Usefulness of microspheres composed of gelatin with various cross-linking density.

The release rate of insulin, as a model peptide, from gelatin microspheres (GM) prepared with gelatin having various cross-linking densities in vitro was examined. The release of insulin from GM showed the burst effect, followed by a slow release phase regardless of the cross-linking density of gelatin. The total amount of insulin released in 2 weeks decreased with increasing cross-linking density of gelatin. The release rate of insulin within 6 h was well correlated with the cross-linking density of gelatin. The remaining amounts of both insulin and GM after injection of insulin incorporated in GM to mice femoral muscle tissue were also examined in vivo. Both insulin and GM rapidly disappeared from the injection site within 1 day, and thereafter slowly disappeared over 14 days. The time courses of the remaining amounts were fairly similar to each other. Furthermore, the remaining amount of insulin 1 day after administration was well correlated with the cross-linking density of gelatin. These data suggest that insulin was released from GM with the degradation of GM in mice muscular tissue and that the release rate of insulin can be controlled by modifying the cross-linking density of gelatin. In conclusion, the control of the release rate of insulin from GM can be achieved under both in vitro and in vivo conditions by gelatin through the alteration of cross-linking conditions.

Pharmacokinetic-pharmacodynamic modelling of human insulin: validity of pharmacological availability as a substitute for extent of bioavailability.

A method for assessing the extent of bioavailability (EBA) of human insulin from pharmacological data was determined. The time course governing increases in the plasma concentration of immuno-reactive insulin (IRI), as well as its pharmacological effects (glucodynamics), was determined after the intravascular administration of varying doses of human insulin. Pharmacokinetic (PK), pharmacodynamic (PD), and link models were constructed to elucidate the quantitative relationship between plasma IRI levels and pharmacological effects. After extravascular administration of the test formulation, only the time course governing the observed pharmacological effects was determined. The pharmacological data was translated into theoretical plasma concentration data, using the PK-PD model. Following this, the area under the theoretical plasma concentration-time curve (AUC) of the test formulation was calculated. The EBA was then estimated against a reference (intravascular) formulation, using a conventional equation. Since the pharmacological effects of insulin were observed to be highly dosing-rate-dependent, the PD model used in this study was modified to apply over a wide range of infusion rates. The results of the PK-PD analysis indicate that the doses administered can be accurately predicted from pharmacological data. To validate this method, the EBAs of controlled release formulations (the Osmotic Mini Pumps) of insulin, subcutaneously administered to the rat, were estimated. The EBA values obtained (92-96%) fell within a reasonable range. The area under the effect-time curves (AUE) obtained following subcutaneous applications of the Osmotic Mini Pump were calculated in a model-independent manner, in addition to pharmacological availabilities (PA), which were estimated against the reference (intravascular) formulations. The estimated PA values varied from 312% to 78%, in accordance with the intravascular input rates of the reference formulations. This indicates that PA should not be used as a substitute for EBA, unless data involving similar intravascular dosing rates to that of the reference formulations is available.

Effects of low-viscosity sodium hyaluronate preparation on the pulmonary absorption of rh-insulin in rats.

PURPOSE: A low-viscosity formulation for pulmonary delivery of rh-insulin as model peptide drugs was developed using a solution of sodium hyaluronate. METHOD: The effects of different concentrations and pH values of low-viscosity solutions of hyaluronate on the pulmonary absorption of rh-insulin were examined after intratracheal administration in rats. The permeation of fluorescein isothiocyanate (FITC)-dextran (molecular weight 4300; FD-4) and insulin through excised rat trachea in vitro were also examined. RESULTS: The hyaluronate (2140 kDa) solutions (0.1% and 0.2% w/v) at pH 7.0 significantly enhanced the pharmacological availability (PAB) of insulin compared to the aqueous solution of insulin at pH 7.0. The absorption-enhancing effect at a concentration of 0.1% w/v hyaluronate was greater than that at a concentration of 0.2% w/v hyaluronate. Furthermore, the greatest absorption-enhancing effect was obtained, regardless of the molecular weight of hyaluronate, when the concentration of hyaluronate was adjusted to 0.47 microM. Absorption-enhancing effects were consistent with the effect of a 0.1 w/v hyaluronate preparation at pH 4.0 and 7.0 on the permeation of FITC-dextran and insulin through excised rat trachea in vitro. CONCLUSION: Low-viscosity hyaluronate preparation was shown to be a useful vehicle for pulmonary delivery of peptide drugs.

Evaluation of gelatin microspheres for nasal and intramuscular administrations of salmon calcitonin.

The suitability of gelatin microspheres for nasal and intramuscular delivery of salmon calcitonin (sCT) was examined. Negatively and positively charged gelatin microspheres were prepared using acidic gelatin [isoelectric point (IEP) value of 5.0] and basic gelatin (IEP=9.0), respectively. The average diameters of positively charged gelatin microspheres in their dried state were 3.4, 11.2, 22.5 and 71.5 microm, while that of negatively charged gelatin microspheres was 10.9 microm. Both types of gelatin microspheres were capable of adhering to the nasal mucosa. The mucoadhesion of positively charged gelatin microspheres was significantly higher than that of their negatively charged counterparts. The absorption of sCT after intranasal and intramuscular administration was evaluated by calculating the area above the hypocalcemic-time curve (AAC) in rats. The AAC values after nasal administration of sCT in positively and negatively charged gelatin microspheres were significantly greater than that in pH 7.0 PBS. Therefore, the nasal absorption of sCT was enhanced by both types of gelatin microspheres. The hypocalcemic effect after administration of sCT in positively charged gelatin microspheres of 11.2 microm was significantly greater than that of negatively charged gelatin microspheres of the same size. On the other hand, AAC values were not affected by their particle sizes. The AAC values after the intramuscular administration of sCT in positively and negatively charged gelatin microspheres were significantly increased compared to that in PBS. Furthermore, the time-courses of the plasma calcium levels differed between positively and negatively charged gelatin microspheres. The hypocalcemic effect of the negatively charged gelatin microspheres tended to appear more slowly and last longer compared to that of positively charged gelatin microspheres. The hypocalcemic effects after intramuscular administration of sCT in gelatin microspheres were not affected by their particle sizes as well as those after intranasal administration. In conclusion, the gelatin microspheres have been shown to be a useful vehicle for nasal or intramuscular delivery of sCT.

Bioavailability assessment of disopyramide using pharmacokinetic-pharmacodynamic (PK-PD) modeling in the rat.

The relationship between the serum concentration and the pharmacological effect of disopyramide was investigated quantitatively to estimate the extent of its oral bioavailability (EBA(p.o.) and to evaluate the drug interaction with miconazole, a CYP3A4 inhibitor. An integrated pharmacokinetic-pharmacodynamic (PK-PD) model was used to describe the relationship between the serum concentrations and changes in QT interval (pharmacological data) of disopyramide after intra-vascular infusion for 15 min (i.v. short-term infusion) to rats. A two-compartment model was applied to the pharmacokinetics of disopyramide. The pharmacological data after short-term infusion were well explained using a PK-PD link model. To validate the present PK-PD model. disopyramide was administered intra-vascularly in separate experiments, and the doses were predicted only from the pharmacological data. The model predicted doses were identical to the actual doses, regardless of the dosing rates. This result indicates that the PK-PD model used in the present study is appropriate, and that the relationship between the serum concentrations and changes in QT intervals is independent of the dosing (input) rate. When miconazole was co-administered orally 1 h before disopyramide infusion, the serum disopyramide concentrations were significantly higher than that following disopyramide alone. The raised serum concentrations under miconazole co-administration were well explained by nonlinear elimination clearance. The pharmacological effects of disopyramide under miconazole co-administration, were also greater than those following disopyramide alone. The results of the PK-PD analysis indicated that the enhanced pharmacological response under miconazole co-administration was simply caused by a pharmacokinetic change. The EBA(p.o.) values estimated from the pharmacological effects predicted the observed values reasonably well. In conclusion, we demonstrated following: (1) the pharmacological effect after intra-vascular administration of disopyramide is related quantitatively to the serum concentrations using a PK-PD model; (2) miconazole affects only the elimination clearance of disopyramide to enhance the pharmacological effect; (3) the EBA of disopyramide can estimated reasonably only well from the pharmacological data using the PK-PD model; (4) there is no dosing-rate-dependent or dosing-route-dependent pharmacological effect of disopyramide.

Gelatin microspheres as a pulmonary delivery system: evaluation of salmon calcitonin absorption.

The use of negatively and positively charged gelatin microspheres for pulmonary delivery of salmon calcitonin was examined in rats. The microspheres were prepared using acidic gelatin (isoelectric point (IEP):, 5.0) and basic gelatin (IEP, 9.0) for the negatively and positively charged microspheres, respectively. The average diameters of positively charged gelatin microspheres in the dry state were 3.4, 11.2, 22.5 and 71.5 microm, and that of negatively charged gelatin microspheres was 10.9 microm. Neither positively nor negatively charged gelatin microspheres underwent any degradation in pH 7.0 PBS and there was less than 8% degradation in bronchoalveolar lavage fluid (BALF) after 8 h. In in-vitro release studies in pH 7.0 PBS, salmon calcitonin was rapidly released from positively charged gelatin microspheres within 2 h, and its cumulative release was approximately 85%. In addition, the release profiles were not influenced by particle sizes. The release rates of salmon calcitonin from negatively charged gelatin microspheres were lower than that from positively charged gelatin microspheres. The cumulative release was approximately 40% after 2 h, but there was no evidence of any sustained release. The pulmonary absorption of salmon calcitonin from gelatin microspheres was estimated by measuring its hypocalcaemic effect in rats. The pharmacological availability after administration of salmon calcitonin in positively and negatively charged gelatin microspheres was significantly higher than that in pH 7.0 PBS. The pharmacological availability after administration of salmon calcitonin in positively charged gelatin microspheres was significantly higher than that in negatively charged gelatin microspheres. Administration of salmon calcitonin in positively charged gelatin microspheres with smaller particle sizes led to a higher pharmacological availability. The pharmacological availability after pulmonary administration of salmon calcitonin in positively charged gelatin microspheres with particle sizes of 3.4 and 11.2 microm was approximately 50%. In conclusion, the gelatin microspheres have been shown to be a useful vehicle for pulmonary delivery of salmon calcitonin.

Effects of sodium glycocholate and protease inhibitors on permeability of TRH and insulin across rabbit trachea.

The permeabilities of thyrotropin-releasing hormone (TRH) and insulin as model peptides were examined to characterize the tracheal epithelial barrier in in vitro experiments using excised rabbit trachea. TRH was not metabolized during 150 min duration of tracheal permeation and the apparent permeability coefficient (Papp) for TRH was about 3 x 10(-7) cm/s. The tracheal permeability of TRH was increased about three times by 10 mM glycocholate as a permeation enhancer. Insulin showed a slight degradation during 150 min duration of tracheal permeation, the Papp for insulin was 7 x 10(-9) cm/s. The tracheal permeability of insulin was significantly increased by 10 mM glycocholate, 1 mM bestatin (aminopeptidase B and leucine aminopeptidase inhibitor), and 10,000 KIU/ml aprotinin (trypsin and chymotrypsin inhibitor). The peptidase activities of rabbit tracheal epithelium were found to be the following; di-peptidyl-aminopeptidase IV (DPP IV) > Leu-aminopeptidase > cathepsin-B > trypsin. These activities were significantly lower than those of jejunal mucosal tissues. These results suggest that the tracheal absorption of peptide drugs through the respiratory tract may contribute to the systemic delivery of these drugs following the pulmonary administration of these drugs by intratracheal insufflation and instillation.

Usefulness of liposomes as an intranasal dosage formulation for topical drug application.

The potential of liposomes as an intranasal dosage formulation for topical application was investigated in rats. When 5(6)-carboxyfluorescein (CF), a model absorbable drug, dissolved in phosphate-buffered saline (PBS) was administered intranasally, CF was rapidly absorbed into the systemic circulation and no adhesion of CF to the nasal mucosa was observed. The fraction of CF absorbed from the nasal mucosa reached about 48% 1 h after administration. On the other hand, only 3% of the dose was absorbed when CF was encapsulated in liposomes consisting of dipalmitoylphosphatidylcholine and cholesterol (DPPC-liposomes). In addition, the amount of CF adhering to the nasal mucosa after administration as DPPC-liposomes was 20- to 28-fold greater than that in PBS solution. In particular, positively charged liposomes markedly enhanced the adhesion of CF to the nasal mucosa. Differences in the lipid composition of liposomes did not affect the absorption of CF. However, the ability of liposomes to adhere to the nasal mucosa was consistent with the fluidity of the liposomal membrane. Furthermore, the action of liposomes on the anti-histaminic effect of diphenhydramine hydrochloride (DH) was studied in rats by measuring the amount of protein leaking into the nasal cavity under quasi-allergic conditions. The anti-histaminic effect of DH was strong but of short-duration when DH was administered as a PBS solution. However, liposomes prolonged the anti-histaminic effect of DH, suggesting that liposomes may adhere to the nasal mucosa and release DH slowly. In conclusion, liposomes suppress drug absorption into the systemic circulation and concurrently increase drug retention in the nasal cavity.

Bioavailability assessment of arginine-vasopressin (AVP) using pharmacokinetic-pharmacodynamic (PK-PD) modeling in the rat.

A novel method of assessing the extent of oral bioavailability of arginine-vasopressin (AVP) from pharmacological data was presented. After intravascular administration (i.v. bolus or short-term infusion) of AVP to rats, the relationship between blood concentrations and its effect on both mean arterial pressure (hemodynamic effect) and urinary sodium concentration (anti-diuretic effect) was described on the basis of an integrated pharmacokinetic-pharmacodynamic (PK-PD) model. A direct model was used for the hemodynamic response, while an indirect response model, rather than a hypothetical link model was used for the anti-diuretic response. A sigmoid Emax model was applied to describe the drug-receptor interaction. Pharmacological responses after intravascular administration of AVP were reasonably described by the PK-PD model. However, PD parameters estimated by the PK-PD analysis suggested that apparent receptor affinity rather than efficacy in i.v. bolus study was significantly higher than that in the short-term infusion study. This fact indicated that PK-PD relationship was influenced by the intravascular input rate of AVP. We then investigated the relationship between plasma concentration and amount of AVP bound to the V2 receptors in the kidney. The result indicated that the amount of AVP bound to the receptors after i.v. bolus injection was always greater than that after short-term infusion. Since the PK-PD relationship after oral administration was almost identical with that after short-term infusion, the PK-PD model obtained in the short-term infusion study was used to assess the extent of oral bioavailability (EBAPp.o.). The EBAp.o. values, estimated from pharmacological effects (hemodynamic effect and anti-diuretic effect) after oral administration of 5 microg/kg of AVP were 0.68% to 0.93% and were almost identical with the actual EBAPp.o. value (0.81%). From these results, we concluded that oral bioavailability of AVP was reasonably predicted by the PK-PD model, provided that appropriate pharmacological effects and appropriate intravascular dosing rate as a reference formulation are available. The method may be an alternative to methods based on plasma concentrations, when drug concentration cannot be measured and when appropriate pharmacological data are available.

Tracheal barrier and the permeability of hydrophilic drugs and dipeptides.

The permeability of model hydrophilic compounds with different molecular weights and model dipeptides were examined to characterize the tracheal epithelial barrier in in vitro experiments using excised rabbit trachea. 6-Carboxyfluorescein (6-CF; 376 Da) and fluorescein isothiocyanate (FITC)-dextrans (FDs) with varying molecular weights (4 to 70 kDa) were used as model hydrophilic and macromolecular compounds, and glycyl-D-phenylalanine (Gly-D-Phe) and glycyl-L-phenylalanine (Gly-L-Phe) were used as model dipeptides in this experiment. The apparent permeability coefficients (Papp) of 6-CF and FDs with Mw 376 Da to 70 kDa ranged from 2.35x10(-7) to 4.05x10(-10)cm/s and exhibited a good inverse correlation with their molecular weights. The tracheal permeability of 6-CF, FD-4 (4 kDa) and FD-10 (10 kDa) were increased over three fold by 10 mM glycocholate, which is an absorption enhancer. The Papp of Gly-D-Phe was 1.03x10(-6)cm/s and there was no metabolism during tracheal permeation. Gly-L-Phe was immediately degraded in the mucosal fluid and its intact form was not detected in serosal fluid during the 150 min experimental period. These results suggest that absorption of some peptide drugs via the respiratory tract may contribute to their systemic delivery following pulmonary administration by intratracheal insufflation and instillation.

Application of surface-coated liposomes for oral delivery of peptide: effects of coating the liposome's surface on the GI transit of insulin.

We prepared two kinds of surface-coated liposomes and investigated their potencies as oral dosage forms for peptide drugs by focusing on their effects on the gastrointestinal (GI) transit of drugs. The surface of the liposomes was coated with poly(ethylene glycol) 2000 (PEG-Lip) or the sugar chain of mucin (Mucin-Lip). As a model peptide drug, insulin was encapsulated in these liposomes. Coating the surface with poly(ethylene glycol) was found to reduce the transit rate of liposomes in the small intestine after oral administration to rats in vivo. Mucin-Lip was retained in the stomach longer than PEG-Lip or uncoated liposomes. The effect of surface coating on the intestinal transit of liposomes was determined by means of in situ single pass perfusion in the rat small intestine. Statistical moment analysis was applied to the outflow pattern of both liposomes and encapsulated insulin. The mean transit time (MTT) and deviation of transit time (DTT) in the intestinal tract were calculated. The MTT of PEG-Lip was much longer than those of uncoated liposomes and Mucin-Lip and was significantly shortened after removal of the intestinal mucous layer. These results indicated that PEG-Lip interacts strongly with the intestinal mucous layer, leading to its slow transit in the intestine. In contrast, coating the liposome's surface with mucin did not affect either the MTT or DTT of liposomes in the intestine. This result is in accordance with the in vivo observation that Mucin-Lip was highly retained in the stomach, but not in any region of the small intestine in vivo. Both the MTT and DTT values of insulin encapsulated in PEG-Lip and Mucin-Lip were almost the same as those of liposomes themselves, suggesting that surface-coated liposomes retained insulin in the intestinal tract. However, MTT and DTT of insulin were significantly shorter than those of uncoated liposomes because these liposomes degraded and released significant amounts of insulin during single pass perfusion. The ability of surface-coated liposomes, especially of PEG-Lip, to interact with the mucus layer and slow the transit rate in the GI tract is considered desirable for oral delivery of peptide drugs. Modification of the liposomal surface with appropriate materials, therefore, should be an effective method by which to achieve the oral delivery of peptide drugs.

Influence of absorption enhancers (bile salts) and the preservative (benzalkonium chloride) on mucociliary function and permeation barrier function in rabbit tracheas.

Effects of bile salts and benzalkonium chloride on the ciliary beat activity (frequency) and the mucociliary transport rate of tracheas, and permeabilities of 6-carboxyfluorescein (6-CF; Mw 376) and FITC-dextrans (FD-4; Mw 4300) as hydrophilic compounds through trachea were investigated for intratracheal delivery of drugs. Ciliary beat activity was measured by an in vitro photoelectric method by using excised rabbit tracheas. Transport rate was determined by an in vivo endoscopic method in rabbit tracheas. Permeation test was carried out by using excised rabbit tracheas. The ciliary beat activities and mucociliary transport rates were not significantly affected by 1, 10 and 20 mM sodium glycocholate, while they were significantly decreased by 1 and 10 mM sodium taurodeoxycholate and immediately halted after application of 20 mM taurodeoxycholate. They were not significantly affected by 0.02% of benzalkonium chloride, whereas they were completely halted by 0.05% of benzalkonium chloride. The apparent permeability coefficients (Papp) of 6-CF and FD-4 were 2.35x10(-7) and 2.22x10(-8) cm/s, respectively. One mmol of glycocholate did not significantly increase the Papp of 6-CF and FD-4, while, 10 mM of glycocholate and 1 and 10 mM of taurodeoxycholate significantly increased the Papp. Benzalkonium chloride (0.01%) did not significantly increase the Papp of 6-CF, whereas 0.03% significantly increased the Papp of 6-CF. Benzalkonium chloride (0.01 and 0.03%) slightly increased the Papp of FD-4. Therefore, sodium glycocholate may be a safe and useful absorption enhancer for intratracheal delivery of drugs.

Enhancing effects of unsaturated fatty acids with various structures on the permeation of indomethacin through rat skin.

Effects of straight-chain, cis-type, unsaturated fatty acids with various structures (alkyl chain lengths, numbers of double bonds, position of double bonds, and cis- and trans-positional isomers) on the skin permeation of indomethacin were examined by using rat skins in-vitro. Furthermore, the disordering degrees of the intercellular lipid domain in the stratum corneum, which were treated with preparations of unsaturated fatty acids, were measured by the Fourier transform infrared (FT-IR) method using excised rabbit ear skins. Unsaturated fatty acids enhanced the permeation of indomethacin through rat skins. These permeation-enhancing effects by unsaturated fatty acids were affected by changes of their alkyl chain length from C14 to C22. The lag-times on the permeation of indomethacin were shortened by unsaturated fatty acids in the following order: C20 = C18 = C22 < C16 < C14. These fluxes were increased by unsaturated fatty acids in the following order: C20 > C22 = C18 = C16 > C14. Therefore, gondoic acid (cis-11-eicosenoic acid; C20H38O2) mostly enhanced the skin permeation of indomethacin. However, the enhancing effects of unsaturated fatty acids (C18 chain) were not affected by their differences of position and numbers of double bonds. These permeation-enhancing effects which were evaluated by flux were related to the degrees of wave-number shift in the frequency of the antisymmetric CH bond stretching absorbance (near 2920 cm-1) on FT-IR spectra of the fatty acid-treated stratum corneum. Therefore, the perturbation increase of lipid domain in the stratum corneum by these fatty acids probably was the cause of the enhancing effects of permeation of indomethacin.

Pharmacokinetic and pharmacodynamic studies of centrally acting drugs in rat: effect of pentobarbital and chlorpromazine on electroencephalogram in rat.

Electroencephalogram (EEG) alterations in rat after the i.v. administration of pentobarbital (PTB) and chlorpromazine (CPZ) were measured by power spectral analysis. The time courses of PTB concentrations in plasma, cerebrospinal fluid (CSF) and brain were determined after the i.v. administration of PTB (20, 40 mg/kg) by GC-MS. The PTB concentrations in plasma, CSF and brain could be described by a biexponential equation, a CSF model and a blood flow limited model, respectively. The relationship between the alteration of EEG and the PTB concentrations in the CSF or brain or the effect compartment were analyzed using the sigmoid Emax model. The alteration of EEG after PTB administration could be described by the PTB concentration in these compartments using the sigmoid Emax model. These results indicated that the site of action for the alteration of EEG after PTB administration is in instantaneous equilibrium with the CSF, the brain and the effect compartment. Thus, alterations in EEG after PTB administration can be predicted by monitoring the total PTB concentration in plasma. The alteration of EEG after i.v. administration of CPZ (4 mg/kg) showed a two-phase variation. Although the relationship between the alteration of EEG and the CPZ concentrations in CSF or the striatum or the effect compartment (total and free drug) were analyzed using the linear model, the Emax model or the sigmoid Emax model, the two-phase alteration of EEG after CPZ administration could not be described by any of these models. These results indicated that the pharmacokinetic and pharmacodynamic modeling of CPZ during the alteration of EEG may be complicated due to several pharmacokinetic and pharmacodynamic factors, such as an alteration of the free fraction of CPZ in the striatum, the formation of active metabolites, and two different intrinsic effects of CPZ on the EEG (one in an increase and the other in a decrease of the brain's electrical activity.

Kinetics of combined drug action.

For the purpose of obtaining quantitative concentration-effect relationship for combined drugs, rationales of the Hill equation were inferred and five models, i.e., normal distribution (NRD), derivative of R (DRV), vacancy-dependent binding (VDB), equiresponse (EQR), and independence (IND), were proposed to estimate the intensity of the combined drug action. In conclusion, we could not come up to the unique concentration-effect relationship. Among the five models, the EQR, NRD, and VDB models gave almost identical response intensity. Discrimination of these three models is not of great importance. The DRV model gave a characteristic concave isobologram (overadditive), for a given ratio of Hill constants and independent of pharmacologic effect. In contrast, the IND model was able to cope with convex isobolograms (underadditive).

Two-layer membrane model for iontophoretic drug transport through excised rat skin.

Iontophoretic and passive transport of an ionized drug (sulfisoxazole) across excised rat skin was studied using a two-chamber cell with four electrodes under successive experimental conditions: without electrical current (stage-I) and with electrical current (stage-II). Two iontophoretic/diffusion models, i.e. a one-layer membrane model and a two-layer membrane model, in which a difference in the electrical potential gradient was taken into account between the stratum corneum and epidermis/dermis layer, were constructed to describe the non-steady-state drug permeation process during ionotrophoresis. The observed iontophoretic lag-time was two times greater than the calculated value based on the one-layer membrane model. According to the two-layer membrane model, the calculated ionotophoretic lag-time agreed with the observed value. It was revealed by model adaptation to the observed data that the stratum corneum fraction of the electro-chemical potential difference across the whole skin caused by the iontophoresis was around 90%. This result was consistent with the observation that the direct current resistance of whole skin was seven times greater than that of stripped skin.

Effect of l-menthol on the permeation of indomethacin, mannitol and cortisone through excised hairless mouse skin.

The effect of l-menthol on the skin permeability of mannitol, cortisone or indomethacin was examined by an in vitro penetration technique with hairless mouse skin. The donor solution was prepared with phosphate buffered saline, ethanol:buffered saline (20:80, v/v) or ethanol:buffered saline (20:80, v/v) containing 1% (w/v) l-menthol. Although ethanol showed little enhancing effect, l-menthol in an aqueous ethanol vehicle at pH 7.4 increased the permeability coefficients of mannitol and indomethacin by about 100 times that of the control (an aqueous vehicle) and increased that of cortisone by about 10 times. l-Menthol, however, scarcely enhanced the penetration of indomethacin at pH 3.0, the majority of the species being in unionized form. These results suggested that the menthol-ethanol-aqueous system enhanced skin permeability through a direct effect on the polar and/or lipid pathways, while the thermodynamic activity of the penetrant molecule in the delivery vehicle might also influence the effectiveness of the penetration enhancer.

Scopadulcic acid B, a new tetracyclic diterpenoid from Scoparia dulcis L. Its structure, H+, K(+)-adenosine triphosphatase inhibitory activity and pharmacokinetic behaviour in rats.

The structure of scopadulcic acid B (2, SDB), a major ingredient of the Paraguayan herb "Typychá kuratu" (Scoparia dulcis L.), was elucidated mainly by comparison of its spectral data with that of scopadulcic acid A (1). SDB inhibited both the K(+)-dependent adenosine triphosphatase (ATPase) activity of a hog gastric proton pump (H+, K(+)-ATPase) with a value of 20-30 microM for IC50 and proton transport into gastric vesicles. Pharmacokinetic studies of SDB in rats indicated that plasma SDB concentrations after i.v. injection of the sodium salt of SDB (SDB-Na) were described reasonably well by a two-compartment open model with Michaelis-Menten elimination kinetics. Plasma concentrations after oral administration of SDB-Na or SDB showed a much slower decline than what was expected following the i. v. study. It was suggested that the sustained plasma level of SDB after oral administration of SDB-Na or SDB was accounted for by relatively slow but efficient gastro-intestinal absorption in rats.

Transfer of diclofenac sodium across excised guinea pig skin on high-frequency pulse iontophoresis. I. Equivalent circuit model.

High frequency pulse iontophoresis of diclofenac sodium across excised guinea-pig skin was carried out in vitro. An equivalent circuit model was constructed to simulate the time courses of voltage drop across the donor solution and the skin. Parameter values obtained by the least-squares adaptation of the model to observed data were consistent with expectation and validated the proposed model.

Transfer of diclofenac sodium across excised guinea pig skin on high-frequency pulse iontophoresis. II. Factors affecting steady-state transport rate.

Some of the factors affecting the steady-state transport rate of diclofenac sodium across excised guinea-pig skin during high-frequency pulse iontophoresis were examined. The same mathematical expression was employed for enhancement ratio as a function of applied voltage as the one derived for direct-current iontophoresis. The effective voltage drop across the skin was only 1.1% of the applied voltage. The steady-state flux value increased with increase of the donor concentration.