The influence of caprate on rectal absorption of phenoxymethylpenicillin: experience from an in-vivo perfusion in humans.

The aim of this in-vivo perfusion study in humans was to investigate the influence of a penetration enhancer, sodium caprate, on the rectal absorption of phenoxymethylpenicillin and antipyrine. Six subjects, 3 male and 3 female, were included in two separate studies using perfusion solution of different pH (T1 and T2, respectively). Each in-vivo rectal perfusion investigation lasted for 200 min and consisted of two periods of 100 min, the first serving as a control, and sodium caprate being added in the second period in both T1 and T2. The concentrations of phenoxymethylpenicillin, antipyrine and sodium caprate in the outlet perfusate were assayed by HPLC, as was the plasma concentrations of phenoxymethylpenicillin. At pH 6.0 (0-100 min) the fraction absorbed (f(abs)) and effective permeability (P(eff)) of phenoxymethylpenicillin were 0.3% and 0.06 x 4 cm s(-1), respectively, and remained unaffected by the addition of sodium caprate. When the same subjects were perfused at pH 7.4, the f(abs) and P(eff) of phenoxymethylpenicillin were 2.4% and 0.11 x 10(-4) cm s(-1) (0-100 min), respectively, also remaining unchanged by addition of sodium caprate (100-200 min). It was possible to determine the plasma AUC of phenoxymethylpenicillin after addition of sodium caprate in three subjects at both pHs; this was in the range of 14.0-62.8 and 56.4-231 (min micromol L(-1)) at pH 6.0 and 7.4, respectively. Interestingly, there was a correlation between P(eff) for sodium caprate and the individual plasma AUC and C(max) of phenoxymethyl-penicillin, which indicates that the permeability of the enhancer in the tissue upon which it should act is crucial for achieving an effect. The f(abs) and the P(eff) of antipyrine were not affected at either pH when sodium caprate was added to the perfusion solution. In conclusion, the plasma pharmacokinetics of phenoxymethylpenicillin suggested a slightly increased rectal absorption at pH 7.4 in subjects where sodium caprate was transported into the rectal tissue. However, the increased P(eff) for phenoxymethylpenicillin wastoo small to detectfrom the outlet perfusate, which suggests that sodium caprate alone has a limited effect on the permeability in-vivo across the rectal epithelium when it is presented in a solution.

Sequencing and tissue distribution of the canine MRP2 gene compared with MRP1 and MDR1.

The effects of xenobiotic drugs and toxic compounds depend largely on their kinetic properties, which can be influenced by transmembrane drug transporters like MDR1/P-glycoprotein and the drug-conjugate transporters multidrug resistance protein (MRP) 1 and 2. As the dog is a preferential species used in the pharmacological and toxicological evaluation of new drugs, we sequenced the canine MRP2 cDNA and investigated its expression in various canine tissues compared with the related transporters MRP1 and P-glycoprotein. The tissue distribution pattern of these ABC-transporters differs partially from the distribution described in humans. So we found relatively high renal and low hepatic canine MRP2 expression levels, relatively high hepatic canine MRP1 expression levels, and quite high levels of MRP1 and P-glycoprotein in the dog brain. The knowledge of the tissue distribution pattern of these transporters will aid to interpret pharmacokinetic and toxicokinetic data gained from dog studies and to extrapolate them to humans.

Evaluation of a vincristine resistant Caco-2 cell line for use in a calcein AM extrusion screening assay for P-glycoprotein interaction.

AIM: To develop a fast fluorometric screening assay based on vincristine resistant Caco-2 cells (Caco-2VCR) in order to elucidate potential P-glycoprotein (Pgp) interactions of compounds, and to characterise Caco-2VCR cells with regard to their expression of the efflux transporters Pgp, MRP1 and MRP2. METHODS: We applied the Caco-2VCR cells to a 96-well plate-based calcein AM extrusion assay. The Caco-2VCR cells were cultured as monolayers and incubated with calcein AM with/without addition of Pgp modulators. Fourteen known Pgp modulators were tested in the assay (chloropromazine, cyclosporin A, domperidone, digoxin, ivermectin, ketoconazole, loperamide, metoprolol, propranolol, progesterone, quinidine, quinine, verapamil and vincristine). For each compound an EC50 value was calculated. Protein and mRNA levels of the efflux transporters were analysed by Western blot and polymerase chain reaction techniques. RESULTS: All compounds with the exception of digoxin displayed increased calcein levels. Protein and mRNA analysis showed increased levels of Pgp after vincristine exposure, while expression of the efflux transporters MRP1 and MRP2 remained unchanged. CONCLUSIONS: The calcein AM extrusion assay applied to Caco-2VCR cells can be a valuable tool as a screening assay for new compounds and their potential interaction with P-glycoprotein.

The influence of frusemide formulation on diuretic effect and efficiency.

AIMS: Changes in drug delivery rate may result in clinically important changes in drug effects. For the loop diuretic frusemide, it would be desirable to develop controlled release preparations, that could maintain an effective urinary excretion rate over a prolonged period of time. The aim of this study was to investigate the influence of frusemide formulation on frusemide recovery, diuretic effect and efficiency. METHODS: Twelve subjects were given 60 mg of four different frusemide controlled release formulations in a single-dose, double-blind, randomized 4-way cross-over design. The formulations were three study drugs with different extended dissolution rates (ER1Tab, ER2Tab and ER3Caps ) and one reference drug (LR). Urinary volume and contents of frusemide in urine were measured in samples collected over 24 h. RESULTS: Substantial differences in frusemide recovery and diuretic efficiency were observed between LR and all other formulations. At 24 h, mean total frusemide recoveries of ER1Tab, ER2Tab and ER3Caps were 52%, 36% and 57% lower, respectively, compared with LR (P<0.01). Also at 24 h, mean total diuretic efficiency for ER1Tab, ER2Tab and ER3Caps was 83%, 31% and 135% higher, respectively, compared to LR. The rapid dissolution and absorption of LR resulted in a high diuretic response from 0 to 3 h after dosing. However, from 0 to 24 h, there were no differences in diuretic response between the formulations. CONCLUSIONS: Controlled release formulations of frusemide with a low and extended rate of dissolution lead to a more prolonged absorption and subsequent diuresis, but still maintain a similar cumulative response, due to their higher diuretic efficiency.

Critical dissolution tests of oral systems based on statistically designed experiments. II. In vitro optimization of screened variables on ER-coated spheres for the establishment of an in vitro/in vivo correlation.

The study was designed to optimize the effects of the screened in vitro dissolution variables agitation, temperature, osmolality, and polarity on the release of the neuroleptic compound remoxipride from extended release coated spheres. The variables were varied independently by means of a fractional factorial design. The in vitro tests were performed with the Basket method (USP). The polarity and the osmolality of the medium had significant effects on the dissolution rate of remoxipride. A statistical model was calculated based on the obtained dissolution in vitro. The model was then used to predict the in vitro conditions that most closely correlated with the dissolution rate of remoxipride in vivo, after administration of the formulation to 16 volunteers. The predicted in vitro conditions were experimentally verified, and an excellent association with the in vivo behavior of the formulation was found. Validation of the optimal in vitro conditions was performed on another batch of the formulation. The dissolution profile obtained showed a significant association with the corresponding dissolution profile in vivo. The use of statistically designed experiments in the development of critical dissolution tests for the establishment of in vitro/in vivo correlations seems to be a useful working approach, and supports further application to other oral solid systems.

Critical dissolution tests of oral systems based on statistically designed experiments. III. In vitro/in vivo correlation for multiple-unit capsules of paracetamol based on PLS modeling.

The main aims of the present study were to establish an in vitro/in vivo correlation for multiple-unit capsules of paracetamol by means of statistical prediction models and to investigate the effect of a number of in vitro variables on the discussion rate of paracetamol from the formulation. A fractional factorial screening design was used to investigate the effects of the variables agitation, pH, osmolality, viscosity, and the presence of bile salt on the dissolution rate of paracetamol. The effects were evaluated in two separate partial least-squares models, in which the responses were expressed as the cumulative percentage of paracetamol dissolved at specified time-points (model I) and as the shape (beta) and scale (eta) parameters according to the Weibull function (model II). It was concluded that agitation and viscosity had significant effects on the dissolution rate of paracetamol. Statistical models based on the responses from models I and II were then used to predict the in vitro conditions most closely correlated with the in vitro dissolution of paracetamol after administration of the formulation to 10 healthy volunteers. The predicted optimal in vitro conditions were similar for the two models and not too far from what is expected from the gastrointestinal tract. The experimental verification of the in vitro conditions showed that both models were equally good, and contributed to high degrees of correlation with the in vivo dissolution behavior of the formulation during 9 hr. The relationships obtained when plotting the percentage dissolved in vitro versus in vivo were y = 1.1x (r2 = 0.98) and y = 1.1x (r2 = 0.94) for models I and II, respectively. Based on these results, it is difficult to state a preference for one of the models. Finally, the use of statistical prediction models to develop critical in vitro tests is a successful approach in the establishment of associations between dissolution behavior in vitro and in vivo for oral extended-release systems.

Comparative dissolution studies of rectal formulations using the Basket, the Paddle and the Flow-Through methods. I. Paracetamol in suppositories and soft gelatin capsules of both hydrophilic and lipophilic types.

The applicabilities of the Paddle, the Basket and the Flow-Through methods have been investigated for seven different rectal compositions of hydrophilic and lipophilic type. The formulations were studied with respect to in vitro dissolution rate and behaviour in the different techniques. It was found that the composition has a considerable influence on the behaviour of the dosage form and this must be taken into account when judging the applicabilities of the three dissolution tests. The Paddle, the Basket and the Flow-Through methods are considered to be equivalent methods for the dissolving suppositories tested. The Flow-Through method is applicable for all the seven compositions tested; however, a low flow rate (8 ml/min) is necessary to use for soft gelatin capsules when both the coefficient of variation and the behaviour of the dosages within the techniques is taken into consideration.