Influence of histamine, cimetidine and pyrilamine on naloxone-induced jumping in morphine-dependent mice

In the present study, the effects of histamine on naloxone-induced jumping in the presence or absence of adrenoceptor or acetylcholine receptor antagonists in morphine-dependent mice were examined. In these experiments, the drugs were used before s.c. injection of naloxone (2 mg/kg), to test their effects on the expression of jumping. The i.c.v. administration of histamine (5-20 microg/mouse) 15 min before naloxone injection decreased the number of jumps in mice. When the histamine H(2) receptor antagonist, cimetidine (5-20 mg/kg), and the histamine H(1) receptor antagonist, pyrilamine (5-20 mg/kg), were administered i.p. to morphine-dependent mice, only cimetidine enhanced the jumping behaviour. Administration of cimetidine (20 mg/kg, i.p.), 30 min, of the beta-adrenoceptor antagonist, propranolol (2.5-10 mg/kg, i.p.), 15 min but not of pyrilamine (20 mg/kg, i.p.), 30 min before naloxone injection, decreased the histamine effect. The i.p. administration of an acetylcholine receptor antagonist, atropine (5 and 10 mg/kg, i.p.), the alpha(1)-adrenoceptor antagonist, prazosin (0.5, 1 and 2 mg/kg, i.p.), and alpha(2)-adrenoceptor antagonist, yohimbine (0.5, 1 and 2 mg/kg, i.p.), 15 min before naloxone injection, had no effect on the histamine response. Single administration of propranolol, atropine or prazosin decreased, while yohimbine increased the naloxone-induced jumping. It is concluded that the histamine H(2) receptor mechanism may be involved in the influence of histamine on the expression of naloxone-induced jumping in morphine-dependent mice.

Automated online dual-column extraction coupled with teicoplanin stationary phase for simultaneous determination of (R)- and (S)-propranolol in rat plasma using liquid chromatography-tandem mass spectrometry

An automated online sample extraction method for rat plasma was developed and validated for the quantification of (R)- and (S)-propranolol following the intravenous administration of either the racemate or the individual enantiomers at 5 mg/kg. A dual-column extraction system coupled to a chiral stationary phase (CSP) was used in conjunction with liquid chromatography-tandem mass spectrometry. In this method, two Oasis HLB extraction columns (50x1.0 mm) in parallel were used for online plasma sample purification and teicoplanin CSP (Chirobiotic T) was used for the enantiomeric separation. This method allowed the use of one of the extraction columns for purification while the other was being equilibrated. Hence, the time required for re-conditioning the extraction columns did not contribute to the total analysis time per sample, which resulted in a relatively shorter run time and higher throughput. The lower limit of detection was 0.5 ng/ml and the lower limit of quantification was 2 ng/ml for each enantiomer using 25 microl of rat plasma. The method was validated with a linear calibration curve between 2 and 2000 ng/ml for (R)- and (S)-propranolol, respectively. The intra- and inter-day precision (C.V.) was no more than 7.6% and the accuracy of the assay was between 92 and 103%. The teicoplanin CSP proved to be rugged with excellent reproducibility of chromatographic parameters.

Enhanced ex vivo buccal transport of propranolol: evaluation of phospholipids as permeation enhancers

The aim of the present study was to evaluate the effects of two phospholipid permeation enhancers, lysophosphatidylcholine (LPC) and didecanoylphosphatidylcholine (DDPC), along with a fusidic acid derivative, sodium taurodihydrofusidate (STDHF) and ethanol (EtOH) on the buccal transport of propranolol hydrochloride (PPL) using an ex vivo buccal diffusion model. The permeation rate of [3H]PPL as measured by steady-state fluxes increased with increasing EtOH concentration. A significant flux enhancement (P<0.05) was achieved by EtOH at 20 and 30 %v/v concentrations. At a 0.5 %w/v permeation enhancer concentration, the buccal permeation of [3H]PPL was significantly enhanced by all the enhancers studied (i.e., LPC, DDPC and STDHF) compared to the control (phosphate-buffered saline pH 7.4, PBS). LPC and DDPC displayed a greater degree of permeation enhancement compared with STDHF and EtOH-PBS mixtures with an enhancement ratio of 3.2 and 2.9 for LPC and DDPC, respectively compared with 2.0 and 1.5 for STDHF and EtOH:PBS 30:70 %v/v mixture, respectively. There was no significant difference between LPC and DDPC for the flux values and apparent permeability coefficients of [3H]PPL. These results suggest that phospholipids are suitable as permeation enhancers for the buccal delivery of drugs.

Pharmacokinetics of propranolol after single and multiple dosing with sustained release propranolol or propranolol CR (innopran XL) , a new chronotherapeutic formulation

Blood pressure rises rapidly upon waking and may be responsible, in part, for the increased incidence of myocardial infarction and stroke during the morning hours. Current formulations and dosing of antihypertensive drugs do not provide maximum coverage during this vulnerable period. This study was performed to demonstrate that propranolol CR (Innopran XL), a novel chronotherapeutic formulation of propranolol designed for nighttime dosing, has appropriate pharmacokinetics to provide maximum cardioprotective effect in the morning. Pharmacokinetics of propranolol CR and sustained-release propranolol after single and multiple doses were determined in normal male volunteers in this open-label, 2-period crossover study. The drugs were dosed in the evening and serial blood samples were taken for determination of propranolol concentration the next 24 to 72 hours. After a single 160-mg dose of propranolol CR administered at 10 pm, absorption was delayed by about 4 hours, after which plasma concentration rose steadily, reaching a peak at about 10:00 am. In contrast, after dosing with sustained release propranolol, plasma levels of propranolol began to rise almost immediately, reaching a plateau between 4:00 am and 10:00 am. During multiple dosing, steady-state trough plasma concentrations were achieved after 2 days with either drug. After the final dose, the plasma profiles of both drugs were similar to those observed in the single-dose study. Bioavailability was similar for both formulations of propranolol. Propranolol CR exhibited appropriate pharmacokinetics for a chronotherapeutic approach to the treatment of hypertension.

Disease-drug interaction: Reduced response to propranolol despite increased concentration in the rat with inflammation

Inflammatory conditions reduce clearance, hence increase plasma concentration of drugs such as propranolol that are efficiently cleared by the liver. The therapeutic consequences of this increased plasma drug concentration is mainly unknown. However, for sotalol, another beta-adrenergic antagonist, inflammation causes reduced potency. Sotalol, however, is renally cleared; hence, its clearance is unaffected by inflammation. We examined if the inflammation-induced increased plasma propranolol concentration compensates for the reduced responsiveness. A modified lead I ECG was used to record PR interval and heart rate (HR). ECG was monitored following oral administration of 3, 5, 10, 15, 20, 25, and 30 mg/kg propranolol to both control and adjuvant arthritis (AA) rats. To confirm altered pharmacokinetics, single 25 mg/kg doses of propranolol were administered to both AA and control rats, with an inserted cannula in their right jugular vein for serial blood sampling. As expected, AA caused a significant reduction in the propranolol oral clearance and subsequently substantial increases in plasma total and unbound drug concentration. Interestingly, however, despite the elevated propranolol concentrations, the effect on HR remained unchanged and the prolongation of PR interval was significantly reduced in AA compared with control rats. The reduced sensitivity to propranolol in AA rats is suggestive of altered beta-adrenergic receptors function.

The increased intestinal absorption rate is responsible for the reduced hepatic first-pass extraction of propranolol in rats with cisplatin-induced renal dysfunction

The mechanisms responsible for the increased bioavailability of propranolol in renal dysfunction were investigated in rats. Experimental acute renal failure (ARF) was induced by intraperitoneal injection of cisplatin (5 mg kg(-1)). ARF induced a significant increase in blood propranolol concentration after intra-intestinal administration. The extent of bioavailability (F) of propranolol at an intestinal dose of 15 mg kg(-1) was 16.4% and 26.9% in control and ARF rats, respectively, and the F value at a 37.5 mg kg(-1) dose was 54.7% and 81.4% in control and ARF rats, respectively. In contrast, the blood propranolol concentration following intraportal infusion was not increased significantly in ARF rats. The hepatic first-pass extraction (E(h)) was dose-dependent and saturable: E(h) of propranolol in control rats was 58.0% and 18.3% at 8 and 20 mg kg(-1), respectively, and E(h) in ARF rats was 50.8% and 19.9% at 8 and 20 mg kg(-1), respectively. The initial absorption rate of propranolol from the intestine in ARF rats was significantly greater compared with control rats. These results indicated that the increased bioavailability of propranolol in rats with cisplatin-induced renal dysfunction was mainly a result of the increased absorption rate in the intestine followed by the partial saturation of hepatic first-pass metabolism.

Comparative pharmacokinetics of propranolol and atenolol in primary hyperlipidemia

The study was aimed to examine the effects of different types of hyperlipidemia on the pharmacokinetics of lipophilic propranolol and hydrophilic atenolol. Thirty subjects were divided into four study groups: normolipemics, hypercholesterolemics, hypertriglyceridemics, and patients with mixed form of hyperlipidemia. The drugs were administered orally at a single dose of 80 mg for propranolol and 100 mg for atenolol, using a cross-over study design. Pharmacokinetic parameters of the drugs were calculated using a noncompartmental open model. The results of the present study demonstrated a possible influence of dyslipidemia on pharmacokinetics of both the lipophilic and hydrophilic drugs. As for the lipophilic drug propranolol, a significant decrease in elimination rate constant was found (from 0.24 +/- 0.08 h(-1) to 0.16 +/- 0.04 h(-1), p < 0.03) in comparison to normolipemic subjects. In the case of the hydrophilic atenolol, the most marked alterations were also seen in subjects with mixed form of hyperlipidemia, especially significantly lower values of area under the concentration-time curve (8950.8 +/- 2060.5 ng/ml x h and 6715.4 +/- 1813.8 ng/ml x h, p < 0.05) as well as higher elimination rate constant (0.08 +/- 0.03 h(-1) and 0.13 +/- 0.05 h(-1), p < 0.05) in comparison with the controls, respectively. Total body clearance per kg of body weight of propranolol as well as atenolol was not influenced by dyslipidemias. The results of the study indicate that lipid metabolism disturbances might to some extent influence the pharmacokinetics of propranolol and atenolol, with the most significant alterations seen in the patients with mixed form of hyperlipidemia.

Matrix-assisted laser desorption/ionisation mass spectrometry in the study of polycondensation of Ti(OBun)4 in the presence of Si(OEt)4

The hydrolysis-polycondensation behaviour of alcoholic solutions containing Si(OEt)4 and Ti(OBun)4, in different molar ratios (Si/Ti = 10-0.2), was analysed by laser desorption/ionisation (LDI) and matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry. The solutions were prepared using operating conditions usually employed in the sol-gel synthesis of SiO2-TiO2 materials. In accord with the well-known procedures for controlling the different chemical reactivities of the alkoxides, the pre-hydrolysis of the slower reacting silicon ethoxide and the chelation by acetylacetone of the faster reacting titanium butoxide were performed before mass spectrometric analysis. While LDI-MS did not provide evidence for the presence of mixed Si-Ti species in samples obtained from these reactions, MALDI-MS of samples diluted with chloroform and using 2,5-dihydroxybenzoic acid (DHB) as matrix led to detection of various oligomers with different contents of Si and Ti atoms. The results suggest that the formation of Si-Ti mixed oligomers seems to be the favoured process, especially for solutions in which one of the two components is diluted.

Dose-response relationships of propranolol in Chinese subjects with different CYP2D6 genotypes

BACKGROUND

For clinical treatment, a smaller dosage of propranolol is often used among Chinese people. Propranolol is metabolized by polymorphic CYP2D6. We postulate that the lower propranolol dosage in Chinese is due to a slower CYP2D6 metabolism. A majority of the Chinese population has the nucleotide T188 in the CYP2D6 gene (CYP2D6*10) instead of C188 (CYP2D6*1), which most white subjects have. Chinese subjects of different CYP2D6*1/CYP2D6*10 genotypes have been shown to have different propranolol pharmacokinetic characteristics. In this study, we compared the beta-blockade effects of propranolol in Chinese subjects of the two different CYP2D6 genotypes.

METHODS

Based on the nucleotide 188 genotypes, two groups of 10 healthy subjects each were selected. Each subject was given a 10-, 20-, or 40-mg rac-propranolol tablet three times a day for 3 days in 3 different phases. Heart rate and blood pressure were measured in both supine and upright positions. The heart rate was also determined during treadmill exercise test. Plasma concentration of S-propranolol at 2 hrs after the last-dose administration was measured.

RESULTS

Despite therebeing higher S-propranolol plasma concentration in CYP2D6*10 subjects than in CYP2D6*1 subjects at 10- and 20-mg dosage, the dose-response relationship was not significantly different in these subjects.

CONCLUSIONS

Our results do not support the hypothesis that CYP2D6*1/CYP2D6*10 polymorphism may affect the beta-blockade effect of propranolol in Chinese subjects.

Common solubilizers to estimate the Caco-2 transport of poorly water-soluble drugs

Solubilizers are often used to enhance the bioavailability of drugs with poor aqueous solubility. This study focuses on the use of the Caco-2 system containing solubilizers to predict the absorption of poorly water-soluble drugs in humans. First, the effects of propylene glycol (PG), hydroxypropyl-beta-cyclodextrin (HP-beta-CD), polyethylene glycol 400 (PEG 400), and Tween 80 on the viability (transepithelial electrical resistance, TEER) of 3-day cultured Caco-2 monolayers were evaluated. These solubilizers, even at the low concentration, reduce the viability of Caco-2 monolayers; these results indicate the impossibility for 3-day cultured Caco-2 monolayers to be used for this test. Next, the effects of PG, Tween 80, PEG 400, HP-beta-CD, Pluronic F-68 (Pluronic), HCO-40, sodium lauryl sulfate (SLS), Gelucire 44/14, Transcutol P, and extract gall powder on the viability of 21-day cultured Caco-2 monolayers and the apparent permeability (P(app)) of propranolol (PPL), Nadolol (NDL), and FITC-dextran 4000 (FD-4) were investigated. Five different solubilizing methods (20% PG, 5% Tween 80, 5% PEG 400, 5% HP-beta-CD, and 5% Tween 80+5% PEG 400) did not affect the viability of 21-day cultured Caco-2 monolayers. Furthermore, the P(app) values of the three compounds containing these solubilizers did not differ from the values for control formulations (without solubilizers). These results clearly suggest that the use of PG, Tween 80, PEG 400, or HP-beta-CD as solubilizing excipients and the testing of these formulations on 21-day cultured Caco-2 monolayers can predict intestinal absorption of poorly water-soluble drugs in humans.

Region-dependent modulation of intestinal permeability by drug efflux transporters: in vitro studies in mdr1a(-/-) mouse intestine

Information on the extent to which xenobiotics interact with P-glycoprotein (PGP) during transit through the intestine is crucial in determining the influence of PGP on oral drug absorption. We have recently described a novel use of isolated ileum from PGP-deficient mdr1a(-/-) mice to resolve PGP- and non-PGP-dependent drug efflux and provide a definitive measure of intrinsic drug permeability without recourse to inhibitors. The present study uses this approach to investigate the impact of PGP on intestinal permeability of paclitaxel and digoxin in different regions of the mouse intestine (jejunum, ileum, and proximal and distal colon). Absorption of paclitaxel and digoxin in tissues from wild-type mice was low and showed little regional variation. In contrast, absorption of both drugs was markedly higher in mdr1a(-/-) intestine, although the increase was highly region-dependent, with the ileum and distal colon showing the greatest effect and much smaller changes in the jejunum and proximal colon. These effects were accompanied by the abolition of paclitaxel and digoxin secretion in mdr1a(-/-) mice, suggesting that regional variations in intestinal permeability are masked by differential PGP expression, confirmed by immunoblotting studies. Propranolol permeability, which is not influenced by PGP, showed similar regional variation in both wild-type and mdr1a(-/-) tissues, suggesting that differences are at the level of transcellular permeability. These data suggest that the ileum and the distal colon are regions of relatively high transcellular permeability for xenobiotics that are compensated by enhanced expression of PGP.

Physically cross-linked chitosan hydrogels as topical vehicles for hydrophilic drugs

Physically cross-linked chitosan hydrogels with lauric, myristic, palmitic or stearic acid were prepared by freeze-drying and have been studied for topical use. This study selected propranolol hydrochloride as a hydrophilic model drug to design a transdermal delivery system. We evaluated the effect of the nature of the cross-linker on drug permeation through porcine skin and the main permeation parameters (diffusion coefficient, flux and lag time) were calculated. All the chitosan hydrogels analysed provided more transcutaneous permeation of propranolol hydrochloride than the corresponding solution of the commercial drug. Among the different chitosan vehicles, chitosan-laurate and chitosan-myristate hydrogels enhanced lyophilised drug diffusion through the skin with respect to chitosan-palmitate and chitosan-stearate hydrogels. This can been explained by the interaction of the hydrogels with the stratum corneum, increasing the solubility of the drug in the skin.

The effect of various surfactants on the release rate of propranolol hydrochloride from hydroxypropylmethylcellulose (HPMC)-Eudragit matrices

Hydrophilic and lipophilic polymers are widely used excipients to control the release rate of drugs from matrices. Researchers found that surfactants are able to control the release rate of drugs. The aim of the present investigation is to determine the effects of surfactant type, its concentration and the different ratios of surfactants on the release rate of highly soluble drug (propranolol HCl). In this study, sodium lauryl sulphate (SLS) as an anionic surfactant, cetyl trimethyl ammonium bromide (CTAB) as a cationic surfactant, Tween 65 and Arlacel 60 as non-ionic surfactants were selected. The different concentrations of surfactants were incorporated into hydroxypropylmethylcellulose-Eudragit matrices and then dissolution rate of the drug from the matrices were evaluated at pH 1.2 or 6.8. The results showed that the release rate of propranolol decreased as the concentration of SLS increased. This is due to that SLS is able to form complex with propranolol. In contrast Tween 65 caused an increase in the release rate of the drug. Cationic surfactant (CTAB) had little effect on the release rate of the drug. It was shown that as the ratio of CTAB:SLS increased the release rate of propranolol increased from matrices. This indicated that as CTAB is able to interact with SLS molecules, therefore number of the interacting anionic molecules with the cationic drug was decreased. It can be concluded that, the type and ionization of surfactant, hydrophilicity and lipophilicity of surface active agent and various ratios of surfactants are important factors in controlling the release rate of propranolol.

[Relationship of propranolol pharmacokinetic parameters with portosystemic shunt in CCl4-induced cirrhotic rats]

BACKGROUND/AIMS

This study was designed to determine the relationship of propranolol pharmacokinetic parameters with portosystemic shunt in CCl4-induced cirrhotic rats.

METHODS

Cirrhotic rats(n=6) were induced by intramuscular injection of CCl4 in olive oil(two time per weeks) for 12 weeks. Controls (n=6) were injected intramuscularly with the same dose of olive oil for 12 weeks. We evaluated the amount of portosystemic shunt by thallium-201 per rectal scintigraphy. After intravenous bolus injection of propranolol (2mg/kg) to rats, the serum propranolol concentrations were analyzed by a HPLC-fluorimetric detector system. Pharmacokinetic parameters such as C0, AUC, t1/2(beta), and CLp were determined in each group. Then, a small amount of heptic tissue was obtained and subjected to determination of the hepatic collagen content by quantitating 4-hydroxyproline and were inspected by microscope after hematoxylin and eosin stain.

RESULTS

In liver biopsy, liver fibrosis progressed in CCl4-induced cirrhotic rats. The serum concentrations of propranolol were significantly (p < 0.01) elevated in CCl4-induced cirrhotic rats. Mean amount of 4-hydroxyproline, mean H/L ratio, and mean AUC in CCl4-induced cirrhotic rats was significantly (p < 0.01) higher than that in control rats. There was a relationship between AUC, H/L ratio, and amount of 4-hydroxyproline.

CONCLUSION

H/L ratio may help in the selection of drug dosage (especially blood flow dependent drug) in pre-clinical studies for chronic liver disease during the drug development process.

Liquid crystalline pharmacogel based enhanced transdermal delivery of propranolol hydrochloride

A novel pharmacogel was developed for the enhanced transdermal delivery of propranolol hydrochloride (PH). The synthesized prodrugs, propranolol palmitate hydrochloride (PPH) and propranolol stearate hydrochloride (PSH) self-assembled to form gel simply upon mixing alcoholic solution of prodrug with an aqueous solution in a specified ratio. By varying the ratio of prodrug, alcohol and water, three-component phase diagram was constructed which revealed isotropic-gel-vesicular dispersion regions, respectively concomitant to increasing the ratio of water. The gel phase is termed 'Pharmacogel' and exhibits birefringence under plane-polarized light corroborating the presence of lamellar liquid crystals. The pharmacogel by virtue of high chemical potential gradient and improved physicochemical properties showed the enhanced in-vitro skin permeation flux of 51.5+/-3.7 and 42.5+/-3.1 microg/cm(2)/h from PPH and PSH gel, respectively, as compared to 1.9+/-0.1 microg/cm(2)/h for control; and decrease in lag time (1.8 and 2.8 h for PPH and PSH gel, respectively) compared to control (7.6 h) was observed. The admixing of egg lecithin (EL) in increasing ratio concomitantly decreased the flux values to 31.7+/-2.1 microg/cm(2)/h (at a mole ratio of 50:50 PPH:EL) and increased the lag time. In the gel containing 50% EL, the addition of span 40 and cholesterol slightly reduced the permeation while sodium deoxycholate and Tween-80 improved it. The plasma drug levels following transdermal application of control were low (C(max)=23 ng/ml) while in PPH gel, it increased with time reaching C(max) of 94 ng/ml at 8 h post-application of PPH gel (C(max) of 75 ng/ml at 12 h post application of PL5 gel) and maintained for longer times. The AUC(0-32 h) for PPH gel was much higher (1968 ng h/ml) than control (AUC(0-18 h) was 239 ng h/ml), while EL mixed gel also showed better absorption (AUC(0-32 h) was 1707 ng h/ml). The gel formulations also caused less irritation than control, while mixed gel showed least irritation. This novel self-assembled pharmacogel providing high transdermal permeation with many variables to regulate the delivery is therefore having a great potential in percutaneous delivery.

PKQuest: a general physiologically based pharmacokinetic model. Introduction and application to propranolol

BACKGROUND

A "physiologically based pharmacokinetic" (PBPK) approach uses a realistic model of the animal to describe the pharmacokinetics. Previous PBPKs have been designed for specific solutes, required specification of a large number of parameters and have not been designed for general use.

METHODS

This new PBPK program (PKQuest) includes a "Standardhuman" and "Standardrat" data set so that the user input is minimized. It has a simple user interface, graphical output and many new features: 1) An option that uses the measured plasma concentrations to solve for the time course of the gastrointestinal, intramuscular, intraperotineal or skin absorption and systemic availability of a drug - for a general non-linear system. 2) Capillary permeability limitation defined in terms of the permeability-surface area products. 4) Saturable plasma and tissue protein binding. 5) A lung model that includes perfusion-ventilation mismatch. 6) A general optimization routine using either a global (simulated annealing) or local (Powell) minimization applicable to all model parameters.

RESULTS

PKQuest was applied to measurements of human propranolol pharmacokinetics and intestinal absorption. A meal has two effects: 1) increases portal blood flow by 50%; and 2) decreases liver metabolism by 20%. There is a significant delay in the oval propranolol absorption in fasting subjects that is absent in fed subjects. The oral absorption of the long acting form of propranolol continues for a period of more than 24 hours.

CONCLUSIONS

PKQuest provides a new general purpose, easy to use, freely distributed www.pkquest.com and physiologically rigorous PBPK software routine.

Prediction of pharmacokinetics prior to in vivo studies. II. Generic physiologically based pharmacokinetic models of drug disposition

Many in vitro data on physicochemical properties and specific absorption, distribution, metabolism, and elimination (ADME) processes are already available at early stages of drug discovery. These data about new drug candidates could be integrated/connected in physiologically based pharmacokinetic (PBPK) models to estimate a priori the overall plasma and tissue kinetic behaviors under in vivo conditions. The objective of the present study was to illustrate that generic PBPK models integrating such data can be developed in drug discovery prior to any in vivo studies. This approach was illustrated with three example compounds, including two lipophilic bases (diazepam, propranolol) and one neutral more hydrophilic drug (ethoxybenzamide). Distribution and liver metabolism were the processes integrated in the generic rat PBPK models of disposition. Tissue:plasma partition coefficients (P(t:p)s) used for description of distribution were estimated from established tissue composition-based equations, which need only in vitro data on drug lipophilicity and plasma protein binding as sole input parameters. Furthermore, data on intrinsic clearance (CL(int)) determined in vitro with hepatocytes were scaled to the in vivo situation to estimate hepatic metabolic clearance. These prediction approaches were both incorporated in the PBPK models to enable automated estimation of distribution and liver metabolism for each drug studied. The generic PBPK models suggested can simulate a priori concentration-time profiles of plasma and several tissues after intravenous administrations to rat. The results indicate that most of the simulated concentration-time profiles of plasma and 10 tissues are in reasonable agreement with the corresponding experimental data determined in vivo (less than a factor of two). However, some more relevant deviations were observed for specific tissues (brain and gut for diazepam; liver and gut for ethoxybenzamide; lung for propranolol) because of important ADME processes were probably neglected in the PBPK models of these drugs. In this context, generic PBPK models were also used for mechanistic evaluations of pharmacokinetics for generating research hypotheses to understand these deviations. Overall, the present generic and integrative PBPK approach of drug disposition suggested as a tool for a priori simulations and mechanistic evaluations of pharmacokinetics has the potential to improve the selection and optimization of new drug candidates.

The influence of core materials and film coating on the drug release from coated pellets

The objective of this study was to analyse the influence of the composition of the core of the pellets on the in vitro drug release profile. The different materials (drugs and fillers) were chosen according to their relative solubility. Pellets were prepared by a standardised process of extrusion/spheronisation. A selected fraction size (1-1.4 mm diameter) of pellets of each preparation was coated with Surelease (an aqueous dispersion of ethyl cellulose) to give 5% weight gain. The dissolution studies were performed and data analysed in terms of the Area under the Curve (AUC) of the % dissolved as function of time and Mean Dissolution Time (MDT). ANOVA was applied in order to identify the influence factors and the relationship of cross effects. Canonical analysis and multiple regression were employed to quantify these relationships. The film coat was found to be the major factor controlling the drug release. The results however, show that both drug and filler solubility influenced the drug release profile. Some of the unusual results could only be explained if consideration was given to the physical characteristics of both powder and pellets. In particular, the specific surface area of calcium phosphate compared with other fillers played an important role on the release profile of the model drug.

Synthesis and evaluation of radiolabeled antagonists for imaging of beta-adrenoceptors in the brain with PET

Five potent, lipophilic beta-adrenoceptor antagonists (carvedilol, pindolol, toliprolol and fluorinated analogs of bupranolol and penbutolol) were labeled with either carbon-11 or fluorine-18 and evaluated for cerebral beta-adrenoceptor imaging in experimental animals. The standard radioligand for autoradiography of beta-adrenoceptors, [125I]-iodocyanopindolol, was also included in this survey. All compounds showed either very low uptake in rat brain or a regional distribution that was not related to beta-adrenoceptors, whereas some ligands did display specific binding in heart and lungs. Apparently, the criteria of a high affinity and a moderately high lipophilicity were insufficient to predict the suitability of beta-adrenergic antagonists for visualization of beta-adrenoceptors in the central nervous system.

Release of propranolol and diclofenac from low Mw DL-poly(lactic acid)

The controlled release of two drugs, i.e. the sodium salt of diclofenac and propranolol was studied, by using low molecular weight D,L-Poly(lactic acid) as a matrix. Tablets of the above polymer containing those drugs were immersed into buffers with various pH values and delivery was recorded as a function of time, via UV-spectroscopy. The results showed that the polymer is appropriate for such biomedical applications, as generally, it ensures complete drug delivery within 45-60 days, which is acceptable for most cases. On the other hand, the release rate depends on many parameters including the interactions among drug, matrix and the surrounding liquid, which adds complexity to the process and requires careful investigation for proper design of a controlled release system.

[Pharmacokinetic comparison of propranolol and atenolol in people with primary hypertension]

The influence of primary hyperlipidemia on the pharmacokinetics of lipophilic propranolol and hydrophilic atenolol was studied. Thirty patients with hypercholesterolemia, hypertriglyceridemia and mixed hyperlipidemia and healthy subjects were enrolled. A single dose of 80 mg propranolol or 100 mg atenolol was administered orally using a cross-over study design. Pharmacokinetic parameters were calculated according to the noncompartmental open model. The results reflect the general tendency to altered pharmacokinetics of lipophilic and hydrophilic drugs in patients with disorders of lipid metabolism. In the case of lipophilic propranolol, the most pronounced changes were observed in mixed hyperlipidemia, with a tendency to reduced steady state distribution volume, decrease in the elimination rate constant and total body clearance. In conclusion, the present study revealed an influence of lipid disorders on the pharmacokinetics of beta-blockers, with the most significant alterations seen in mixed hyperlipidemia. The dosage of beta-blockers should be modified in patients with an abnormal lipid profile in serum.

Determination of propranolol concentration in small volume of rat plasma by HPLC with fluorometric detection

A simple, rapid and sensitive fluorescence high performance liquid chromatographic method was developed to determine propranolol concentration in the small volume of rat plasma without the solvent extraction step using pronethanol as the internal standard. The analysis was accomplished using a 5 microm CAPCELL PAK analytical cyano column at room temperature and a mobile phase consisted of 1% aqueous acetic acid containing 0.2% triethylamine and acetonitrile (65:35, v/v; pH 3.8). The flow-rate was kept at 0.5 mL/min and column effluent was monitored with a fluorescence detector at an excitation wavelength of 230 nm and an emission wavelength of 340 nm. Retention times for pronethalol and propranolol were 8.5 min and 10.5 min, respectively. Linear regressions for the standard curves were linear in the range 2-800 ng/mL, giving correlation coefficients above 0.998. The detection limit was 1.34 ng/mL. No analytical interference was observed from endogenous components in rat plasma. This simple and sensitive assay method was feasibly applied to the pharmacokinetic study of propranolol after intravenous administration of 2 mg/kg of propranolol to normal and carbon tetrachloride-induced liver cirrhotic rats.

Contributions of electromigration and electroosmosis to iontophoretic drug delivery

PURPOSE

To determine the electromigration and electroosmotic contributions to the iontophoretic delivery of lidocaine hydrochloride, in addition to the more-lipophilic quinine and propranolol hydrochlorides, in the presence and absence of background electrolyte.

METHODS

In vitro experiments, using excised pig ear skin and both vertical and side-by-side diffusion cells, were performed as a function of drug concentration and with and without background electrolytes in the anodal formulation. Concomitantly, the contribution of electroosmosis in each experimental configuration was monitored by following the transport of the neutral, polar marker molecule, mannitol.

RESULTS

Electromigration was the dominant mechanism of drug iontophoresis (typically representing approximately 90% of the total flux). In the presence of background electrolyte, lidocaine delivery increased linearly with concentration as it competed more and more effectively with Na+ to carry the charge across the skin. However, iontophoretic delivery of quinine and propranolol increased non-linearly with concentration. Without electrolytes, on the other hand, electrotransport of the three drugs was essentially independent of concentration over the range 1-100 mM. Transport efficiency of lidocaine was approximately 10%, whereas that of the more lipophilic compounds was significanly less, with the major charge carrier being Cl- moving from beneath the skin into the anodal chamber. Both quinine and propranolol induced a concentration-dependent attenuation of electroosmotic flow in the normal anode-to-cathode direction.

CONCLUSION

Dissecting apart the mechanistic contributions to iontophoretic drug delivery is key to the optimization of the formulation, and to the efficient use of the drug substance.

Inactivation of rat cytochrome P450 2D enzyme by a further metabolite of 4-hydroxypropranolol, the major and active metabolite of propranolol

Repetitive administration of propranolol (PL) in rats decreases the activities of cytochrome P450 (CYP) 2D enzyme(s) in hepatic microsomes. We examined the properties of 4-hydroxypropranolol (4-OH-PL) as an inactivator of rat liver microsomal CYP2D enzyme(s) using bunitrolol (BTL) 4-hydroxylation and PL 5- and 7-hydroxylations as indices of CYP2D enzyme activity. Rat microsomal BTL 4-hydroxylase activity was inhibited by the addition of 4-OH-PL to the incubation medium. The inhibition was greater after preincubation of microsomes with 4-OH-PL in the presence of NADPH than in its absence. The type of inhibition kinetics of BTL 4-hydroxylase by 4-OH-PL was changed from a competitive type to a noncompetitive type by the preincubation. The inhibition of rat liver microsomal PL 5- and 7-hydroxylases by 4-OH-PL was blocked efficiently by co-incubation with quinine, a typical inhibitor of rat CYP2D enzyme(s), or to a lesser extent by BTL. However, quinidine, a diastereomer of quinine, did not significantly protect against the enzyme inactivation. The protective capacities of the substrate and inhibitors reflected their affinities for rat CYP2D enzyme(s). BTL hydroxylase was not affected by either 1,4-naphthoquinone or 1,4-dihydroxynaphthalene which are possible metabolites of 4-OH-PL. These results provide further evidence to support the notion that PL is biotransformed by rat CYP2D enzyme(s) to 4-OH-PL, which is further oxidized to a chemically reactive metabolite in the active site. The inactivation of CYP is likely the result of covalent binding of the reactive species to an amino acid residue of the active site.