Estimation of impurity profiles of drugs and related materials. 12. Isolation and identification of an isomeric impurity in danazol

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.

The use of BDDCS in classifying the permeability of marketed drugs

We recommend that regulatory agencies add the extent of drug metabolism (i.e., >or=90% metabolized) as an alternate method in defining Class 1 marketed drugs suitable for a waiver of in vivo studies of bioequivalence. That is, >or=90% metabolized is an additional methodology that may be substituted for >or=90% absorbed. We propose that the following criteria be used to define>or=90% metabolized for marketed drugs: Following a single oral dose to humans, administered at the highest dose strength, mass balance of the Phase 1 oxidative and Phase 2 conjugative drug metabolites in the urine and feces, measured either as unlabeled, radioactive labeled or nonradioactive labeled substances, account for >or=90% of the drug dosed. This is the strictest definition for a waiver based on metabolism. For an orally administered drug to be >or=90% metabolized by Phase 1 oxidative and Phase 2 conjugative processes, it is obvious that the drug must be absorbed. This proposal, which strictly conforms to the present>or=90% criteria, is a suggested modification to facilitate a number of marketed drugs being appropriately assigned to Class 1.

Danazol-beta-cyclodextrin binary system: a potential application in emergency contraception by the oral route

This study explored the potential of beta-cyclodextrin to improve the aqueous solubility and dissolution of danazol, investigated a simple and less expensive method for preparation of a danazol-beta-cyclodextrin binary system, and explored the potential application of a danazol-beta-cyclodextrin binary system as a single-dose emergency contraceptive. Phase solubility analysis indicated formation of a first-order soluble complex with stability constant 972.03 M(-1), while Job's plot affirmed 1:1 stoichiometry. The hyperchromic shift in the UV-Vis spectrum of danazol in the presence of beta-cyclodextrin indicated solubilization capability of beta-cyclodextrin for danazol. The extrinsic Cotton effect with a negative peak at 280.7 nm confirmed the inclusion of danazol in the asymmetric locus of beta-cyclodextrin. (1)H-nuclear magnetic resonance analysis suggested that the protons of the steroidal skeleton of danazol display favorable interactions with the beta-cyclodextrin cavity. The danazol-beta-cyclodextrin binary system was prepared by kneading, solution, freeze-drying, and milling methods. The extent of the enhancement of dissolution rate was found to be dependent on the preparation method. Dissolution studies showed a similar relative dissolution rate (2.85) of the danazol-beta-cyclodextrin binary system prepared by the freeze-drying and milling (in the presence of 13% moisture) methods. In a mouse model, the danazol-beta-cyclodextrin binary system at 51.2 mg/kg (equivalent to a 400-mg human dose) showed 100% inhibition of implantation when given postcoitally. Moreover, the danazol-beta-cyclodextrin binary system is safe up to 2000 mg/kg in the mouse (15.52 g/70 kg human) as a single oral dose. Thus, the danazol-beta-cyclodextrin binary system could serve as a new therapeutic application: an oral emergency contraceptive at a physiologically acceptable single dose.

The suitability of an in situ perfusion model for permeability determinations: utility for BCS class I biowaiver requests

The FDA has published recommendations for sponsors who wish to request a waiver of in vivo bioavailability (BA) or bioequivalence (BE) studies for immediate release (IR) solid oral dosage forms based on the Biopharmaceutics Classification System (BCS). Biowaivers can be requested for IR formulations in which the active ingredient is shown to be a BCS class I drug: that is, a drug showing high permeability and high solubility over a pH range of 1-7.5. For permeability determinations, a variety of experimental methods can be used, such as the rat in situ single pass perfusion or Caco-2 cell culture models, once the suitability of the particular method is established. Following the recommended procedure for assessing the suitability of permeability determinations, we determined the permeability of 20 test drugs using the in situ single pass perfusion model in rats. The test compounds were coperfused through jejunal intestinal segments with an internal permeability reference standard (metoprolol) over a 90 min time period. Sample analysis was performed by HPLC, and the ratio of the effective permeability, Peff (cm/s), of test compound to that of metoprolol was determined. To address the question of test drug permeabilities that approach that of the internal standard, we propose that a statistical analysis such as the "0.8-1.25 rule" used for in vivo or in vitro bioequivalence studies provide guidance for permeability classification using the in situ single pass perfusion model. We developed a method using the 90% confidence interval of the permeability ratio of the test to internal reference standard in order to differentiate between high and low permeability compounds. This analysis allowed for the proper permeability classification of all of the test compounds and suggests a robust means for assessing drug permeability classification.

Recent Advances in the Analysis of Steroid Hormones and Related Drugs

The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis.

LC determination of impurities in methoxsalen drug substance: isolation and identification of isopimpinellin as a major impurity by atmospheric pressure chemical ionization LC/MS and NMR

A gradient elution LC method was developed to separate methoxsalen from three of its known impurities: isopimpinellin, bergapten, and ammidin. The method employs a methanol-6%THF (aq) mobile phase, phenyl column, and detection at 254 nm. The gradient LC procedure was applied to seven lots of methoxsalen from five different manufacturers. Six of the seven lots tested contained isopimpinellin as the major impurity at a concentration range of 0.2-2.5%. Identification of the impurity as isopimpinellin was accomplished by a combination of analytical and preparative LC, atmospheric pressure chemical ionization liquid chromatography/mass spectrometry, and NMR.

Isolation of a 2:1 hydrochlorothiazide-formaldehyde adduct impurity in hydrochlorothiazide drug substance by preparative chromatography and characterization by electrospray ionization LC-MS

Hydrochlorothiazide drug substance (19 lots) from five different manufacturers and four different countries of origin (USA, Italy, Hungary, and Croatia) were analyzed for the presence of impurities using a gradient elution chromatographic system, with acetonitrile-water as the mobile phase. Two known impurities of hydrochlorothiazide, 4-amino-6-chloro-1,3-benzenedisulfonamide and chlorothiazide, were separated, as well as a late-eluting, unknown, recurring impurity. The unknown impurity was isolated by preparative liquid chromatography followed by preparative thin-layer chromatography. It was characterized by electrospray ionization LC-MS as a 2:1 hydrochlorothiazide-formaldehyde adduct of the parent drug substance. The adduct is believed to form through the double condensation reaction of hydrochlorothiazide with excess formaldehyde during the parent compound's synthesis. The concentration of this impurity ranged from 0.02 to 1.1% (area%), and was above the 0.1% USP Other Impurities threshold in 16 of the 19 lots examined.

Human intestinal permeability

This review focuses on permeability measurements in humans, briefly discussing different perfusion techniques, the relevance of human Peff values, and various aspects of in vivo transport mechanisms. In addition, human Peff values are compared with corresponding data from three preclinical transport models. The regional human jejunal perfusion technique has been validated in several important ways. One of the most important findings is that there is a good correlation between the measured human effective permeability values and the extent of absorption of drugs in humans determined by pharmacokinetic studies. Estimations of the absorption half-lives from the measured Peff agree very well with the time to maximal amount of the dose absorbed achieved after an oral dose in humans. We have also shown that it is possible to determine the Peff for carrier-mediated transported compounds and to classify them according to the proposed biopharmaceutical classification system (BCS). Furthermore, human in vivo permeabilities can be predicted using preclinical permeability models, such as in situ perfusion of rat jejunum, the Caco-2 model, and excised intestinal segments in the Ussing chamber. The permeability of passively transported compounds can be predicted with a particularly high degree of accuracy. However, special care must be taken for drugs with a carrier-mediated transport mechanism, and a scaling factor has to be used. Finally, the data obtained in vivo in humans emphasize the need for more clinical studies investigating the effect of physiological in vivo factors and molecular mechanisms influencing the transport of drugs across the intestinal and as well as other membrane barriers. It will also be important to study the effect of antitransport mechanisms (multidrug resistance, MDR), such as efflux by P-glycoprotein(s) and gut wall metabolism, for example CYP 3A4, on bioavailability.

Human jejunal effective permeability and its correlation with preclinical drug absorption models

This review focuses on intestinal permeability measurements in humans and various aspects of in-vivo transport mechanisms. In addition, comparisons of human data with preclinical models and the blood-brain barrier is discussed. The regional human jejunal perfusion technique has been validated by several crucial points. One of the most important findings is that there is a good correlation between the measured human effective permeability values and the extent of absorption of drugs in humans determined by pharmacokinetic studies. We have also shown that it is possible to determine the effective permeability (Peff) for carrier-mediated transported compounds, and to classify them according to the proposed Biopharmaceutical Classification System (BCS). Furthermore, it is possible to predict human in-vivo permeability using preclinical permeability models, such as in-situ perfusion of rat jejunum, the Caco-2 model and excized intestinal segments in the Ussing chamber. The permeability of passively transported compounds can be predicted with a particularly high degree of accuracy. However, special care must be taken for drugs with a carrier-mediated transport mechanism, and a scaling factor has to be used. It is also suggested that it is possible to roughly estimate the permeability of the blood-brain barrier using measurements of intestinal permeability, even if the quantitative role of efflux of P-glycoprotein(s) in-vivo still remains to be clarified. Finally, the data obtained in-vivo in humans emphasize the need for more clinical studies investigating the effect of physiological in-vivo factors and molecular mechanisms influencing the transport of drugs across the intestinal and as well as other membrane barriers. It is also important to study the effect of anti-transport mechanisms, such as efflux by P-glycoprotein(s), and gut wall metabolism, for example CYP 3A4, on the bioavailability.

Jejunal permeability and hepatic extraction of fluvastatin in humans

OBJECTIVES

The primary objective was to investigate the effective permeability and the hepatic extraction of fluvastatin, a new 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, during a jejunal perfusion in humans. The secondary objective was to investigate the relationship between human jejunal effective permeability values and physicochemical properties for four different drugs.

METHODS

Nine healthy male volunteers were included in the study, which consisted of two sequential study parts. In the first part, the jejunal effective permeability of fluvastatin, antipyrine, metoprolol, and atenolol was assessed with use of the regional jejunal perfusion approach (150 minutes, 2.0 ml/min). After a washout period of at least 5 days, the same subjects received an intravenous infusion of fluvastatin (20 minutes, 2.0 mg). Plasma samples were taken in both parts of the study and were analyzed for the content of fluvastatin.

RESULTS

The mean hepatic extraction of fluvastatin was 67% after the jejunal perfusion and 73% after the intravenous infusion. The half-life of fluvastatin was approximately 60 minutes after both administration routes. The jejunal effective permeability and the fraction absorbed both correlated (r2 = 0.968, p < 0.05; and r2 = 0.994, p < 0.05) with the partition coefficient (log D, pH 6.5) but not with the molecular size or the hydrogen bond number.

CONCLUSION

Fluvastatin is extracted by the liver to a large extent (about 70%) and has a short half-life after both oral and intravenous administration. In this study, the human jejunal effective permeability and the fraction absorbed for these four drugs were better predicted by log D (pH 6.5) than both the molecular size and the hydrogen bond number.

Estimation of impurity profiles of drugs and related materials. Part 14: the role of HPLC/diode-array UV spectroscopy in the identification of minor components (impurities, degradation products, metabolites) in various matrices

The possibility of the rapid identification of drug related minor components by HPLC/diode-array UV spectroscopy is demonstrated by three examples. Hydroxylated impurities (degradation products) of norgestrel (6 alpha and beta, 10 beta-hydroxy derivatives) were identified on the basis of their UV spectra and retention matching with the synthesized impurities. The position of the phenolic hydroxyl groups in the mono- and dihydroxylated metabolites of bisaramil was established by UV spectroscopy and retention matching with the synthesized metabolites. The discrimination between the isomeric 4-ene-3-ketone and 1-ene-3-ketone components in crude 19-nortestosterone, product of the Birch reduction of 3-methoxy-1,3,5(10)-oestratriene-17 beta-ol, was also based on the diode-array UV spectra.