Predictivity of standardized and controlled permeation studies: Ex vivo - In vitro - In vivo correlation for sublingual absorption of propranolol.

In preclinical drug development, ex vivo and in vitro permeability studies are a decisive element for specifying subsequent development steps. In this context, reliability, physiological alignment and appropriate in vivo correlation are mandatory for predictivity regarding drug absorption. Especially in oromucosal drug delivery, these prerequisites are not adequately met, which hinders its progressive development and results in the continuous need for animal experiments. To address current limitations, an innovative, standardized, and controlled ex vivo permeation model was applied. It is based on Kerski diffusion cells embedded in automated sampling and coupled to mass spectrometric quantification under physiologically relevant conditions. This study aimed to evaluate the predictivity of the developed model using porcine mucosa (ex vivo) in relation to data of sublingual propranolol absorption (in vivo). In addition, the usefulness of biomimetic barriers (in vitro) as a replacement for porcine mucosa was investigated. Therefore, solubility and permeability studies considering microenvironmental conditions were conducted and achieved good predictivity (R2 = 0.997) for pH-dependent permeability. A multiple level C correlation (R2 ≥ 0.860) between obtained permeability and reported pharmacokinetic animal data (AUC, Cmax) was revealed. Furthermore, a point-to-point correlation was demonstrated for several sublingual formulations. The successful IVIVC confirms the standardized ex vivo model as a viable alternative to animal testing for estimating the in vivo absorption behavior of oromucosal pharmaceuticals.

Vanillin enhances the passive transport rate and absorption of drugs with moderate oral bioavailability in vitro and in vivo by affecting the membrane structure.

Vanillin is a popular flavoring agent in the food, tobacco, and perfume industries. In this paper, we investigated the effect of vanillin on the transport rates of drugs with different levels of permeability (acyclovir, hydrochlorothiazide, propranolol and carbamazepine) through a Caco-2 cell bidirectional transport experiment. We also explored the underlying mechanism using an in silico technique and fluorescence anisotropy measurements. The influence of vanillin on the pharmacokinetics of drugs whose transport rates were affected by vanillin in vitro was then studied in vivo. Results showed that vanillin (100 µM) increased the cumulative amount of passively transported drugs (2.1-fold of hydrochlorothiazide, 1.49-fold of propranolol, 1.35-fold of acyclovir, and 1.34-fold of carbamazepine) in vitro. Molecular dynamics simulations revealed that vanillin disordered the structure of the lipid bilayer and reduced the energy barrier of drugs across the center of the membrane. The anisotropy of TMA-DPH also decreased in Caco-2 cells after treatment with vanillin (25 and 100 µM) and indicated an increase in membrane fluidity, which was dose-dependent. An oral bioavailability study indicated that vanillin (100 mg kg-1) significantly enhanced the Cmax and AUC0-6 of hydrochlorothiazide by 1.42-fold and 1.28-fold, respectively, and slightly elevated the Cmax of propranolol. In conclusion, vanillin can significantly increase the absorption of drugs with moderate oral bioavailability in vitro and in vivo by loosening the membrane. Thus, the concurrent consumption of drugs with food containing vanillin may result in increased drug plasma concentration and pose potential health risks.

Morphological and physicochemical evaluation of the propranolol HCl-Eudragit® RS100 electrosprayed nanoformulations.

The aim of this study was to fabricate propranolol hydrochloride (Prop. HCl) (as a water-soluble drug):Eudragit® RS100 (Eud) nanobeads and nanofibres applying the electrospraying method as an economical and one-step technique. Different ratios of Prop. HCl:Eud (i.e. 1:5 and 1:10) at total solution concentrations of 10-20% W/V were investigated. The FE-SEM studies revealed that morphology and size of the samples were highly affected by the solution concentration; so that, the nanobeads (a mean diameter of 82.9 nm) were formed in low concentration and at the highest concentration of the solution, nanofibres (a mean diameter of 232.3 nm) were resulted. Besides the morphological changes, the size of processed nanoformulations was increased with an increment of the solution concentrations. X-ray diffraction results as well as DSC thermograms clearly indicated that the drug crystallinity decreased in the electrosprayed samples. Furthermore, in vitro dissolution test showed that the electrosprayed samples had relatively slower release patterns toward the pure drug and physical mixtures, where the samples with the drug:polymer ratio of 1:10 indicated a faster release rate toward 1:5 ratio; nevertheless, the concentration of the injected formulations did not remarkably impressed the release behaviours. The current study established the suitability of electrospraying method in the fabrication of the water-soluble drugs nanobeads/nanofibres; however, in vivo effectiveness of the prepared nanoformulations should be meticulously considered.

Chronotherapeutic drug delivery of Tamarind gum, Chitosan and Okra gum controlled release colon targeted directly compressed Propranolol HCl matrix tablets and in-vitro evaluation.

The main objective of this investigation is to develop a chronotherapeutic drug delivery of various natural polymers based colon targeted drug delivery systems to treat early morning sign in BP. The polymers such as Tamarind gum, Okra gum and Chitosan were used in the formulation design. A model drug Propranolol HCl was incorporated in the formulation in order to assess the controlled release and time dependent release potential of various natural polymers. A novel polymer Tamarind gum was extracted and used as a prime polymer in this study to prove the superiority of this polymer over other leading natural polymer. Propranolol HCl was used as a model drug which undergoes hepatic metabolism and witnesses the poor bioavailability. The matrix tablets of Propranolol HCl were prepared by direct compression. The tablets were evaluated for various quality control parameters and found to be within the limits. Carbopol 940 was used as an auxiliary polymer to modify the drug release and physicochemical characteristics of the tablets. The in vitro release studies were performed in 0.1N HCl for 1.5h, followed by pH 6.8 phosphate buffer for 2h and pH 7.4 phosphate buffer till maximum amount of drug release. The in vitro release profile of the formulations were fitted with various pharmacokinetic mathematical models and analyzed for release profile. The formulations prepared with Tamarind gum prolonged the release for an extended period of time compared to other polymer based formulation and showed an excellent compression characteristic.

Formulation, characterization and clinical evaluation of propranolol hydrochloride gel for transdermal treatment of superficial infantile hemangioma.

The objective of the present study is to formulate and characterize propranolol hydrochloride (PPL · HCl) gel, and to evaluate the efficacy of this formulation in transdermal treatment for superficial infantile hemangioma (IH). The transdermal PPL · HCl gel was prepared by a direct swelling method, which chose hydroxypropyl methylcellulose (HPMC) as the matrix and used terpenes plus alcohols as permeation enhancer. Permeation studies of PPL · HCl were carried out with modified Franz diffusion cells through piglet skin. Our results pointed to that among all studied permeation enhancers, farnesol plus isopropanol was the most effective combination (Q24, 6027.4 ± 563.1 µg/cm(2), ER, 6.8), which was significantly higher than that of control gel (p < 0.05). High percutaneous penetration with related lower plasma drug level of PPL · HCl gel was confirmed by microdialysis technique in rats using the homemade PPL · HCl oral solution as a control. Clinical studies also confirmed the excellent therapeutic response and few side effects of the PPL · HCl gel. These results suggest that transdermal application of the PPL · HCl gel is an effective and safe formulation in treating superficial IH.

In vitro and in vivo evaluations of a novel pulsed and controlled osmotic pump capsule.

OBJECTIVE: For better treatment of circadian cardiovascular events, a novel Propranolol hydrochloride (PNH) delayed-release osmotic pump capsule was developed. METHODS: The capsule body was designed of asymmetric membrane and the capsule cap was made impermeable. The physical characteristics of capsule body walls and membrane permeability were compared among different coating solutions. RESULTS: The formulation with the glycerin and diethyl phthalate (DEP) ratio of 5:4 appeared to be the best. The lag time and subsequent drug release were investigated through assembling the capsule body with capsule caps of different length. WSR N-10 was chosen as the suspending for its moderate expanding capacity. The influence of factors (WSR N-10 content, NaCl content and capsule cap length) on the responses (lag time and drug release rate) was evaluated using central composite design-response surface methodology. A second-order polynomial equation was fitted to the data and actual response values were in good accordance with the predicted ones. The optimized formulation displayed complete drug delivery, zero-order release rate with 4-h lag time. The results of in vivo pharmacokinetics in beagle dogs clearly suggested the controlled and sustained release of PNH from the system and that the relative bioavailability of this preparation was about 1.023 comparing the marketed preparation. CONCLUSIONS: These results indicate that by the adjustment of capsule cap length, PNH could be developed as a novel pulsatile and controlled drug delivery system.

Design and in vitro evaluation of effervescent gastric floating drug delivery systems of propanolol HCl.

Abstract. The purpose of this research was to develop and evaluate effervescent gastric floating tablets of propranolol HCl. The oral delivery of antihypertensive propranolol HCl was facilitated by preparing an effervescent floating dosage form which could increase its absorption in the stomach by increasing the drug's gastric residence time. In the present work, effervescent floating tablets were prepared with a hydrophilic carrier such as polyethylene oxide (PEO WSR N 60K and PEO WSR 303) as a release retarding agent and sodium bicarbonate as a gas generating agent. The prepared tablets were evaluated for all their physicochemical properties, in vitro buoyancy, drug release and rate order kinetics. From the results, P9 was selected as an optimized formulation based on their 12 h drug release, minimal floating lag time and maximum total floating time. The optimized formulation followed first order rate kinetics with erosion mechanism. The optimized formulation was characterized with FTIR studies and no interaction between the drug and the polymers were observed.

Design and in vitro evaluation of effervescent gastric floating drug delivery systems of propanolol HCl / Diseño y evaluación in vitro de sistemas de administración de tabletas flotantes gástricas everfescentes de HCl propanolol

The purpose of this research was to develop and evaluate effervescent gastric floating tablets of propranolol HCl. The oral delivery of antihypertensive propranolol HCl was facilitated by preparing an effervescent floating dosage form which could increase its absorption in the stomach by increasing the drug’s gastric residence time. In the present work, effervescent floating tablets were prepared with a hydrophilic carrier such as polyethylene oxide (PEO WSR N 60K and PEO WSR 303) as a release retarding agent and sodium bicarbonate as a gas generating agent. The prepared tablets were evaluated for all their physicochemical properties, in vitro buoyancy, drug release and rate order kinetics. From the results, P9 was selected as an optimized formulation based on their 12 h drug release, minimal floating lag time and maximum total floating time. The optimized formulation followed first order rate kinetics with erosion mechanism. The optimized formulation was characterized with FTIR studies and no interaction between the drug and the polymers were observed.

El propósito de la presente investigación fue desarrollar y evaluar tabletas flotantes, efervescentes de HCL propranolol. La administración oral del antihipertensivo HCL propranolol se facilitó mediante la preparación de una forma de dosificación flotante y efervescente que permitiría su absorción en el estómago, mediante el aumento del tiempo de residencia gástrico de la droga. En el presente trabajo, las tabletas flotantes efervescentes fueron preparadas con un portador hidrofílico, tal como el óxido de polietileno (PEO WSR N 60K and PEO WSR 303), como agente retardador y bicarbonato de sodio como un agente generador de gas. Se evaluaron todas las propiedades fisicoquímicas de las tabletas preparadas, su flotación in vitro y su tasa de orden cinético. Se seleccionó el P9 a partir de los resultados obtenidos, como una fórmula óptima, basados en la liberación de la droga a las 12 h, tiempo mínimo de retraso para flotación y máximo tiempo total de flotación. La formulación optimizada siguió una tasa cinética de primer orden con mecanismo de erosión. Esta fórmula óptima se caracterizó mediante estudios FITR y no se observó ninguna interacción entre la droga y los polímeros utilizados.

Design and evaluation of a bioadhesive film for transdermal delivery of propranolol hydrochloride.

The objective of the study was to develop a suitable trans-dermal delivery system for propranolol hydrochloride (PPL) via employing chitosan as a film former. Drug concentration uniformity, thickness, moisture uptake capacity and skin bioadhesion of the films were characterized. The effects of chitosan and PPL concentration and different penetration enhancers on the release and permeation profiles from the films were investigated. Skin irritation of the candidate film was evaluated. Chitosan film (PPL 2 mg cm(-2), chitosan 2%, m/m, cineol 10%, m/m) was found nonirritant and achieved 88.2% release after 8 hours in phosphate buffer. Significant high (p < 0.001) permeation of PPL through rat skin was obtained using this film compared to the film without enhancer (about 8 times enhancement factor), making it a promising trans-dermal delivery system for PPL.

Modification of propranolol's bioavailability by Eurycoma longifolia water-based extract.

WHAT IS KNOWN AND BACKGROUND: Eurycoma longifolia (E. longifolia), a herb commonly consumed for its aphrodisiac properties, is widely used by Asian males. This may include hypertensive patients receiving propranolol which may cause sexual dysfunction as one of its side-effects. There is no published study of the potential pharmacokinetic interaction between propranolol and the herb. OBJECTIVE: To study propranolol's pharmacokinetics when E. longifolia is consumed, comparing volunteers given either propranolol or a placebo. METHODS: This is a placebo-controlled randomized single-blinded crossover study of the effect of a water-based extract of E. longifolia on the pharmacokinetics of a single dose of proporanolol (Inderal(®)) in 14 healthy non-smoker young males. Eighty milligram of propranonol was orally administered with (i) placebo (Lactose) or (ii) 200 mg of water-based extract of E. longifolia (0·0272 ± 0·0026%eurycomanone) following an overnight fasting. Blood samples were collected at 0, 0·5, 1, 1·5, 2, 3, 4, 6, 8 and 10 h for propranolol's plasma concentration determinations using a validated high-performance liquid chromatography (HPLC) method. RESULTS AND DISCUSSION: When propranolol was administered with E. longifolia, its bioavailability (AUC0-∞) decreased by 29% while C(max) was reduced by 42% and T(max) was significantly prolonged by almost 86%. The terminal elimination half-life, however, was not significantly affected. CONCLUSION: The bioavailability of propranolol is significantly decreased when consumed together with E. longifolia. The interaction is due to a reduction in absorption, rather than an increase in propranolol's metabolism. Although the pharmacodynamics of propranolol was not affected in healthy volunteers, caution is still advisable with co-administration of the drug and the herb.

The intestinal permeability of neolignans from the seeds of Myristica fragrans in the Caco-2 cell monolayer model.

The intestinal permeability and transport of 10 neolignans isolated from MYRISTICA FRAGRANS were studied by using the Caco-2 cell monolayer model. The 10 neolignans were measured by HPLC. Transport parameters and permeability coefficients were then calculated and compared with those of the model compounds, propranolol and atenolol. Among the 10 neolignans, the 8- O-4'-type neolignans demonstrated high permeability while the benzofuran-type neolignans were of poor to moderate permeability. Among them, eight neolignans were transported mainly VIA passive diffusion. These findings indicate that the 8- O-4'-type neolignans are well-absorbed compounds and can be used as oral leading compounds in drug discovery.

Development of a novel system for estimating human intestinal absorption using Caco-2 cells in the absence of esterase activity.

Both mRNA and protein levels of the carboxylesterase (CES) isozymes, hCE1 and hCE2, in Caco-2 cells increase in a time-dependent manner, but hCE1 levels are always higher than those of hCE2. In human small intestine, however, the picture is reversed, with hCE2 being the predominant isozyme. Drugs hydrolyzed by hCE1 but not by hCE2 can be hydrolyzed in Caco-2 cells, but they are barely hydrolyzed in human small intestine. The results in Caco-2 cells can be misleading as a predictor of what will happen in human small intestine. In the present study, we proposed a novel method for predicting the absorption of prodrugs in the absence of CES-mediated hydrolysis in Caco-2 cells. The specific inhibition against CES was achieved using bis-p-nitrophenyl phosphate (BNPP). The optimal concentration of BNPP was determined at 200 microM by measuring the transport and hydrolysis of O-butyryl-propranolol (butyryl-PL) as a probe. BNPP concentrations of more than 200 microM inhibited 86% of hydrolysis of butyryl-PL, resulting in an increase in its apparent permeability. Treatment with 200 microM BNPP did not affect paracellular transport, passive diffusion, or carrier-mediated transport. Furthermore, the proposed evaluation system was tested for ethyl fexofenadine (ethyl-FXD), which is a superior substrate for hCE1 but a poor one for hCE2. CES-mediated hydrolysis of ethyl-FXD was 94% inhibited by 200 microM BNPP, and ethyl-FXD was passively transported as an intact prodrug. From the above observations, the novel evaluation system is effective for the prediction of human intestinal absorption of ester-type prodrugs.

A new simple cell-based homogeneous time-resolved fluorescence QRET technique for receptor-ligand interaction screening.

In this article, a single-label separation-free fluorescence technique is presented as a potential screening method for cell-based receptor antagonists and agonists.The time-resolved fluorescence technique, quenching resonance energy transfer (QRET), relies on a single-labeled binding partner in combination with a soluble quencher. The quencher efficiently suppresses the luminescence of the unbound labeled ligand, whereas the luminescence of the bound fraction is not affected. This approach allows the development of cell-based screening assays in a simple and cost-effective manner. The authors have applied the technique to the screening of beta(2)-adrenoreceptor (beta(2)AR) antagonists and agonists in intact human embryonic kidney HEK293(i) cells overexpressing human beta(2)-adrenergic receptors. Two antagonists (propranolol, alprenolol) and 2 agonists (metaproterenol, terbutaline) for beta(2)AR were investigated in a displacement assay using europium(III)-labeled pindolol ligand. The assay Z' values ranged from 0.68 to 0.78, the coefficient of variation was less than 10%, and the K(i) values were 19 nM for propranolol and alprenolol and 14 and 5.9 microM for metaproterenol and terbutaline, respectively. The QRET technique with beta(2)AR was also applied to LOPAC compound library screening, yielding nearly error-free recognition of known binders. This simple and cost-effective technique can be readily adapted to laboratory and industrial-scale screening.

Exploration of the African green monkey as a preclinical pharmacokinetic model: oral pharmacokinetic parameters and drug-drug interactions.

African green monkeys (vervets) have been proposed as an alternate species that might allow improved access and provide high-quality pharmacokinetic results comparable with other primates. However, no oral data are available in vervets to evaluate cross-species predictive performance. Therefore, this study was conducted to evaluate the use of the vervet to predict human oral pharmacokinetics and drug interactions. Oral pharmacokinetic studies were conducted in the vervet for eight compounds: phenytoin, moxifloxacin, erythromycin, lidocaine, propranolol, ciprofloxacin, metroprolol, and prednisolone. To assess drug-drug interactions, co-administration experiments were conducted with ketoconazole and either propranolol or erythromycin. In general, the vervet provided similar predictivity for human oral exposure as cynomolgus or rhesus monkeys. In all non-human primates, human exposure to phenytoin would be over-predicted, and erythromycin, lidocaine, and propranolol under-predicted, with good predictivity for the other compounds studied. Furthermore, in the vervet, ketoconazole co-administration resulted in a six-fold increase in exposure to erythromycin, demonstrating proof of concept for drug-drug interaction screening. These data support further exploration of the vervet as an alternate primate species for use in preclinical pharmacokinetic screening.

HO-1-u-1 model for screening sublingual drug delivery--influence of pH, osmolarity and permeation enhancer.

HO-1-u-1 (Ueda-1) is a human tumor cell line established from human sublingual squamous cell carcinoma. In previous study, HO-1-u-1 cell line was grown on cell culture inserts and utilized as in vitro model for screening sublingual drug delivery. The aim of current study was to further investigate the effects of pH, osmolarity and permeation enhancer, sodium glycodeoxycholate (GDC) on the permeability of three beta-blockers with different lipophilicities. The cytotoxicity was evaluated by MTS/PES assay. The permeability studies were carried out using the cell culture model and compared with that obtained from fresh porcine sublingual mucosa. The results showed the enhancement effects caused by pH, osmolarity and GDC were highly lipophilicity-dependent and in the order atenolol>metoprolol>propranolol. The apparent permeability coefficients (P(app)) of all the three beta-blockers were significantly increased by increasing pH. However, less enhancing effects were observed by non-physiological osmolarity or the presence of GDC in permeability study using both cell culture and porcine sublingual mucosa. The present results suggested that the HO-1-u-1 cell culture model maybe a useful and effective in vitro model for evaluating the enhancement effects and mechanism in sublingual drug delivery.

Evaluation of the use of UPLC-TOFMS with simultaneous [14C]-radioflow detection for drug metabolite profiling: application to propranolol metabolites in rat urine.

The non-selective beta-adrenergic receptor antagonist propranolol [1-(isopropylamino)-3-(1-naphthoxy)-2-propanol] is metabolised extensively in vivo. Enumerating and identifying the many metabolites that result from multiple biotransformations provides a considerable analytical challenge, greatly aided by efficient chromatography coupled to sensitive mass spectrometric detection. Here the use of the newly introduced high-resolution technique of "ultra performance liquid chromatography" (UPLC) linked to quadrupole time-of-flight mass spectrometry (TOFMS) with simultaneous [(14)C]-radioflow detection was applied to rapid metabolite profiling. [14C]-propranolol, dosed intraperitoneally to rat at 25 mg kg(-1) and 200 microCi kg(-1) was used as a model compound for this evaluation. Some 14 metabolites were detected in the urine by this technique including a number of conjugated metabolites such as sulphates, several isobaric glucuronides and two novel di-glucuronides.

Development of a reservoir-type transdermal enantioselective-controlled delivery system for racemic propranolol using a molecularly imprinted polymer composite membrane.

The aims of this study were to develop a transdermal patch for selective controlled delivery of the active S-enantiomer from racemic propranolol, and to evaluate its performance in vivo using Wistar rats. A molecularly imprinted polymer (MIP) thin-layer composited cellulose membrane with selectivity for S-propranolol was employed as the enantioselective-controlled release system. The effect of gel reservoir (poloxamer and chitosan) on enantioselective delivery was investigated. The chitosan gel allowed excellent selectivity for delivery of the S-propranolol enantiomer, whilst the more rheologically structured poloxamer gel formulation provided no selective release of S-propranolol. The chitosan gel exhibited high flux and had the ability to enantioselective deliver S-propranolol across excised rat skin. The results from confocal laser scanning microscopy study, carried out with the R- and S-propranolol enantiomers labeled with a 1-pyrenebutyric acid probe as fluorescent markers, suggested that the MIP composite membrane selectively regulated the release of the recognised S-enantiomer via a facilitated transport pathway through complex formation with the selective receptor sites, while the release of the R-enantiomer was via a non-selective route. The reservoir patch for enantiomer-controlled delivery of propranolol was therefore fabricated by incorporating the chitosan gel formulation containing racemic propranolol hydrochloride into the MIP composite membrane laminated backing. These patch devices were shown to exhibit the significant stereoselectivity uptake of propranolol when attached to the skin, using pharmacokinetic studies in rats. S-Propranolol enantiomer plasma concentration profiles for the transdermal patch in the in vivo study were comparable to data for the gel formulations that were applied directly to skin, and containing a single S-enantiomer of propranolol. The results demonstrate that the transdermal patch based on the MIP composite membrane-controlled release system may have potential in the enantioselective-controlled delivery of the S-isomer of racemic propranolol.

A novel time-controlled release system based on drug-resin complexes and elementary osmotic pump.

A novel time-controlled system based on elementary osmotic pump tablet containing a drug-resin complexes (DRCs) core is presented. In the traditional osmotic pump tablets (OPTs), the lag time was always minimized. On the contrary, in the DRCs osmotic pump tablet (DRCOPT), the lag time was increased to achieve time-controlled delivery. The system led to a zero-order drug release after an initial lag time. Polyethylene oxide (PEO) N80 was used as suspension agent and NaCl was applied as ion-exchange, osmotic pressure (electrolyte supplementary) agent, respectively. To examine the mechanism of this system, drug release behaviors were investigated under conditions of various osmotic pressures. A new method of combination of conductivity and HPLC was applied to determine the different fractions of NaCl in producing osmotic pressure, ion-exchange and electrolyte supplement. The pharmacokinetic studies conducted in beagle dogs showed that a steadier and controlled drug release behavior was obtained compared with the traditional formulations. On the basis of prescription of the DRCOPT, a good in-vitro-in-vivo correlation (IVIVC, R(2)=0.9541) was achieved. In addition, a lag time of 4 h was observed in in vivo experiment, which indicated that the DRCOPT can be used in therapeutic regimens with the characteristics of chronotherapy.

Anthranoid laxatives influence the absorption of poorly permeable drugs in human intestinal cell culture model (Caco-2).

Interactions between widely used anthranoid laxatives and other simultaneously administered drugs are not known. In this paper, the influence of rhein, danthron, sennidins A/B, sennosides A/B, and senna leaf infusion was investigated on the permeability of furosemide, ketoprofen, paracetamol, propranolol, verapamil, digoxin, and Rhodamine 123 across Caco-2 monolayers. The effects on monolayer integrity ([(14)C]mannitol permeability, TEER) were also determined. The in vitro absorption of highly permeable drugs was not strongly affected during co-administration of the laxatives. Furosemide permeability was enhanced by rhein and danthron (3.6 and 3.0-fold), which may partly be due to opening of the paracellular spaces and/or effects on active efflux. However, the secretory permeability of digoxin and Rho 123 was not strongly affected by rhein and danthron, suggesting that inhibition of MDR1 was not responsible for the increased permeation of furosemide. The absorptive permeability of digoxin was decreased by rhein and danthron, offering evidence for effects on apical membranes. The effects on monolayer integrity were detectable, but reversible. According to presented experiments, daily use of laxatives with well-absorbing drugs would seem unlikely to affect drug permeability, but the effects on the absorption of poorly permeable drugs cannot be excluded.

Induction of propranolol metabolism by Ginkgo biloba extract EGb 761 in rats.

Ginkgo biloba is one of the most popular herbal medicines in the world, due to its purported pharmacological effects, including memory-enhancing, cognition-improving, and antiplatelet effects. When used in the elderly, Ginkgo has a high potential for interactions with cardiovascular drugs. This study aimed to investigate the effects of the standard Ginkgo biloba extract (EGB 761) treatment on the pharmacokinetics of propranolol and its metabolism to form N-desisopropylpropranolol (NDP) in rats. We also examined the activity and expression of cytochrome P450 (CYP) 1A and other CYPs in rats treated with EGb 761 at 10 and 100 mg/kg/day for 10 days. A single oral dose of propranolol (10 mg/kg) was administered on day 11 and the concentrations of both propranolol and NDP were determined using validated liquid chromatography-mass spectrometry (LC-MS) methods. The levels of mRNA and protein of various CYPs were determined by RT-PCR and Western blotting analysis, respectively. Pretreatment of EGb 761 at 100 mg/kg, but not 10 mg/kg, for 10 days significantly reduced the area under the plasma concentration-time curve (AUC) and maximum plasma concentration (Cmax) of propranolol, whereas those values of NDP were significantly increased. CYP1A1, 1A2, 2B1/2, and 3A1 activities and gene expression in the rat liver were significantly increased in a dose-dependent manner by pretreatment with EGb 761. The ex-vivo formation of NDP in liver microsomes from rats pretreated with EGb 761 was markedly enhanced. The formation of NDP from propranolol in liver microsomes was significantly inhibited by alpha-naphthoflavone (ANF, a selective CYP1A2 inhibitor), but not by quinidine (a CYP2D inhibitor). These results indicated that EGb 761 pretreatment decreased the plasma concentrations of propranolol by accelerated conversion of parental drug to NDP due to induction of CYP1A2. EGb 761 pretreatment also significantly induced CYP2B1/2 and CYP3A1, suggesting potential interactions with substrate drugs for these two enzymes. Further study is needed to explore the potential for gingko-drug interactions and the clinical impact.