Search

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing lamivudine as the only active pharmaceutical ingredient were reviewed. The solubility and permeability data of lamivudine as well as its therapeutic index, its pharmacokinetic properties, data indicating excipient interactions, and reported BE/bioavailability (BA) studies were taken into consideration. Lamivudine is highly soluble, but its permeability characteristics are not well-defined. Reported BA values in adults ranged from 82% to 88%. Therefore, lamivudine is assigned to the biopharmaceutics classification system (BCS) class III, noting that its permeability characteristics are near the border of BCS class I. Lamivudine is not a narrow therapeutic index drug. Provided that (a) the test product contains only excipients present in lamivudine IR solid oral drug products approved in the International Conference on Harmonization or associated countries in usual amounts and (b) the test product as well as the comparator product fulfills the BCS dissolution criteria for very rapidly dissolving; a biowaiver can be recommended for new lamivudine multisource IR products and major post-approval changes of marketed drug products., (Copyright © 2011 Wiley-Liss, Inc.)

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing ciprofloxacin hydrochloride as the only active pharmaceutical ingredient (API) are reviewed. Ciprofloxacin hydrochloride's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. Solubility and BA data indicate that ciprofloxacin hydrochloride is a BCS Class IV drug. Therefore, a biowaiver based approval of ciprofloxacin hydrochloride containing IR solid oral dosage forms cannot be recommended for either new multisource drug products or for major scale-up and postapproval changes (variations) to existing drug products., (2010 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release solid oral dosage forms containing mefloquine hydrochloride as the only active pharmaceutical ingredient (API) are reviewed. The solubility and permeability data of mefloquine hydrochloride as well as its therapeutic use and therapeutic index, its pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability studies were taken into consideration. Mefloquine hydrochloride is not a highly soluble API. Since no data on permeability are available, it cannot be classified according to the Biopharmaceutics Classification System with certainty. Additionally, several studies in the literature failed to demonstrate BE of existing products. For these reasons, the biowaiver cannot be justified for the approval of new multisource drug products containing mefloquine hydrochloride. However, scale-up and postapproval changes (HHS-FDA SUPAC) levels 1 and 2 and most EU type I variations may be approvable without in vivo BE, using the dissolution tests described in these regulatory documents., (2010 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature and new experimental data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing furosemide are reviewed. The available data on solubility, oral absorption, and permeability are sufficiently conclusive to classify furosemide into Class IV of the Biopharmaceutics Classification System (BCS). Furosemide's therapeutic use and therapeutic index, its pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability (BA) problems are also taken into consideration. In view of the data available, it is concluded that the biowaiver procedure cannot be justified for either the registration of new multisource drug products or major postapproval changes (variations) to existing drug products., ((c) 2009 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing doxycycline hyclate are reviewed. According to the Biopharmaceutics Classification System (BCS), doxycycline hyclate can be assigned to BCS Class I. No problems with BE of IR doxycycline formulations containing different excipients and produced by different manufacturing methods have been reported and hence the risk of bioinequivalence caused by these factors appears to be low. Doxycycline has a wide therapeutic index. Further, BCS-based dissolution methods have been shown to be capable of identifying formulations which may dissolve too slowly to generate therapeutic levels. It is concluded that a biowaiver is appropriate for IR solid oral dosage forms containing doxycycline hyclate as the single Active Pharmaceutical Ingredient (API) provided that (a) the test product contains only excipients present in doxycycline hyclate IR solid oral drug products approved in the International Conference on Harmonization (ICH) or associated countries; and (b) the comparator and the test products comply with the BCS criteria for "very rapidly dissolving" or, alternatively, when similarity of the dissolution profiles can be demonstrated and the two products are "rapidly dissolving."., (2009 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature data are reviewed relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing quinidine sulfate. Quinidine sulfate's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. The available data are not fully conclusive, but do suggest that quinidine sulfate is highly soluble and moderately to highly permeable and would likely be assigned to BCS Class I (or at worst BCS III). In view of the inconclusiveness of the data and, more important, quinidine's narrow therapeutic window and critical indication, a biowaiver based approval of quinidine containing dosage forms cannot be recommended for either new multisource drug products or for major postapproval changes (variations) to existing drug products.

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing rifampicin as the only Active Pharmaceutical Ingredient (API) are reviewed. Rifampicin's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. Solubility and absolute BA data indicate that rifampicin is a BCS Class II drug. Of special concern for biowaiving is that many reports of failure of IR solid oral dosage forms of rifampicin to meet BE have been published and the reasons for these failures are yet insufficiently understood. Moreover, no reports were identified in which in vitro dissolution was shown to be predictive of nonequivalence among products. Therefore, a biowaiver based approval of rifampicin containing IR solid oral dosage forms cannot be recommended for either new multisource drug products or for major scale-up and postapproval changes (variations) to existing drug products.

Literature data are reviewed regarding the scientific advisability of allowing a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing either diclofenac potassium and diclofenac sodium. Within the biopharmaceutics classification system (BCS), diclofenac potassium and diclofenac sodium are each BCS class II active pharmaceutical ingredients (APIs). However, a biowaiver can be recommended for IR drug products of each salt form, due to their therapeutic use, therapeutic index, pharmacokinetic properties, potential for excipient interactions, and performance in reported BE/bioavailability (BA) studies, provided: (a) test and comparator contain the same diclofenac salt; (b) the dosage form of the test and comparator is identical; (c) the test product contains only excipients present in diclofenac drug products approved in ICH or associated countries in the same dosage form, for instance as presented in this paper; (d) test drug product and comparator dissolve 85% in 30 min or less in 900 mL buffer pH 6.8, using the paddle apparatus at 75 rpm or the basket apparatus at 100 rpm; and (e) test product and comparator show dissolution profile similarity in pH 1.2, 4.5, and 6.8.

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing (biowaiver) for the approval of immediate release (IR) solid oral dosage forms containing aciclovir are reviewed. Aciclovir therapeutic use and therapeutic index, pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability (BA) studies were also taken into consideration in order to ascertain whether a biowaiver can be recommended. According to the Biopharmaceutics Classification System (BCS) and considering tablet strengths up to 400 mg, aciclovir would be BCS Class III. However, in some countries also 800 mg tablets are available which fall just within BCS Class IV. Aciclovir seems not to be critical with respect to a risk for bioinequivalence, as no examples of bioinequivalence have been identified. It has a wide therapeutic index and is not used for critical indications. Hence, if: (a) the test product contains only excipients present in aciclovir solid oral IR drug products approved in ICH or associated countries, for instance as presented in this article; and (b) the comparator and the test product both are very rapidly dissolving, a biowaiver for IR aciclovir solid oral drug products is considered justified for all tablet strengths.

Literature data are reviewed relevant to the decision for a biowaiver of immediate release (IR) solid oral dosage forms containing metoclopramide hydrochloride. In addition, new solubility data, obtained under Biopharmaceutics Classification System (BCS) conditions are presented. Metoclopramide HCl is conservatively assigned to BCS Class III. Taken also into consideration excipient interactions reported in metoclopramide drug products, its pharmacokinetic properties and therapeutic use and therapeutic index, a biowaiver can be recommended when: (a) the test product contains only excipients present also in metoclopramide HCl containing IR solid oral drug products approved in ICH or associated countries, for instance as presented in this paper, (b) in amounts in normal use in IR solid oral dosage forms, and (c) the test product and the comparator both comply with the criteria for very rapidly dissolving.

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing pyrazinamide as the only active pharmaceutical ingredient (API) are reviewed. Pyrazinamide is BCS Class III, with linear absorption over a wide dosing range. The risk of bioinequivalence is estimated to be low. Depending on the definition used, pyrazinamide can be classified as a narrow therapeutic index (NTI) drug, which is usually a caveat to biowaiving but may be deemed acceptable if the Summary of Product Characteristics (SmPCs) of the test product stipulates the need for regular monitoring of liver function. It is concluded that a biowaiver can be recommended for IR solid oral dosage only when the test product (a) contains only excipients present in pyrazinamide IR solid oral drug products approved in ICH or associated countries, (b) these excipients are present in amounts normally used in IR solid oral dosage forms, (c) the test product is very rapidly dissolving, (d) the SmPC of the test product indicates the need for monitoring of the patient's liver function.

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing acetazolamide are reviewed. Acetazolamide's solubility and permeability characteristics according to the Biopharmaceutics Classification System (BCS), as well as its therapeutic use and therapeutic index, its pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability (BA) problems are taken into consideration. The available data on solubility, on oral absorption and permeability are not sufficiently conclusive to classify acetazolamide with certainty. Taking a conservative approach, no biowaiver is considered justified for the registration of new multisource drug products. However, SUPAC level 1 and level 2 postapproval changes and most EU Type I variations can be approved waiving in vivo BE studies.

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing ethambutol dihydrochloride as the only active pharmaceutical ingredient (API) are reviewed. Ethambutol dihydrochloride is a Biopharmaceutics Classification System (BCS) Class III drug with permeability properties approaching the border between BCS Class I and III. BE problems of ethambutol formulations containing different excipients and different dosages forms have not been reported and hence the risk of bioinequivalence caused by excipients is low. Ethambutol has a narrow therapeutic index related to ocular toxicity. However, as long as the prescribers' information of the test product stipulates the need for regular monitoring of ocular toxicity, the additional patient risk is deemed acceptable. It is concluded that a biowaiver can be recommended for IR solid oral dosage forms provided that the test product (a) contains only excipients present in ethambutol IR solid oral drug products approved in ICH or associated countries, for instance as presented in this paper, (b) complies with the criteria for "very rapidly dissolving" and (c) has a prescribers' information indicating the need for testing the patient's vision prior to initiating ethambutol therapy and regularly during therapy., (2007 Wiley-Liss, Inc)

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing prednisone are reviewed. Due to insufficient data prednisone cannot be definitively classified according to the current Biopharmaceutics Classification System (BCS) criteria as both the solubility and the permeability of prednisone are on the borderline of the present criteria of BCS Class I. Prednisone's therapeutic indications and therapeutic index, pharmacokinetics and the possibility of excipient interactions were also taken into consideration. Available evidence indicates that a biowaiver for IR solid oral dosage forms formulated with the excipients tabulated in this article would be unlikely to expose patients to undue risks.

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing isoniazid as the only active pharmaceutical ingredient (API) are reviewed. Isoniazid's solubility and permeability characteristics according to the Biopharmaceutics Classification System (BCS), as well as its therapeutic use and therapeutic index, its pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. Isoniazid is "highly soluble" but data on its oral absorption and permeability are inconclusive, suggesting this API to be on the borderline of BCS Class I and III. For a number of excipients, an interaction with the permeability is extreme unlikely, but lactose and other deoxidizing saccharides can form condensation products with isoniazid, which may be less permeable than the free API. A biowaiver is recommended for IR solid oral drug products containing isoniazid as the sole API, provided that the test product meets the WHO requirements for "very rapidly dissolving" and contains only the excipients commonly used in isoniazid products, as listed in this article. Lactose and/or other deoxidizing saccharides containing formulations should be subjected to an in vivo BE study., (2006 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing prednisolone are reviewed. Data on its solubility, oral absorption, and permeability are not totally conclusive, but strongly suggest a BCS Class 1 classification. Prednisolone's therapeutic indications and therapeutic index, pharmacokinetics, and the possibility of excipient interactions were also taken into consideration. Available evidence indicates that a biowaiver for IR solid oral dosage forms formulated with the excipients tabulated in this article would be unlikely to expose patients to undue risks., ((c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association.)

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing cimetidine are reviewed. According to the current Biopharmaceutics Classification System (BCS), cimetidine would be assigned to Class III. Cimetidine's therapeutic use and therapeutic index, its pharmacokinetic properties, data related to the possibility of excipient interactions, and reported BE/bioavailability (BA) problems were also taken into consideration. On the basis of the overall evidence, a biowaiver can be recommended for cimetidine IR products, provided that the test product contains only those excipients reported in this paper in their usual amounts, and that the test and the comparator drug products both are "rapidly dissolving" as per BCS., ((c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature data are reviewed on the properties of acetaminophen (paracetamol) related to the biopharmaceutics classification system (BCS). According to the current BCS criteria, acetaminophen is BCS Class III compound. Differences in composition seldom, if ever, have an effect on the extent of absorption. However, some studies show differences in rate of absorption between brands and formulations. In particular, sodium bicarbonate, present in some drug products, was reported to give an increase in the rate of absorption, probably caused by an effect on gastric emptying. In view of Marketing Authorizations (MAs) given in a number of countries to acetaminophen drug products with rapid onset of action, it is concluded that differences in rate of absorption were considered therapeutically not relevant by the Health Authorities. Moreover, in view of its therapeutic use, its wide therapeutic index and its uncomplicated pharmacokinetic properties, in vitro dissolution data collected according to the relevant Guidances can be safely used for declaring bioequivalence (BE) of two acetaminophen formulations. Therefore, accepting a biowaiver for immediate release (IR) acetaminophen solid oral drug products is considered scientifically justified, if the test product contains only those excipients reported in this paper in their usual amounts and the test product is rapidly dissolving, as well as the test product fulfils the criterion of similarity of dissolution profiles to the reference product.

Literature data are reviewed on the properties of ibuprofen related to the biopharmaceutics classification system (BCS). Ibuprofen was assessed to be a BCS class II drug. Differences in composition and/or manufacturing procedures were reported to have an effect on the rate, but not the extent of absorption; such differences are likely to be detectable by comparative in vitro dissolution tests. Also in view of its therapeutic use, its wide therapeutic index and uncomplicated pharmacokinetic properties, a biowaiver for immediate release (IR) ibuprofen solid oral drug products is scientifically justified, provided that the test product contains only those excipients reported in this paper in their usual amounts, the dosage form is rapidly dissolving (85% in 30 min or less) in buffer pH 6.8 and the test product also exhibits similar dissolution profiles to the reference product in buffer pH 1.2, 4.5, and 6.8., (Copyright (c) 2005 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature and experimental data relevant to the decision to allow a waiver of in vivo bioequivalence testing for the approval of immediate release (IR) solid oral dosage forms containing ranitidine hydrochloride are reviewed. According to the current Biopharmaceutics Classification System (BCS), ranitidine hydrochloride should be assigned to Class III. However, based on its therapeutic and therapeutic index, pharmacokinetic properties and data related to the possibility of excipient interactions, a biowaiver can be recommended for IR solid oral dosage forms that are rapidly dissolving and contain only those excipients as reported in this study., ((c) 2005 Wiley-Liss, Inc. and the American Pharmacists Association)

Literature data on the properties of chloroquine phosphate, chloroquine sulfate, and chloroquine hydrochloride related to the Biopharmaceutics Classification System (BCS) are reviewed. The available information indicates that these chloroquine salts can be classified as highly soluble and highly permeable, i.e., BCS class I. The qualitative composition of immediate release (IR) tablets containing these Active Pharmaceutical Ingredients (APIs) with a Marketing Authorization (MA) in Belgium (BE), Germany (DE), Finland (FI), and The Netherlands (NL) is provided. In view of these MA's and the critical therapeutic indication of chloroquine, it is assumed that the registration authorities had evidence that these formulations are bioequivalent to the innovator. It is concluded that IR tablets formulated with these excipients are candidates for a biowaiver., ((c) 2005 Wiley-Liss, Inc.)

Literature data related to the Biopharmaceutics Classification System (BCS) are presented on verapamil hydrochloride, propranolol hydrochloride, and atenolol in the form of BCS-monographs. Data on the qualitative composition of immediate release (IR) tablets containing these active substances with a Marketing Authorization (MA) in the Netherlands (NL) are also provided; in view of these MA's the assumption was made that these tablets were bioequivalent to the innovator product. The development of a database with BCS-related data is announced by the International Pharmaceutical Federation (FIP)., (Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:1945-1956, 2004)

The synthesis and evaluation of mono-N-carboxymethyl chitosan (MCC) as an intestinal permeation enhancer for macromolecular therapeutics is presented. MCCs were synthesized from two different viscosity grade chitosans to yield both high and low viscosity grade products. These MCCs were tested on Caco-2 cells for their efficiency to decrease the transepithelial electrical resistance (TEER) and to increase the paracellular permeability of the anionic macromolecular anticoagulant low molecular weight heparin (LMWH). For in vivo studies, LMWH was administered intraduodenally with or without MCC to rats. Both types of experiments were performed at pH 7.4. Results show that both viscosity grade MCCs managed to significantly decrease the TEER of Caco-2 cell monolayers when they were applied apically at concentrations of 3-5% (w/v). Transport studies with Caco-2 cells revealed substantial increases of LMWH permeation in the presence of both viscosity grade MCCs compared with controls. In rats, 3% (w/v) low viscosity MCC significantly increased the intestinal absorption of LMWH, reaching the therapeutic anticoagulant blood levels of LMWH. Both in vitro and in vivo results indicate that the polyampholytic chitosan modification MCC is a suitable and functional polymer for the delivery and intestinal absorption of anionic macromolecular therapeutics like LMWH., (Copyright 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90: 38-46, 2001)

Octreotide acetate is a somatostatin analogue used for the control of endocrine tumors of the gastrointestinal (GI) tract and the treatment of acromegaly. The oral absorption of octreotide is limited because of the limited permeation across the intestinal epithelium. Both chitosan hydrochloride and N-trimethyl chitosan chloride (TMC), a quaternized chitosan derivative, are nonabsorbable and nontoxic polymers that have been proven to effectively increase the permeation of hydrophilic macromolecules across mucosal epithelia by opening the tight junctions. This study investigates the intestinal absorption of octreotide when it is coadministered with the polycationic absorption enhancer TMC. Caco-2 cell monolayers were used as an in vitro intestinal epithelium model, and male Wistar rats were used for in vivo studies. Octreotide with or without polymers (TMC; chitosan hydrochloride) was administered intrajejunally in rats, and serum peptide levels were measured by radioimmunoassay. All applications and administrations were performed at neutral pH values (i.e., pH = 7.4). In vitro transport studies with Caco-2 cells revealed an increased permeation of octreotide in the presence of TMC. Enhancement ratios ranged from 34 to 121 with increasing concentrations of the polymer (0.25-1.5%, w/v). In rats, 1.0% (w/v) TMC solution significantly increased the absorption of the peptide analogue, resulting in a 5-fold increase of octreotide bioavailability compared with the controls (octreotide alone). Coadministration of 1.0% (w/v) chitosan hydrochloride did not enhance octreotide bioavailability. These results in combination with the nontoxic character of TMC suggest that this polymer is a promising excipient in the development of solid dosage forms for the peroral delivery and intestinal absorption of octreotide.

Previous studies have established that a partially quaternized derivative of chitosan, N-trimethyl chitosan chloride (TMC), can be used as an absorption enhancer for large hydrophilic compounds across mucosal surfaces. This study evaluates and compares the effects of the degree of quaternization of TMC, in a neutral environment, on the permeability of intestinal epithelial cells in vitro, where normal chitosan salts are ineffective as absorption enhancers. The effects of TMC-H [61.2% quaternized, (0.05-1.5% w/v)], TMC-L [12.3% quaternized, (0.5-1.5% w/v)], and chitosan hydrochloride [0.5-1.5% w/v] on the transepithelial electrical resistance (TEER) and permeability, for the hydrophilic model compound [14C]mannitol, of intestinal epithelial Caco-2 cell monolayers, were investigated at pH values of 6.20 and 7.40. The viability of the monolayers was checked with the trypan blue exclusion technique. At a pH of 6.20, all the polymers caused a pronounced reduction (37-67% at 0.5% w/v concentrations) in the TEER of Caco-2 cells. On the contrary, at a pH of 7.40, only TMC-H was able to decrease the TEER values, even in a concentration as low as 0.05% w/v (35% reduction). Comparable results were obtained with the permeation of [14C]mannitol. Large increases in the transport rate (18-23-fold at 0.5% w/v concentrations) were found at pH 6.20, whereas only TMC-H was able to increase the permeation of [14C]mannitol at pH 7.40 (31-48-fold at 0.05-1.5% w/v concentrations of TMC-H). For all the polymers studied, no deleterious effects to the cells could be demonstrated with the trypan blue exclusion technique. It is concluded that highly quaternized TMC is a potent absorption enhancer and the potential use of this polymer, especially in neutral and basic environments where normal chitosan salts are not effective, is expected to be an important contribution to the development of effective delivery systems for hydrophilic compounds such as peptide drugs.

Buccal delivery of fluorescein isothiocyanate labeled dextran 4400 (FD4) was investigated in-vivo in pigs. The delivery device consisted of an application chamber with a solution of FD4 and was adhered to the buccal mucosa for 4 h using an adhesive patch. A randomized crossover study including intravenous administration and buccal delivery without and with 10 mM sodium glycodeoxycholate (GDC) as absorption enhancer was performed in five pigs. After buccal administration, steady state plasma levels were rapidly reached. Coadministration of 10 mM GDC increased the absolute bioavailability of FD4 from 1.8 +/- 0.5% to 12.7 +/- 2.0%. Since FD4 is a macromolecular and hydrophilic compound such as peptide and protein drugs, buccal delivery would provide an adequate alternative to the parenteral administration of these drugs.

The structure of fully hydrated human stratum corneum was investigated by means of freeze-fracture electron microscopy. Mammary and abdominal stratum corneum were incubated for 48 h with phosphate-buffered saline, pH 7.4, occlusively or phosphate buffer, pH 7.4, occlusively and non-occlusively. The micrographs showed the corneocytes aligned parallel to the surface of the stratum corneum embedded in intercellular lipids. The corneocytes were swollen by the uptake of water. New features located in the intercellular lamellar regions were rough structures, water pools, and occasionally vesicle-like structures. The nature of the vesicle-like structures was not completely clear. The presence of water pools, mostly in close contact with the rough structures, suggests that a lipid-water phase separation occurred. The localization of water in the intercellular region and the corneocytes offers new insights into the penetration enhancement property of water (and into the pathways of drug penetration).