Sample preparation for the HPLC analysis of drugs in biological fluids

Detection and quantification of Covid-19 antiviral drugs in biological fluids and tissues

Since coronavirus disease 2019 (COVID-19) started as a fast-spreading pandemic, causing a huge number of deaths worldwide, several therapeutic options have been tested to counteract or reduce the clinical symptoms of patients infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Currently, no specific drugs for COVID-19 are available, but many antiviral agents have been authorised by several national agencies. Most of them are under investigation in both preclinical and clinical trials; however, pharmacokinetic and metabolism studies are needed to identify the most suitable dose to achieve the desired effect on SARS-CoV-2. Therefore, the efforts of the scientific community have focused on the screening of therapies able to counteract the most severe effects of the infection, as well as on the search of sensitive and selective analytical methods for drug detection in biological matrices, both fluids and tissues. In the last decade, many analytical methods have been proposed for the detection and quantification of antiviral compounds currently being tested for COVID-19 treatment. In this review, a critical discussion on the overall analytical procedure is provided, i.e (a) sample pre-treatment and extraction methods such as protein precipitation (PP), solid-phase extraction (SPE), liquid–liquid extraction (LLE), ultrasound-assisted extraction (UAE) and QuEChERS (quick, easy, cheap, effective, rugged and safe), (b) detection and quantification methods such as potentiometry, spectrofluorimetry and mass spectrometry (MS) as well as (c) methods including a preliminary separation step, such as high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) coupled to UV–Vis or MS detection. Further current trends, advantages and disadvantages and prospects of these methods have been discussed, to help the analytical advances in reducing the harm caused by the SARS-CoV-2 virus.

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Fourteen antiviral drugs were tested to counteract the effects of COVID-19.

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A review of analytical methods for antivirals detection is presented.

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Method validation, drugs extraction, separation and detection are discussed.

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LC-MS and MS/MS is mostly used for accurate and sensitive drugs quantification.

Simple and reliable extraction and a validated high performance liquid chromatographic assay for quantification of amoxicillin from plasma

This study presents the development of an efficient extraction protocol for amoxicillin from plasma with improved solubility and stability using pH control. Solubility and stability of amoxicillin in commonly used extraction solvents were determined using a newly developed stability-indicating high-performance liquid chromatography (HPLC) method. Following this, protein precipitation (PP) mediated sample purification protocol was developed and validated along with the HPLC method for the extracted amoxicillin from rabbit plasma. The protocol was applied in a pharmacokinetic study in rabbits. A five-fold increase in solubility and two-fold increase in stability of amoxicillin was found by addition of acetate buffer (0.1 M, pH 5.0) in acetonitrile. PP mediated extraction protocol containing acetate buffer-acetonitrile (1:18 v/v) resulted in an extraction recovery of >80% for all the samples. The HPLC assay following extraction was found linear (R²   >0.9999) over the range of 0.2-20 µg/mL with a lower limit of quantification of 0.2 µg/mL. The accuracy of the quality control samples was found between 97-115% and the relative standard deviation (RSD) was found to be below 6% for all samples. The samples were stable in the mobile phase (pH 5.0) for 72 h post-extraction. Amoxicillin-spiked plasma samples were found stable for up to three freeze-and-thaw cycles but, nearly 50% samples had degraded following storage for two months at -20 °C. Pharmacokinetic analysis indicated a half-life of amoxicillin of nearly 1 h following intravenous injection in rabbits, which is similar to that in humans. Thus, a simple and repeatable, extraction protocol was developed using pH control for quantification of amoxicillin from plasma based on its physicochemical properties.

Solid Phase Extraction for Monitoring of Occupational Exposure to Cr (III)

Chromium is an important constituent widely used in different industrial processes for production of various synthetic materials. For evaluation of workers' exposure to trace toxic metal of Cr (III), environmental and biological monitoring are essential processes, in which, preparation of samples is one of the most time-consuming and error-prone aspects prior to analysis. The use of solid-phase extraction (SPE) has grown and is a fertile technique of sample preparation as it provides better results than those produced by liquid-liquid extraction (LLE). SPE using mini columns filled with XAD-4 resin was optimized regarding to sample pH, ligand concentration, loading flow rate, elution solvent, sample volume, elution volume, amount of resins, and sample matrix interferences. Chromium was retained on solid sorbent and was eluted with 2 M HNO3 followed by simple determination of analytes by using flame atomic absorption spectrometery. Obtained recoveries of metal ion were more than 92%. The optimized procedure was also validated with three different pools of spiked urine samples and showed a good reproducibility over six consecutive days as well as six within-day experiments. Through this study, suitable results were obtained for relative standard deviation, therefore, it is concluded that, this optimized method can be considered to be successful in simplifying sample preparation for trace residue analysis of Cr in different matrices for evaluation of occupational and environmental exposures. To evaluate occupational exposure to chromium, 16 urine samples were taken, prepared, and analyzed based on optimized procedure.

Advances in sample preparation in electromigration, chromatographic and mass spectrometric separation methods

The quality of sample preparation is a key factor in determining the success of analysis. While analysis of pharmaceutically important compounds in biological matrixes has driven forward the development of sample clean-up procedures in last 20 years, today's chemists face an additional challenge: sample preparation and analysis of complex biochemical samples for characterization of genotypic or phenotypic information contained in DNA and proteins. This review focuses on various sample pretreatment methods designed to meet the requirements for the analysis of biopolymers and small drugs in complex matrices. We discuss the advances in development of solid-phase extraction (SPE) sorbents, on-line SPE, membrane-based sample preparation, and sample clean-up of biopolymers prior to their analysis by mass spectrometry.

Impact of gastric emptying on the pharmacokinetics of ethanol as influenced by cisapride

AIMS

To examine the influence of cisapride on the pharmacokinetics of ethanol and the impact of gastric emptying monitored by the paracetamol absorption test.

METHODS

Ten healthy male volunteers took part in a cross-over design experiment. They drank a moderate dose of ethanol 0.30 g kg-1 body weight exactly 1 h after eating breakfast either without any prior drug treatment or after taking cisapride (10 mg three times daily) for 4 consecutive days. In a separate study, the same dose of ethanol was ingested on an empty stomach (overnight fast). Paracetamol (1.5 g) was administered before consumption of ethanol to monitor gastric emptying. Venous blood was obtained at 5-10 min intervals for determination of ethanol by headspace gas chromatography and paracetamol was analysed in serum by high performance liquid chromatography (h.p.l.c.). Results The maximum blood-ethanol concentration (Cmax ) increased from 3.8+/-1.7 to 5.6+/-2.3 mmol l-1 (+/-s.d.) after treatment with cisapride (95% confidence interval CI on mean difference 0.28-3.28 mmol l-1 ). The area under the blood-ethanol curve (AUC) increased from 6.3+/-3.5 to 7.9+/-2.6 mmol l-1 h after cisapride (95% CI -0. 74-3.9 mmol l-1 h). The mean blood ethanol curves in the cisapride and no-drug sessions converged at approximately 2 h after the start of drinking. Both Cmax and AUC were highest when the ethanol was ingested on an empty stomach (Cmax 9.5+/-1.7 mmol l-1 and AUC 14. 6+/-1.9 mmol l-1 h), compared with drinking 1 h after a meal and regardless of pretreatment with cisapride.

CONCLUSIONS

A small but statistically significant increase in Cmax occurred after treatment with cisapride owing to faster gastric emptying rate as shown by the paracetamol absorption test. However, the rate of absorption of ethanol, as reflected in Cmax and AUC, was greatest after drinking the alcohol on an empty stomach. The cisapride-ethanol interaction probably lacks any clinical or forensic significance.

Sample preparation for the determination of purine nucleotide analogues in tissues

A sample treatment procedure for the determination of thiopurine and ganciclovir nucleotides in human tissues was developed. Owing to the lack of suitable standards for most of the active nucleotide analogues, the procedure was based on two steps: (1) perchloric acid homogenization and deproteinization of the tissue specimen and (2) conversion of purine nucleotides into parent drug or free bases by enzymatic or acid hydrolysis. The parent drug or purine bases formed were then analyzed on a Hypersil ODS column using isocratic elution with dihydrogenphosphate buffer for ganciclovir nucleotides or the gradient elution mode with dihydrogenphosphate buffermethanol for thiopurine nucleotides. The sample treatment procedure was evaluated using guanosine triphosphate (GTP), 6-thioinosinic acid (6TIMP) and 6-thioguanosine monophosphate (6TGMP) as standards. Mean analytical recoveries determined by adding known concentrations of standards to the tissue specimen before sampling processing were higher than 97%. The sample preparation described is simple and represents a suitable method for the investigation of active nucleotide pool in tissues.

Solid-phase extraction of arginine vasotocin and isotocin in fish samples and subsequent gradient reversed-phase high-performance liquid chromatographic separation

Gradient high-performance liquid chromatography (HPLC) preceded by a solid-phase extraction (SPE) step is described for determining arginine vasotocin and isotocin, the neurohypophysial nonapeptides, in fish plasma samples. The combination of these two methods significantly improves the separation and increases the sensitivity of the assay. The proposed assay may be a useful alternative for analysis of similar nonapeptides in plasma without the use of radioisotopes, while taking into consideration a difference in detection sensitivity.

Analysis of pharmaceutical creams: a useful approach based on solid-phase extraction (SPE) and UV spectrophotometry

Solid-phase extraction (SPE) using C-18, diol and ion-exchange sorbents followed by UV spectrophotometric (conventional and derivative mode) assay was applied to the analysis of basic, acidic and neutral drugs commercially available in creams. A representative set of drugs (promethazine, chlorhexidine, benzydamine, ketoprofen, ibuprofen, fentiazac, piroxicam, fluorouracil, crotamiton and hydrocortisone acetate) was selected, and for each drug the appropriate SPE conditions (adsorption, washing and elution) were investigated to obtain a practical and reliable sample clean-up. It was shown that the developed SPE procedures were capable of removing interfering cream components (excipients including preservatives) allowing accurate spectrophotometric analyses to be performed. In some applications, derivative spectrophotometry was advantageous over the conventional absorption mode with respect to higher selectivity and versatility.

Endogenous hypercholecystokininemia, but not aspirin, reduces the gallstone incidence in the hamster model

BACKGROUND

Studies in humans and rodents indicate that gallstone development may be prevented by inhibiting gallbladder mucus hypersecretion with non-steroidal anti-inflammatory drugs or by preventing stasis of gallbladder bile with administration of cholecystokinin.

METHODS

The effect of oral aspirin and pancreaticobiliary diversion with endogenous hypercholecystokininemia on crystal and gallstone formation was studied in Syrian golden hamsters fed a lithogenic diet for 8 weeks.

RESULTS

None of the control animals fed a normal diet developed gallstones or crystals in gallbladder bile. Gallstones developed in 67% of the animals fed a lithogenic diet only. The gallstone prevalence did not differ significantly in animals on a lithogenic diet and a daily aspirin dose of 6 mg/kg (gallstone prevalence, 60%) or 100 mg/kg (gallstone prevalence, 70%), whereas it was significantly lower in animals with endogenous hypercholecystokininemia on a lithogenic diet (gallstone prevalence, 29%). The prevalence of crystals in gallbladder bile did not differ significantly between any of the experimental groups.

CONCLUSIONS

It is concluded that in hamsters on a lithogenic diet, aspirin does not prevent gallstone formation, whereas endogenous hypercholecystokininemia reduces the prevalence of stones without affecting the occurrence of crystals in gallbladder bile.

Enantiospecific determination of ibuprofen in rat plasma using chiral fluorescence derivatization reagent, (-)-2-[4-(1-aminoethyl)phenyl]-6- methoxybenzoxazole

A highly sensitive and reversed-phase high-performance liquid chromatographic method for the determination of the enantiomeric composition of ibuprofen in rat plasma is described. The method is based on the resolution of the diastereomeric amides formed on reaction of the ibuprofen enantiomers with (-)-2-[4-(1-aminoethyl)phenyl]-6-methoxybenzoxazole ((-)-APMB) in the presence of 2,2'-dipyridyl disulphide (DPDS) and triphenylphosphine (TPP) in dichloromethane. The reaction mixture was allowed to stand at room temperature for 5 min, and the reaction was completed by evaporation with a stream of nitrogen at 40 degrees C. The minimum quantifiable concentrations were 0.2 microgram/mL and 0.4 microgram/mL for S-ibuprofen and R-ibuprofen, respectively, in a 10 microL injection volume. The method was applied to the determination of enantiomeric ibuprofen in plasma after oral administration to rats.

Knowledge-based system for the automated solid-phase extraction of basic drugs from plasma coupled with their liquid chromatographic determination. Application to the biodetermination of beta-receptor blocking agents

Techniques for the preparation of biological samples are often based nowadays on solid-phase extraction (SPE). The different SPE steps can be performed automatically on disposable extraction cartridges (DECs) by means of a sample processor. A knowledge-based system was developed to facilitate the development of fully automated methods for the solid-phase extraction of relatively hydrophobic basic drugs from plasma, coupled with their determination by high-performance liquid chromatography (HPLC). The DEC filled with 50 mg of cyanopropyl-bonded silica phase is first conditioned with methanol and buffer solution (pH 7.4). After sample application, the DEC sorbent is washed with the same buffer. The analytes are then desorbed with an appropriate eluent and the eluate is finally diluted with the same buffer as used in the HPLC mobile phase before injection. Under these conditions, only three variables are still to be optimized: the composition and volume of the elution solvent and the volume of buffer to be added to the eluate. On the basis of this general strategy, a decision tree providing information about suggested starting conditions and guidelines for the optimization of the three variables was developed and implemented by use of a hypermedia software. This didactic expert system was evaluated using several beta-receptor blocking agents as model compounds and the operating conditions obtained for the automated SPE of these compounds are presented. A method for the determination of propranolol in plasma using the SPE conditions deduced from the knowledge-based system was validated. The absolute recovery of propranolol is ca. 93% and the limit of detection is 1.3 ng ml-1. The mean within-day and between-day reproducibilities are 2.3 and 3.6%, respectively.

Quantitation of human plasma levels of the anticancer agent carboxyamidotriazole by high-performance liquid chromatography

The predominant cause of death of cancer patients is growth and metastasis of their tumors. By targeting signal transduction pathways as sites of therapeutic intervention, we have identified a novel anticancer drug carboxyamidotriazole (CAI). A straight-forward and reliable method of detection and quantitation of human CAI plasma levels using solid-phase organic extraction followed by isocratic reversed-phase chromatography is now reported. This assay detected CAI over the concentration range 0.04-10.0 micrograms/ml, which brackets the range shown to be physiologically and biochemically effective. Linearity was demonstrated by linear regression analysis of calibration curves (r2 = 0.999). Equivalence of recovery of extracted versus non-extracted CAI over a broad concentration range was demonstrated (r2 = 0.998, coefficients of variability < 10%). The method was applied to quantitate CAI plasma levels from patients now entered on the Phase I clinical trial underway at the National Cancer Institute.

Determination of verapamil and norverapamil in human plasma by liquid chromatography: comparison between a liquid-liquid extraction procedure and an automated liquid-solid extraction method for sample preparation

A conventional liquid-liquid extraction (LLE) procedure with high-performance liquid chromatography (HPLC) has been developed for the determination of verapamil and its main metabolite, norverapamil, in plasma. After addition of the internal standard, plasma samples were basified with phosphate buffer (pH 9.0) and extracted with a mixture of cyclohexane-dichloromethane. After centrifugation, the organic layer was separated and the analytes were extracted back into a 0.1 N sulphuric acid solution containing 2-aminoheptane. An aliquot of this aqueous phase was then injected directly onto the HPLC column. This LLE procedure has been compared with an automated liquid-solid extraction (LSE) method that has been developed in parallel. Good linearity was obtained using both extraction methods. The absolute recoveries for the two analytes were ca 95% with the automated LSE procedure and slightly lower (ca 84%) for the LLE method. The automated method gives better results with respect to detectability and precision, but the LLE procedure is simpler to develop, requires much less expensive equipment, and remains a useful alternative when the number of samples to be analysed is limited.

"On-line internal surface reversed-phase cleaning": the direct HPLC analysis of crude biological samples. Application to the kinetics of degradation of oligonucleotides in cell culture medium

An "on-line" HPLC analysis of crude biological samples is described. A precolumn of internal surface reversed-phase material allows the passage of proteins and other unwanted products while retaining analytes which are transferred, concentrated and chromatographed on a conventional reverse-phase or ion-exchange HPLC column. This protocol allows precise kinetics of the degradation of an oligonucleotide in cell culture to be obtained without radiolabeling or sample preparation.

Direct analysis of whole blood by internal surface reversed-phase chromatography: an examination of the binding and metabolism of technetium dioxime complexes

We have developed a method using internal surface reversed-phase (ISRP) packing for rapid on-line separation of small hydrophobic compounds from cellular whole blood components. This is achieved by the use of 75-microns ISRP chromatographic material packed into a small high-performance liquid chromatographic (HPLC) column, in conjunction with column switching. We have applied this analytical method to study the in vitro metabolism of 99mTc-BATO (boronic acid adducts of technetium dioxime) cerebral and myocardial perfusion tracers in whole blood. The results from the ISRP procedure were compared with a conventional centrifugation method of analysis. This novel HPLC methods provides a rapid, convenient and reliable method for the analysis of radioactive and non-radioactive lipophilic components in whole blood.

Automatic determination of diltiazem and desacetyldiltiazem in human plasma using liquid-solid extraction on disposable cartridges coupled to HPLC--Part II: Optimization of liquid-solid extraction

An automatic liquid-solid extraction (LSE) procedure to be coupled to HPLC for the determination of diltiazem and desacetyldiltiazem in plasma has been developed. The LSE operations are performed on disposable extraction cartridges (DECs) by means of a sample processor equipped with a robotic arm holding a needle through which the different liquids are dispensed. The operating parameters of LSE have been optimized with respect to recovery, detectability and reproducibility by using, whenever possible, aqueous solutions of the analytes. Different kinds of DECs have been tested. For the compounds studied, DECs filled with 50 mg of cyanopropyl silica have been selected. The influence of the pH of the buffer used in the washing step has been studied, leading finally to the selection of the same phosphate buffer (pH 7.4) as in the HPLC mobile phase. The minimum volume of methanol which still gives a nearly complete elution of the analytes from the extraction cartridges has been determined. Under these conditions, a high sensitivity can be obtained without an evaporation step. Moreover, the volume of buffer to be added to the methanolic eluate before injection into the HPLC system has been optimized in such a way that a focusing effect is obtained at the top of the analytical column while the dilution of the extract is minimized.