pH-Metric log K calculations of famotidine, naproxen, nizatidine, ranitidine and salicylic acid

A Kinetic Approach to Determining Drug Distribution in Complex Biphasic Systems

Pharmaceutical emulsions contain multiple components, such as micellar, aqueous, and oil phases, leading to complex drug transfer and equilibrium phenomena. These complex components present challenges for the bioequivalence assessment of the drug products. The objective of the study was to develop a method that can probe the underlying mechanism and process of drug distribution. The concept of drug partitioning into biphasic systems was used to simplify the complex transfer phenomenon. A kinetic method was developed taking into account the biphasic diffusion. Using this approach, both the rate (kinetics) and the extent (equilibrium) of distribution can be determined. For method development purpose, 3 model compounds (triamcinolone acetonide, difluprednate, and cyclosporine), with expected partition coefficient values ranging from 2 to 6, were tested using the kinetic method and the traditional shake-flask method. The values obtained by the 2 methods for all compounds correlated well (r² = 0.825). Various organic and aqueous solvents which are commonly encountered in formulations were also tested to determine the impact of phase composition on drug distribution. The kinetic method was found to offer more flexibility in terms of solvent composition and can lead to better understanding for drug distribution and potential drug release in complex biphasic systems.

Prediction of Aqueous pK a Values for Guanidine-Containing Compounds Using Ab Initio Gas-Phase Equilibrium Bond Lengths

In this work, we demonstrate the existence of linear relationships between gas-phase equilibrium bond lengths of the guanidine skeleton of 2-(arylamino)imidazolines and their aqueous pK _a value. For a training set of 22 compounds, in the most stable conformation of their lowest energy tautomeric form, three bonds were found to exhibit r ² and q ² values >0.95 and root-mean-squared-error of estimation values ≤0.25 when regressed individually against pK _a. The equations describing these one-bond-length linear relationships, in addition to a multiple linear regression model using all three bond lengths, were then used to predict the experimental pK _a values of an external test set of further 27 derivatives. The optimal protocol we derive here shows an overall mean absolute error (MAE) of 0.20 and standard deviation of errors of 0.18 for the test set. Predictions for a second test set of diphenyl-based bis(2-iminoimidazolidines) yielded an MAE of 0.27 and a standard deviation of 0.10. The predictive power of the optimal model is further demonstrated by its ability to correct erroneously reported experimental values. Finally, a previously established guanidine model is recalibrated at a new level of theory, and predictions are made for novel phenylguanidine derivatives, showing an MAE of just 0.29. The protocols established and tested here pass both of Roy's modern and stringent MAE-based criteria for a "good" quantitative structure-activity relationship/quantitative structure-property relationship model predictivity. Notably, the ab initio bond length high correlation subset protocol developed in this work demonstrates lower MAE values than the Marvin program by ChemAxon for all test sets.

Degradation of nitro-based pharmaceuticals by UV photolysis: Kinetics and simultaneous reduction on halonitromethanes formation potential

This study investigated the degradation kinetics and halonitromethanes formation potential (HNMsFP) of two nitro-based pharmaceuticals (i.e., ranitidine (RNTD) and nizatidine (NZTD)) during ultraviolet (UV) photolysis. It was found that the degradation kinetics of RNTD and NZTD exhibited pH-dependent trends, in accordance with their deprotonation equilibria. The neutral species of RNTD and NZTD were more photo-reactive than their corresponding deprotonated species, with their specific fluence-based first-order rate constants varying in the range of 5.64-31.90 m² E^-1. Both the RNTD and NZTD were prone precursors of HNMs (with molar yields of 5.6± 0.3% and 4.7± 0.4%, respectively at pH 7.0). Acidic and neutral circumstances facilitated the HNMs formation. The UV photolysis of RNTD and NZTD could reduce their HNMsFP simultaneously. Positive linear relationships between residual RNTD or NZTD concentration and HNMsFP were observed and the denitration during the UV photolysis accounted for the HNMsFP reduction. With the mandatory UV disinfection fluences in China (i.e. 20-80 mJ cm^-2), the effective abatement of RNTD and NZTD and their HNMsFP could not be fully achieved, highlighting the necessity of increasing UV fluence or developing UV-based advanced oxidation process in future.

Evaluation of SimpleTreat 4.0: Simulations of pharmaceutical removal in wastewater treatment plant facilities

In this study, the removal of pharmaceuticals from wastewater as predicted by SimpleTreat 4.0 was evaluated. Field data obtained from literature of 43 pharmaceuticals, measured in 51 different activated sludge WWTPs were used. Based on reported influent concentrations, the effluent concentrations were calculated with SimpleTreat 4.0 and compared to measured effluent concentrations. The model predicts effluent concentrations mostly within a factor of 10, using the specific WWTP parameters as well as SimpleTreat default parameters, while it systematically underestimates concentrations in secondary sludge. This may be caused by unexpected sorption, resulting from variability in WWTP operating conditions, and/or QSAR applicability domain mismatch and background concentrations prior to measurements. Moreover, variability in detection techniques and sampling methods can cause uncertainty in measured concentration levels. To find possible structural improvements, we also evaluated SimpleTreat 4.0 using several specific datasets with different degrees of uncertainty and variability. This evaluation verified that the most influencing parameters for water effluent predictions were biodegradation and the hydraulic retention time. Results showed that model performance is highly dependent on the nature and quality, i.e. degree of uncertainty, of the data. The default values for reactor settings in SimpleTreat result in realistic predictions.

The development of a high-throughput measurement method of octanol/water distribution coefficient based on hollow fiber membrane solvent microextraction technique

This paper describes the development of a novel high-throughput hollow fiber membrane solvent microextraction technique for the simultaneous measurement of the octanol/water distribution coefficient (logD) for organic compounds such as drugs. The method is based on a designed system, which consists of a 96-well plate modified with 96 hollow fiber membrane tubes and a matching lid with 96 center holes and 96 side holes distributing in 96 grids. Each center hole was glued with a sealed on one end hollow fiber membrane tube, which is used to separate the aqueous phase from the octanol phase. A needle, such as microsyringe or automatic sampler, can be directly inserted into the membrane tube to deposit octanol as the accepted phase or take out the mixture of the octanol and the drug. Each side hole is filled with aqueous phase and could freely take in/out solvent as the donor phase from the outside of the hollow fiber membranes. The logD can be calculated by measuring the drug concentration in each phase after extraction equilibrium. After a comprehensive comparison, the polytetrafluoroethylene hollow fiber with the thickness of 210 μm, an extraction time of 300 min, a temperature of 25 °C and atmospheric pressure without stirring are selected for the high throughput measurement. The correlation coefficient of the linear fit of the logD values of five drugs determined by our system to reference values is 0.9954, showed a nice accurate. The -8.9% intra-day and -4.4% inter-day precision of logD for metronidazole indicates a good precision. In addition, the logD values of eight drugs were simultaneously and successfully measured, which indicated that the 96 throughput measure method of logD value was accurate, precise, reliable and useful for high throughput screening.

Extension of the liquid chromatography/quantitative structure-property relationship method to assess the lipophilicity of neutral, acidic, basic and amphotheric drugs

A reported chromatographic method to determine the 1-octanol/water partition coefficient (logP(o/w)) has been used to estimate the lipophilicity of 33 drugs with diverse structures and functionalities, including neutral, acid, basic, and amphoteric compounds. The applicability of the chromatographic method has been extended to the UHPLC technique, and the results obtained were compared to those obtained from conventional HPLC. No significant difference between the results obtained by both techniques is noticed. Thus, the suitability of UHPLC, which involves shorter run times, for lipophilicity assessment is demonstrated. In order to show the consistency of this chromatographic method, the logP(o/w) values of those drugs which have acid-base properties have been also determined by potentiometry, and the final results have been compared with both values derived from the chromatographic method and the ones from the literature.

A new sensitive flow-injection chemiluminescence method for the determination of H2-receptor antagonists

Based on the chemiluminescence (CL) intensity generated from the potassium ferricyanide [K(3)Fe(CN)(6)]-rhodamine 6G system in sodium hydroxide (NaOH) medium, a new sensitive flow-injection chemiluminescence (FI-CL) method has been developed, validated and applied for the determination of three kinds of H(2)-receptor antagonists: cimetidine (CIMT), ranitidine (RANT) hydrochloride and famotidine (FAMT). Under the optimum conditions, the linear range for the determination was 1.0 x 10(-9)-7.0 x 10(-5) g/ml for CIMT, 1.0 x 10(-9)-5.0 x 10(-5) g/mL for RANT hydrochloride and 5.0 x 10(-9)-7.0 x 10(-5) g/mL for FAMT. During 11 repeated measurements of 1.0 x 10(-6) g/mL sample solutions, the relative standard deviations (RSDs) were all <5%. The detection limit was 8.56 x 10(-10) g/mL for CIMT, 8.69 x 10(-10) g/mL for RANT hydrochloride and 2.35 x 10(-9) g/mL for FAMT (S:N = 3). This method has been successfully implemented for the analysis of H(2)-receptor antagonists in pharmaceuticals.

In vitro studies on the application of colloidal emulsion aphrons to drug overdose treatment

Colloidal emulsion aphrons (CEAs) are considered as the micron-sized water-in-oil (W/O) emulsion-cores encapsulated by a "soapy shell" consisting of multi-layer surfactant molecules. In this dispersion, the emulsion-core sizes are mainly in 10-100 microm and that of the inner phase droplets are in 1-5 microm. CEAs not only behave analogously to emulsion liquid membrane (ELM) in extraction with advantages of high concentration ratio, counter-concentration extraction and combination of extraction with backwash together, but also have the large interface areas, easy scatteration and quick extraction which colloidal liquid aphrons (CLAs) possess. CEA extraction overcomes the restriction of partition equilibrium between the water and the oil phase that CLAs have. They have greater extraction capacity than CLAs. In this study, the application of CEAs to drug overdose treatment was studied using salicylic acid as the model drug, paraffin oil as the membrane phase, PEG-30 dipolyhydroxystearate (P135) as the hydrophobic surfactant, nonylphenol ethoxylate-10 (NP10) as the hydrophilic surfactant and NaOH solution as the receptor phase. Also some factors affecting the stability of this dispersion and extraction ratio were investigated. In order to prepare CEAs successfully, the concentrations of NP10 and P135 should be in 1.5-3.0% (w/v) and 0.25-1.0% (w/v), respectively, together with the ratio of the volume of oil phase to the volume of inner aqueous phase of CEAs, R(oi)> or =1:1. For the extraction of salicylic acid, the pH value of the feed phase was supposed to be lower than 2.0 and the suitable NaOH concentration of the receptor phase was higher than 0.02 mol/L. Under this condition, more than 98.7% of salicylic acid was transported into receptor phase in half a minute.

Ketene aminal-based lactam derivatives as a novel class of orally active FXa inhibitors

N,N'-Disubstituted ketene aminals are good bioisosteres of thiourea functional groups. We report the design and synthesis of a novel class of ketene aminal-based lactam derivatives as potent and orally active FXa inhibitors.