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BCS classification is a vital tool in the development of both generic and innovative drug products. The purpose of this work was to provisionally classify the world’s top selling oral drugs according to the BCS, using in silico methods. Three different in silico methods were examined: the well-established group contribution (CLogP) and atom contribution (ALogP) methods, and a new method based solely on the molecular formula and element contribution (KLogP). Metoprolol was used as the benchmark for the low/high permeability class boundary. Solubility was estimated in silico using a thermodynamic equation that relies on the partition coefficient and melting point. The validity of each method was affirmed by comparison to reference data and literature. We then used each method to provisionally classify the orally administered, IR drug products found in the WHO Model list of Essential Medicines, and the top-selling oral drug products in the United States (US), Great Britain (GB), Spain (ES), Israel (IL), Japan (JP), and South Korea (KR). A combined list of 363 drugs was compiled from the various lists, and 257 drugs were classified using the different in silico permeability methods and literature solubility data, as well as BDDCS classification. Lastly, we calculated the solubility values for 185 drugs from the combined set using in silico approach. Permeability classification with the different in silico methods was correct for 69–72.4% of the 29 reference drugs with known human jejunal permeability, and for 84.6–92.9% of the 14 FDA reference drugs in the set. The correlations (r2) between experimental log Pvalues of 154 drugs and their CLogP, ALogP and KLogP were 0.97, 0.82 and 0.71, respectively. The different in silico permeability methods produced comparable results: 30–34% of the US, GB, ES and IL top selling drugs were class 1, 27–36.4% were class 2, 22–25.5% were class 3, and 5.46–14% were class 4 drugs, while ∼8% could not be classified. The WHO list included significantly less class 1 and more class 3 drugs in comparison to the countries’ lists, probably due to differences in commonly used drugs in developing vs industrial countries. BDDCS classified more drugs as class 1 compared to in silico BCS, likely due to the more lax benchmark for metabolism (70%), in comparison to the strict permeability benchmark (metoprolol). For 185 out of the 363 drugs, in silico solubility values were calculated, and successfully matched the literature solubility data. In conclusion, relatively simple in silico methods can be used to estimate both permeability and solubility. While CLogP produced the best correlation to experimental values, even KLogP, the most simplified in silico method that is based on molecular formula with no knowledge of molecular structure, produced comparable BCS classification to the sophisticated methods. This KLogP, when combined with a mean melting point and estimated dose, can be used to provisionally classify potential drugs from just molecular formula, even before synthesis. 49–59% of the world’s top-selling drugs are highly soluble (class 1 and class 3), and are therefore candidates for waivers of in vivo bioequivalence studies. For these drugs, the replacement of expensive human studies with affordable in vitro dissolution tests would ensure their bioequivalence, and encourage the development and availability of generic drug products in both industrial and developing countries.

Orally administered, immediate-release (IR) drug products in the top 200 drug product lists from the United States (US), Great Britain (GB), Spain (ES), and Japan (JP) were provisionally classified based on the Biopharmaceutics Classification System (BCS). The provisional classification is based on the aqueous solubility of the drugs reported in readily available reference literature and a correlation of human intestinal membrane permeability for a set of 29 reference drugs with their calculated partition coefficients. Oral IR drug products constituted more that 50% of the top 200 drug products on all four lists, and ranged from 102 to 113 in number. Drugs with dose numbers less than or equal to unity are defined as high-solubility drugs. More than 50% of the oral IR drug products on each list were determined to be high-solubility drugs (55-59%). The provisional classification of permeability is based on correlations of the human intestinal permeabilities of 29 reference drugs with the calculated Log Por CLogP lipophilicity values for the uncharged chemical form. The Log P and CLogP estimates were linearly correlated (r2 0.79) for 187 drugs. Metoprolol was chosen as the reference compound for permeability and Log Por CLogP. A total of 62-69.0% and 56-60% of the drugs on the four lists exhibited CLogP and Log P estimates, respectively, greater than or equal to the corresponding metoprolol value and are provisionally classified as high-permeability drugs. We have compared the BCS classification in this study with the recently proposed BDDCS classification based on fraction dose metabolism. Although the two approaches are based on different in vivo processes, fraction dose metabolized and fraction dose absorbed are highly correlated and, while depending on the choice of reference drug for permeability classification, e.g., metoprolol vs cimetidine or atenolol, show excellent agreement in drug classification. In summary, more than 55% of the drug products were classified as high-solubility (Class 1 and Class 3) drugs in the four lists, suggesting that in vivo bioequivalence (BE) may be assured with a less expensive and more easily implemented in vitro dissolution test.

The transport of valacyclovir, the l-valyl ester of acyclovir, has been suggested to be mediated by several carrier-mediated pathways in cell culture and animal models. The role and importance of these transporters in modulating valacyclovir absorption in humans has not been determined, however. Recent advances in genomic technology have facilitated the rapid and simultaneous determination of global mRNA expression profiles for thousands of genes in tissue biopsies directly associated with the absorption process, thereby dramatically increasing the value of studies in humans. In this article, we describe correlations of pharmacokinetic parameters following oral valacyclovir or acyclovir administration with expression levels of intestinal genes in humans. Highly positive and significant correlations were observed with 4F2hc, an activator of cation-preferring amino acid transport systems, and human oligopeptide transporter (HPT1), an oligopeptide transporter expressed at higher levels in the human intestine compared with oligopeptide transporter (PEPT1). The validation of HPT1 microarray data with reverse transcription-polymerase chain reaction and the enhanced valacyclovir uptake in HeLa/HPT1 cells suggest that the role of HPT1 in transport of peptides and peptidomimetics drugs needs to be examined in more detail. The interrelation of 4F2hc and HPT1 in transport may be of interest. No significant correlations of valacyclovir pharmacokinetic parameters with PEPT1 and with organic cation or anion transporter expression levels were observed. The highly negative correlations observed with known efflux pumps such as MDR1 (P-glycoprotein) and MRP2 (cMOAT), as well as with the CYP450 IIIA subfamily may indicate that these proteins may regulate the cellular accumulation and metabolism of acyclovir.

In a previous report (1), we showed that the rate and extent of uptake of cyclosporin-A (CsA) following topical application of nonionic liposomal formulations composed of glyceryl dilaurate (GDL), cholesterol (CH), and polyoxyethylene-10-stearyl ether (POE-10) into and through hairless mouse skin mounted on Franz diffusion cells could be controlled by varying the ratios of GDL to POE-10 (CH being held constant at 15 wt%). However, the pathways of transport as well as the dominant factors that control drug delivery from these formulations are not well understood. In this report, we describe results from studies similar in design to that reported earlier but using the melted form of the lipid components as a vehicle for transport of CsA into and through hairless mouse skin. The results suggest that the transport of CsA from liposomal formulations into and through the skin occurs as a result of dehydration of the liposomes followed by melting of the lipid components on the skin. Microautoradiographic studies suggest that CsA is predominantly transported via the pilosebaceous pathway.

Asymmetric liposomes containing phosphatidylinositol 4,5-bisphosphate (PIP2) predominantly on the inner leaflet of the bilayer were prepared by means of a non-penetrating enzyme, phosphoinositide-specific phospholipase C isolated from adult human platelets. Symmetric liposomes prepared by a modification of the reverse-phase evaporation method were incubated with partially purified enzyme in the presence of Ca2+ at 37°C. The resultant liposomes were collected by high-speed centrifugation. Hydrolysis of PIP2 on the outer leaflet of the membrane was completed after approximately 4 h of incubation. Since PIP2 is predominantly located in the inner leaflet of biological membranes, these asymmetric liposomes should be suitable for investigation of structural and functional roles of PIP2 in biomembranes.

The deposition of a-interferon into living skin strata of hairless mouse following topical in vivo application of a glyceryl dilaurate: POE-10: cholesterol liposomal formulation was much higher than from a glyceryl distearate: POE-10: cholesterol liposomal formulation or from an aqueous solution. The kinetics and extent of drug deposition from the liposomal formulations appear to correspond to the extent of release of bilayer lipid components following topical application and subsequent action of the lipid components as skin permeation enhancers.

Expression plasmid DNA for the human interleukin-1 receptor antagonist (IL-1ra) protein was formulated with nonionic:cationic (NC) liposomes or phosphatidylcholine:cationic (PC) liposomes and applied to the auricular skin of hamsters in single- and multiple-dose protocols. Confocal microscopy identified delivery of plasmid DNA proximal to perifollicular cells, and successful transfection of perifollicular cells was identified by immunohistochemistry and ELISA. Skin treated for 3 days with the NC liposomes had statistically significant levels of transgenic IL-1ra present for 5 days post-treatment. Expression of transgenic IL-1ra was specific to areas of skin treated with NC liposomes but not PC liposomes. The results indicate that the NC liposomes can deliver expression plasmid DNA to perifollicular cells and mediate transient transfection in vivo.

Our previous reports using hairless mouse skin model showed that topical delivery of cyclosporin-A (CsA) could be achieved and controlled with nonionic liposomal and nonionic lipid-based formulations composed of glyceryl dilaurate (GDL), cholesterol (CH), and polyoxyethylene-10-stearyl ether (POE-10) at varying weight ratios (1,2). However, the distribution profiles were obtained using radiolabeled CsA and thus could represent intact drug as well as its metabolites. The present studies aim to investigate if the previously reported profiles actually represented intact CsA. The studies were carried out using a "high-pressure" liquid chromatography (HPLC) method and in vitro skin deposition studies with a metabolic inhibitor (sodium azide) incorporated in the receptor fluid. The results indicated that skin metabolism of CsA and hence its effect on percutaneous absorption of CsA is minimal and that the CsA distribution profiles obtained using radiolabeled CsA represented distribution of intact drug and not its metabolites.

In an earlier report (1) we described the controlled follicular delivery of hydrophobic macromolecules from nonionic lipid-based formulations composed of glyceryl dilaurate (GDL), cholesterol (CH), and polyoxyethylene-10-stearyl ether (POE-10). However, the influence of lipid composition on topical delivery of marginally hydrophobic and hydrophilic drugs from these nonionic lipid-based systems has not been investigated. In this report we describe the effect of variation of GDL to POE-10 ratio in the nonionic lipid-based formulations on the extent and route of delivery of hydrocortisone and mannitol, a marginally hydrophobic and hydrophilic model drug, respectively, into and through hairless mouse skin mounted on Franz diffusion cells. The results indicate that the extent of hydrocortisone uptake increased with increasing GDL to POE-10 weight ratio whereas mannitol uptake was quite the opposite and decreased with increasing GDL to POE-10 weight ratio. The diametrically opposite trends for the two drug markers suggests strongly that hydrocortisone and mannitol are transported into and across skin from the nonionic lipid-based formulations via two distinctly different routes. Further, the finding from microautoradiographic studies that the delivery of hydrocortisone from nonionic lipid-based lipid melt formulations was predominantly across the transfollicular route compared to its transport across both the trans-epidermal and transfollicular pathways from nonionic lipid-based liposomes, suggests that it is possible to tailor formulations for specific and targeted delivery across a certain route.

Expression plasmid DNA for the human interleukin-1 receptor antagonist (IL-1ra) protein was formulated with nonionic:cationic (NC) liposomes or phosphatidylcholine:cationic (PC) liposomes and applied to the auricular skin of hamsters in single- and multiple-dose protocols. Confocal microscopy identified delivery of plasmid DNA proximal to perifollicular cells, and successful transfection of perifollicular cells was identified by immunohistochemistry and ELISA. Skin treated for 3days with the NC liposomes had statistically significant levels of transgenic IL-1ra present for 5days post-treatment. Expression of transgenic IL-1ra was specific to areas of skin treated with NC liposomes but not PC liposomes. The results indicate that the NC liposomes can deliver expression plasmid DNA to perifollicular cells and mediate transient transfection in vivo.

Previous studies in our laboratories showed that a novel nonionic liposome formulation composed of glyceryl dilaurate (GDL), cholesterol (CH), and polyoxyethylene-10-stearyl ether (POE-10) at a weight ratio composition of 57:15:28 delivered more cyclosporin-A (CsA) into and through the skin than phospholipid-based liposomal formulations and more conventional formulations that were tested. Since only a single GDL:CH:POE-10 composition was tested, we initiated studies to determine if it would be possible to control the rate and extent of drug uptake by varying the ratios of the liposome-forming components of the formulation. This report describes how the GDL to POE-10 ratio (CH being held constant at 15 wt%) influences the rate and extent of uptake of CsA following topical application of nonionic liposomal formulations to hairless mouse skin mounted on Franz diffusion cells. The results indicate that the rate and extent of CsA uptake is highest between GDL/POE-10 ratios of about 1 to 1.5 and decreases steadily at ratios above and below this range. The effect of liposomal composition on CsA deposition is probably the result of a number of complex and interrelated factors including partitioning of CsA from the formulation into the skin and permeation enhancer effects.