Determination of the novel non-peptidic HIV-protease inhibitor tipranavir by HPLC-UV after solid-phase extraction

An HPLC method previously described for the assay of amprenavir (APV), ritonavir (RTV), indinavir (IDV), saquinavir (SQV), nelfinavir (NFV), lopinavir (LPV), atazanavir (ATV), nevirapine (NVP) and efavirenz (EFV) can be also conveniently applied, with minor gradient program adjustment, for the determination of the novel non-peptidic HIV protease inhibitor tipranavir (TPV) in human plasma, by off-line solid-phase extraction (SPE) followed by HPLC coupled with UV-diode array detection (DAD). After viral inactivation by heat, the plasma is diluted with phosphate buffer (pH 7), and subjected to a SPE on a C18 cartridge. Matrix components are eliminated with a solution of 0.1% H3PO4 solution neutralised to pH 7, and TPV is eluted with MeOH. The resulting eluate is evaporated and reconstituted in 100 microl MeOH/H2O 50/50. A 40 microl volume is injected onto a Nucleosil C18 AB column and TPV is analysed by UV detection at 201 nm using a gradient elution program constituted of MeCN and phosphate buffer adjusted to pH 5.12 and containing 0.02% sodium heptanesulfonate. The calibration curves are linear up to 75 microg/ml, with a lower limit of quantification of 0.125 microg/ml. The mean absolute recovery of TPV is 77.1+/-4.0%. The method is precise with mean inter-day coefficient of variations (CVs) within 2.2-3.4%, and accurate (range of inter-day deviations from 0.7 to 1.2%). The method has been validated and is currently applied to the monitoring of TPV plasma levels in HIV patients.     

Determination of imatinib (Gleevec) in human plasma by solid-phase extraction-liquid chromatography-ultraviolet absorbance detection

A sensitive HPLC method has been developed for the assay of imatinib in human plasma, by off-line solid-phase extraction followed by HPLC coupled with UV-Diode Array Detection. Plasma (750 microl), with clozapine added as internal standard, is diluted 3 + 1 with water and subjected to a solid-phase extraction on a C18 cartridge. After matrix components elimination with 2000 microl of water (in two aliquots of 1000 microl), imatinib is eluted with 3 x 500 microl MeOH. The resulting eluate is evaporated under nitrogen at room temperature and is reconstituted in 180 microl 50% methanol. A 50 microl volume is injected onto a Nucleosil 100-5 microm C18 AB column. Imatinib is analyzed using a gradient elution program with solvent mixture constituted of methanol and water containing both 0.05% ammonium acetate. Imatinib is detected by UV at 261 nm. The calibration curves are linear between 0.1 and 10 microg/ml. The limit of quantification and detection are 0.05 and 0.01 microg/ml, respectively. The mean absolute recovery of imatinib is 96%. The method is precise with mean inter-day CVs within 1.1-2.4%, and accurate (range of inter-day deviations -0.6 to +0.7%). The method has been validated and is currently being applied in a clinical study assessing the imatinib plasma concentration variability in a population of chronic myeloid leukemia- and gastro-intestinal stromal tumor-patients.     

Simultaneous quantification of lopinavir and ritonavir in human plasma by high performance liquid chromatography coupled with UV detection

High performance liquid chromatography was coupled with UV detection for simultaneous quantification of lopinavir (LPV) and ritonavir (RTV) in human plasma. This assay was sensitive, accurate and simple, and only used 200 μL of plasma sample. Samples were liquid-liquid extracted, and diazepam was used as an internal standard. The chromatographic separation was achieved on a C18 reversed-phase analytic column with a mobile phase of acetonitrile-sodium dihydrogen phosphate buffer (10 mmol L⁻¹, pH 4.80) (60:40, v/v). UV detection was conducted at 205 nm and the column oven was set at 40°C. Calibration curves were constructed between 0.5–20 μg mL⁻¹ for LPV and 0.05–5 μg mL⁻¹ for RTV. The relative standard deviations were 2.16%–3.20% for LPV and 2.12%–2.60% for RTV for intra-day analysis, and 2.34%–4.04% for LPV and 0.31%–4.94% for RTV for inter-day analysis. The accuracy was within 100%±10%. The mean extraction recoveries were 79.17%, 52.26% and 91.35% for RTV, LPV and diazepam, respectively. This method was successfully applied to human plasma samples from patients orally administered a salvage regimen of lopinavir-ritonavir tablets.     

Determination of aciclovir and ganciclovir in human plasma by liquid chromatography-spectrofluorimetric detection and stability studies in blood samples

A sensitive HPLC method has been developed for the assay of aciclovir and ganciclovir in human plasma, by HPLC coupled with spectrofluorimetric detection. Plasma (1000 microl), with 9-ethyl-guanine added as internal standard, is submitted to protein precipitation with trichloroacetic acid solution 20%. The supernatant, evaporated to dryness at 37 degrees C, is reconstituted in 100 microl of a solution of sodium heptanosulfonate 0.4% adjusted with acetic acid to pH 2.60 and a 30 microl volume is then injected onto a Nucleosil 100-5 microm C18 column. Aciclovir and ganciclovir are analysed by spectrofluorimetric detection set at 260 nm (excitation) and 380 nm (emission) using a gradient elution program with solvents constituted of acetonitrile and a solution of sodium heptanosulfonate 0.4% adjusted to pH 2.60. The calibration curves are linear between 0.1 and 10 microg/ml. The mean absolute recovery of aciclovir and ganciclovir are 99.2+/-2.5 and 100.3+/-2.5%, respectively. The method is precise (with mean inter-day C.V.s within 1.0-1.6% for aciclovir and 1.2-3.5% for ganciclovir), and accurate (range of inter-day deviations -1.6 to +1.6% for aciclovir and -0.4 to -1.4% for ganciclovir). The method has been applied in stability studies of ganciclovir in patients' blood samples, demonstrating its good stability in plasma at -20 degrees C and at room temperature. The distribution of ganciclovir and aciclovir in plasma and red blood cells was also investigated in vitro in spiking experiments with whole blood, which showed an initial drop of ganciclovir and aciclovir levels in plasma (about -25%) due to the cellular uptake of aciclovir and ganciclovir by red blood cells. The method has been validated and is currently applied in a clinical study assessing the ganciclovir plasma concentration variability after administration of valganciclovir in a population of solid organ transplant patients.     

A simple and sensitive assay for determining plasma tipranavir concentration in the clinical setting by new HPLC method

A simple method for the quantification of tipranavir, the first non-peptidic HIV protease inhibitor, was developed and validated. Quinoxaline, as internal standard, was added to 50 microl of plasma before a liquid-liquid extraction by 600 microl of protein precipitation solution. The extracts were diluted before being injected in the chromatographic system. Chromatographic separation was made on a C18 column using potassium phosphate buffer (pH 3.2) and acetonitrile with gradient. Detection was performed by an UV detector at 260 nm. Relative error at three control quality concentrations ranged from -1.81 to 1.72%. Intra-day (CV%) and inter-day (CV%) precision ranged from 0.94 to 2.55% and from 3.07 to 4.24%, respectively. LOQ and LOD were 0.090 microg/ml and 0.035 microg/ml, respectively. Mean recovery was 87.1%+/-2.4%. Calibration curve was linear up to 180 microg/ml. Concentration range when optimized (0.703-180 microg/ml) proved to be adequate to measure tipranavir concentration in HIV-1-positive patients, therefore this method could be suitable for therapeutic drug monitoring of this drug.     

HPLC-MS method for the simultaneous quantification of the new HIV protease inhibitor darunavir, and 11 other antiretroviral agents in plasma of HIV-infected patients

A new method using high performance liquid chromatography coupled with electrospray mass spectrometry (HPLC-MS) was developed and validated, for the quantification of plasma concentration of the new protease inhibitors darunavir (DRV) and other 11 antiretroviral agents (ritonavir, amprenavir, atazanavir, lopinavir, saquinavir, indinavir, nelfinavir and its metabolite M-8, nevirapine, efavirenz and tipranavir). A simple protein precipitation extraction procedure was applied on 50 microl of plasma aliquots and chromatographic separation of drugs and Internal Standard (quinoxaline) was achieved with a gradient (acetonitrile and water with formic acid 0.05%) on an C-18 reverse phase analytical column with 25 min of analytical run. Calibration curves were optimised according to expected ranges of drug concentrations in patients, and correlation coefficient (r2) was higher than 0.998 for all analytes. Mean intra- and inter-day precision (relative standard deviation %) for all compounds were 8.4 and 8.3%, respectively, and mean accuracy (% of deviation from nominal level) was 3.9%. Extraction recovery ranged within 93 and 105% for all drugs analysed. This novel HPLC-MS methodology allows a specific, sensitive and reliable determination of DRV and 11 other antiretrovirals. In our hand, it was used to measure DRV and ritonavir plasma concentration in HIV-positive patients, and it is now successfully applied for routine therapeutic drug monitoring and pharmacokinetics studies.     

Current Efavirenz (EFV) or Ritonavir-Boosted Lopinavir (LPV/r) Use Correlates with Elevate Markers of Atherosclerosis in HIV-Infected Subjects in Addis Ababa,Ethiopia

Background

HIV patients on antiretroviral therapy have shown elevated incidence of dyslipidemia, lipodystrophy, and cardiovascular disease (CVD). Most studies, however, focus on cohorts from developed countries, with less data available for these co-morbidities in Ethiopia and sub-Saharan Africa.

Methods

Adult HIV-negative (n = 36), treatment naïve (n = 51), efavirenz (EFV)-treated (n = 91), nevirapine (NVP)-treated (n = 95), or ritonavir-boosted lopinavir (LPV/r)-treated (n=44) subjects were recruited from Black Lion Hospital in Addis Ababa, Ethiopia. Aortic pressure, augmentation pressure, and pulse wave velocity (PWV) were measured via applanation tonometry and carotid intima-media thickness (cIMT) and carotid arterial stiffness, and brachial artery flow-mediated dilation (FMD) were measured via non-invasive ultrasound. Body mass index, waist-to-hip circumference ratio (WHR), skinfold thickness, and self-reported fat redistribution were used to quantify lipodystrophy. CD4+ cell count, plasma HIV RNA levels, fasting glucose, total-, HDL-, and LDL-cholesterol, triglycerides, hsCRP, sVCAM-1, sICAM-1, leptin and complete blood count were measured.

Results

PWV and normalized cIMT were elevate and FMD impaired in EFV- and LPV/r-treated subjects compared to NVP-treated subjects; normalized cIMT was also elevated and FMD impaired in the EFV- and LPV/r-treated subjects compared to treatment-naïve subjects. cIMT was not statistically different across groups. Treated subjects exhibited elevated markers of dyslipidemia, inflammation, and lipodystrophy. PWV was associated with age, current EFV and LPV/r used, heart rate, blood pressure, triglycerides, LDL, and hsCRP, FMD with age, HIV duration, WHR, and glucose, and cIMT with age, current EFV use, skinfold thickness, and blood pressure.

Conclusions

Current EFV- or LPV/r-treatment, but not NVP-treatment, correlated with elevated markers of atherosclerosis, which may involve mechanisms distinct from traditional risk factors.     

Determination of tadalafil in small volumes of plasma by high-performance liquid chromatography with UV detection

Tadalafil is a potent reversible phosphodiesterase-5 inhibitor used for the treatment of erectile dysfunction. This study describes a simple and sensitive high-performance liquid chromatographic (HPLC) method for the determination of tadalafil in 50 microl of rat plasma. Tadalafil and the internal standard lamotrigine were extracted with 0.5 ml of tert-butyl methyl ether, after the samples alkalinized with 20 microl of sodium hydroxide solution (1N). Chromatographic separation was achieved on a C18 column with the mobile phase of acetonitrile-water containing 20 mM phosphate buffer (pH 7) (35/65, v/v), at a flow rate of 1 ml/min. The eluant was detected at 290 nm. The retention time was about 4.5 min for lamotrigine and 15 min for tadalafil. No endogenous substances were found to interfere. Calibration curves were linear from 10 to 2000 ng/ml. The recovery of tadalafil from plasma was greater than 77%. The limit of quantitation was 10 ng/ml. The intra- and inter-day imprecision (expressed as coefficient of variation, C.V.) did not exceed 10.7%, and the accuracy was within 5.9% deviation of the nominal concentration. The method is suitable in pharmacokinetic investigation and monitoring tadalafil concentration.     

Coadministration of Lopinavir/Ritonavir and Rifampicin in HIV and Tuberculosis Co-Infected Adults in South Africa

Background

In HIV-infected patients receiving rifampicin-based treatment for tuberculosis (TB), the dosage of lopinavir/ritonavir (LPV/r) is adjusted to prevent sub-therapeutic lopinavir concentrations. In this setting, South African clinicians were advised to administer super-boosted LPV/r (400 mg/400 mg) twice daily, instead of standard dosed LPV/r (400 mg/100 mg) twice daily. We sought to determine – in routine practice – the tolerability and HIV treatment outcomes associated with super-boosted LPV/r compared to unadjusted LPV/r in combination with rifampicin-based TB treatment.

Methodology/Principle Findings

We conducted a retrospective review of HIV-infected patients who receiving second-line ART with a LPV/r-containing regimen who required concomitant TB treatment. We identified 29 patients; the median age was 36 years (IQR 29–40), 22 (76%) were female, the median CD4 cell count and viral load at first-line ART failure was 86 cells/mm³ (IQR 21–159) and 39,457 copies/mL (IQR 6,025–157,500), respectively. According to physician preference, 15 (52%) of 29 patients received super-boosted LPV/r (400 mg/400 mg) every 12 hours during TB treatment and 14 (48%) of 29 patients received standard dose LPV/r (400 mg/100 mg) twice daily during TB treatment. Among patients who received super-boosted LPV/r there was a trend towards a higher rate of symptomatic transaminitis (27% vs. 7%; p = 0.3), gastrointestinal toxicity (20% vs. 0%; p = 0.2) and a significantly increased need for treatment discontinuation (47% vs. 7%; p = 0.035. The durability of coadministered treatment was significantly shorter in patients who received super-boosted lopinavir/ritonavir with TB treatment compared to patients who received standard lopinavir/ritonavir dosing (log rank, P = 0.036). The rate of virologic failure was not higher in patients with unadjusted LPV/r dosing.

Conclusions/Significance

We observed a high rate of toxicity and need for treatment discontinuation among patients on standard rifampicin-based TB treatment who received super-boosted LPV/r.     

Determination of donepezil, an acetylcholinesterase inhibitor, in human plasma by high-performance liquid chromatography with ultraviolet absorbance detection

A simple and sensitive high-performance liquid chromatographic (HPLC) method with UV absorbance detection is described for the quantification of donepezil, a centrally and selectively acting acetyleholinesterase inhibitor, in human plasma. After sample alkalinization with 0.5 ml of NaOH (0.1 M), the test compound was extracted from I ml of plasma using isopropanol-hexane (3:97, v/v). The organic phase was back-extracted with 75 microl of HCl (0.1 M) and 50 microl of the acid solution was injected into a C18 STR ODS-II analytical column (5 microm, 150x4.6 mm I.D.). The mobile phase consisted of phosphate buffer (0.02 M, pH 4.6), perchloric acid (6 M) and acetonitrile (59.5:0.5:40, v/v) and was delivered at a flow-rate of 1.0 ml/min at 40 degrees C. The peak was detected using a UV detector set at 315 nm, and the total time for a chromatographic separation was approximately 8 min. The method was validated for the concentration range 3-90 ng/ml. Mean recoveries were 89-98%. Intra- and inter-day relative standard deviations were less than 7.3 and 7.6%, respectively, at the concentrations ranging from 3 to 90 ng/ml. The method shows good specificity with respect to commonly prescribed psychotropic drugs, and it could be successfully applied for pharmacokinetic studies and therapeutic drug monitoring.     

Quantification of free mycophenolic acid and its glucuronide metabolite in human plasma by liquid-chromatography using mass spectrometric and ultraviolet absorbance detection

The immunosuppressant drug mycophenolic acid (MPA) and its major metabolite, mycophenolic acid glucuronide (MPAG), are highly bound to albumin. An HPLC-tandem-MS (HPLC/MS/MS) and an HPLC-UV assay were developed to measure free (unbound) concentrations of MPA and MPAG, respectively. Ultrafiltrate was prepared from plasma (500 microl) by ultrafiltration at 3000 x g for 20 min (20 degrees C). Both MPA and MPAG were isolated from ultrafiltrate (100 microl) by acidification and C18 solid-phase extraction. Free MPA was measured by electrospray tandem mass spectrometry using selected reactant monitoring (MPA: m/z 338.2--> 206.9) in positive ionisation mode. Chromatography was performed on a PFPP column (50 mm x 2 mm, 5 microm). Total analysis time was 7 min. The assay was linear over the range 1-200 microg/l with a limit of quantification of 1 microg/l. The inter-day accuracy and imprecision of quality controls (7.5, 40, 150 microg/l) were 94-99% and < 7%, respectively. Free MPAG was chromatographed on a C18 Nova-Pak column (150 mm x 3.9 mm, 5 microm) using a binary gradient over 20 min. The eluent was monitored at 254 nm. The assay was linear over the range 1-50 mg/l with the limit of quantification at 2.5 mg/l. The inter-day accuracy and imprecision of quality controls (5, 20, 45 mg/l) was 101-107% and < 8% (n = 4), respectively. For both methods no interfering substances were found in ultrafiltrate from patients not receiving MPA. The methods described have a suitable dynamic linear range to facilitate the investigation of free MPA and MPAG pharmacokinetics in transplant patients. Further, this is the first reported HPLC-UV method to determine free MPAG concentrations.     

Gas chromatographic determination of novel valproyl taurinamide derivatives in mouse and dog plasma

Valproyl taurinamides are a novel group of compounds that possess anticonvulsant activity. In this study a gas chromatographic micromethod was developed for the quantification of selected valproyl taurinamides and some of their metabolites in biological samples. Valproyl taurinamide (VTD), N-methyl valproyl taurinamide (M-VTD), N,N-dimethyl valproyl taurinamide (DM-VTD) and N-isopropyl valproyl taurinamide (I-VTD) were analyzed in mouse and dog plasma and in dog urine using gas chromatography. Flame ionization detection and mass spectrometric detection were compared. The plasma samples were prepared by solid-phase extraction using C(18) cartridges. The urine samples were prepared by liquid-liquid extraction. The sample volume used was 100 microl of dog plasma, 50 microl of mouse plasma and 20 microl of dog or mouse urine. The quantification range of the method was 1.5-50 mg/l in dog plasma (VTD only), 2.5-250 mg/l in mouse plasma (0.7-90 pmol injected) and 0.04-2 mg/ml in dog urine (VTD only). The inter-day precision in plasma and urine samples was around 10% for all quantified concentrations except LOQ (15-20%). The accuracy for all four compounds was between 90 and 110% within the entire concentration range. The developed method was suitable for quantification of a series of CNS-active valproyl taurineamide derivatives in biological samples at relevant in vivo concentrations.     

Determination of inositol hexanicotinate in rat plasma by high performance liquid chromatography with UV detection

A HPLC method with UV detection at 262nm was developed to analyze inositol hexanicotinate in rat plasma. Plasma samples were extracted with an equal volume of acetonitrile, followed by dilution with mobile phase buffer (5mM phosphate buffer, pH 6.0) to eliminate any solvent effects. Inositol hexanicotinate and the internal standard (mebendazole) were separated isocratically using a mobile phase of acetonitrile/phosphate buffer (35:65, v/v, pH 6.0) at a flow rate of 1.0mL/min and a reverse-phase XTerra MS C(18) column (4.6mmx150mm, 3.5microm). The standard curve was linear over a concentration range of 1.5-100.0microg/mL of inositol hexanicotinate in rat plasma. The HPLC method was validated with intra- and inter-day precisions of 1.55-4.30% and 2.69-21.5%, respectively. The intra- and inter-day biases were -0.75 to 19.8% and 2.58-22.0%, respectively. At plasma concentrations of 1.5-100microg/mL, the mean recovery of inositol hexanicotinate was 99.6%. The results of a stability study indicated that inositol hexanicotinate was unstable in rat plasma samples, but was stable in acetonitrile extracts of rat plasma for up to 24h at 4 degrees C. The assay is simple, rapid, specific, sensitive, and reproducible and has been used successfully to analyze inositol hexanicotinate plasma concentrations in a pharmacokinetic study using the rat as an animal model.     

Development and validation of an HPLC-UV method for iodixanol quantification in human plasma

Iodixanol is a widely used iso-osmolar contrast medium agent. Similar to iohexol, it can also be a good exogenous marker for the measurement of glomerular filtration rate (GFR). This article describes the development and validation of an HPLC-UV method for quantification of iodixanol in human plasma. Internal standard, iohexol (20 microl, 1 mg/ml), and perchloric acid (30 microl, 20%, v/v) were added to plasma samples (300 microl), followed by neutralization with 10 microl potassium carbonate (5M). Samples were centrifuged and 10 microl of the supernatant was injected onto a C(18) EPS analytical column (3 microm particle size, 150 mm x 4.6 mm). The extraction method yielded >95% recovery for both iodixanol and iohexol. The mobile phase consisted of 0.1% (w/v) sodium formate buffer and acetonitrile. Iohexol and iodixanol peaks were eluted at approximately 5 and 9 min, respectively using a fast gradient method. The assay lower limit of detection was 2.0 microg/ml and lower limit of quantification was 10 microg/ml. The calibration curves, assessed in six replicates, were linear over an iodixanol concentration range of 10-750 microg/ml. Intra- and inter-day accuracy was >95% and precision expressed as % coefficient of variation was <10%. This method is simple, accurate, precise and robust and can potentially be used for iodixanol quantification in large-scale clinical studies.     

A simple and rapid liquid chromatography method for simultaneous determination of zidovudine and nevirapine in plasma

We describe a simple, fast, isocratic, reversed-phase high performance liquid chromatographic method for simultaneous determination of plasma zidovudine and nevirapine with UV detection at 260 nm. The method involves liquid-liquid extraction with ethyl acetate and using 3-isobutyl 1-methyl xanthine as internal standard. The system requires a C(18) column (150 mm x 4.6 mm I.D.) and a mobile phase composed of potassium dihydrogen phosphate (15 mM; pH 7.5) and acetonitrile in the ratio of 80:20 (v/v). The assay was linear from 0.025 to 10.0 microg/ml for zidovudine and 0.05 to 10.0 microg/ml for nevirapine. The intra- and inter-day variations were less than 10% for both the drugs. The method was specific and sensitive enough to allow quantification of zidovudine and nevirapine in concentrations observed clinically. The average recoveries of zidovudine and nevirapine from plasma were 95 and 94%, respectively. The method was applied to a pharmacokinetic study in HIV-infected patients who were receiving antiretroviral treatment with zidovudine and nevirapine containing regimens. The method spans the blood concentration range of clinical interest. Due to its simplicity, the assay can be used for pharmacokinetic studies and therapeutic drug monitoring in patients taking a combination treatment of zidovudine and nevirapine.