Quantitative determination of efavirenz (DMP 266), a novel non-nucleoside reverse transcriptase inhibitor, in human plasma using isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection

A Concise Analytical Profile of Efavirenz: Analytical Methodologies

Non-nucleoside reverse transcriptase inhibitors are the prime members of antiretroviral therapy that are presently employed for the management of the human immunodeficiency virus. It uses an enzyme i.e., reverse transcriptase to convert its ribonucleic acid into reverse transcription; these agents impede the function of reverse transcriptase and reverse transcription counter human immunodeficiency virus from replicating. Efavirenz is the first-generation non-nucleoside reverse transcriptase inhibitor agent. Similar to the other non-nucleoside reverse transcriptase inhibitor agents; it is prescribed with other inhibitors in combination for regimens antiretroviral therapy. To enhance survival and avoid aggressive infections in patients affected with human immunodeficiency virus infection, adequate antiretroviral therapy is the most significant treatment. Accordingly, the development and validation of such therapeutic agents are challenging work for the analysts. Therefore, the proposed review integrally addresses the analytical reports of efavirenz recorded in the literature databases like Scopus, Web of Science, Google Scholar, Pub-Med, and through many other sources. It has been remarked that for the development of efavirenz many analytical techniques were used for addressing the qualitative and quantitative estimation of efavirenz from various pharmaceutical and biological matrices. This review plan to review the stereochemistry, mechanism of action, resistance, pharmacokinetics, pharmacodynamics, safety and adverse reaction, and various analytical approaches assessed for the same. The hyphenated and chromatographic techniques are frequently used for analysis of cited drug.

Development and validation of reversed-phase HPLC gradient method for the estimation of efavirenz in plasma

Efavirenz is an anti-viral agent of non-nucleoside reverse transcriptase inhibitor category used as a part of highly active retroviral therapy for the treatment of infections of human immune deficiency virus type-1. A simple, sensitive and rapid reversed-phase high performance liquid chromatographic gradient method was developed and validated for the determination of efavirenz in plasma. The method was developed with high performance liquid chromatography using Waters X-Terra Shield, RP18 50 x 4.6 mm, 3.5 μm column and a mobile phase consisting of phosphate buffer pH 3.5 and Acetonitrile. The elute was monitored with the UV-Visible detector at 260 nm with a flow rate of 1.5 mL/min. Tenofovir disoproxil fumarate was used as internal standard. The method was validated for linearity, precision, accuracy, specificity, robustness and data obtained were statistically analyzed. Calibration curve was found to be linear over the concentration range of 1-300 μg/mL. The retention times of efavirenz and tenofovir disoproxil fumarate (internal standard) were 5.941 min and 4.356 min respectively. The regression coefficient value was found to be 0.999. The limit of detection and the limit of quantification obtained were 0.03 and 0.1 μg/mL respectively. The developed HPLC method can be useful for quantitative pharmacokinetic parameters determination of efavirenz in plasma.

Intranasal chitosan-g-HPβCD nanoparticles of efavirenz for the CNS targeting

Incompetence of antiretrovirals (ARV) in complete eradication of HIV from the CNS is the biggest issue in neuro-AIDS treatment. The ineffectiveness is largely due to the poor penetration of ARV. Hence, the present study is attempted to enhance the CNS uptake of efavirenz (EFV) by designing intranasal EFV nanoparticles (EFV-NPs). EFV-NPs were fabricated using chitosan-g-HPβCD by ionic gelation method and optimized using quadratic response surface methodology (RSM) employing two-factor, five-level circumscribed central composite design. NPs containing drug: polymer ratio (1.25:0.79) were spherical with 198 ± 4.4 nm size, 23.28 ± 1.5% drug loading and 38 ± 1.43% entrapment efficiency. NPs showed sustained drug release (99.03 ± 0.30% in 8 h) and followed Fickian diffusion mechanism. It gave 4.76 times greater permeability than plain drug solution through porcine nasal mucosa. Enhanced CNS bioavailability (12.40-fold that of i.v solution) of EFV, high drug-targeting percentage (99.24%) and drug-targeting index (141.3) post-intranasal administration of NPs was observed. These results are corroborated by gamma scintigraphy images, which revealed high CNS uptake. NPs appeared histocompatible with porcine nasal mucosa and non-toxic to L929 cell line. Thus, CS-g-HPβCD served as a potential carrier in developing intranasal mucoadhesive EFV-NPs for the CNS targeting.

Universal efavirenz determination in transport study, rat placenta perfusion and placenta lysate by HPLC-UV

Efavirenz is an antiretroviral drug used in the treatment of HIV-positive patients. A simple, fast and sensitive high-performance liquid chromatography (HPLC) method was developed in order to determine efavirenz in three types of samples provided from pharmacokinetic studies. The analysis took 5min and was performed using a C18 analytical column (Discovery HS C18, 150×4.6mm, particle size of 5μm) in isocratic mode with a mobile phase containing acetonitrile and water (65:35, v/v), a flow rate of 1.6mLmin^-1, a sample volume of 10μL and UV detection at 245nm. Three different sample matrices (Opti-MEM medium, Krebs perfusion liquid and tissue lysate) and their treatment (dilution, SPE) were considered. The validated method was applied for the analysis of 805 real samples arising from in vitro transcellular transport assays and in vivo organ perfusion experiments in order to evaluate the interaction of efavirenz with ATP-dependent drug efflux transporters. The lack of interaction of efavirenz with ABCB1, ABCG2 and ABCC2 transporters as well as technical aspects of this analysis, including the adhesion of efavirenz to the plastic materials and the stability of the drug during different tissue lysis approaches are discussed.

Factors associated with HIV viral load "blips" and the relationship between self-reported adherence and efavirenz blood levels on blip occurrence: a case-control study

Background

The uncertain etiology of HIV viral load (VL) blips may lead to increased use of clinical resources. We evaluated the association of self-reported adherence (SRA) and antiretroviral (ART) drug levels on blip occurrence in US Military HIV Natural History Study (NHS) participants who initiated the single-tablet regimen efavirenz/emtricitabine/tenofovir disoproxil fumarate (EFV/FTC/TDF).

Methods

ART-naïve NHS participants started on EFV/FTC/TDF between 2006 and 2013 who achieved VL suppression (<50 copies/mL) within 12 months and had available SRA and stored plasma samples were included. Participants with viral blips were compared with those who maintained VL suppression without blips. Untimed EFV plasma levels were evaluated on consecutive blip and non-blip dates by high performance liquid chromatography, with a level ≥1 mcg/mL considered therapeutic. SRA was categorized as ≥85 or <85 %. Descriptive statistics were performed for baseline characteristics and univariate and multivariate Cox proportional hazard models were used to assess the relationship between covariates and blip occurrence.

Results

A total of 772 individuals met inclusion criteria, including 99 (13 %) blip and 673 (87 %) control participants. African-American was the predominant ethnicity and the mean age was 29 years for both groups. SRA ≥ 85 % was associated with therapeutic EFV levels at both blip and non-blip time points (P = 0.0026); however no association was observed between blips and SRA or EFV levels among cases. On univariate analysis of cases versus controls, blips were associated with higher mean pre-treatment VL (HR 1.45, 95 % CI 1.11–1.89) and pre-treatment CD4 count <350 cells/µL (68.1 vs 49.7 %). Multivariate analysis also showed that blips were associated with a higher mean VL (HR 1.42, 95 % CI 1.08–1.88; P = 0.0123) and lower CD4 count at ART initiation, with CD4 ≥500 cells/µL having a protective effect (HR 0.45, 95 % CI 0.22–0.95; P = 0.0365). No association was observed for demographic characteristics or SRA.

Conclusion

Blips are commonly encountered in the clinical management of HIV-infected patients. Although blip occurrence was not associated with SRA or EFV blood levels in our study, blips were associated with HIV-related factors of pre-ART high VL and low CD4 count. Additional studies are needed to determine the etiology of blips in HIV-infected patients.

Identification of a novel human circulating metabolite of tenofovir disoproxil fumarate with LC-MS/MS

BACKGROUND

Tenofovir disoproxil fumarate (TDF) is an antiretroviral drug used for the treatment of Human Immunodeficiency Virus and Hepatitis B infections.

RESULTS

A metabolite that has previously not been observed in the circulation of humans was detected by LC-MS/MS in early time point plasma samples following administration of TDF to healthy volunteers. The metabolite was identified using a range of LC-MS/MS-based techniques as a monoester of TDF, derived from the partially hydrolyzed bis-ester prodrug. TDF, when spiked into plasma, was observed to degrade first to the putative monoester and subsequently to tenofovir.

CONCLUSION

The presence of this unstable metabolite in some samples has implications for sample collection, handling and storage in studies of tenofovir where serum concentrations are determined.

A simple, rapid, economical, and practical method for the determination of efavirenz in plasma of Chinese AIDS patients by reverse phase high-performance liquid chromatography with ultraviolet detector

This study aimed to develop a reverse phase high-performance liquid chromatographic (RP-HPLC) method for the determination of efavirenz in human plasma and to use it for determining the concentrations of efavirenz in Chinese AIDS patient. A simple mobile phase consisting of 0.01 mol/L NaH2PO4 solution and acetonitrile (38:62, V/V) was pumped at a flow rate of 1.0 mL/min through a reverse phase Diamonsil C18 column maintained at 30°C. Diazepam was used as an internal standard and monitored with efavirenz at 247 nm. The protein of 100 μL plasma sample was precipitated before 20 μL of the supernatant was directly injected into the column. The linear response over the concentration ranges 0.10-20.0 μg/mL was obtained and the linear regression equations was Y = 2.2873X ‒ 0.1449 (r = 0.9999). The intra-day and inter-day precisions (1.9-2.6%, 2.2-7.2%, respectively), the relative and absolute recovery (99.3-106.3%, 75.6-80.3%, respectively) met the international standards. Stability of plasma samples were evaluated for short-term (ambient temperature for 16 h) and long-term (-20°C for 30 days) storage conditions and were found to be stable. The mean plasma concentration of efavirenz of the 406 patients was 2.21 ± 1.95 μg/mL, 77.3% of which were within the therapeutic window (1-4 μg/mL), 15.1% were below the window, and 7.6% were over it. In conclusion, the method had advantages of convenience, rapidity, necessary accuracy and precision, high practicality and met the needs for therapeutic drug monitoring and the pharmacokinetic study of efavirenz, especially in underdeveloped countries. For Chinese AIDS patients, it was beneficial to use efavirenz under the guidance of therapeutic drug monitoring.

A sensitive and selective liquid chromatography/tandem mass spectrometry method for quantitative analysis of efavirenz in human plasma

A selective and a highly sensitive method for the determination of the non-nucleoside reverse transcriptase inhibitor (NNRTI), efavirenz, in human plasma has been developed and fully validated based on high performance liquid chromatography tandem mass spectrometry (LC-MS/MS). Sample preparation involved protein precipitation followed by one to one dilution with water. The analyte, efavirenz was separated by high performance liquid chromatography and detected with tandem mass spectrometry in negative ionization mode with multiple reaction monitoring. Efavirenz and ¹³C₆-efavirenz (Internal Standard), respectively, were detected via the following MRM transitions: m/z 314.20243.90 and m/z 320.20249.90. A gradient program was used to elute the analytes using 0.1% formic acid in water and 0.1% formic acid in acetonitrile as mobile phase solvents, at a flow-rate of 0.3 mL/min. The total run time was 5 min and the retention times for the internal standard (¹³C₆-efavirenz) and efavirenz was approximately 2.6 min. The calibration curves showed linearity (coefficient of regression, r>0.99) over the concentration range of 1.0-2,500 ng/mL. The intraday precision based on the standard deviation of replicates of lower limit of quantification (LLOQ) was 9.24% and for quality control (QC) samples ranged from 2.41% to 6.42% and with accuracy from 112% and 100-111% for LLOQ and QC samples. The inter day precision was 12.3% and 3.03-9.18% for LLOQ and quality controls samples, and the accuracy was 108% and 95.2-108% for LLOQ and QC samples. Stability studies showed that efavirenz was stable during the expected conditions for sample preparation and storage. The lower limit of quantification for efavirenz was 1 ng/mL. The analytical method showed excellent sensitivity, precision, and accuracy. This method is robust and is being successfully applied for therapeutic drug monitoring and pharmacokinetic studies in HIV-infected patients.

Voltammetric studies on the HIV-1 inhibitory drug Efavirenz: the interaction between dsDNA and drug using electrochemical DNA biosensor and adsorptive stripping voltammetric determination on disposable pencil graphite electrode

The interaction of Efavirenz (EFV) with fish sperm dsDNA immobilized onto pencil graphite electrode (PGE) has been studied by using differential pulse voltammetric technique using an electrochemical DNA biosensor. The guanine signal was lower with (double stranded-DNA) dsDNA-treated PGE than the untreated electrode after the interaction with EFV occurred. The changes in the experimental parameters such as the accumulation time and the concentration of EFV were also studied. All necessary parameters such as sensitivity, selectivity, accuracy and precision were calculated. In addition, the detection and determination limits, reproducibility and applicability of the analysis to pharmaceutical dosage forms were also investigated. These results showed that this DNA biosensor could be used for the sensitive, rapid simple and cost effective detection and determination of EFV-dsDNA interaction. The linearity was between 2 and 24 ppm of EFV concentration on guanine signal decreasing curve. EFV showed an irreversible oxidation behavior at all investigated pH values. This oxidation step was adsorption controlled on PGE. Hence, differential pulse adsorptive stripping (AdsDPV) voltammetric method was developed for the determination of EFV. Accumulation time and potential were optimized. Under these conditions, the current showed a linear dependence with concentration in the range between 0.018 and 2.56 ppm. Both determination methods were fully validated and applied for the analysis of EFV pharmaceutical dosage form.

Amprenavir and Lopinavir Pharmacokinetics following Coadministration of Amprenavir or Fosamprenavir with Lopinavir/Ritonavir, with or without Efavirenz

Background

Amprenavir (APV), fosamprenavir (FPV), lopinavir (LPV), ritonavir (RTV) and efavirenz (EFV) are to varying degrees substrates, inducers and inhibitors of CYP3A4. Coadministration of these drugs might result in complex pharmacokinetic drug-drug interactions.

Methods

Two prospective, open-label, non-randomized studies evaluated APV and LPV steady-state pharmacokinetics in HIV-infected patients on APV 750 mg twice daily + LPV/RTV 533/133 mg twice daily with EFV ( n=7) or without EFV ( n=12) + background nucleosides (Study 1) and after switching FPV 1,400 mg twice daily for APV ( n=10) (Study 2).

Results

In Study 1 EFV and non-EFV groups did not differ in APV minimum plasma concentration (Cmin; 1.10 versus 1.06μg/ml, P=0.89), area under the concentration-time curve (AUC; 17.46 versus 24.34μg•h/ml, P=0.22) or maximum concentration (Cmax; 2.61 versus 4.33 μg/ml, P=0.08); for LPV there was no difference in Cmin (median: 3.66 versus 6.18μg/ml, P=0.20), AUC (81.84 versus 93.75 μg•h/ml, P=0.37) or Cmax (10.36 versus 10.93 μg/ml, P=0.61). In Study 2, after switching from APV to FPV, APV Cmin increased by 58% (0.83 versus 1.30 μg/ml, P=0.0001), AUC by 76% (19.41 versus 34.24 μg•h/ml, P=0.0001), and Cmax by 75% (3.50 versus 6.14, P=0.001). Compared with historical controls, LPV and RTV pharmacokinetics were not changed. All treatment regimens were well tolerated. Seven of eight completers (88%) maintained HIV-1 RNA <400 copies/ml 12 weeks after the switch (1 lost to follow up).

Conclusions

EFV did not appear to significantly alter APV and LPV pharmacokinetic parameters in HIV-infected patients taking APV 750 mg twice daily + LPV 533/133 mg twice daily. Switching FPV 1,400 mg twice daily for APV 750 mg twice daily resulted in an increase in APV Cmin, AUC, and Cmax without changing LPV or RTV pharmacokinetics or overall tolerability.

Stability of analytes in biosamples - an important issue in clinical and forensic toxicology?

Knowledge of the stability of drugs in biological samples is important for the interpretation of toxicological findings. This paper reviews data on the stability of drugs in blood, plasma, or serum. Since such data have already been reviewed for classic drugs of abuse, the focus here is on newer drugs of abuse and on therapeutic drugs. Key information about the conditions of the stability experiments will be provided and the following drugs or drug classes are covered: amphetamines, amphetamine-derived, piperazine-derived, and phenethylamine-derived designer drugs, antidepressants, neuroleptics, anti-HIV drugs, antiepileptics, cardiovascular drugs, and others. In addition, aspects of stability experiments and their evaluations are discussed. The data presented show that the majority of drugs are stable in blood, plasma, or serum samples under the conditions usually encountered in a clinical or forensic toxicology laboratory. Instability usually only occurs for drugs carrying ester moieties, sulfur atoms, or other easily oxidized or reduced structures. Nevertheless, clinical or forensic specimens should always be stored at least in the refrigerator and preferably at -20 degrees C or lower to avoid any degradation. Finally, results obtained from biosamples that have been stored at room temperature for a longer time should be interpreted with great care and partial degradation should always be considered.

Efavirenz and Nevirapine in HIV-1 Infection

Nevirapine and efavirenz are nonnucleoside reverse transcriptase inhibitors used in antiretroviral regimens to treat HIV infection. Therapeutic drug monitoring in patients on antiretroviral regimens that include these agents has been suggested to be beneficial in terms of efficacy and toxicity. Various analytical methods are available to quantify nevirapine and efavirenz concentrations. A previously published, nine-step, decision-making algorithm has been used to evaluate the utility of therapeutic drug monitoring of efavirenz and nevirapine. A relationship has been found between efavirenz concentrations and toxicity and between nevirapine concentrations and virological efficacy. For efavirenz, the recommended therapeutic range is 1-4 mg/L; for nevirapine, minimum trough concentrations of >3.4 mg/L have been suggested. Both drugs have demonstrated interindividual pharmacokinetic variability. The pharmacokinetic parameters of nevirapine vary in female patients, patients coinfected with hepatitis B virus, and patients from different geographical locations. The pharmacokinetic parameters of efavirenz have also been shown to vary depending on patients' race, baseline bilirubin level, and geographical location. Drug interactions and resistance mutations can also be confounders in the pharmacokinetic parameters of these drugs. Coinfection with hepatitis C can also contribute to increased drug concentrations. The risk of hepatotoxicity can be increased in the presence of elevated nevirapine concentrations. As patients with HIV-1 infection will be managed with different combinations of antiretroviral regimens over the course of their lives, the limitations of having only four drug classes from which to choose make it even more important to maximise the usefulness of each of these drug classes. The available evidence suggests that therapeutic drug monitoring of efavirenz and nevirapine may contribute to the clinician's ability to evaluate efficacy and safety in patients taking these drugs. Patients at risk of toxicity from drug interactions or disease interactions and patients who may be noncompliant may gain the greatest benefit from therapeutic drug monitoring of efavirenz and nevirapine.

Simple and rapid liquid chromatography method for determination of efavirenz in plasma

A simple and rapid high performance liquid chromatographic method for determination of efavirenz in human plasma was developed. The method involved extraction of sample with ethyl acetate and analysis using a reversed-phase C(18) column (150 mm) with UV detection. The assay was linear from 0.0625 to 10.0 microg/ml. The method was specific for efavirenz estimation and the drug was stable in plasma up to one month at -20 degrees C. The average recovery of efavirenz from plasma was 101%. Due to its simplicity, the assay can be used for pharmacokinetic studies and therapeutic drug monitoring of efavirenz.

[Efavirenz and nevirapine plasma levels in HIV-infected patients with hemophilia]

The aim of this study was to evaluate efavirenz and nevirapine plasma levels in HIV-infected hemophilic patients seen in two hospitals in Barcelona. Plasma levels of these drugs were determined by high-performance liquid chromatography (HPLC) at four-month intervals, together with viral load and CD4 cell count. Nineteen patients treated with efavirenz and 8 with nevirapine were included, and 68 efavirenz and 31 nevirapine determinations were performed. Mean study time was 12 months. Median efavirenz plasma concentration was 2.95 .g/ml (interval: 1.54-5.26 .g/ml) in patients with favorable virological response and 1.86 .g/ml (0.82-4.88 .g/ml) in patients with detectable viral load (p = 0.32). Nevirapine plasma concentrations were 4.41 .g/ml (3.50-6.72 .g/ml) and 3.12 .g/ml (2.44-3.80 .g/ml) respectively (p = 0.18).

High versus standard dose vancomycin for osteomyelitis

It is important to identify the optimal dosage and best method of infusion of parenteral vancomycin to be used over a several week period for the treatment of osteomyelitis. A retrospective study was undertaken to compare a high dose vancomycin treatment (HD: 40 mg/kg/d) with a standard dose treatment (SD: 20 mg/kg/d), and also to compare the modality of infusion using either intermittent vancomycin infusion (IVI) or continuous vancomycin infusion (CVI). 89 patients with Gram-positive cocci osteomyelitis requiring vancomycin treatment were followed, and the outcome and therapeutic safety were compared. There were significantly more adverse drug reactions (acute renal failure) in the IVI subgroup (HD-IVI vs SD-IVI, p-value 0.007). No cases of renal failure were found in the HD-CVI subgroup. The best outcome was found in the subgroup of patients who received HD-CVI (HD-CVI vs SD-IVI, overall log rank p-value 0.02). HD-CVI treatment appears to provide an improved outcome with fewer adverse drug reactions.

Pharmacokinetics of emtricitabine, didanosine and efavirenz administered once-daily for the treatment of HIV-infected adults (pharmacokinetic substudy of the ANRS 091 trial)

OBJECTIVE

This study was conducted to investigate the pharmacokinetics of emtricitabine (FTC), didanosine (ddI), and efavirenz (EFV) when administered in a once-daily combination.

METHODS

Nine antiretroviral-naïve HIV-infected adults who received FTC [200 mg once a day (q.d.)], ddI (400 mg q.d. if > or =60 kg; 250 mg q.d. if <60 kg) and EFV (600 mg q.d.) were studied. The following pharmacokinetic (PK) parameters were determined over 24 h at steady-state after 4 weeks of treatment: area under the plasma concentration vs. time curve (AUC(0-24 h)), maximum (Cmax) and minimum (Cmin) plasma concentrations, time to reach Cmax (Tmax), and the elimination half-life (t(1/2)). EFV plasma concentrations were also measured during follow-up.

RESULTS

Median PK parameters for FTC, ddI and EFV, respectively, were as follows. AUC(0-24 h): 7.2, 7.0 and 36.4 h x mg/L; Cmax: 1.8, 2.6 and 2.5 mg/L; Cmin: 0.04, <0.01 and 1.0 mg/L; Tmax: 1.8, 1.1 and 2.5 h; t(1/2): 7.4, 2.3, and 23.7 h. EFV plasma concentrations measured 10-13 h postdosing were higher during follow-up than during the PK study (2.57 vs. 1.19 mg/L, P<0.01).

CONCLUSION

The simultaneous administration of FTC, ddI and EFV did not affect the PK parameters of FTC when compared to historical controls. EFV Cmax and Cmin were lower than expected, but the data may have been slightly underestimated in this study. High ddI AUC and Cmax were measured in these patients, and further studies are warranted to confirm this finding.

Simple and rapid method for the simultaneous determination of the non-nucleoside reverse transcriptase inhibitors efavirenz and nevirapine in human plasma using liquid chromatography

Efavirenz and nevirapine are non-nucleoside reverse transcriptase inhibitors for the treatment of HIV-1-infected individuals. A simple and rapid high-performance liquid chromatographic method for the simultaneous quantification of efavirenz and nevirapine in human plasma suitable for therapeutic drug monitoring is described. Sample pre-treatment consisted of protein precipitation with acetonitrile and subsequently dilution with distilled water. The drugs were separated from endogenous compounds by isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection at 275 nm. The method was validated over the therapeutically relevant concentration range of 0.05-15.0 mg l(-1) and 0.25-15.0 mg l(-1) for efavirenz and nevirapine, respectively, using a volume of 100 microl of plasma. The calibration curves were linear over this concentration range. Carbamazepine was used as internal standard. The assay proved to be accurate (accuracies varied between -12.7 and 8.5%) and precise (intra- and inter-assay precisions were less then 5.9%). The tested batches of control human plasma and frequently co-administered drugs did not interfere with the described methodology. Efavirenz and nevirapine were stable under various relevant storage conditions. This validated assay is suited for use in pharmacokinetic studies with efavirenz and nevirapine and can readily be implemented in the setting of a hospital laboratory for the monitoring of efavirenz and nevirapine concentrations.

Subtherapeutic antiretroviral plasma concentrations in routine clinical outpatient HIV care

The objective of this study was to evaluate plasma concentrations of nonnucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) within several dosing schemes in a cohort of HIV-infected patients in routine clinical practice and to find possible explanations for subtherapeutic plasma concentrations. Patients were included if a PI or NNRTI was part of their antiretroviral regimen, at least one plasma concentration was obtained, and a complete medication overview from community pharmacy records was available. The study period was from January 1998 to September 2001. Each plasma concentration was related to median plasma concentrations of a pharmacokinetic reference curve, yielding a concentration ratio (CR). A cutoff CR was defined for each antiretroviral drug per specific regimen, discriminating between >or=therapeutic and subtherapeutic concentrations. For the patients with subtherapeutic concentrations, it was sorted out whether drug interactions, adverse events and self-reported symptoms, or nonadherence could be the cause of the lower than expected plasma concentration. Ninety-seven HIV-infected patients fulfilled the criteria. During the defined period, 1145 plasma concentrations were available (median, 11; interquartile range, 8-14). Three hundred fourteen (27.4%) plasma concentrations were classified subtherapeutic. Drug interactions (2; 0.6%), adverse events and self-reported symptoms (67; 21.3%), and nonadherence (14; 4.5%) could only partly explain the subtherapeutic drug levels. Consequently, a large number of the subtherapeutic plasma concentrations (73.6%) remained inexplicable. A high number of subtherapeutic plasma concentrations were observed. No clear causes were found; thus, corrective measures will be difficult to employ. Therefore, therapeutic drug monitoring (TDM) must maintain its crucial place in routine clinical care to be able to identify patients who need extra attention so that therapeutic plasma concentrations are achieved.

Sensitive and specific determination of eight antiretroviral agents in plasma by high-performance liquid chromatography-mass spectrometry

Therapeutic drug monitoring of antiretroviral drugs has become more and more important. Therefore, a highly specific method is presented, which is capable of quantifying the different proteinase inhibitors (amprenavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir) and non-nucleoside reverse transcriptase inhibitors (efavirenz, nelfinavir). The antiretroviral agents were separated and detected using LC-MS and atmospheric pressure chemical ionization. After solid-phase extraction, the antiretrovirals were separated within 21 min using gradient elution. The calibration range of each drug was linear including the expected minimum and maximum concentrations measured in plasma after the administration of the different drugs. All within-day and between-day coefficients of variation were below 10% and the recovery rates were between 34.8 and 124%. The respective quantification limits were 1 microg/l (indinavir), 10 microg/l (amprenavir, efavirenz), 50 microg/l (saquinavir), 90 microg/l (nelfinavir), 200 microg/l (nevirapine, ritonavir) and 250 microg/l (lopinavir).

Simultaneous determination of rifampicin and efavirenz in plasma

Complex drug interactions involving antiretroviral agents and drugs for the management of opportunistic infections demand the monitoring of plasma drug concentrations to prevent treatment failure. The high occurrence of tuberculosis in HIV-infected subjects makes the management of HIV treatment complex. Rifampicin, a potent inducer of the cytochrome P 450 metabolic pathway, is a very active antituberculosis drug that accelerates the metabolism of protease inhibitors. Regimens containing efavirenz, a non-nucleoside reverse transcription inhibitor, could be an alternative, but efavirenz plasma concentrations may be altered after the coadministration of rifampicin. Efavirenz is also a cytochrome P 450 inducer and may alter rifampicin plasma levels. Due to the increasing need to monitor plasma concentrations in HIV patients with tuberculosis, a high-performance liquid chromatographic (HPLC) method has been developed to measure rifampicin and efavirenz at the same time in a small amount of sample. This HPLC method is highly sensitive and precise, suitable for pharmacokinetic studies or routine clinical monitoring of rifampicin and efavirenz simultaneously in HIV patients with tuberculosis.

Determination of lamivudine/stavudine/efavirenz in human serum using liquid chromatography/electrospray tandem mass spectrometry with ionization polarity switch

A high-performance liquid chromatography/tandem mass spectrometry (LC-MS-MS) method with ionization polarity switch was developed and validated in human serum for the determination of a lamivudine (3TC)/stavudine (d4T)/efavirenz combination HIV therapy. Solid phase extraction (SPE) was used to extract these anti-HIV drugs and internal standard aprobarbital. A gradient mobile phase consisting of acetonitrile and 20 mM ammonium acetate buffer with pH adjusted to 4.5 using glacial acetic acid was utilized to separate these drugs on a hexylsilane column (150 x 2.0 mm i.d.). The total run time between injections was 18 min. The precursor and major product ions of these drugs were monitored on a triple quadrupole mass spectrometer in the multiple reactions monitoring (MRM) mode. Ionization polarity was switched in the middle of the LC run allowing these anti-HIV drugs with different physicochemical properties to be detected simultaneously. The effect of ion suppression from human serum was studied and no interference with the analysis was noted. The method was validated over the range of 1.1-540 ng/mL for 3TC, 12.5-6228 ng/mL for d4T and 1.0-519 ng/mL for efavirenz. The method was shown to be accurate, with intra-day and inter-day accuracy less than 14.0% and precise, with intra-day and inter-day precision less than 13.1%. The extraction recoveries of all analytes were higher than 90%.

Determination of efavirenz, a selective non-nucleoside reverse transcriptase inhibitor, in human plasma using HPLC with post-column photochemical derivatization and fluorescence detection

Methods for the quantitative determination of efavirenz in human plasma and the qualitative assessment of the stereochemical integrity of efavirenz in post-dose human plasma samples are described. After the addition of an internal standard, plasma samples were extracted with hexane-methylene chloride (65/35, v/v%). The extracts were evaporated to dryness and reconstituted in mobile phase. Upon exposure to UV light, the analyte was found to form fluorescent products; the major fluorescent product was isolated and identified as a substituted quinoline. Thus, the plasma extracts were analyzed via HPLC with post-column photochemical derivatization and fluorescence detection. Reverse phase chromatography was used for the quantitative assay, whereas chromatography with a column containing a chiral stationary phase (dinitrobenzoyl leucine) was used for the stereochemical assessment. The quantitative assay has been validated in the concentration range of 50-1000 ng/ml using 0.5 ml samples. Analyte recovery was better than 89% at all points on the standard curve. Intra-day precision was better than 5% C.V., while accuracy was between 95 and 104% of nominal over the range of the assay. The selective detection method reduces the likelihood of interference by co-administered medications or endogenous species. The stereochemical configuration of efavirenz was confirmed to remain intact in post-dose human plasma samples. The quantitative method has been successfully utilized to support a study in which a possible drug interaction between co-administered HIV protease inhibitors and efavirenz was evaluated.

Determination of efavirenz in human plasma by high-performance liquid chromatography with ultraviolet detection

Efavirenz is a non-nucleoside reverse transcriptase inhibitor for the treatment of the HIV infection. A simple, high-performance liquid chromatographic method has been developed and validated for the quantitative determination of efavirenz in human plasma. The method involved solid-phase extraction of the drug and the internal standard (L-737,354) from 300 microl of human plasma. The analysis was via UV detection at 250 nm using a reversed-phase C8 analytical column and a isocratic mobile phase consisting of phosphate buffer (pH 5.75)-acetonitrile that resolved the drug and internal standard from endogenous matrix components and potential coadministered drugs. Within- and between-day precisions were less than 8.6% for all quality control samples. The lower limit of quantification was 0.1 microg/ml. Recovery of efavirenz from human plasma was greater than 83%. This validated assay is being used in pharmacokinetic studies with efavirenz.

High-performance liquid chromatographic method for the determination of HIV-1 non-nucleoside reverse transcriptase inhibitor efavirenz in plasma of patients during highly active antiretroviral therapy

A new high-performance liquid chromatographic method for the determination of efavirenz in human plasma is described. Quantitative recovery following liquid-liquid extraction with diethylether from 200 microl of human plasma was achieved. Subsequently, the assay was performed with 67 mM potassium dihydrogen phosphate-acetonitrile as a mobile phase, a XTerraRP 18 column protected with a Phenomenex C18 column and UV detection at 246 nm. Linear standard curves were obtained for concentrations ranging from 25 to 15,000 ng/ml. The calculated intra- and inter-day coefficients of variation were below 10%.

Simultaneous determination of the HIV protease inhibitors indinavir, amprenavir, saquinavir, ritonavir, nelfinavir and the non-nucleoside reverse transcriptase inhibitor efavirenz by high-performance liquid chromatography after solid-phase extraction

As part of an on-going study on the suitability of a formal therapeutic drug monitoring (TDM) of antiviral drugs for improving the management of HIV infection, a high-performance liquid chromatography method has been developed to quantify simultaneously in plasma five HIV protease inhibitors (PIs) (i.e., indinavir, amprenavir, saquinavir, ritonavir, nelfinavir) and the novel non-nucleoside reverse transcriptase inhibitor efavirenz. After viral inactivation by heat (60 degrees C for 60 min), plasma (600 microl), with clozapine added as internal standard, is diluted 1:1 with phosphate buffer, pH 7 and subjected to a solid-phase extraction on a C18 cartridge. Matrix components are eliminated with 2 x 500 microl of a solution of 0.1% H3PO4 neutralised with NaOH to pH 7. PIs and efavirenz are eluted with 3 x 500 microl MeOH. The resulting eluate is evaporated under nitrogen at room temperature and is reconstituted in 100 microl 50% MeOH. A 40-microl volume is subjected to HPLC analysis onto a Nucleosil 100, 5 microm C18 AB column, using a gradient elution of MeCN and phosphate buffer adjusted to pH 5.15 and containing 0.02% sodium heptanesulfonate: 15:85 at 0 min-->30:70 at 2 min-->32:68 at 8 min-->42:58 at 18 min-->46:54 at 34 min, followed by column cleaning with MeCN-buffer, pH 5.15 (90:10), onto which 0.3% AcOH is added. Clozapine, indinavir, amprenavir, saquinavir, ritonavir, efavirenz and nelfinavir are detected by UV at 201 nm at a retention time of 8.2, 13.0, 16.3, 21.5, 26.5, 28.7 and 31.9 min, respectively. The total run time for a single analysis is 47 min, including the washing-out and reequilibration steps. The calibration curves are linear over the range 100-10,000 ng/ml. The absolute recovery of PIs/efavirenz is always higher than 88%. The method is precise with mean inter-day relative standard deviations within 2.5-9.8% and accurate (range of inter-day deviations -4.6 to +4.3%). The in vitro stability of plasma spiked with PIs/efavirenz at 750, 3000 and 9000 ng/ml has been studied at room temperature, -20 degrees C and +60 degrees C. The method has been validated and is currently applied to the monitoring of PIs and efavirenz in HIV patients. This HPLC assay may help clinicians confronted to questionable compliance, side effects or treatment failure in elucidating whether patients are exposed to adequate circulating drug levels. The availability of such an assay represents an essential step in elucidating the utility of a formal TDM for the optimal follow-up of HIV patients.