A Novel Two-Step Liquid-Liquid Extraction Procedure Combined with Stationary Phase Immobilized Human Serum Albumin for the Chiral Separation of Cetirizine Enantiomers along with M and P Parabens

The association of chiral characteristic with drug withdrawal due to safety: A comparative analysis

AIMS

Chirality of drugs might be associated with safety issues through pharmacokinetic or pharmacodynamic variations, interactions, or direct toxicological responses. We aimed to compare chiral status of the available drugs to that of drugs withdrawn due to adverse drug reactions (ADRs).

METHODS

We searched the literature regarding withdrawn drugs due to safety-related issues (n = 391) to compare them with all available small-molecule drugs (n = 1633). We examined their chiral status and assigned as achiral compound, chiral mixture or pure enantiomer. We compared the mean survival (i.e., nonwithdrawal) time and withdrawal rates of drugs by their chirality, with further stratification by the launch year, ATC-1 (Anatomical Therapeutic Chemical) level and ADR.

RESULTS

We identified higher withdrawal rate in achiral drugs (hazard ratio 2.1, 95% CI: 1.6-2.7) and chiral mixtures (hazard ratio 2.6, 95% CI: 1.9-3.5) compared to that in pure enantiomers. Pure enantiomers had the longest mean survival time (62.4 ± 0.8 years), followed by achiral drugs (55.4 ± 0.9 years, P < .01) and chiral mixtures (52.4 ± 1.4 years, P < .01). Pure enantiomers had higher survival rates than chiral mixtures if launched before 1941 (P = .02), in 1961-1980 (P < .001) or 1981-2000 (P < .001). Pure enantiomers had lower withdrawal rate (18.2%) vs. chiral mixtures (35.1%, P = .02) in nervous system drugs. Pure enantiomers had lower withdrawal rate than chiral mixtures in hepatotoxic (P < .01) and cardiovascular ADRs (P < .01).

CONCLUSION

Our study showed lower likelihood of withdrawal for pure enantiomers compared to that in chiral mixtures and achiral drugs, which was more remarkable for those launched in certain time periods and several ADRs, including hepatotoxicity and cardiovascular toxicity.

Enantioresolution and Binding Affinity Studies on Human Serum Albumin: Recent Applications and Trends

The interaction between proteins and drugs or other bioactive compounds has been widely explored over the past years. Several methods for analysis of this phenomenon have been developed and improved. Nowadays, increasing attention is paid to innovative methods, such as high performance affinity liquid chromatography (HPALC) and affinity capillary electrophoresis (ACE), taking into account various advantages. Moreover, the development of separation methods for the analysis and resolution of chiral drugs has been an area of ongoing interest in analytical and medicinal chemistry research. In addition to bioaffinity binding studies, both HPALC and ACE al-low one to perform other type of analyses, namely, displacement studies and enantioseparation of racemic or enantiomeric mixtures. Actually, proteins used as chiral selectors in chromatographic and electrophoretic methods have unique enantioselective properties demonstrating suitability for the enantioseparation of a large variety of chiral drugs or other bioactive compounds. This review is mainly focused in chromatographic and electrophoretic methods using human serum albumin (HSA), the most abundant plasma protein, as chiral selector for binding affinity analysis and enantioresolution of drugs. For both analytical purposes, updated examples are presented to highlight recent applications and current trends.

Distinct binding of cetirizine enantiomers to human serum albumin and the human histamine receptor H1

Cetirizine, a major metabolite of hydroxyzine, became a marketed second-generation H₁ antihistamine that is orally active and has a rapid onset of action, long duration of effects and a very good safety record at recommended doses. The approved drug is a racemic mixture of (S)-cetirizine and (R)-cetirizine, the latter being the levorotary enantiomer that also exists in the market as a third-generation, non-sedating and highly selective antihistamine. Both enantiomers bind tightly to the human histamine H₁ receptor (hH₁R) and behave as inverse agonists but the affinity and residence time of (R)-cetirizine are greater than those of (S)-cetirizine. In blood plasma, cetirizine exists in the zwitterionic form and more than 90% of the circulating drug is bound to human serum albumin (HSA), which acts as an inactive reservoir. Independent X-ray crystallographic work has solved the structure of the hH₁R:doxepin complex and has identified two drug-binding sites for cetirizine on equine serum albumin (ESA). Given this background, we decided to model a membrane-embedded hH₁R in complex with either (R)- or (S)-cetirizine and also the complexes of both ESA and HSA with these two enantiomeric drugs to analyze possible differences in binding modes between enantiomers and also among targets. The ensuing molecular dynamics simulations in explicit solvent and additional computational chemistry calculations provided structural and energetic information about all of these complexes that is normally beyond current experimental possibilities. Overall, we found very good agreement between our binding energy estimates and extant biochemical and pharmacological evidence. A much higher degree of solvent exposure in the cetirizine-binding site(s) of HSA and ESA relative to the more occluded orthosteric binding site in hH₁R is translated into larger positional fluctuations and considerably lower affinities for these two nonspecific targets. Whereas it is demonstrated that the two known pockets in ESA provide enough stability for cetirizine binding, only one such site does so in HSA due to a number of amino acid replacements. At the histamine-binding site in hH₁R, the distinct interactions established between the phenyl and chlorophenyl moieties of the two enantiomers with the amino acids lining up the pocket and between their free carboxylates and Lys179 in the second extracellular loop account for the improved pharmacological profile of (R)-cetirizine.

Chiral Stationary Phases for Liquid Chromatography: Recent Developments

The planning and development of new chiral stationary phases (CSPs) for liquid chromatography (LC) are considered as continuous and evolutionary issues since the introduction of the first CSP in 1938. The main objectives of the development strategies were to attempt the improvement of the chromatographic enantioresolution performance of the CSPs as well as enlarge their versatility and range of applications. Additionally, the transition to ultra-high-performance LC were underscored. The most recent strategies have comprised the introduction of new chiral selectors, the use of new materials as chromatographic supports or the reduction of its particle size, and the application of different synthetic approaches for preparation of CSPs. This review gathered the most recent developments associated to the different types of CSPs providing an overview of the relevant advances that are arising on LC.