling, the basolateral amygdala (BLA) and their interactions in the expression of anxiety-like behavioral responses to stress. Despite clinical evidence for the efficacy of a β-noradrenergic receptor blockade with propranolol in the alleviation of anxiety symptoms and the secondary prevention of post traumatic stress disorder, preclinical evidence for a β-noradrenergic modulation of BLA activity in humans is missing.

METHOD

We combined functional magnetic resonance imaging in healthy volunteers with probabilistic mapping of intra-amygdalar responses to fearful, neutral and happy facial expressions to test the hypothesis that a β-noradrenergic receptor blockade with propranolol would inactivate the BLA.

RESULTS

Consistent with our a priori hypothesis, propranolol diminished BLA responses to facial expressions, independent of their emotional valence. The absence of activity changes in probabilistically defined visual control regions underscores the specific action of propranolol in the BLA.

CONCLUSIONS

Our findings provide the missing link between the anxiolytic potential of propranolol and the biological basis of β-noradrenergic activation in the human BLA as a key target for the pharmacological inhibition of anxiety neurocircuitry. Moreover, our findings add to emerging evidence that NE modulates both the reactivity (sensitivity) and the operating characteristics (specificity) of the BLA via β-noradrenergic receptors.

Acute and chronic hemodynamic changes after propranolol in patients with cirrhosis under primary and secondary prophylaxis of variceal bleeding: a pilot study

BACKGROUND AND AIM

Prophylactic treatment of variceal bleeding in cirrhotic patients with beta-blockers is effective in only some patients. Our aim was to determine whether the response of the hepatic venous pressure gradient (HVPG) to the intravenous administration of propranolol predicts the response after chronic oral propranolol treatment.

PATIENTS AND METHODS

We included prospectively cirrhotic patients with esophageal varices under primary prophylaxis (PP) and secondary prophylaxis (SP). The HVPG was measured at baseline and after a propranolol bolus (0.15 mg/kg intravenous). A patient was considered a good-responder if HVPG decreased to 12 mmHg or 20% from baseline. Patients then received oral propranolol (heart rate titrated). Poor-responders under SP were also included in a variceal band ligation program. After at least 3 months, a second hemodynamic study was conducted.

RESULTS

Fifty-six patients were included (36 SP and 20 PP). Response rate was similar (32.1 and 41.9%, P=0.7) and the Pearson's correlation coefficient was 0.61 (P=0.001). In 81.4% patients, the first study predicted the response status of the second. Six patients rebled on follow-up between the studies, all of them were poor responders to intravenous propranolol.

CONCLUSION

A single hemodynamic study using intravenous propranolol seems to predict chronic response to propranolol.

A model to study intestinal and hepatic metabolism of propranolol in the dog

A model to investigate hepatic drug uptake and metabolism in the dog was developed for this study. Catheters were placed in the portal and hepatic veins during exploratory laparotomy to collect pre- and posthepatic blood samples at defined intervals. Drug concentrations in the portal vein were taken to reflect intestinal uptake and metabolism of an p.o. administered drug (propranolol), while differences in drug and metabolite concentrations between portal and hepatic veins reflected hepatic uptake and metabolism. A significant difference in propranolol concentration between hepatic and portal veins confirmed a high hepatic extraction of this therapeutic agent in the dog. This technically uncomplicated model may be used experimentally or clinically to determine hepatic function and metabolism of drugs that may be administered during anaesthesia and surgery.

The effect of propranolol in malay patients with liver cirrhosis - a pharmacodynamic evaluation

The pharmacodynamics of propranolol were studied in 12 cirrhotic Malay patients. Fifteen healthy Malay volunteers were selected and several clinical parameters were obtained. The effects of three doses of propranolol in reducing the heart rate (HR) of these patients were observed to be significantly different. These differences were seen at dosing of 10 mg vs 20 mg and 10 mg vs 30 mg (P<0.001 and P<0.01, respectively). However, no significant difference was seen for doses between 20 mg vs 30 mg. At 20 mg the reduction in HR is more pronounced than the effect seen with the other two doses. The effects of propranolol in reducing V(max) and V(mean) of portal vein blood flow were found to be not significant at doses of 10 mg vs 30 mg, but between 10 mg vs 20 mg and 20 mg vs 30 mg there was significant difference (P<0.05 and P<0.01, respectively). Reduction of V(max) of more than 10% of baseline was achieved at doses of 10 mg and 20 mg. However, at a dose of 20 mg a more significant reduction was observed than at a dose of 10 mg. Dose-concentration-effect relationship was seen to be significantly different between HR reduction and propranolol concentration of the three steady-state levels (P<0.001). Similar results were obtained with V(max) and V(mean). The V(max) was found to be a reliable parameter for the assessment of therapeutic effect of the drugs in conferring changes in portal haemodynamics of liver cirrhotic patients. Further, Child-Pugh score is thought to be an important supporting factor in evaluating prognosis. The results of this pharmacodynamics studies suggest that the optimal dose of propranolol may be 20 mg propranolol thrice daily for cirrhotic Malay patients.

Beta-adrenergic blockers in systemic hypertension: pharmacokinetic considerations related to the current guidelines

Beta-adrenergic blockade has provided one of the major pharmacotherapeutic advances of the 20th century. Beta-blockers are first-line drugs for the management of systemic hypertension, used alone and in combination with other antihypertensive agents. Drugs in the beta-blocking class have the common property of blocking the binding of catecholamines to beta-adrenergic receptor sites; however, there are significant pharmacodynamic and pharmacokinetic differences between the individual agents that are of clinical importance. Among these differences are the completeness of gastrointestinal absorption, the degree of hepatic first-pass metabolism, lipid solubility, protein binding, brain penetration, concentration within the cardiac tissue, rate of hepatic biotransformation, and renal clearance of drug and/or metabolites. Long-acting formulations of existing beta-blockers are currently in use, and ultra-short-acting agents are also available. Age, race, cigarette smoking and concomitant drug therapy can also influence the pharmacokinetics of beta-blocking drugs. The wide interpatient variability in plasma drug concentrations observed with beta-blockers makes this parameter unreliable in routine patient management. Despite the pharmacokinetic differences among beta-blockers, these drugs should always be titrated to achieve the desired individual patient response.

Modulation by dietary salt of verapamil disposition in humans

BACKGROUND

The intestine is an increasingly well-recognized site of first-pass drug metabolism. In this study, we determined the influence of dietary salt on the steady-state disposition of verapamil, a drug that undergoes extensive first-pass metabolism.

METHODS AND RESULTS

Eight normal volunteers received 120 mg of racemic verapamil orally twice a day for 21 days. The disposition kinetics of verapamil enantiomers were determined after coadministration of intravenous deuterated verapamil with the morning oral dose on days 7, 14, and 21. Each study day was preceded by 7 days on a fixed-salt diet: in 5 subjects, the initial study was conducted during a low-salt (10 mEq/d) diet, the second study during a high-salt (400 mEq/d) diet, and the third during a low-salt diet, whereas in the other 3 subjects, the sequence of diets was reversed. Plasma concentrations of both unlabeled enantiomers (ie, from oral therapy) were significantly (P<0.05) lower during the high-salt phase (eg, mean area under the time-concentration curve [0 to 12 hours] for S-verapamil: 7765+/-2591 ng. min. mL-1 [high salt] versus 12 514+/-3527 ng. min. mL-1 [low salt], P<0.05). Peak plasma concentrations were significantly lower and the extent of PR interval prolongation significantly blunted with the high-salt diet. In contrast, data with labeled drug (ie, reflecting the intravenous route) were nearly identical for the 2 diets.

CONCLUSIONS

These data indicate that a clinically important component of presystemic drug disposition occurs at the prehepatic (presumably intestinal) level and is sensitive to dietary salt.

Pharmacokinetics and pharmacodynamics of propranolol in hypertensive patients after sublingual administration: systemic availability

The bioavailability of propranolol depends on the degree of liver metabolism. Orally but not intravenously administered propranolol is heavily metabolized. In the present study we assessed the pharmacokinetics and pharmacodynamics of sublingual propranolol. Fourteen severely hypertensive patients (diastolic blood pressure (DBP) > or = 115 mmHg), aged 40 to 66 years, were randomly chosen to receive a single dose of 40 mg propranolol hydrochloride by sublingual or peroral administration. Systolic (SBP) and diastolic (DBP) blood pressures, heart rate (HR) for pharmacodynamics and blood samples for noncompartmental pharmacokinetics were obtained at baseline and at 10, 20, 30, 60 and 120 min after the single dose. Significant reductions in BP and HR were obtained, but differences in these parameters were not observed when sublingual and peroral administrations were compared as follows: SBP (17 vs 18%, P = NS), DBP (14 vs 8%, P = NS) and HR (22 vs 28%, P = NS), respectively. The pharmacokinetic parameters obtained after sublingual or peroral drug administration were: peak plasma concentration (CMAX): 147 +/- 72 vs 41 +/- 12 ng/ml, P < 0.05; time to reach CMAX (TMAX): 34 +/- 18 vs 52 +/- 11 min, P < 0.05; biological half-life (t1/2b): 0.91 +/- 0.54 vs 2.41 +/- 1.16 h, P < 0.05; area under the curve (AUCT): 245 +/- 134 vs 79 +/- 54 ng h-1 ml-1, P < 0.05; total body clearance (CLT/F): 44 +/- 23 vs 26 +/- 12 ml min-1 kg-1, P = NS. Systemic availability measured by the AUCT ratio indicates that extension of bioavailability was increased 3 times by the sublingual route. Mouth paresthesia was the main adverse effect observed after sublingual administration. Sublingual propranolol administration showed a better pharmacokinetic profile and this route of administration may be an alternative for intravenous or oral administration.

(S)-4'-hydroxypropranolol causes product inhibition and dose-dependent bioavailability of propranolol enantiomers in the isolated perfused rat liver and in rat liver microsomes

1. Previous evidence suggests that the dose-dependent bioavailability of racemic propranolol may be partly due to product inhibition. We have examined this further by studying the individual enantiomers of propranolol in the perfused rat liver (IPRL) and in rat liver microsomes. 2. In recirculating IPRL experiments, (R)-propranolol (n = 7) or (S)-propranolol (n = 4) were infused at rates of 75, 150 and 231 nmol/min for three sequential 36-min phases. In single-pass experiments, (R)-propranolol (n = 4) or (S)-propranolol (n = 4) were administered at rates of 80, 136 and 239 nmol/min for three sequential 30-min phases. Steady-state bioavailability increased 10-20-fold over this dose range with both enantiomers in both recirculating and single-pass experiments. At the higher administration rates of (S)-propranolol, bioavailability in recirculating experiments was significantly greater than that in single-pass experiments, whereas there was no significant difference for (R)-propranolol. This suggests product inhibition of (S)- but not (R)-propranolol metabolism. 3. Of the metabolites examined, racemic 4'-hydroxypropranolol (4-OHP) inhibited the formation of 4-OHP, 5'-hydroxypropranolol (5-OHP) and desisopropylpropranolol (DIP) from (S)-propranolol and (R)-propranolol in microsomal studies (IC50 20 microM). Tissue levels of (S)-4-OHP in recirculating experiments (28.0 microM) at the highest dose (239 nmol/ min) of (S)-propranolol were greater than its IC50 of 20 microM, suggesting that 4-OHP is the inhibiting metabolite in the intact liver. The absence of evidence for product inhibition with (R)-propranolol in perfused livers suggests that (S)-4-OHP inhibits 4-hydroxylation of each isomer but (R)-4-OHP does not. 4. We conclude that in the recirculating IPRL, product inhibition of propranolol metabolism is evident with the (S)-isomer, but not he (R)-isomer, and that the inhibiting metabolite is (S)-4-OHP.

Product inhibition and dose-dependent bioavailability of propranolol in the isolated perfused rat liver preparation

We investigated in the isolated perfused rat liver (IPRL) whether product inhibition of metabolism contributes to the dose-dependent bioavailability of propranolol, a drug with a high, but saturable, hepatic first-pass effect. (+/-)-Propranolol was infused in the IPRL, using a recirculating design, for three 36-min periods (n = 9). Mean steady-state reservoir, i.e. hepatic inflow concentrations (Cin), were 4.97, 10.4, and 20.4 microM, respectively. Mean reservoir concentrations of the metabolites 4'-hydroxypropranolol, 5'-hydroxypropranolol, N-desisopropylpropranolol, and naphthoxylactic acid (NLA), a major side-chain-oxidation metabolite, increased disproportionately with propranolol dose, but their production rate did not reach steady state. In separate experiments (n = 4), perfusate containing 7.1, 12.8, and 21.6 microM (+/-)-propranolol, corresponding to administration rates of 114, 205, and 346 nmol/min, respectively, was passed through the liver for 30 min each using a single-pass design. The bioavailability (hepatic outflow concentration/Cin) of propranolol increased with Cin from 0.012 to 0.150 to 0.288 in the recirculating IPRL. In the single-pass IPRL the increase (0.0077 in 0.0669 to 0.136) was significantly less (P < 0.001). The greater bioavailability of propranolol in recirculating experiments was attributed to product inhibition since metabolites do not accumulate with the single-pass design. NLA did not appear to be the inhibiting metabolite because in further single-pass experiments with propranolol Cin of 21.6 microM the presence of NLA (21.6 microM) in perfusate had no effect on propranolol bioavailability (n = 7) compared with control experiments (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Enzymatic basis for the non-linearity of hepatic elimination of propranolol in the isolated perfused rat liver

Propranolol (PL) metabolism was studied in the isolated perfused rat liver under single-pass and steady-state conditions. An attempt was made to predict the data observed in the isolated rat liver perfusion at PL infusion rates of 89-1317 nmol/min using the microsomal kinetic parameters obtained in our previous paper (Ishida et al., Biochem Pharmacol 43: 2489-2492, 1992) and the unbound PL fractions in rat liver microsomes and the perfusion medium. The values of kinetic parameters obtained in rat liver microsomes were corrected for the whole liver. Two groups of cytochrome P450 isozymes having high (Km < 0.5 microM)- and low (Km > 20 microM)-affinities participate in the metabolism of PL and sudan III pretreatment induces the low-affinity enzymes rather than the high-affinity enzymes in control rats. Of high-affinity isozyme(s) PL 4-hydroxylase and 7-hydroxylase made a major contribution to the overall activity, while for low-affinity isozymes PL 4-hydroxylase and N-desisopropylase did. A nonlinear relationship between the PL concentrations entering and leaving the liver was predicted from these corrected kinetic parameters using the venous equilibrium model. The outflow concentrations and the metabolic rates of PL for the predicted curves were over-estimated at higher inflow PL concentrations and under-estimated at higher substrate concentrations, respectively. On the other hand, the prediction for them was successfully carried out for the livers whose intrinsic clearance was altered due to the induction of low-affinity enzymes in PL metabolism by sudan III pretreatment. The outflow rates of 4-hydroxypropranolol showed a downward curvature at lower substrate concentrations, followed a linear rise in the livers from control rats, while the outflow rates of 5- and 7-hydroxypropranolol exhibited their respective limiting values. The outflow rates of 4-hydroxypropranolol and N-desisopropylpropranolol were enhanced markedly with increasing the outflow unbound concentration of PL by sudan III pretreatment. These results indicate that non-linear PL first-pass metabolism is due to the saturation of the reactions for the high-affinity enzymes among enzymes engaging in PL ring hydroxylations.

Propranolol disposition in the rat: variation in hepatic extraction with unbound drug fraction

The plasma protein binding of propranolol has been described as nonrestrictive for its hepatic extraction to explain the observation that propranolol is efficiently removed by the liver, in spite of extensive protein binding. The present study was designed to examine the relationship between propranolol protein binding, metabolism by isolated hepatocytes, and extraction by the isolated perfused rat liver. In isolated hepatocytes, the intrinsic clearance of free drug increased three- to fourfold as albumin and alpha 1-acid glycoprotein (AAG) concentrations increased, suggesting that albumin and AAG facilitate the elimination of propranolol by hepatocytes. In the isolated perfused liver, propranolol extraction was almost complete (E = 0.996) in the absence of albumin and AAG. With 40 g/L of albumin and 2 g/L of AAG in the perfusate, the free fraction of propranolol decreased to 0.031, but extraction remained high (E = 0.960). With 40 g/L of albumin and 10 g/L of AAG in the perfusate, the free fraction further decreased to 0.014 and extraction dropped sharply (E = 0.820). The observed relationship between propranolol extraction and the free fraction of propranolol was in good agreement with that predicted using estimates of intrinsic clearance measured in isolated hepatocytes suspensions. These data indicate that propranolol extraction is sensitive to changes in binding at very low free fraction values and suggest a facilitation of propranolol clearance by albumin and AAG.

Pharmacokinetic optimisation of therapy with beta-adrenergic blocking agents

beta-Adrenergic blockade has provided one of the major pharmacotherapeutic advances of this century. The drugs in this class have the common property of blocking the binding of catecholamines to beta-adrenergic receptor sites; however, there are pharmacodynamic and pharmacokinetic differences between the individual agents which are of clinical importance. Among these differences are the completeness of gastrointestinal absorption, degree of hepatic first-pass metabolism, lipid solubility, protein binding, brain penetration, concentration within cardiac tissue, rate of hepatic biotransformation, and renal clearance of drug and/or metabolites. Long-acting formulations of existing beta-blockers are currently in use, and ultrashort-acting agents are also available. The pharmacokinetics of beta-blocking drugs can also be influenced by race, age, cigarette smoking and concomitant drug therapy. The wide interpatient variability in plasma drug concentration observed with beta-blockers makes this parameter unreliable in routine patient management. Despite the pharmacokinetic differences among the beta-blockers, these drugs should always be titrated in the individual patient to achieve the desired clinical response.

Isolated perfused cirrhotic human liver obtained from liver transplant patients: a feasibility study

Cirrhotic livers obtained from eight patients who underwent orthotopic liver transplantation were perfused through the portal vein and hepatic artery in a closed recycling system for periods ranging from 2 to 7 hr. An average perfusion flow of 451 ml/min was used, with about 80% coming from the portal vein and 20% from the hepatic artery. The livers appeared to remain viable as assessed by gross appearance, stable portal vein and hepatic artery pressures, oxygen consumption and bile production. The extraction ratio of indocyanine green by the perfused livers averaged 0.098 (range = 0.023 to 0.168); that of propranolol averaged 0.445 (range = 0.126 to 0.813). Using the multiple-indicator dilution-curve method, shunts greater than 15 microns in diameter were demonstrated between the portal and hepatic veins in six of eight cases, whereas shunts from the hepatic artery to the hepatic veins were absent. Perfusion of human livers obtained during hepatic transplantation is a fairly simple procedure that will allow researchers to gain new insights into cirrhosis in humans.

Pharmacokinetics and metabolism of oral doses of a 4'-methylthio derivative of propranolol in man

1. The objective of this study was to determine the oral dose pharmacokinetics and metabolism of 4'-methylthiopropranolol (MTP) in man and compare the results with observations for propranolol in previous studies. 2. Three women and five men received single oral doses of MTP, dose range 5-320 mg. Plasma concentration of MTP over time were measured by gas chromatography-mass spectrometry. MTP metabolites in urine were identified by comparative high-performance liquid chromatographic (HPLC) retention times and mass spectrometry with previously characterized reference compounds and quantified by HPLC. 3. The oral clearance of MTP of 1.2-1.4 l/min for the 80, 160 and 320 mg doses was about one third of the value previously reported for propranolol. The half-life for MTP (3.3-4.1 h) was, however, similar to that of propranolol. In contrast to propranolol, the peak (2.5 h) plasma concentrations of MTP increased linearly with dose (5-320 mg). 4. The oral clearance for MTP was about 2-fold higher in the men than in the women (P less than 0.01). In addition, the clearance of the (S)-enantiomer was about 30% higher than that of the (R)-enantiomer (P less than 0.05), which was a reversal of that seen with propranolol. 5. The metabolism of MTP resulted mainly in sulphur oxidation to sulphoxide and sulphone metabolites. These two metabolites accounted for 75% of the MTP dose. This switching from aromatic carbon oxidation for propranolol to sulphur oxidation for MTP is proposed as the basis of the lower oral clearance of MTP. 6. This study also demonstrated higher plasma binding of MTP (unbound fraction 3.7%) than of propranolol (10.5%; P less than 0.01), a factor probably contributing to decreased tissue distribution of MTP.

Enzyme induction and inhibition

The rate and extent of drug metabolism significantly influences drug effect. Enzyme induction by increasing the metabolism of drugs may result in important drug interactions. Other implications of enzyme induction include alterations in the metabolism of endogenous substrates, vitamins and activity of extrahepatic enzyme systems. Similarly a wide range of drugs may produce clinically significant drug interactions following enzyme inhibition. Assessment of enzyme induction and inhibition in man involves diverse methods including the use of model drugs.

Erythrocytes as barriers for drug elimination in the isolated rat liver. II. Propranolol

The potential of erythrocytes (RBC) to serve as "barriers" of hepatic elimination of propranolol, a drug with rapid equilibration in blood, was studied in rats under two conditions: (I) the drug was preequilibrated in blood before infusion into the liver, and (II) the drug was directly infused into the liver. The mean fractions of dose escaping elimination during each pass under conditions I and II were 0.0561 +/- 0.040 and 0.0290 +/- 0.024, respectively (P less than 0.02). Contrary to the early study on doxorubicin, most drug molecules in RBC were found to be available for elimination. Implications of the present findings in the prediction of hepatic first-pass effect after oral administration, on the basis of intravenous data, are discussed. Marked underestimation of oral bioavailability of propranolol in humans is consistent with the RBC "barrier" effect hypothesis.

The effects of encainide versus diltiazem on the oxidative metabolic pathways of antipyrine

The effects of diltiazem and encainide on the pharmacokinetics and metabolism of antipyrine were compared in nine healthy male volunteers. Diltiazem 90 mg every 8 hours for 5 days decreased the oral clearance of antipyrine from 2.34 to 1.86 L/hour (p less than 0.05) and increased half-life from 12.7 to 15.9 hours (p less than 0.05). Diltiazem reduced the formation rate constants for 3-hydroxymethylantipyrine by 27% (p less than 0.05) and 4-hydroxyantipyrine by 37% (p less than 0.05). There was also a 21% reduction in the formation rate constant for norantipyrine (0.05 less than p less than 0.10). Encainide 25 mg every 8 hours for 5 days had no apparent effect on the oral clearance or half-life of antipyrine, or on the formation rate constants for metabolites of antipyrine. In contrast to a previously published report in rats, encainide, unlike diltiazem, does not inhibit the oxidative metabolism of antipyrine in humans.

High-performance liquid chromatographic determination of beta-adrenoceptor blocking agents in body fluids

Several reports have been published reviewing high-performance liquid chromatographic (HPLC) methods for the determination of beta-adrenoceptor blocking agents (beta-blockers) in biological materials (Flouvat et al., 1981; Mehta, 1983; Marko and Soltés, 1984; Ahnoff et al., 1985; Tkaczyková and Safarík, 1987). Of these, the paper by Mehta (1983) briefly summarizes the interrelationship between physiocochemical properties of beta-blockers with prechromatographic treatment of biological samples, as well as with the HPLC methods used for the determination of 12 beta-adrenoceptor blocking drugs. The work by Ahnoff et al. (1985) concerning the monitoring of cardiovascular drugs also deals with HPLC assays of 18 beta-blockers in plasma. The Appendix to this report presents the great majority of HPLC methods for determining 30 beta-blockers in various body fluids. HPLC methods providing resolution and determination of individual beta-blocker enantiomers have not been included since this topic is being covered by Walle and Walle (1989). The Appendix is just a guide to the methods reviewed for the HPLC determination of parent beta-blockers as well as some of their metabolites co-assayed in various body fluids. It does not include details such as the internal standard, recovery, setting of the detector, limit of determination, etc., given in the individual methods listed. The isolation technique of the drug(s) from the given body fluid represents the main step in the sample work-up procedure. Along with this information, only the type of the HPLC column packing and the detection principle used by each method's developers are given.

Pharmacodynamic and pharmacokinetic study of propranolol in patients with cirrhosis and portal hypertension

1. The aim of this study was to investigate the pharmacokinetics and the beta-adrenoceptor blocking activity according to time of conventional (C) and long acting (LA) propranolol in cirrhotic patients. Twenty-four patients with alcoholic cirrhosis and oesophageal varices were randomly assigned to receive either 160 mg C propranolol, 160 mg LA propranolol or placebo acutely and then following repeated administration (acute and chronic phases). Thereafter propranolol concentrations and beta-adrenoceptor blockade (resting and exercise heart rates) were measured at different intervals. 2. The Cmax was significantly higher with C propranolol in both phases. The time of Cmax was significantly later with LA propranolol in both phases. The AUCs were significantly higher after chronic administration with both formulations of propranolol. 3. The exercise peaks of beta-adrenoceptor blockade were similar between the two formulations and between the two phases of administration of propranolol. The duration of effective beta-adrenoceptor blockade was significantly longer in the chronic phase and seemed to be longer with LA than with C propranolol although this was not significant (72 +/- 31 vs 48 +/- 18 h, respectively). 4. There was a significant correlation between the log propranolol concentration and exercise heart rate but not with resting heart rate. No correlation could be demonstrated between pharmacological data and the Child Pugh score. 5. We conclude that in cirrhotic patients exercise testing was a reliable method in the assessment of beta-adrenoceptor blockade. Pharmacology of propranolol was found to be different according to the formulation or to the phase of administration.

Metoprolol-controlled release, zero order kinetics

Metoprolol CR/ZOK (controlled release, zero order kinetics) is a new formulation of an extensively used beta 1-selective, beta-adrenoceptor blocking drug, (beta 1-blocker), designed to provide continuous, even, plasma concentrations in the therapeutic range. It should, therefore, provide an effective well-tolerated treatment for hypertension and angina pectoris and for use in secondary prevention following a myocardial infarct. The purpose of this review is to consider the need for such a formulation, to describe its pharmaceutical development, review its pharmacology and assess its efficacy and tolerability compared with other available agents.

Saturable first-pass kinetics of propranolol

Reduced bioavailability (F) due to hepatic first-pass extraction of an oral dose (D) is a well-known pharmacokinetic phenomenon. An integrated solution for Michaelis-Menten kinetics of the first-pass effect is derived from the maximal metabolic rate (Vm), volume of distribution (Vd), first order absorption rate constant (ka), Michaelis constant (Km), and liver blood flow (Q). F = 1 - VmVd/kaD ln (1 + kaD/QKm) This equation for single dosage can also be extended to steady state kinetics after multiple dosing in which the amount of a drug present in the hepatic circulation is considered. According to the literature, the bioavailability of a single 80 mg oral dose of propranolol (F = 0.22) increases after multiple doses Fss = 0.36). Based on the first pass equations for single dosage and multiple dosing, the maximal metabolic rate (Vm = 0.043 mg l-1 h-1) corresponding to 310 mg per day and the Michaelis constant (Km = 0.10 mg/l) were calculated for propranolol. Incorporation of nonlinear plasma protein binding in this concept may explain the lack of threshold phenomenon for a single dose of less than 40 mg propranolol. Zero order absorption kinetics could explain why cumulation kinetics seem linear even at an excessive dosage of 960 mg propranolol per day. From these derivations it may be concluded that multiple dosing, increase in plasma protein binding, high absorption rate, and increased portal venous blood flow will increase bioavailability, whereas slow release formulations, fractional drug dosage, and saturable absorption kinetics will decrease bioavailability of first-pass drugs like propranolol.

Initial dosage selection of antiarrhythmic therapy

The success or failure of antiarrhythmic drug treatment depends, in part, on the selection of the initial dosage. Too low a dosage can lead to unnecessary (and frequently life-endangering) delays in achievement of arrhythmia suppression. Conversely, an excessively high dosage can lead to intolerable toxicity and cessation of treatment. The recommended approach to therapy is to begin with a relatively low dosage, i.e., the lowest dosage with a reasonable chance of producing a favorable response, and titrating the dose upward as needed. Dose titration should be guided by clinical response and, when appropriate, concentrations of the drug and any active metabolites in the plasma. In situations frequently encountered in practice, however, the initial dosage must be modified because of interindividual differences in drug disposition. These changes in drug pharmacokinetics can arise from a variety of factors, including disease processes (e.g., congestive heart failure, cirrhosis and renal failure), concomitant medications (e.g., hepatic enzyme inducers such as phenytoin and inhibitors such as amiodarone), drug formulation, protein binding and inherited drug metabolism capacity. Knowledge of these factors can help the clinician to avoid potential pitfalls in initial dosage selection and can enhance the changes of successful drug treatment of arrhythmias.

Nonlinear accumulation of propranolol enantiomers

The accumulation of (+)- and (-)-propranolol was investigated in nine subjects who received 160 mg of racemic propranolol as a single dose and then once daily for 7 days. The serum concentrations of propranolol enantiomers were measured by h.p.l.c. using a novel chiral stationary phase allowing direct resolution of underivatized propranolol. The (+)-propranolol AUC increased from 412 +/- 223 ng ml-1 h after single doses (0-infinity) to 584 +/- 279 ng ml-1 h at steady-state (0-24 h) (P less than 0.05). Similarly, (-)-propranolol AUC increased from 609 +/- 304 to 777 +/- 370 ng ml-1 h (P less than 0.05). The AUC ratio (-)/(+) was 1.52 +/- 0.36 and 1.32 +/- 0.17 after single doses and steady-state, respectively (P greater than 0.05). Therefore, nonlinear accumulation occurs with both enantiomers although there is a trend for the (-)/(+) ratio to decrease at steady-state.

The assessment of bioavailability in the presence of nonlinear elimination

The simultaneous administration of an oral dose and intravenous tracer dose, as a method to determine bioavailability, was examined by means of computer simulation for drugs exhibiting Michaelis-Menten type elimination. A physiological pharmacokinetic model parameterized for man and including first-order absorption and elimination solely from the liver was employed. This tracer method provided good estimates of the true availability, with an error of 6% or less, over a wide range of dosing and dispositional conditions. Poorer estimates were noted when large doses of drugs with very short half-lives were considered. This poor performance was improved by administering the intravenous tracer at some time after the oral dose but an a priori basis for establishing this time was not apparent. The tracer method, therefore, appears to be a robust means of assessing, in man, oral bioavailability in the presence of Michaelis-Menten type elimination for drugs characterized by the general properties of the physiological model employed and with half-lives in excess of approximately 40 min. These findings together with the statistical power and simplicity of performance of the tracer method indicate that it is a valid technique for the assessment of bioavailability under a wide range of kinetic conditions.

Pharmacokinetics of indoramin and its 6-hydroxylated metabolite after repeated oral dosing

The pharmacokinetics of indoramin and its active 6-hydroxylated metabolite have been studied in healthy male volunteers after repeated oral dosing with 37.5 mg twice daily for 2 weeks. Plasma concentrations of indoramin accumulated, on average, three to four-fold above those anticipated on the basis of the kinetics after the first dose, though steady state was achieved by the end of the first week and no further increase was observed after 2 weeks. The degree of accumulation was consistent between subjects, with a highly significant (p less than 0.001) correlation between the concentration 2 h after a single dose and the average steady-state concentration. Possible explanations for the accumulation of indoramin are discussed. Plasma concentrations of 6-hydroxyindoramin, in contrast, did not accumulate on multiple dosing. At steady state, concentrations of the metabolite, as represented by the AUC0-8h, were approximately 30-40 per cent of those of the unchanged drug. Since the two compounds are approximately equipotent the metabolite may accounts for 25 per cent of the hypotensive activity of indoramin during a typical clinical regime of 37.5 mg twice daily.

Systemic and hepatic hemodynamics after variceal hemorrhage: effects of propranolol and placebo

Hepatic and systemic hemodynamics were measured in 19 cirrhotic patients with variceal bleeding enrolled in a controlled trial of propranolol for the prevention of rebleeding. The patients were studied on three separate occasions. The first study was performed before randomization within 24 h of the bleeding episode, once hemodynamic stabilization had been achieved. The second study was performed after 10 days of treatment, and the third after 6 mo without rebleeding. Propranolol dosage was titrated according to blood levels. Wedged and free hepatic venous pressures and the hepatic venous pressure gradient were recorded. Hepatic blood flow and cardiac output were also measured. Before treatment, the groups of patients treated with propranolol (n = 11) or placebo (n = 8) were comparable according to clinical, biochemical, and hemodynamic parameters. After 10 days, hepatic venous pressure gradient decreased similarly in the two groups (-20% in the propranolol group, -25% in the placebo group). Cardiac output fell only in the propranolol group (-40%). Hepatic blood flow remained unchanged in either group. After 6 mo, hepatic venous pressure gradient remained lower than the values from the first (within 24 h of bleeding) study in both the propranolol group (n = 5) and the placebo group (n = 6). Our results suggest that portal pressure increases shortly after hemorrhage with a return to baseline values 10 days later, and that propranolol does not further magnify these changes. Spontaneous changes in hepatic hemodynamics after variceal hemorrhage must be taken into account when evaluating the effect of pharmacologic agents on portal pressure.

Beta-blockers in anxiety disorders

Studies evaluating the antianxiety and antipanic properties of beta-blockers do not support their routine use in treating either generalized anxiety disorder or panic disorder. The use of propranolol for anxiety disorders accompanied by physical symptoms, especially cardiovascular complaints, may be effective in some patients when combined with benzodiazepines or perhaps in some non-responders to conventional treatment. Better designed studies are needed to evaluate the exact role of beta-blocking agents in treating anxiety. The efficacy of propranolol in patients with panic disorder has not been widely researched, but preliminary results have not been encouraging. Propranolol may provide symptomatic relief in some patients with residual somatic complaints (i.e., palpitations and tachycardia), when combined with the patient's ongoing drug regimen. Because beta-blockers may induce depression, they should be used cautiously--if at all--in panic patients with concurrent depressive illness.

Disposition and availability of 5-fluorouracil prodrug 5'-deoxy-5-fluorouridine after oral administration in rats

5'-Deoxy-5-fluorouridine (dFUR) is a prodrug of 5-fluorouracil (FU) and requires metabolic activation by enzymes that are abundant in several tumors as well as in some normal tissues. 5'-Deoxy-5-fluorouridine is presently under investigation as an orally administered anticancer drug. This study examines the absorption and disposition of orally administered dFUR and its systemic availability in female Fischer rats. Animals were given an oral dose of unlabeled dFUR solution (500 mg.kg-1) and, 5 min later, an intravenous (i.v.) tracer dose of [6-3H]dFUR over a period of 1 min. The concomitant i.v. dose was given to assess the drug clearance during absorption of the oral dose. The blood concentrations of radiolabeled and unlabeled dFUR and FU were analyzed by high-pressure liquid chromatography and liquid scintillation counting. The clearance of the i.v. tracer dose of [6-3H]dFUR was 18.5 +/- 2.5 mL.kg-1.min-1 (mean +/- SD, n = 5). The oral bioavailability, calculated using the clearance of [6-3H]dFUR and the area under the blood concentration-time curve (AUC) of unlabeled dFUR, was 63.4 +/- 16.9%. Eighty to ninety percent of the absorption was completed by 8 h. The absorption rate of dFUR, analyzed by the Loo-Riegelman method, suggests that drug absorption took place in part by saturable mechanisms. The AUC of FU after the oral dose was 15-35% higher than that after i.v. injections of dFUR at the same dose. Analysis of the FU data indicates that a fraction of the dFUR dose was metabolized to FU during the presystemic first pass.

Pharmacokinetics of long acting propranolol. Implications for therapeutic use

Beta-adrenoceptor antagonists are among the most commonly prescribed classes of drugs. They are indicated for the treatment of diseases such as hypertension and angina pectoris, in which long term therapy is often required. Since many beta-adrenoceptor antagonists have short plasma elimination half-lives, divided daily dosing has often been necessary in order to provide continuous beta-blockade throughout the day. However, such multiple-dose schedules may promote patient non-compliance and failure of the prescribed regimen. Long acting propranolol is a sustained release formulation of propranolol which has been developed to maintain therapeutic plasma propranolol concentrations throughout a 24-hour period while allowing once-daily dosing. Compared with conventionally formulated propranolol, long acting propranolol has a prolonged terminal half-life (8 to 11 hours), due to slower absorption from the gut. Systemic bioavailability of long acting propranolol is 30 to 50% less than that of the conventional formulation. This difference may result from increased hepatic metabolism. Peak drug concentrations are significantly lower than following identical doses of conventional propranolol, and the time to peak drug concentrations following administration is delayed. Relatively constant plasma concentrations and clinically significant inhibition of exercise-induced tachycardia are maintained throughout a 24-hour dosing interval following once-daily long acting propranolol. Once-daily long acting propranolol is as effective as divided doses of conventional propranolol for the treatment of hypertension and angina pectoris. Efficacy also appears comparable with once-daily administration of long acting conventional beta-adrenoceptor antagonists such as atenolol and nadolol. Once-daily long acting propranolol provides clinically significant sustained beta-adrenoceptor blockade and offers the potential for improved patient compliance due to once-daily dosing. Since provision of sustained beta-adrenoceptor blockade appears to be particularly important in the treatment of angina, this may be the principal indication for which long acting propranolol has a therapeutic advantage independent of its potential to improve compliance.

Propranolol pharmacokinetics and pharmacodynamics after single doses and at steady-state

The duration and extent of cardiac beta-blockade and their relationship to propranolol pharmacokinetics were assessed in nine healthy volunteers. Each subject received 160 mg of regular propranolol (R), 160 mg of sustained-release propranolol (SR) and no drug (control), both as single doses and once daily for 7 days. After single doses and at steady-state, both products caused a decrease in exercise heart rate for at least 24 h, compared to control. The time course of effect was similar to the time course of serum propranolol concentration. The oral clearance of propranolol decreased from single doses to steady-state for both R and SR; however, the difference achieved statistical significance only for R. These changes were reflected in mean accumulation ratios (AUC steady-state 0-24 h/AUC single dose 0-infinity) of 1.49 and 1.68 for R and SR, respectively. The pharmacokinetic data are consistent with a decrease in intrinsic hepatic clearance of propranolol, leading to an increase in bioavailability at steady-state. Despite a two-fold difference in the bioavailability of R and SR, there was no difference in the area under the effect-time curve at steady-state.

Controlled-release formulations of propranolol and verapamil

The in vitro and clinical behavior of new controlled-release formulations of propranolol and verapamil are reviewed. In vitro dissolution studies have proved to be of little value in determining the clinical activity of these new dosage forms. There is a difference between the blood levels found with the new formulations and those of the reference products. The once-daily verapamil product was evaluated in black hypertensive patients with promising results and suggests that this dosage form of verapamil may be successful as monotherapy for treating this patient population.

Propranolol for the prevention of recurrent variceal hemorrhage: a controlled trial

We conducted a prospective, randomized single-blind trial of propranolol for the prevention of recurrent variceal bleeding. Seventy-nine patients shown to have variceal hemorrhage at endoscopy were included in the study within 72 hr following diagnosis. Fifty-seven patients had alcoholic cirrhosis, 10 cryptogenic cirrhosis, 6 posthepatitic cirrhosis, 4 biliary cirrhosis, 1 portal vein thrombosis without cirrhosis and 1 idiopathic portal hypertension. The severity of liver disease at inclusion was assessed according to the Pugh modification of the Child-Turcotte classification: 9 (11%) had Class A; 41 (52%) Class B, and 29 (37%) Class C disease. Patients were randomly assigned by sealed envelope to the propranolol group (42 patients) or the placebo group (37 patients). Propranolol dosage was titrated in order to produce plasma concentrations of propranolol of 50 to 150 ng per ml. beta-blockade was also confirmed by isoproterenol testing. The cumulative percentages of patients free of rebleeding 1 and 2 years after inclusion were 31 and 21% in the propranolol group, and 25 and 17% in the placebo group; both differences were not significant. Cumulative 1 and 2 years survival were also comparable: 64 and 54% in the propranolol group vs. 70 and 63% in the placebo group. There was no evidence for a therapeutic effect of propranolol after adjusting for potential confounding variables by multiple logistic regression. We conclude that propranolol is not effective for the prevention of variceal rebleeding, when administered early following the initial bleed, in cirrhotics unselected with respect to the severity of the liver disease.

Effects of nifedipine on hemodynamics and cardiac function in patients with normal left ventricular ejection fraction already treated with propranolol

The interaction between nifedipine and propranolol on cardiac hemodynamics and function was investigated in 9 patients with normal left ventricular (LV) function who were undergoing cardiac catheterization for complaints of chest pain. Only 2 patients had angiographic evidence of significant coronary artery disease but no patient had clinical evidence of ischemia during the study. All patients were pre-treated with propranolol, 30 to 320 mg/day (mean +/- standard deviation 210 +/- 122); the propranolol serum level ranged from 43 to 246 ng/ml (mean 203 +/- 62). The administration of nifedipine resulted in a decrease in blood pressure (from 94 +/- 11 to 85 +/- 13 mm Hg, p less than 0.05), increase in heart rate (from 59 +/- 6 to 65 +/- 7 beats/min, p less than 0.05), and an increase in both mean right atrial and mean pulmonary artery wedge pressures (from 8 +/- 3 to 9 +/- 3 mm Hg and from 13 +/- 3 to 14 +/- 4 mm Hg, respectively, both p less than 0.05). Cardiac index increased (from 2.3 +/- 0.3 to 2.7 +/- 0.2 liters/min/m2, p less than 0.01). Stroke volume index also increased significantly (from 39 +/- 5 to 43 +/- 6 ml/m2) and systemic vascular resistance decreased (from 1,715 +/- 369 to 1,255 +/- 271 dynes s cm-5, p less than 0.01). No significant change was noted in pulmonary vascular resistance (148 +/- 94 vs 140 +/- 62 dynes s cm-5), LV stroke work index (44 +/- 9 vs 42 +/- 10 g-m/m2), LV end-diastolic pressure (15 +/- 2 vs 16 +/- 2 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Partial metabolic clearances as determinants of the oral bioavailability of propranolol

The objective of this study was to determine the relationships between the total oral clearance of propranolol and the partial clearances through its primary metabolic pathways, i.e. glucuronidation, side-chain oxidation and ring oxidation. Seven young, white males were given single 80 mg oral doses of the drug together with tritium-labelled propranolol. Plasma propranolol was measured by GC/MS and fourteen metabolites were measured in urine by h.p.l.c. with radiometric detection. The total oral clearance of propranolol in these subjects varied about three-fold, from 27.5 to 71.4 ml min-1 kg-1. The clearance through glucuronidation was very similar in all subjects, ranging from 6.8 to 9.9 ml min-1 kg-1. The clearance through side-chain oxidation varied 2.4-fold, from 10.9 to 25.8 ml min-1 kg-1. Increased clearance through this pathway correlated with increased total oral clearance (r = 0.84; P less than 0.02). The clearance through ring oxidation varied as much as 5.6-fold, from 7.5 to 41.8 ml min-1 kg-1. Increased clearance through this pathway correlated highly with increased total oral clearance (r = 0.94; P less than 0.002). These observations indicate that the intersubject variability in the oral clearance of propranolol in young, white males is due mainly to differences in the activity of the ring oxidation pathway, to some extent in the side-chain oxidation pathway, but not to differences in the glucuronidation pathway. The partial metabolic clearance approach adopted in this study may be useful in the investigation of factors influencing the oral bioavailability of propranolol.