Stereoselective renal tubular secretion of levocetirizine and dextrocetirizine, the two enantiomers of the H1-antihistamine cetirizine

Volumetric and conductivity studies of the interaction between levocetirizine dihydrochloride and the amino acids l-alanine and l-glutamine in aqueous solutions

Levocetirizine dihydrochloride (LCTZ) is a second-generation antihistamine known for its efficacy without sedation. However, the binding mechanism with plasma protein which makes it devoid of sedative effects is yet to be uncovered. In this study, we elucidated thermodynamic parameters of solute-solvent and solute-cosolute interactions between LCTZ, and the amino acids l-alanine (Ala) and l-glutamine (Gln) in aqueous solutions. The volumetric and conductance parameters were calculated using the experimental density and conductance data of aqueous solutions of Ala and Gln (concentration range of 0.02-0.20 mol kg^-1) and LCTZ (concentration range of 0.01, 0.07, and 0.13 mol kg^-1) at 298.15, 303.15, 308.15, and 313.15 K. Volumetric analysis study revealed that the apparent molar volume (V_φ), limiting apparent molar volume (V_φ ⁰), and Masson's coefficient (S_v) values indicated predominantly solute-solvent interactions that were influenced by the solute's concentration and temperature. Meanwhile, partial molar expansibilities (E_φ ⁰), transfer volume Δ_trV_φ ⁰ and Hepler's constant (δ²V₀/δT²) established the solution system's structure-breaking tendency. The Gibb's free energy (ΔG₀) values derived from conductometry data indicated the system's spontaneity. These calculated constants provided a detailed understanding of the different types of intermolecular interactions found in the ternary (LCTZ + water + amino acids) system.

In vitro drug interaction of levocetirizine and diclofenac: Theoretical and spectroscopic studies

Levocetirizine dihydrochloride is known to interact with some anti-inflammatory drugs. We report here a comprehensive integrated theoretical and experimental study for the in vitro drug interaction between levocetirizine dihydrochloride (LEV) and diclofenac sodium (DIC). The interaction of the two drugs was confirmed by the molecular ion peak obtained from the mass spectrum of the product. Moreover, FTIR and ¹HNMR spectra of the individual drugs and their interaction product were inspected to allocate the possible sites of interaction. In addition, quantum mechanical DFT calculations were performed to search for the interaction sites and to verify the types of interactions deduced from the spectroscopic studies such as charge-transfer and non-bonding π-π interactions. It was found that the studied drugs interact with each other in aqueous solution via four types of interactions, namely, ion-pair formation, three weak hydrogen bonds, non-bonding π-π interactions and charge-transfer from DIC to LEV.

Cellular Uptake of Levocetirizine by Organic Anion Transporter 4

The pharmacokinetics of cetirizine, a nonsedating antihistamine, is profoundly affected by transporter-mediated membrane transport in the kidney. In this study, we aimed to investigate the transport mechanism of levocetirizine, the pharmacologically active enantiomer of cetirizine, via human organic anion transporter 4 (OAT4) expressed in the apical membrane of renal proximal tubules and the basal plasma membrane of placental syncytiotrophoblasts. In cells expressing human OAT4 under the control of tetracycline, levocetirizine uptake was increased by tetracycline treatment. On the other hand, OAT4 expression did not facilitate efflux of preloaded levocetirizine from the cells, either in the presence or absence of extracellular Cl^-. The OAT4-mediated levocetirizine uptake was concentration-dependent with a K_m of 38 μM. The uptake rate of levocetirizine via OAT4 was approximately twice that of racemic cetirizine, indicating stereoselective uptake of levocetirizine. On the other hand, OAT4-mediated [³H]dehydroepiandrosterone sulfate uptake was inhibited by dextrocetirizine and levocetirizine. Overall, our findings indicate that OAT4 mediates levocetirizine uptake but is unlikely to mediate the efflux.

Novel minimal physiologically-based model for the prediction of passive tubular reabsorption and renal excretion clearance

PURPOSE

Develop a minimal mechanistic model based on in vitro-in vivo extrapolation (IVIVE) principles to predict extent of passive tubular reabsorption. Assess the ability of the model developed to predict extent of passive tubular reabsorption (Freab) and renal excretion clearance (CLR) from in vitro permeability data and tubular physiological parameters.

METHODS

Model system parameters were informed by physiological data collated following extensive literature analysis. A database of clinical CLR was collated for 157 drugs. A subset of 45 drugs was selected for model validation; for those, Caco-2 permeability (Papp) data were measured under pH6.5-7.4 gradient conditions and used to predict Freab and subsequently CLR. An empirical calibration approach was proposed to account for the effect of inter-assay/laboratory variation in Papp on the IVIVE of Freab.

RESULTS

The 5-compartmental model accounted for regional differences in tubular surface area and flow rates and successfully predicted the extent of tubular reabsorption of 45 drugs for which filtration and reabsorption were contributing to renal excretion. Subsequently, predicted CLR was within 3-fold of the observed values for 87% of drugs in this dataset, with an overall gmfe of 1.96. Consideration of the empirical calibration method improved overall prediction of CLR (gmfe=1.73 for 34 drugs in the internal validation dataset), in particular for basic drugs and drugs with low extent of tubular reabsorption.

CONCLUSIONS

The novel 5-compartment model represents an important addition to the IVIVE toolbox for physiologically-based prediction of renal tubular reabsorption and CLR. Physiological basis of the model proposed allows its application in future mechanistic kidney models in preclinical species and human.

Predictive Performance of Physiologically Based Pharmacokinetic and Population Pharmacokinetic Modeling of Renally Cleared Drugs in Children

Predictive performance of physiologically based pharmacokinetic (PBPK) and population pharmacokinetic (PopPK) models of drugs predominantly eliminated through kidney in the pediatric population was evaluated. After optimization using adult clinical data, the verified PBPK models can predict 33 of 34 drug clearance within twofold of the observed values in children 1 month and older. More specifically, 10 of 11 of predicted clearance values were within 1.5‐fold of those observed in children between 1 month and 2 years old. The PopPK approach also predicted 19 of 21 drug clearance within twofold of the observed values in children. In summary, our analysis demonstrated both PBPK and PopPK adult models, after verification with additional adult pharmacokinetic (PK) studies and incorporation of known ontogeny of renal filtration, could be applied for dosing regimen recommendation in children 1 month and older for renally eliminated drugs in a first‐in‐pediatric study.

Chiral Switch Drugs for Asthma and Allergies: True Benefit or Marketing Hype

Enantiomers are one of several possible molecular configurations present in a drug that has at least 1 chiral center. A drug containing 2 or more enatiomers is called a racemic mixture. Enatiomers are being developed from racemic mixtures as drugs in their own right often to extend patent protection of highly popular drugs. However, the therapeutic advantages of single enantiomer drugs developed for respiratory use such as levalbuterol, arformoterol, and levocetirizine over their racemate has been disappointing. In addition, single enantiomer drugs may be several fold more expensive than the racemic drug. New single enantiomer drugs, which are stable (no interconversion back to the racemate) and have fewer adverse effects and a more predictable pharmacodynamic or pharmacokinetic profile would confer a therapeutic advantage and thus would be beneficial for clinical use.

Binding of licarbazepine enantiomers to mouse and human plasma proteins

Racemic licarbazepine (Lic) is the active metabolite of oxcarbazepine (OXC) and eslicarbazepine acetate (ESL), appearing in human plasma as S-licarbazepine (S-Lic) and R-licarbazepine (R-Lic). However, human metabolism of OXC and ESL to Lic differs in the S-Lic/R-Lic enantiomeric ratio observed in plasma. S-Lic appears in higher proportion after ESL administration than after OXC (95% versus 80%). Enantioselective pharmacokinetics of Lic enantiomers have been found in mice after their separate administration and in humans following OXC treatment. Since protein binding of drugs may be enantioselective and a determining factor of pharmacokinetics, the binding of S-Lic and R-Lic to mouse and human total plasma proteins and, specifically, to human serum albumin (HSA) and alpha(1)-acid glycoprotein (AGP) were herein investigated for the first time. Free and bound fractions of S-Lic and R-Lic were separated by ultrafiltration after previous in vitro incubation of spiked plasma samples and protein solutions with each enantiomer at 10, 25 and 50 microg/ml. The results revealed that the extent of binding of Lic enantiomers to total plasma proteins was 30% and independent of the drug concentration and species considered. The data also suggest that the binding of Lic enantiomers to HSA is greater than that to AGP. Moreover, absence of enantioselectivity in the binding of Lic enantiomers to mouse and human plasma proteins and to HSA and AGP is evident. In conclusion, these findings suggest that the enantioselectivity observed in vivo in the biodisposition of S-Lic and R-Lic is not dependent on their affinity to plasma proteins.

Drug metabolism and pharmacokinetics

In this article, aspects of absorption, distribution, metabolism, and excretion have been described bearing in mind the pathogenesis of allergic diseases and their possible therapeutic opportunities. The importance of the routes of administration of the different therapeutic groups has been emphasized. The classical aspects of drug metabolism and disposition related to oral administration have been reviewed, but special emphasis has been given to intranasal, cutaneous, transdermal, and ocular administration as well as to the absorption and the subsequent bioavailability of drugs. Drug-metabolizing enzymes and transporters present in extrahepatic tissues, such as nasal mucosa and the respiratory tract, have been particularly discussed. As marketed antiallergic drugs include both racemates and enantiomers, aspects of stereoselective absorption, distribution, metabolism, and excretion have been discussed. Finally, a new and promising methodology, microdosing, has been presented, although it has not yet been applied to drugs used in the treatment of allergic diseases.

Chiral toxicology: it's the same thing...only different

Chiral substances possess a unique architecture such that, despite sharing identical molecular formulas, atom-to-atom linkages, and bonding distances, they cannot be superimposed. Thus, in the environment of living systems, where specific structure-activity relationships may be required for effect (e.g., enzymes, receptors, transporters, and DNA), the physiochemical and biochemical properties of racemic mixtures and individual stereoisomers can differ significantly. In drug development, enantiomeric selection to maximize clinical effects or mitigate drug toxicity has yielded both success and failure. Further complicating genetic polymorphisms in drug disposition, stereoselective metabolism of chiral compounds can additionally influence pharmacokinetics, pharmacodynamics, and toxicity. Optically pure pharmaceuticals may undergo racemization in vivo, negating single enantiomer benefits or inducing unexpected effects. Appropriate chiral antidotes must be selected for therapeutic benefit and to minimize adverse events. Enantiomers may possess different carcinogenicity and teratogenicity. Environmental toxicology provides several examples in which compound bioaccumulation, persistence, and toxicity show chiral dependence. In forensic toxicology, chiral analysis has been applied to illicit drug preparations and biological specimens, with the potential to assist in determination of cause of death and aid in the correct interpretation of substance abuse and "doping" screens. Adrenergic agonists and antagonist, nonsteroidal anti-inflammatory agents, SSRIs, opioids, warfarin, valproate, thalidomide, retinoic acid, N-acetylcysteine, carnitine, penicillamine, leucovorin, glucarpidase, pesticides, polychlorinated biphenyls, phenylethylamines, and additional compounds will be discussed to illustrate important concepts in "chiral toxicology."