Non-linear Increases in Danazol Exposure with Dose in Older vs. Younger Beagle Dogs: The Potential Role of Differences in Bile Salt Concentration, Thermodynamic Activity, and Formulation Digestion

Danazol

A comprehensive profile of danazol describing the nomenclatures, formulae, elemental composition, appearance, uses and applications is presented. The profile contains the method which was utilized for the preparation of the drug substance and its respective scheme is outlined. The physical characteristics of the drug including the solubility, X-ray powder diffraction pattern, differential scanning calorimetry, thermal behavior and spectroscopic studies are described. The methods which were used for the analysis of the drug substance in bulk drug and/or in pharmaceutical formulations including the compendial, spectrophotometric, electrochemical and the chromatographic methods are reported. The stability, toxicity, pharmacokinetics, bioavailability, drug evaluation and monitoring, comparisons, pharmacology, in addition to several compiled reviews on the drug substance which were involved. Finally, two hundred and seventy-nine references are listed at the end of this profile.

Danazol oral absorption modelling in the fasted dog: An example of mechanistic understanding of formulation effects on drug pharmacokinetics

Oral bioavailability of poorly water soluble (BCS II) drugs like danazol can be minimal without the necessary formulation strategies. Availability of in vitro physicochemical and in vivo pharmacokinetic studies can be valuable when designing these strategies but cannot reveal the drug-formulation-gastrointestinal physiology interplay that impact the successful optimization of intestinal solubilization and resulting oral drug absorption. In silico mechanistic oral drug absorption models can serve as a tool for providing this important perspective and for integrating information generated across various in vivo and in vitro studies. In this work, we detail the development and application of the Simcyp canine ADAM model to nine danazol oral formulations and compare the model predictions to caninein vivo pharmacokinetic data from published literature. The application of this mechanistic approach revealed insights suggesting: (1) complete danazol solubilization in vitro may lead to an over-estimation of oral bioavailability when predictions are not corrected for the in vivo conditions promoting gut luminal precipitation; (2) some solubilizing excipients can influence intestinal physiology in a manner that may reduce danazol absorption; (3) danazol-formulation-luminal bile salts interplay can result in the formation of mixed micelles that negatively impact danazol intestinal permeability; and (4) the magnitude of danazol bioavailability enhancement associated with the use of solubilizing agents can be affected by the presence of saturable gut metabolism that can lead to concentration-dependent differences in its influence in vivo formulation behaviour at high versus low doses.

Polymeric Precipitation Inhibitors Promote Fenofibrate Supersaturation and Enhance Drug Absorption from a Type IV Lipid-Based Formulation

The ability of lipid-based formulations (LBFs) to increase the solubilization, and prolong the supersaturation, of poorly water-soluble drugs (PWSDs) in the gastrointestinal (GI) fluids has generated significant interest in the past decade. One mechanism to enhance the utility of LBFs is to prolong supersaturation via the addition of polymers that inhibit drug precipitation (polymeric precipitation inhibitors or PPIs) to the formulation. In this work, we have evaluated the performance of a range of PPIs and have identified PPIs that are sufficiently soluble in LBF to allow the construction of single phase formulations. An in vitro model was first employed to assess drug (fenofibrate) solubilization and supersaturation on LBF dispersion and digestion. An in vitro-in situ model was subsequently employed to simultaneously evaluate the impact of PPI enhanced drug supersaturation on drug absorption in rats. The stabilizing effect of the polymers was polymer specific and most pronounced at higher drug loads. Polymers that were soluble in LBF allowed simple processing as single phase formulations, while formulations containing more hydrophilic polymers required polymer suspension in the formulation. The lipid-soluble polymers Eudragit (EU) RL100 and poly(propylene glycol) bis(2-aminopropyl ether) (PPGAE) and the water-soluble polymer hydroxypropylmethyl cellulose (HPMC) E4M were identified as the most effective PPIs in delaying fenofibrate precipitation in vitro. An in vitro model of lipid digestion was subsequently coupled directly to an in situ single pass intestinal perfusion assay to evaluate the influence of PPIs on fenofibrate absorption from LBFs in vivo. This coupled model allowed for real-time evaluation of the impact of supersaturation stabilization on absorptive drug flux and provided better discrimination between the different PPIs and formulations. In the presence of the in situ absorption sink, increased fenofibrate supersaturation resulted in increased drug exposure, and a good correlation was found between the degree of in vitro supersaturation and in vivo drug exposure. An improved in vitro-in vivo correlation was apparent when comparing the same formulation under different supersaturation conditions. These observations directly exemplify the potential utility of PPIs in promoting drug absorption from LBF, via stabilization of supersaturation, and further confirm that relatively brief periods of supersaturation may be sufficient to promote drug absorption, at least for highly permeable drugs such as fenofibrate.

Models for Predicting Drug Absorption From Oral Lipid-Based Formulations

In this review, we describe the in vitro tools currently used to identify when a lipid-based formulation has the potential to deliver a poorly water-soluble drug via the oral route. We describe the extent to which these tools reflect the in vivo performance of the formulation and, more importantly, we present strategies that we foresee will improve the in vitro-in vivo correlations. We also present emerging computational methods that are likely to allow large parts of the formulation development to be carried out in the computer rather than in the test tube. We suggest that these computational tools will also improve the mechanistic understanding of in vivo formulation performance in the complex and dynamic environment of the gut.

An in vitro digestion test that reflects rat intestinal conditions to probe the importance of formulation digestion vs first pass metabolism in Danazol bioavailability from lipid based formulations

The impact of gastrointestinal (GI) processing and first pass metabolism on danazol oral bioavailability (BA) was evaluated after administration of self-emulsifying drug delivery systems (SEDDS) in the rat. Danazol absolute BA was determined following oral and intraduodenal (ID) administration of LFCS class IIIA medium chain (MC) formulations at high (SEDDSH-III) and low (SEDDSL-III) drug loading and a lipid free LFCS class IV formulation (SEDDS-IV). Experiments were conducted in the presence and absence of ABT (1-aminobenzotriazole) to evaluate the effect of first pass metabolism. A series of modified in vitro lipolysis tests were developed to better understand the in vivo processing of SEDDS in the rat. Danazol BA was low (<13%) following oral and ID administration of either SEDDS. Increasing drug loading, ID rather than oral administration, and administration of SEDDS-IV rather than SEDDS-III led to higher oral BA. After pretreatment with ABT, however, danazol oral BA significantly increased (e.g., 60% compared to 2% after administration of SEDDSL-III), no effect was observed on increasing drug loading, and differences between SEDDS-III and -IV were minimal. In vitro digestion models based on the lower enzyme activity and lower dilution conditions expected in the rat resulted in significantly reduced danazol precipitation from SEDDS-III or SEDDS-IV on initiation of digestion. At the doses administered here (4-8 mg/kg), the primary limitation to danazol oral BA in the rat was first pass metabolism, and the fraction absorbed was >45% after oral administration of SEDDS-III or SEDDS-IV. In contrast, previous studies in dogs suggest that danazol BA is less dependent on first pass metabolism and more sensitive to changes in formulation processing. In vitro digestion models based on likely rat GI conditions suggest less drug precipitation on formulation digestion when compared to equivalent dog models, consistent with the increases in in vivo exposure (fraction absorbed) seen here in ABT-pretreated rats.