Evaluation of stereoselective transdermal transport and concurrent cutaneous hydrolysis of several ester prodrugs of propranolol: mechanism of stereoselective permeation

PURPOSE

The purpose of this study was to evaluate the stereoselective permeation and concurrent cutaneous hydrolysis of a series of ester prodrugs of propranolol (PL).

METHODS

In vitro studies were performed across full-thickness, stripped and diisopropylfluorophosphate (DFP) treated skins of hairless mouse with flow-through diffusion cells at 37 degrees C.

RESULTS

The permeability coefficients (Kp), which were dependent on partition coefficients (PC), of all the prodrugs were markedly increased compared to the parent drug. In full-thickness skin, the (R) caproyl-PL (CR-PL) showed the highest Kp, which was about 52-fold greater than that of PL. Most of the more lipophilic prodrugs showed stereoselectivity in Kp (R > S). All the prodrugs underwent stereoselective hydrolysis (R > S) during penetration. The prodrugs which showed stereoselectivity in permeation were comparatively lipophilic and showed great differences in hydrolysis percentages between the enantiomers. Permeation studies with stripped skin revealed that prodrugs were more permeable across stratum corneum compared to PL, whereas reverse was happened across viable skin. Although CR-PL showed high stereoselectivity in permeation across full-thickness skin and underwent higher percent of concurrent stereoselective cutaneous hydrolysis, the prodrug showed no stereoselectivity in permeation across DFP, an esterase inhibitor, treated skin and the concurrent cutaneous hydrolysis was also stopped.

CONCLUSIONS

Lipophilic prodrugs may readily pass the stratum corneum but may not be able to penetrate so easily through the deeper tissues. Unlike the (S) isomers, the (R) isomers of lipophilic prodrugs almost completely converted to propranolol in epidermis and can easily pass through the dermis layer, resulting in stereoselective penetration.

Increased sensitivity of propranolol clearance to reduced oxygen delivery in the isolated perfused cirrhotic rat liver

BACKGROUND & AIMS

Capillarization of the sinusoids in cirrhosis is proposed to reduce oxygen availability to the hepatocyte, resulting in the patterns of altered drug metabolism observed in cirrhosis. If this were true, drug metabolism in cirrhotic livers would be expected to be more sensitive to reduced oxygen delivery than in noncirrhotic livers. The aim of this study was to compare the sensitivity of propranolol clearance with reduced oxygen delivery in isolated perfused livers from healthy and cirrhotic rats.

METHODS

Propranolol clearance was measured at steady state in 5 normal and 5 cirrhotic weight-matched perfused rat livers under single-pass conditions with normal oxygen delivery (mean, 71.5 mumol/min) and with graded reductions in oxygen delivery (range, 58.1-18.8 mumol/min).

RESULTS

In noncirrhotic livers, propranolol clearance was independent of oxygen supply for the oxygen delivery range of 73-45 mumol/min but decreased with further reductions in oxygen supply. In cirrhotic livers, propranolol clearance decreased linearly (r2 = 0.92; P < 0.005) for the entire oxygen delivery range (73.4-18.8 mumol/min).

CONCLUSIONS

The increased sensitivity of propranolol clearance in perfused cirrhotic livers to reductions in oxygen delivery is consistent with impaired oxygen delivery to hepatocytes in cirrhosis. These novel findings potentially hold implications for clinical management of patients with cirrhosis.

Racial differences in propranolol enantiomer kinetics following simultaneous i.v. and oral administration

1. Racial differences in propranolol enantiomer kinetics following oral dosing were previously documented in our laboratory. The purpose of this study was to more completely describe propranolol kinetics in black and white subjects with the goal of gaining a better understanding of the mechanism(s) responsible for racial differences in oral propranolol kinetics. 2. Twelve white and 13 black healthy males were included in the study. Poor metabolizers of dextromethorphan and mephenytoin were excluded. Subjects took oral propranolol 80 mg every 8 h for 16 doses and received an intravenous dose of radiolabelled propranolol with the 16th dose. Serum and urine samples were collected for 24 h after the 16th dose. Serum concentrations of R- and S-propranolol and urine concentrations of its three primary metabolites were determined by h.p.l.c. 3. Apparent oral clearances of R- and S-propranolol were higher (P < 0.05) in blacks than whites (R-propranolol: 5036 +/- 4175 ml min-1 vs 2854 +/- 879 ml min-1; S-propranolol 3255 +/- 1723 ml min-1 vs 2125 +/- 510 ml min-1; blacks vs whites). 4. R- and S-propranolol clearances were higher in blacks than whites (R-propranolol 1069 +/- 316 ml min-1 vs 841 +/- 161 ml min-1; S-propranolol 947 +/- 271 ml min-1 vs 771 +/- 142 ml min-1; blacks vs whites, P < 0.05). 5. There were trends (P > 0.05 < 0.10) toward higher side chain oxidation, 4-hydroxylation and R-propranolol glucuronidation in blacks compared with whites. Ethnic differences in the enantiomeric ratios of partial metabolic clearance values were not observed. 6. We conclude the higher propranolol oral clearances in black subjects are explained by blacks having slightly higher hepatic metabolism via all three of its major metabolic pathways. Higher propranolol clearances among black subjects were also observed and we conclude this finding is explained largely by the higher hepatic metabolism, but also by slightly higher liver blood flow among black subjects.

Haemodynamic, electrocardiographic, electrophysiologic and pharmacokinetic activity of 4'-hydroxypropranolol in dogs

We determined the haemodynamic, electrocardiographic and electrophysiologic effects, and the pharmacokinetic properties of 4'-hydroxypropranolol (4'-OHP) by conducting three different experiments in dogs. In experiment 1 the plasma concentrations of 4'-OHP (mg/kg, i.v.) in pentobarbital anaesthetized dogs were determined by HPLC and pharmacokinetic parameter values were estimated. The terminal elimination half-life (t1/2) for 4'-OHP was 69.4 min, the apparent volume of distribution (Vd) was 3.39 L/kg and the total clearance (Clt) was 53.6 mL/min.kg. These data were subsequently used to calculate the loading and maintenance doses of 4'-OHP required to produce targeted steady-state plasma concentrations for 4'-OHP of 30, 60, 120, 240 and 480 ng/mL. In experiment 2 the haemodynamic and electrocardiographic effects for target plasma concentrations of 4'-OHP were determined in two groups of pentobarbital anaesthetized dogs, and beta-blocking activity was assessed by infusion or bolus doses of isoproterenol. The haemodynamic and electrocardiographic effects of the target plasma concentrations (30, 60, 120 ng/mL) of 4'-OHP were first determined in seven pentobarbital anaesthetized dogs (Group 1). Beta blocking activity was assessed by the infusion of 0.1 microgram/kg/min isoproterenol. The infusion of 4'-OHP produced dose dependent decreases in heart rate, cardiac output, dP/dtmax, mean arterial pressure and left ventricular diastolic pressure. The PR interval of the lead II electrocardiogram increased and the QTc interval decreased. These haemodynamic and electrocardiographic changes became apparent at plasma 4'-OHP concentrations equal to or greater than 30 ng/mL. Plasma concentrations of 4'-OHP equal to or greater than 30 ng/mL prevented the haemodynamic and electrocardiographic effects of isoproterenol infusion. In group 2 dogs, (seven dogs) the haemodynamic and electrocardiographic effects of target plasma concentrations (30, 60, 120, 240, 480 ng/mL) of 4'-OHP were evaluated and beta-blocking activity was assessed by the i.v. bolus administration of 1 and 4 micrograms/kg of isoproterenol. The infusion of 4'-OHP produced haemodynamic and electrocardiographic changes similar to those in group 1 dogs. In addition, the QRS duration of the electrocardiogram increased at plasma concentrations of 4'-OHP equal to or greater than 240 ng/ mL. The haemodynamic and electrocardiographic effects of i.v. bolus dose administrations of 1 and 4 micrograms/kg isoproterenol were abolished by plasma concentrations of 4'-OHP equal to or greater than 240 ng/mL. In experiment 3 we determined the electrophysiologic effects of 10(-9) to 10(-5) mmol/L 4'-OHP on Tyrodes superfused bundles of canine Purkinje fibres. Action potential duration and the effective refractory period decreased at superfusate concentrations of 4'-OHP equal to or greater than 10(-7) mmol/L. Action potential overshoot, action potential total amplitude, the rate of rise of phase 0 (dV/dt) and spontaneous rate decreased at superfusage concentrations of 4'-OHP equal to or greater than 800 ng/mL. These studies demonstrate that: 1) 4'-OHP produces haemodynamic. electrocardiographic and electrophysiologic effects similar to those of other beta-blocking drugs in pentobarbital anaesthetized dogs; 2) the haemodynamic and electrocardiographic effects produced by 4'-OHP are apparent at relatively low plasma concentrations (30 ng/mL); 3) the concentrations of 4'-OHP that are required to produce direct cardiac electrophysiologic effects are unlikely to be responsible for clinical antiarrhythmic activity and 4) 4'-OHP blocks the haemodynamic and electrocardiographic effects of infusions and i.v. bolus administration of isoproterenol.

[The effect of phenobarbital and cimetidine on the elimination kinetics and distribution in the heart and liver of propranolol in rats with acute and chronic inflammations]

Intravenous administration of propranolol (10 mg/kg) to rats with turpentine-induced inflammation and adjuvant-induced arthritis results in the reduction of the systemic clearance (Cltot.p), volume distribution (Vd,ss) and free fraction (fu). At the same time the area under the pharmacokinetic curve (AUC) increases and the half-life period (t1/2 beta) remains the same. In the phenobarbital-treated rats with acute inflammation Cltot.p increases, AUC and t1/2 beta decreased. Administration of cimetidine resulted in the opposite effect. In rats with adjuvant arthritis phenobarbital and cimetidine administration did not affect the propranolol elimination kinetics. In the phenobarbital-treated rats with inflammation Vd,ss significantly decreased and virtually did not change in cimetidine treated rats. The fu of propranolol increased markedly after the cimetidine treatment in all rats with inflammation, whereas phenobarbital treatment appeared effective only in rats with acute inflammation. The tissue-to plasma concentration ratio (Kp) of propranolol decreased in the liver of rats both with acute and chronic inflammation, whereas in the heart the effect was observed only in rats with chronic inflammation. The tissue to plasma concentration ratio of unbound propranolol (Kpu) decreased only in the liver of rats with acute inflammation. In the phenobarbital-treated rats with adjuvant arthritis Kp of propranolol in the liver increased and in the heart decreased, whereas cimetidine-treatment did not change Kp of propranolol in heart and decreased it in the liver. The Kpu of propranolol decreased only in the heart of rats with acute inflammation after phenobarbital treatment, whereas after cimetidine administration this parameter decreased in the heart and in the liver of rats regardless of the character of inflammation.

Carboxymethylcellulose-sodium based transdermal drug delivery system for propranolol

Propranolol, a beta-adrenoceptor blocker, suffers from a high degree of first-pass metabolism resulting in very low bioavailability (< 10%) following administration with conventional oral formulations. To circumvent this significant therapeutic hurdle, we formulated a carboxymethylcellulose-sodium (CMC-Na) based transdermal system for propranolol and evaluated the patch for its in-vitro and in-vivo performance. In-vitro permeation studies using the excised hair-free rat skin model resulted in 66.54% permeation at the end of 24 h in a modified Franz diffusion cell. This zero-order permeation profile was characterized by a drug permeation rate of 52.87 +/- 11.63 micrograms cm-2 h-1. Skin irritation studies in rats (n = 5), evaluated for flare-and-wheal with respect to a formalin control, indicated that the drug-containing patch evoked only a mild response over a 7-day period. Preliminary in-vivo studies in male albino rabbits (n = 3), indicated that plasma drug levels averaged 11.75 +/- 3.40 ng mL-1 in a 24-h study period before patch removal.

[Kinetic analysis of hepatobiliary transport of drugs: importance of carrier-mediated transport]

The liver is the major organ involved in the metabolism and elimination of xenobiotics. Evaluating accurately hepatic clearance is very important for predicting the pharmacological effect and/or side-effects of drugs, as well as changes in drug disposition during disease. Recently, for many endogenous and exogenous compounds (including drugs), it has been reported that carrier-mediated transport contributes to hepatic uptake and/or biliary excretion. In particular, primary active transport mechanisms have been shown to be responsible for the biliary excretion of anticancer drugs, endogenous bile acids and organic anions including glutathione and glucuronic acid conjugates. We have found that a rate-limiting step for several drugs in terms of the hepatic clearance was the membrane transport process. For these drugs, such a saturable transport process can be one of the major determinants which influence not only hepatic clearance itself but also disposition (in other words, plasma elimination) in the whole body. We reviewed the carrier-mediated transport mechanisms involved in the hepatic uptake and biliary excretion processes, the multiplicity of transport systems, and further, the physiological meaning of these complex transport systems in the body.

beta-blockers. Drug interactions of clinical significance

The clinician prescribing beta-blockers for his or her patients is faced with an often difficult situation. There are many beta-blockers, each with its own pharmacological profile. Patients are often taking multiple medications, thus increasing the risk of both anticipated and unexpected drug interactions. Reports of drug interactions are frequently anecdotal. The prescriber may not be aware of the patient's other medications or lifestyle habits. Pharmacokinetic and pharmacodynamic drug interactions involving beta-blockers are documented in the literature, but these studies often examine small numbers of patients. For these reasons, it is difficult for the practitioner to distill guidelines for the administration of beta-blockers in conjunction with other medication. In general, beta-blockers are well tolerated, and symptomatic drug interactions are relatively infrequent. It is incumbent upon the clinical practitioner to have knowledge of his or her patient's drug profile and to be aware of the various drug interactions as well as each patient's unique pathophysiological profile when prescribing any medication, including beta-blockers. beta-Blockers may interact with a large number of commonly prescribed drugs, including antihypertensive and antianginal drugs, inotropic agents, anti-arrhythmics, NSAIDs, psychotropic drugs, anti-ulcer medications, anaesthetics, HMG-CoA reductase inhibitors, warfarin, oral hypoglycaemics and rifampicin (rifampin).

[The pharmacokinetics of propranolol and its conjugated metabolites in patients with chronic ischemic heart disease and arterial hypertension with a one-time and course intake of the drug]

Pharmacokinetics of propranolol (P), 4-hydroxy-propranolol sulfate (4HOP-Sulf), and glucoronides of pharmacologically active S-enantiomer P (S-PG) and ballast R-enantiomer of P (R-PG) in the blood serum of 21 patients with chronic ischemic heart disease and/or arterial hypertension has been studied at a single and course oral P administration. The values od AUC and T1/2 for potentially active 4HOP-Sulf were significantly higher than those for unchanged P at a single and course administration. The values od AUC and T1/2 for for S-PG were approximately three times higher than those for P-PG after both a single and course administration. Thus the results presented show that potentially active 4HOP-Sulf and S-PG (which undergoes a partial deconjugation in an organism at oral administration) may contribute essentially to the value and duration of the P pharmacological effect.

A fluorimetric liquid chromatographic method for the determination of propranolol in human serum/plasma

A simple, rapid, and sensitive fluorimetric-high-performance liquid chromatographic method for the determination of propranolol in human serum/plasma has been developed, without the need for solvent extraction. The procedure required 200 microliters of serum/plasma, and the addition of 1 ml of acetonitrile for protein precipitation followed by vortexing and centrifugation at 10 000 g. The clear supernatant was evaporated to dryness under a stream of nitrogen at 50-60 degrees C, the residue was reconstituted in 100 microliters of methanol, and a 90 microliters portion was injected onto the high-performance liquid chromatograph for propranolol quantitation. Chromatography was accomplished using a Hypersil cyano column, a mobile phase of acetonitrile-aqueous acetic acid (1%) containing 0.2% triethylamine (35:65, v/v) (pH 3.6), a flow rate of 1.5 ml min-1, a fluorescence detector set at an excitation wavelength of 230 nm and an emission wavelength of 340 nm, and using pronethalol as the internal standard. Retention times for pronethalol and propranolol were 7.5 min and 9.5 min, respectively. Standard curves were linear in the range 5-200 ng ml-1. Relative standard deviations for both inter-day and intra-day precision analysis were less than 7% for serum. No interference was observed from endogenous serum/plasma components. Specificity was shown for some, but not all, commonly coadministered drugs tested. The advantages of this method include good precision, low sample volume, good reproducibility and recovery, and high sensitivity.

Pharmacokinetic and pharmacodynamic evaluation during coadministration of nefazodone and propranolol in healthy men

Potential interactions between nefazodone (200 mg every 12 hours) and propranolol (40 mg every 12 hours) were assessed in 18 healthy male volunteers in an open-label, randomized, three-way crossover study. The nature, frequency, and severity of adverse events during coadministration of nefazodone and propranolol were similar to those observed with either treatment alone. There were no clinically significant effects on vital signs, electrocardiographic results, or laboratory parameters. With coadministration, the maximum peak concentration (Cmax) and area under the concentration-time curve over the dosing interval (AUC tau) of propranolol decreased 29% and 14%, respectively; Cmax and AUC tau of 4-hydroxy-propranolol decreased 15% and 21%, respectively. Despite decreased plasma concentrations of the beta-antagonists, the reduction in exercise-induced tachycardia and post-exercise double product was slightly greater with coadministration than with propranolol alone. Administration of nefazodone alone did not significantly affect either pharmacologic parameter. The pharmacokinetics of nefazodone and its metabolites were largely unaffected during coadministration. Coadministration of propranolol and nefazodone results in modest pharmacokinetic inequivalencies, but no clinically significant alterations of the pharmacodynamics of propranolol.

The secretion of propranolol enantiomers in human saliva: evidence for active transport?

To study the possible transport routes which may lead to the presence of a drug in saliva, the concentration-time curves of the separate enantiomers of propranolol were measured in human saliva and plasma after oral administration of 10 mg of propranolol hydrochloride. Saliva samples were taken with the Salivette device. Plasma and saliva concentrations of the enantiomers of propranolol were determined by HPLC with fluorescence detection. The transport of propranolol from plasma to the salivary gland appears to be not stereospecific and not saturable. Therefore, there is no indication that the transport of propranolol to the salivary gland is active. The concentrations of both enantiomers of propranolol in saliva, however, were higher than those of both enantiomers in venous plasma. In the past this phenomenon was interpreted as an indication of active transport, but it could be explained by the fact that salivary concentration more closely reflects the central compartment than that of peripheral venous blood.

Effects of sensory (teasing) exposure to food on oral propranolol bioavailability

In order to further examine the mechanism of the increase in the plasma propranolol concentration versus time curve (AUC) caused by ingestion of propranolol with food, we administered R, S-propranolol tablets (0.5 mg kg-1) orally to healthy human volunteers and dogs in the presence and absence of sensory exposure to food without ingestion (teasing). Six healthy human volunteers were fasted on one occasion and on the other they were presented with an appetising meal, without eating it (teasing protocol). There was a strong trend to a greater propranolol AUC in the teasing protocol (139 +/- 54 mg mL-1 h-1 fasting, 178 +/- 105 mg mL-1 h-1 teasing; p = 0.1), and time of peak concentration (tmax) was significantly prolonged (80 +/- 22 min and 120 +/- 32 min, respectively; p < 0.03). Further studies were carried out in dogs who received R-propranolol (2 mg kg-1) as an oral solution by gavage tube on four different occasions: fasting, following intragastric administration of a high-value liquid meal, following teasing with food in the animal house at normal feeding time (high-intensity teasing). There were no significant differences in pharmacokinetic parameters between the fasting and intragastric food protocols. Low-intensity teasing resulted in significantly lower AUC and peak concentrations (Cmax) compared with fasting (p < 0.05), confirming food effect patterns known to occur in dogs. High-intensity teasing resulted in significantly greater AUC and Cmax compared with fasting (p < 0.05), reproducing in dogs the increase in propranolol AUC known to occur with food ingestion in humans. These findings suggest that the mechanism of the 'food effect' may involve physiological responses to the sight and smell of food additional to mechanisms activated by ingestion.

Propranolol disposition in Chinese subjects of different CYP2D6 genotypes

Propranolol pharmacokinetics among different genotypes of CYP2D6 was compared in this study. The Chinese (Han) population consisted of 44 healthy unrelated individuals living in southern Taiwan. Endonuclease tests based on polymerase chain reaction were used to determine C/T188 genotypes of CYP2D6 in leukocyte deoxyribonucleic acid. Based on codon 188 genotypes, subjects were categorized into three groups: homozygous C/C188 (n = 13), heterozygous C/T188 (n = 14); and homozygous T/T188 (n = 17). Each subject was given a 40 mg propranolol tablet. Blood samples were drawn before and 12 hours after propranolol administration to measure propranolol and 4-hydroxypropranolol. Three genotypes showed distinct time profiles of plasma propranolol and 4-hydroxypropranolol. The area under plasma concentration curve values (mean +/- SEM), were 322.0 +/- 40.8, 481.6 +/- 77.5, and 766.1 +/- 92.8 nmol.hr/L, respectively, for C/C188, C/T188, and T/T188 subjects (p < 0.05). The 48-hour excreted amount of 4-hydroxy-S-propranolol-O-glucuronide, but not 4-hydroxy-R-propranolol-O-glucuronide, was significantly higher for C/C188 than for T/T188 subjects (p < 0.05). This study shows a different propranolol disposition in Chinese subjects of different CYP2D6 genotypes.

The lack of effect of aerobic exercise training on propranolol pharmacokinetics in young and elderly adults

The effects of exercise training on the pharmacokinetics of orally administered propranolol were studied in young and elderly healthy volunteers. Twenty-three young (30 +/- 5 years of age) and 20 elderly (67 +/- 5 years of age) adults were randomly assigned to endurance training (N = 12 young subjects, 10 elderly subjects) or nonexercising control (N = 11 young subjects, 10 elderly subjects) groups. Training consisted of treadmill walking, stair climbing, or both three times per week for 40 minutes at 70-85% of maximal heart rate reserve for 16 weeks. Resting plasma propranolol concentrations after a single dose of 80 mg of oral propranolol were measured by high performance liquid chromatography with fluorescence detection, and estimated hepatic blood flow measured was measured using indocyanine green during supine test. Aerobic training increased maximal oxygen uptake (VO2 max) by 13% and 14% in the exercising young and elderly groups, respectively. There was no change in VO2 max in either control group. Adjusted mean estimated hepatic blood flow after exercise corrected for body weight for the young subjects who did not exercise (15.6 mL/min/Kg) and those who did (18.2 mL/min/Kg) groups were of borderline significance. No statistical differences were detected in the experimental propranolol pharmacokinetic parameters (maximal concentration, time of maximal concentration, terminal half-life, area under the curve, and protein binding) or derived pharmacokinetic parameters (intrinsic clearance, bioavailability, clearance, and volume of distribution). These results provide evidence that changes in aerobic fitness do not produce corresponding changes in propranolol pharmacokinetics in young or elderly adults.

Sex differences in pharmacokinetics of oral propranolol in healthy Chinese volunteers

AIM

To determine if the gender-based dimorphism of the distribution and metabolism of oral propranolol (Pro) exists in the healthy Chinese volunteers.

METHODS

Twelve subjects (6 M and 6 F) were given an 80 mg single oral dose of Pro. Plasma Pro levels were determined by HPLC with fluorescence detector and the pharmacokinetic parameters were calculated by using the MCPKP program.

RESULTS

AUC and Cmax in females were about 74% and 99% higher than those in males (P < 0.05), whereas oral clearance and apparent distribution volume were 109% and 120% lower in females than in males (P < 0.05), respectively. The T1/2 tended to be longer in females (P > 0.05). No differences in any other kinetic parameters were found between the sexes.

CONCLUSION

The higher oral bioavailability (AUC and Cmax) of Pro in Chinese women is in part caused by their lower oral clearance and volume of distribution.

Interaction between propranolol and amino acids in the single-pass isolated, perfused rat liver

Propranolol (PL) bioavailability has been shown to increase substantially when it is administered with a protein-rich meal. A change in metabolic capacity or tissue uptake, induced by amino acids (AAs) released as a result of digestion of dietary protein, is a possible contributing mechanism to the food effect. This hypothesis was tested in isolated, perfused rat livers in the single-pass mode. Rac-PL (20 micrograms/ml) was infused to steady-state at 3 ml/min/g liver for 150 min. A balanced mixture of I-AA was coinfused from 70 to 110 min. The AA reversibly increased the steady-state concentration of PL by 18% and reduced steady-state concentrations of 4-hydroxypropranolol, N-deisopropylpranolol, PL glycol, naphthoxylactic acid, and naphthoxyacetic acid by an average of 41% and propanolol conjugates by almost 100%, indicating metabolic inhibition. In a second experiment, PL was coinfused with AAs from the beginning of the experiment, and tissue binding was compared with control livers. There was no significant effect of AAs on PL tissue binding. In a third study, the effect of four different concentrations of AAs coinfused from 70 to 110 min was assessed. The percentage change in PL and phase I metabolite levels was linearly correlated to the influent AA concentration. The large magnitude, reversibility, lack of pathway specificity, and concentration dependence of the AA interaction in the perfused liver are also features of food interaction in humans. These similarities constitute evidence that metabolic inhibition by AAs originating from dietary protein could contribute to the PL-food interaction.

Influence of physicochemical parameters and perfusate flow rate on the distribution of solutes in the isolated perfused rat hindlimb determined by the impulse-response technique

The relationship between solute distribution, physicochemical properties, and tissue physiology was determined by the impulse-response (IR) technique and statistical moment analysis in the isolated perfused rat hindlimb. The concentration of bovine serum albumin (BSA; 2, 4.7, and 7%, w/v), perfusate flow rate (4 and 8 mL/min), and solute physicochemical properties (lipophilicity, P, fraction unbound to protein, fu; fraction ionized, fi; and molecular weight MW) were varied to better understand the underlying determinants of solute distribution. An apparent low availability was found for a number of the solutes as a consequence of tissue sequestration. This low availability precludes the estimation of an apparent volume of distribution (V) for these solutes. The V of solute and tissue (skin, fat, and muscle) blood flow increased with perfusion flow rate (p < 0.01). The unbound distribution volume (Vu) of basic solutes was significantly linear with respect to P. Multiple linear regression analysis showed that the distribution volume of solute in tissue was significantly related to fu (p < 0.01), but not improved by including relationships to P, MW, and fi. Data obtained with this IR technique yield results consistent with in vivo studies in terms of the importance of fu as a determinant of V. This work has shown that the estimations of solute V by the IR technique in a single-pass preparation are unreliable for solutes with a low availability due to apparent solute sequestration into tissue. The parameter V may also be affected by changes in the perfused limb physiology associated with the perfusion conditions used. The Vs for lidocaine and diazepam vary with fu in accordance with deductions based on the results of steady-state studies.

Studies on psychomotor performance in healthy volunteers after diazepam, propranolol and alcohol given alone or in combination

The effects of diazepam, propranolol or alcohol alone or in combination with each other were examined in ten normal healthy volunteers on tests of psychomotor function. Results showed impaired psychomotor performance persisting upto 4-5 h when the aforementioned agents given singly were tested on simple reaction time (SRT), multiple choice reaction time (MCRT) and critical flicker fusion frequency (CFFF) tasks. Digit cancellation task (DCT) was similarly affected by diazepam and alcohol only. No summation of adverse effects on psychomotor performance was noted when a combination of diazepam and alcohol, diazepam-propranol or alcohol plus propranolol were tested on SRT and MCRT. An additive impairment of CFFF was observed with alcohol - propranolol combination only. No summation of pharmacodynamic effects on DCT were noted when different combinations were used.

Development and evaluation of a buccoadhesive propranolol tablet formulation

Buccoadhesive tablets were prepared by directly compressing propranolol with poly(acrylic)acid (PAA), hydroxypropylmethylcellulose (HPMC) and hydroxypropylcellulose (HPC) in different ratios. The release data were fitted to Mt/M infinity = ktn simple equation. The release characteristics has shown a non-Fickian mechanism of release. The best kinetic fit were zero order and slab erosion kinetic. The detachment force between buccoadhesive tablets and bovine buccal mucosa was carried out by the tensile tester apparatus. The high amount of PAA containing formulation demonstrated the greatest adhesive force.

The influence of selected general anesthetics on pharmacokinetic parameters of some antiarrhythmic drugs in rabbits. Part III. Propranolol

The influence of general anesthesia with thiopental (10 mg/kg), ketamine (4 mg/kg), or propofol (10 mg/kg) on the propranolol (0.3 mg/kg) pharmacokinetic parameters was studied in rabbits. It was established that during thiopental or propofol anesthesia the levels of propranolol were significantly higher than in control animals. The following main changes in propranolol pharmacokinetic parameters were found: 1) increase of the distribution rate constant during propofol anesthesia 2) prolonged biological half-life and mean residence time during thiopental or propofol anesthesia 3) increase of the area under drug level curve during thiopental or propofol anesthesia 4) decrease of systemic clearance and volume of distribution during thiopental or propofol anesthesia. The slightest influence on propranolol pharmacokinetics was exerted by ketamine anesthesia.

Interactions between food components and drugs. Part 3. Interactions between pectin and propranolol

Bioavailability of drugs can be affected distinctly by interactions with food components. Effects of structural parameters of the soluble dietary fiber pectin on lipid-membrane transport of propranolol (1) was investigated in vitro using a two-compartment model with a dodecanol-collodium membrane at pH 7.2 and 37 degrees C. Starting from practically fully esterified citrus pectin two series of defined and in their structural parameters gradually varied pectins were prepared. In presence of pectins with a blockwise distribution of free COOH-groups the portion of permeated 1 is significantly diminished with a decreasing degree of esterification (DE). On the other hand, only in the smallest DE pectins having statistically distributed free COOH-groups seemed to affect the transport rate of 1. The viscosity of the tested pectins possessed no significant influence on the passage of 1.

Effects of a Finnish sauna on the pharmacokinetics and haemodynamic actions of propranolol and captopril in healthy volunteers

The effects of a Finnish sauna on propranolol pharmacokinetics and on the pharmacodynamics of propranolol and captopril were studied in healthy, young volunteers (2 males, 6 females) in a double-blind, cross-over trial. The subjects received single oral doses of placebo, propranolol (40 mg) or captopril (12.5 mg) in sauna and control sessions at a one-week interval. The sauna sessions consisted of three repetitive 10-min stays in a sauna (85-100 degrees C, relative humidity 25-35%) separated by two 5-min rest periods in a cool room. Sauna bathing started 35, 50 and 65 min after ingestion of the drugs. Venous blood for plasma propranolol measurement were collected before and 15, 30, 45, 60, 75, 90 min and 2, 3, 4, 5, 7 and 24 h after drug intake. The sauna significantly increased the maximum concentration (Cmax 41 vs. 28 ng.ml-1) of propranolol and the mean plasma propranolol concentration 60 and 90 min, and 2 and 3 h after drug administration. It also significantly increased the AUC0-5h (119 vs 71 micrograms.h.l-1) of propranolol from 0 to 5 hours tmax, t1/2 beta and AUC0-24h of propranolol did not differ between the control and sauna sessions. The higher propranolol levels during and after the cessation of sauna bathing did not lead to significant changes in blood pressure or heart rate compared to the control period. Captopril had no major effects on these parameters during the post-sauna phase.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dosage release formulations on the pharmacokinetics of propranolol stereoisomers in humans

Recent studies in dogs have suggested that the disposition of S- and R-propranolol may depend on the input rate of drug delivered to the liver. Therefore, this study was designed to determine whether differences in the disposition of S- and R-propranolol occur in humans when altering the input rate of propranolol by giving different dosage forms of the drug. Twelve healthy subjects were enrolled in a single-dose, 4-way crossover pharmacokinetic study in which racemic propranolol was given according to 1 of 4 treatments: one 80-mg immediate-release (IR) tablet, phase A; two 80-mg IR tablets, phase B; a 160-mg controlled-release capsule, phase C; or a 10-mg IV bolus, phase D. The results showed no significant differences in the ratios of S/R-propranolol for AUC, clearance, or overall mean concentration among the oral dosage groups. Significant differences in these parameters including Cmax S/R ratio were seen between the oral phases and the IV phase. These differences appear to be related more to the route of administration than to the low input rate. However, at high concentrations there may be input-rate alteration in S/R ratios. Specifically, for phase B, which had the highest Cmax concentrations, the Cmax S/R ratio was significantly lower than the other oral dosage groups A and C (Cmax S/R ratios: 1.44 versus 1.54 and 1.54, respectively; P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)