HIV Protease Inhibitor Atazanavir Research Articles

Epoxide Syntheses and Ring-Opening Reactions in Drug Development

This review concentrates on success stories from the synthesis of approved medicines and drug candidates using epoxide chemistry in the development of robust and efficient syntheses at large scale. The focus is on those parts of each synthesis related to the substrate-controlled/diastereoselective and catalytic asymmetric synthesis of epoxide intermediates and their subsequent ring-opening reactions with various nucleophiles. These are described in the form of case studies of high profile pharmaceuticals spanning a diverse range of indications and molecular scaffolds such as heterocycles, terpenes, steroids, peptidomimetics, alkaloids and main stream small molecules. Representative examples include, but are not limited to the antihypertensive diltiazem, the antidepressant reboxetine, the HIV protease inhibitors atazanavir and indinavir, efinaconazole and related triazole antifungals, tasimelteon for sleep disorders, the anticancer agent carfilzomib, the anticoagulant rivaroxaban the antibiotic linezolid and the antiviral oseltamivir. Emphasis is given on aspects of catalytic asymmetric epoxidation employing metals with chiral ligands particularly with the Sharpless and Jacobsen–Katsuki methods as well as organocatalysts such as the chiral ketones of Shi and Yang, Pages’s chiral iminium salts and typical chiral phase transfer agents.

A Scalable Synthesis of Biaryl Unit of the HIV Protease Inhibitor Atazanavir

Atazanavir is one of the most prescribed HIV-1 protease inhibitors approved by the FDA. It was the first protease inhibitor approved for once-a-day dosing to treat AIDS due to good oral bioavailability and favorable pharmacokinetic profile. This research aims to develop a new synthetic cost effective process for biaryl-hydrazine unit {tert-butyl 2-[4-(2-pyridinyl)benzyl]hydrazinecarboxylate} of atazanavir on a large scale. The synthesis involved palladium catalyzed Suzuki-Miyaura coupling of 2-chloropyridine and (4-cyanophenyl)boronic acid followed by DIBAL-H reduction of cyano group to aldehyde which is then treated with tert-butyl carbazate to furnish hydrazone subsequently in situ reduction with NaBH4. A large scale synthesis of biaryl-hydrazine unit of atazanavir was accomplished in three steps with 71% overall yield. We have developed a short and efficient synthesis of atazanavir key intermediate biaryl-hydrazine unit. The process does not require the usage of Grignard reagent, expensive catalyst, protection/deprotection of aldehyde moiety and catalytic hydrogenation.

Co-treatment With HIV Protease Inhibitor Nelfinavir Greatly Increases Late-phase Apoptosis of Drug-resistant KBV20C Cancer Cells Independently of P-Glycoprotein Inhibition.

The study focused on identifying the mechanisms or drugs that might sensitize resistant KBV20C human oral squamous carcinoma cells overexpressing P-glycoprotein (P-gp) to antimitotic drug treatment. Five HIV protease inhibitors (atazanavir, nelfinavir, darunavir, lopinavir, and ritonavir) were tested to identify drugs that could be used at a relatively low dose for sensitizing antimitotic drug-resistant KBV20C cells. Fluorescence-activated cell sorting, annexin V analyses, and rhodamine uptake tests were performed to further investigate the mechanism of action. Co-treatment with nelfinavir or lopinavir had a high sensitizing effect on vincristine-treated KBV20C cells. Nelfinavir and lopinavir reduced cell viability, increased G2 phase arrest, and up-regulated apoptosis when used as a co-treatment with vincristine. We also demonstrated that eribulin co-treatment with nelfinavir and lopinavir similarly increased sensitization of KBV20C cells. Only lopinavir was found to have a high P-gp-inhibitory activity (similar to verapamil). Interestingly, nelfinavir had very low P-gp-inhibitory activity, suggesting that vincristine-nelfinavir sensitization is independent of the P-gp-inhibitory effect of nelfinavir. We also demonstrated this same combination mainly caused sensitization due to late apoptosis in P-gp-overexpressing drug-resistant KBV20C cells. Highly antimitotic drug-resistant KBV20C cells can be sensitized by co-treatment with the repositioned HIV protease inhibitors nelfinavir and lopinavir. In particular, the sensitizing effect of co-treatment with nelfinavir on antimitotic drug-resistant cancer cells was found to be strong and independent of P-gp-inhibitory activity. As P-gp inhibition can be toxic to normal cells, selecting nelfinavir may be safer for normal cells in patients with drug-resistant cancer.

Transport-Metabolism Interplay of Atazanavir in Rat Hepatocytes.

The aim of this study was to explore the mechanisms governing the intra- to extracellular unbound concentration ratio (Kpu,u) for the HIV protease inhibitor atazanavir (ATV) in rat hepatocytes. We had previously proposed a new method to determine Kpu,u by using the unbound Km values from metabolism studies with suspended rat hepatocytes and rat liver microsomes. Following that method, we determined that the value of ATV Kpu,u was 0.32, indicating that ATV hepatocellular clearance is uptake rate-limited. This hypothesis was supported by the linear correlation between Kpu,u and active uptake clearance (P = 0.04; R(2)=0.82) in the presence of increasing concentrations of the uptake transport inhibitor losartan. Moreover, in contrast to an expected increase of Kpu,u upon inhibition of ATV metabolism, a decrease of Kpu,u was observed, suggesting an increased impact of sinusoidal efflux. In summary, involvement of active uptake transport does not guarantee high intracellular accumulation; however, it has a key role in regulating intracellular drug concentrations and drug metabolism. These findings will help improve future in vitro-to-in vivo extrapolations and likewise physiologically based pharmacokinetic models.

A simple, efficient, and sensitive method for simultaneous detection of anti-HIV drugs atazanavir, ritonavir, and tenofovir by use of liquid chromatography-tandem mass spectrometry.

In the treatment of HIV infection, a combination of anti-HIV drugs is commonly used in highly active antiretroviral therapy (HAART). One such combination recommended for clinical therapy consists of the two HIV protease inhibitors atazanavir and ritonavir and the HIV nucleotide reverse transcriptase inhibitor tenofovir. The detection of plasma and cell drug concentrations provides an assessment of actual drug exposure and patient compliance. We thus developed a simple, efficient, and sensitive method to simultaneously extract and detect these three drugs in plasma and peripheral blood mononuclear cells. The use of a liquid-liquid extraction followed by protein precipitation provided a simple process, yielding a high recovery rate for all three drugs in plasma (>92%) and in cells (>86%). The liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was able to detect 0.01, 0.25, and 2.5 pg (2, 50, and 500 pg/ml, respectively) in 5 μl for atazanavir, ritonavir, and tenofovir, respectively. Validation of the method exhibited high precision and accuracy. This method was subsequently applied to a primate study to determine the concentrations of all three drugs in both plasma and cell samples. This validated method can be useful for an evaluation of drug concentrations in biological samples in an efficient and sensitive manner.

Validation of Simultaneous Quantitative Method of HIV Protease Inhibitors Atazanavir, Darunavir and Ritonavir in Human Plasma by UPLC-MS/MS

Objectives. HIV protease inhibitors are used in the treatment of patients suffering from AIDS and they act at the final stage of viral replication by interfering with the HIV protease enzyme. The paper describes a selective, sensitive, and robust method for simultaneous determination of three protease inhibitors atazanavir, darunavir and ritonavir in human plasma by ultra performance liquid chromatography-tandem mass spectrometry. Materials and Methods. The sample pretreatment consisted of solid phase extraction of analytes and their deuterated analogs as internal standards from 50 μL human plasma. Chromatographic separation of analytes was performed on Waters Acquity UPLC C18 (50 × 2.1 mm, 1.7 μm) column under gradient conditions using 10 mM ammonium formate, pH 4.0, and acetonitrile as the mobile phase. Results. The method was established over a concentration range of 5.0–6000 ng/mL for atazanavir, 5.0–5000 ng/mL for darunavir and 1.0–500 ng/mL for ritonavir. Accuracy, precision, matrix effect, recovery, and stability of the analytes were evaluated as per US FDA guidelines. Conclusions. The efficiency of sample preparation, short analysis time, and high selectivity permit simultaneous estimation of these inhibitors. The validated method can be useful in determining plasma concentration of these protease inhibitors for therapeutic drug monitoring and in high throughput clinical studies.

Role of P-Glycoprotein in the Distribution of the HIV Protease Inhibitor Atazanavir in the Brain and Male Genital Tract

The blood-testis barrier and blood-brain barrier are responsible for protecting the male genital tract and central nervous system from xenobiotic exposure. In HIV-infected patients, low concentrations of antiretroviral drugs in cerebrospinal fluid and seminal fluid have been reported. One mechanism that may contribute to reduced concentrations is the expression of ATP-binding cassette drug efflux transporters, such as P-glycoprotein (P-gp). The objective of this study was to investigate in vivo the tissue distribution of the HIV protease inhibitor atazanavir in wild-type (WT) mice, P-gp/breast cancer resistance protein (Bcrp)-knockout (Mdr1a-/-, Mdr1b-/-, and Abcg2-/- triple-knockout [TKO]) mice, and Cyp3a-/- (Cyp) mice. WT mice and Cyp mice were pretreated with a P-gp/Bcrp inhibitor, elacridar (5 mg/kg of body weight), and the HIV protease inhibitor and boosting agent ritonavir (2 mg/kg intravenously [i.v.]), respectively. Atazanavir (10 mg/kg) was administered i.v. Atazanavir concentrations in plasma (Cplasma), brain (Cbrain), and testes (Ctestes) were quantified at various times by liquid chromatography-tandem mass spectrometry. In TKO mice, we demonstrated a significant increase in atazanavir Cbrain/Cplasma (5.4-fold) and Ctestes/Cplasma (4.6-fold) ratios compared to those in WT mice (P<0.05). Elacridar-treated WT mice showed a significant increase in atazanavir Cbrain/Cplasma (12.3-fold) and Ctestes/Cplasma (13.5-fold) ratios compared to those in vehicle-treated WT mice. In Cyp mice pretreated with ritonavir, significant (P<0.05) increases in atazanavir Cbrain/Cplasma (1.8-fold) and Ctestes/Cplasma (9.5-fold) ratios compared to those in vehicle-treated WT mice were observed. These data suggest that drug efflux transporters, i.e., P-gp, are involved in limiting the ability of atazanavir to permeate the rodent brain and genital tract. Since these transporters are known to be expressed in humans, they could contribute to the low cerebrospinal and seminal fluid antiretroviral concentrations reported in the clinic.

A three step continuous flow synthesis of the biaryl unit of the HIV protease inhibitorAtazanavir

The development of multistep continuous flow reactions for the synthesis of important intermediates for the pharmaceutical industry is still a significant challenge. In the present contribution the biaryl-hydrazine unit of Atazanavir, an important HIV protease inhibitor, was prepared in a three-step continuous flow sequence in 74% overall yield. The synthesis involved Pd-catalyzed Suzuki–Miyaura cross-coupling, followed by hydrazone formation and a subsequent hydrogenation step, and additionally incorporates a liquid–liquid extraction step.

Review of Drug Interactions with Telaprevir and Antiretrovirals

HCV infection is a major cause of mortality worldwide. HCV-related deaths also represent a leading cause of mortality in HIV-coinfected individuals. Telaprevir is an NS3/4A protease inhibitor approved for the treatment of chronic HCV genotype 1 infection in adults in combination with pegylated interferon and ribavirin. Telaprevir-based treatment has been shown to increase rates of sustained viral response in HCV genotype-1-monoinfected patients, and studies in HCV-HIV-coinfected patients are ongoing. Drug-drug interactions of telaprevir with antiretroviral drugs were investigated in a series of studies in healthy subjects. This review summarizes the results of interaction studies with low-dose ritonavir, ritonavir-boosted HIV protease inhibitors (atazanavir, darunavir, fosamprenavir and lopinavir), efavirenz, etravirine, rilpivirine, tenofovir disoproxil fumarate and raltegravir.

Atazanavir Causing CNS Toxicity? Unexplained Neurological Symptoms in Two Patients Recently Started on Atazanavir

To date only one published case report exists of the HIV protease inhibitor atazanavir (ATV) causing central nervous system (CNS) side effects. We report two such cases of patients experiencing disabling CNS side effects shortly after starting ATV-containing regimens whose symptoms only resolved after withdrawing the drug.

Cobicistat Boosts the Intestinal Absorption of Transport Substrates, Including HIV Protease Inhibitors and GS-7340, In Vitro

The experimental pharmacoenhancer cobicistat (COBI), a potent mechanism-based inhibitor of cytochrome P450 3A enzymes, was found to inhibit the intestinal efflux transporters P-glycoprotein and breast cancer resistance protein. Consistent with its transporter inhibition, COBI significantly increased the absorptive flux of potential candidates for clinical coadministration, including the HIV protease inhibitors atazanavir and darunavir and the lymphoid cell- and tissue-targeted prodrug of the nucleotide analog tenofovir, GS-7340, through monolayers of Caco-2 cells in vitro.

Niveau de preuve du suivi therapeutique pharmacologique de l’atazanavir

The HIV protease inhibitor atazanavir presents a wide inter-individual variability related to an intense hepatic metabolism. Dose-dependant elevations of bilirubin have been frequently reported with atazanavir. Relative to literature, the atazanavir therapeutic drug monitoring can it be proposed? In naïve HIV-infected patients, the probability of achieving an undetectable HIV viral load at W48 was significantly associated with a plasma trough concentration (Cmin) of atazanavir >200 ng/mL. Studies in HIV-infected pre-treated patients reported that the genotypic inhibitory quotient was a predictive factor of the virologic response with a threshold value around 200 ng/mL/mutation. Concerning the exposure-toxicity relationship, the risk of occurrence of grade 3-4 hyperbilirubinemia was more frequently associated with Cmin>750-800 ng/mL. Non-randomized studies have reported the interest of atazanavir therapeutic drug monitoring to optimize the virologic response and prevent severe bilirubin elevations. Therefore, the level of evidence of the interest of atazanavir therapeutic drug monitoring is recommended.

In vitro and in vivo cleavage of HIV-1 RNA by new SOFA-HDV ribozymes and their potential to inhibit viral replication

RNA-based compounds are promising agents to inactivate viruses. New specific hepatitis delta virus (HDV)-derived ribozymes are natural molecules that can be engineered to specifically target a viral RNA. We have designed specific on-off adaptor (SOFA)-HDV ribozymes targeting the tat and rev sequences of the human immunodeficiency virus type 1 (HIV-1) RNA. We show that the SOFA-HDV ribozymes cleave their RNA target in vitro. They inhibit the Tat-mediated transactivation of HIV-1 from 62% to 86% in different assays. In vivo, the amount of HIV RNA was decreased by 60 and 86% with two distinct ribozymes, which indicates that the inhibition of HIV production is directly correlated to the decline in spliced and unspliced viral RNAs. These SOFAHDV- ribozymes inhibited the expression and the viral production of four HIV-1 strains, indicating an extended potential to act on multiple HIV variants. In HEK 293T and HeLa cells transfected with pNL4-3 and the SOFA-HDV-ribozymes, the reduced RNA levels consequently decreased the Gag protein expression in the cell and virus production in the supernatant. When transfected before HIV-1 infection, the ribozymes prevented the incoming virus from being expressed. The ribozymes inhibited HIV production up to 90% when transfected in combination with the HIV protease inhibitor Atazanavir. Our results strongly suggest that SOFA-HDV ribozymes have a great potential to target HIV-1 and to be used as therapeutic agents in combination therapy.

No impairment of endothelial function or insulin sensitivity with 4 weeks of the HIV protease inhibitors atazanavir or lopinavir-ritonavir in healthy subjects without HIV infection: a placebo-controlled trial.

Dyslipidemia alone does not fully explain the increase in cardiovascular events among patients receiving protease inhibitor (PI)-based treatment for human immunodeficiency virus infection. Some PIs, such as indinavir, directly induce endothelial dysfunction, an effect that may mediate that portion of the increase in cardiovascular events that is not attributable to dyslipidemia. Endothelium-dependent vasodilation, insulin-mediated vasodilation, and whole-body and leg glucose uptake during use of a 1-h euglycemic hyperinsulinemic clamp (insulin infusion, 40 mU/m(2)/min) were measured in healthy men before and after 4 weeks of treatment with placebo (12 men), with 400 mg atazanavir per day (9 men), or with 400 mg lopinavir and 100 mg ritonavir twice per day (9 men). Median age (36 years) and mean body mass index SD (23.4+/-2.6; calculated as weight in kilograms divided by the square of height in meters) did not differ between groups. Endothelium-dependent vasodilation, expressed as the percentage change in the leg blood flow response to intrafemoral artery infusion of 15 microg/min of the endothelium-dependent vasodilator methacholine, did not change after 4 weeks of treatment in any group:mean percentage change +/- SD, 154+/-102 from baseline and 242+/-254 at week 4 with atazanavir (P=.36), 76+/-62 and 86+/-79, respectively, with lopinavir-ritonavir (P=.68), and 111+/-86 and 127+/-153, respectively,with placebo (P=.63; for between-group differences, P=.55). The response to the endothelium-independent vasodilator nitroprusside was not different at week 4 for any group, nor was insulin-mediated vasodilation or leg or whole-body insulin-mediated glucose uptake (all within-group P values were 1.1). Unlike the dramatic impairment seen with indinavir, the newer PIs atazanavir and lopinavir-ritonavir do not induce endothelial dysfunction in healthy subjects. Thus, endothelial dysfunction does not appear to be a PI drug class effect. The cause of the non-lipid-mediated increase in cardiovascular events that are reported with PIs remains unclear.

An Efficient and Practical Synthesis of the HIV Protease Inhibitor Atazanavir via a Highly Diastereoselective Reduction Approach

An efficient and practical synthesis of the HIV-1 protease inhibitor Atazanavir was developed by employing the diastereoselective reduction of ketomethylene aza-dipeptide isostere 10 as the key and final step. The high diastereoselectivity of the amino ketone reduction by lithium tri-tert-butoxyaluminum hydride in diethyl ether to afford the desired syn-1,2-amino alcohol structure was achieved by Felkin−Anh control as a result of the bulky and chiral N-(methoxycarbonyl)-l-tert-leucinyl moiety as the nitrogen protecting group. The coupling of the two key intermediates, N-(methoxycarbonyl)-l-tert-leucine acylated benzyl hydrazine 7 and chloromethyl ketone 9, via an SN2 reaction furnished the amino ketone 10 in high yield under our optimized conditions. Our new methodology features the late introduction of the S-hydroxyl group and the early acylation of benzyl hydrazine and chloromethyl ketone with N-(methoxycarbonyl)-l-tert-leucine, respectively, which confers high efficiency and easy purification.

Therapeutic drug monitoring of the HIV protease inhibitor atazanavir in clinical practice

Therapeutic drug monitoring (TDM) is being applied for a number of antiretroviral agents. Little is known about the use of TDM for atazanavir. This is a retrospective cohort analysis on the use of TDM of atazanavir at three clinical sites in The Netherlands. Patients were divided into three groups: (i) all patients with evaluable data of plasma atazanavir concentrations and its relationship with hyperbilirubinaemia; (ii) patients who started atazanavir without documented evidence of protease inhibitor (PI) mutations; (iii) patients who started atazanavir with documented evidence of PI mutations. The genotypic inhibitory quotient (GIQ) was calculated by dividing the mean atazanavir plasma trough concentration by the number of PI mutations. A total of 108 patients were included; 70 (65.8%) were using atazanavir/ritonavir (300/100 mg once daily). No significant relationship was observed between atazanavir plasma trough concentration and antiviral response in patients starting atazanavir without PI mutations (group 2; n = 82). In contrast, a significant relationship was observed between atazanavir GIQ and treatment response in patients starting atazanavir while having PI mutations (group 3; n = 26). The cut-off value for GIQ most predictive of virological failure was 0.23 mg/L/mutation: patients (n = 8) with a GIQ equal to or below this value had 50% virological failure whereas patients (n = 18) with a GIQ above 0.23 mg/L/mutation had only 11% virological failure (chi(2): P = 0.030). Atazanavir plasma trough concentrations were significantly related with the occurrence of increased total bilirubin concentrations. TDM of atazanavir might be beneficial for patients with documented PI resistance or patients with hyperbilirubinaemia.

Simultaneous determination of 8 HIV protease inhibitors in human plasma by isocratic high-performance liquid chromatography with combined use of UV and fluorescence detection: Amprenavir, indinavir, atazanavir, ritonavir, lopinavir, saquinavir, nelfinavir and M8-nelfinavir metabolite

A simple, accurate and fast method was developed for determination of the commonly used HIV protease inhibitors (PIs) amprenavir, indinavir, atazanavir, ritonavir, lopinavir, nelfinavir, M8-nelfinavir metabolite and saquinavir in human plasma. Liquid–liquid extraction was used with hexane/ethylacetate from buffered plasma samples with a borate buffer pH 9.0. Isocratic chromatographic separation of all components was performed on an Allsphere hexyl HPLC column with combined UV and fluorescence detection. Calibration curves were constructed in the range of 0.025–10 mg/l. Accuracy and precision of the standards were all below 15% and the lowest limit of quantitation was 0.025 mg/l. Stability of quality control samples at different temperature conditions was found to be below 20% of nominal values. The advantages of this method are: (1) inclusion and determination of the newly approved atazanavir, (2) simultaneous isocratic HPLC separation of all compounds and (3) increased specificity and sensitivity for amprenavir by using fluorescence detection. This method can be used for therapeutic drug monitoring of all PIs currently commercialised and is now part of current clinical practice.

Effects of atazanavir/ritonavir and lopinavir/ritonavir on glucose uptake and insulin sensitivity: demonstrable differences in vitro and clinically

The HIV protease inhibitor (PI) atazanavir does not impair insulin sensitivity acutely but ritonavir and lopinavir induce insulin resistance at therapeutic concentrations. To test the hypothesis that atazanavir combined with a lower dose of ritonavir would have significantly less effect on glucose metabolism than lopinavir/ritonavir in vitro and clinically. Glucose uptake was measured following insulin stimulation in differentiated human adipocytes in the presence of ritonavir (2 micromol/l) combined with either atazanavir or lopinavir (3-30 micromol/l). These data were examined clinically using the hyperinsulinemic euglycemic clamp and oral glucose tolerance testing (OGTT) in 26 healthy HIV-negative men treated with atazanavir/ritonavir (300/100 mg once daily) and lopinavir/ritonavir (400/100 mg twice daily) for 10 days in a randomized cross-over study. Atazanavir inhibited glucose uptake in vitro significantly less than lopinavir and ritonavir at all concentrations. Ritonavir (2 micromol/l) combined with either atazanavir or lopinavir (3-30 micromol/l) did not further inhibit glucose uptake. During euglycemic clamp, there was no significant change from baseline insulin sensitivity with atazanavir/ritonavir (P = 0.132), while insulin sensitivity significantly decreased with lopinavir/ritonavir from the baseline (-25%; P < 0.001) and from that seen with atazanavir/ritonavir (-18%; P = 0.023). During OGTT, the HOMA insulin resistance index significantly increased from baseline at 120 min with atazanavir/ritonavir and at 150 min with lopinavir/ritonavir. The area under the curve of glucose increased significantly with lopinavir/ritonavir but not with atazanavir/ritonavir. Both glucose uptake in vitro and clinical insulin sensitivity in healthy volunteers demonstrate differential effects on glucose metabolism by the combination PI atazanavir/ritonavir and lopinavir/ritonavir.

Full Validation of an Analytical Method for the HIV-Protease Inhibitor Atazanavir in Combination With 8 Other Antiretroviral Agents and its Applicability to Therapeutic Drug Monitoring

Because HIV medications are used in combination, it is important to develop multiplex assays to streamline the therapeutic drug monitoring process and provide rapid turnaround. This article reports full validation of an analytical method that combines atazanavir with 6 HIV-protease inhibitors (indinavir, amprenavir, saquinavir, nelfinavir, ritonavir, and lopinavir) and 2 nonnucleoside reverse transcriptase inhibitors (nevirapine and efavirenz). Using 200 microL of plasma and a simple liquid-liquid extraction method, this analytical method achieved a clean baseline and high extraction efficiencies (90.0% to 99.5%). A Zorbax C-18 (150 x 4.6 mm, 3.5 microm) analytical column was used along with a 27-minute linear gradient elution of the mobile phase to provide sharp peaks at 210 nm. This method was validated over a range of 25 to 10,000 ng/mL and is accurate (90.4% to 110.5%) and precise (precision within a day and between days ranged from 2.3% to 8.3%). Because this method is simple and inexpensive, it may have applicability in countries with low resources.

Simple determination of the HIV protease inhibitor atazanavir in human plasma by high-performance liquid chromatography with UV detection

A simple high-performance liquid chromatography method for the determination of the human immunodeficiency virus protease inhibitor atazanavir in human plasma samples was developed and validated. The method involved a rapid and simple solid-phase extraction of atazanavir using Oasis HLB 1 cc cartridges, an isocratic reversed-phase liquid chromatography on an XTerra RP18 (150 mm × 4.6 mm, 3.5 μm) column, and ultraviolet detection at 203 nm. The mobile phase consisted of phosphate buffer (pH 6, 52.5 mM) and acetonitrile (43:57, v/v). Up to 48 samples could be measured in one day since the run-time of one sample was 30 min. The assay was linear from 0.04 to 10 μg/ml with a lower limit of quantification of 0.04 μg/ml. The mean absolute recovery of ATV was 98.1%. The method was precise, with both intra-day and inter-day coefficients of variation ≤3.0%, and accurate (deviations ranged from −3.0% to 4.5% and from −3.6% to 4.7% for intra-day and inter-day analysis, respectively). There was no interference from 35 tested potentially co-administrated drugs. This method provides a simple, sensitive, precise and reproducible assay for the therapeutic drug monitoring of atazanavir in clinical routine of laboratories with standard equipment.