Effect of macrolide antibiotics on uptake of digoxin into rat liver

Cell permeability beyond the rule of 5

Drug discovery for difficult targets that have large and flat binding sites is often better suited to compounds beyond the "rule of 5" (bRo5). However, such compounds carry higher pharmacokinetic risks, such as low solubility and permeability, and increased efflux and metabolism. Interestingly, recent drug approvals and studies suggest that cell permeable and orally bioavailable drugs can be discovered far into bRo5 space. Tactics such as reduction or shielding of polarity by N-methylation, bulky side chains and intramolecular hydrogen bonds may be used to increase cell permeability in this space, but often results in decreased solubility. Conformationally flexible compounds can, however, combine high permeability and solubility, properties that are keys for cell permeability and intestinal absorption. Recent developments in computational conformational analysis will aid design of such compounds and hence prediction of cell permeability. Transporter mediated efflux occurs for most investigated drugs in bRo5 space, however it is commonly overcome by high local intestinal concentrations on oral administration. In contrast, there is little data to support significant impact of transporter-mediated intestinal absorption in bRo5 space. Current knowledge of compound properties that govern transporter effects of bRo5 drugs is limited and requires further fundamental and comprehensive studies.

Digoxin – a therapeutic agent and mechanistic probe: review of liquid chromatographic mass spectrometric methods and recent nuances in the clinical pharmacology attributes of digoxin

Digoxin is an important therapeutic agent for the treatment of congestive cardiac failure. In spite of its narrow therapeutic index, digoxin has been used extensively by the medical community and, lately, the use of digoxin as a mechanistic probe for p-glycoprotein transporter activity has increased. This review describes recent trends in the bioanalysis of digoxin, where scores of liquid chromatographic–mass spectrometric assays have been successfully employed to measure digoxin in preclinical, clinical and mechanistic studies. It provides various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectral conditions, for example, to enable the development of sound bioanalytical methods for digoxin. Some recent updates with regard to clinical pharmacology, absorption and disposition aspects of digoxin have been included. Overall, liquid chromatographic–mass spectrometric assays represent an important tool for many future preclinical, clinical and mechanistic probe studies that would probe digoxin with or without other coadministered substrates.