Development and validation of an LC-MS/MS assay for the quantification of efavirenz in different biological matrices.

AIM: The non-nucleoside reverse transcriptase inhibitor efavirenz is one of the most prescribed antiretroviral therapeutics. Efavirenz-containing therapy has become associated with the occurrence of CNS side effects, including sleep disturbances, depression and even psychosis. RESULTS: The investigation of efavirenz distribution required the development of a versatile and sensitive method. In addition to plasma, quantification was required in brain tissue and phosphate-buffered saline. The assay presented here was linear from 1.9 to 500 ng/ml. Accuracy and precision ranged between 93.7 and 99.5%, and 1.5 and 5.6%, respectively. DISCUSSION: The method developed here represents a versatile, sensitive and easy-to-use assay. The assay has been applied to in vitro and in vivo samples demonstrating reliable efavirenz quantification in multiple matrices.

Stability-indicating UHPLC method for determination of nevirapine in its bulk form and tablets: identification of impurities and degradation kinetic study.

Nevirapine (NVP), a non-nucleoside reverse transcriptase inhibitor, is a drug widely used in the treatment of Acquired Immunodeficiency Syndrome (AIDS). The evaluation of NVP stability is of fundamental importance in order to guarantee drug product efficacy, safety and quality. In this study, NVP active pharmaceutical ingredient (API) and tablets were subjected to a detailed study of forced degradation, employing several degrading agents (acid, alkaline, water, metal ions, humidity, heat, light and oxidation agents). In order to determine NVP and the degradation products formed, a stability-indicating UHPLC method using fused core column was developed and validated. The separation was carried out using a Poroshell 120C18 column (100×2.1mm i.d.; 2.7µm particle size) and the mobile phase was composed of acetonitrile and water in a gradient elution, at a flow rate of 0.2ml/min. Chemical structures and mechanisms for the formation of three degradation products were proposed by means of LC/MS-MS. Also, NVP degradation kinetic was studied and its order of degradation evaluated. NVP was degraded in acidic and oxidative conditions and the degradation profile for NVP tablets and API were similar. The stability-indicating method proved to be selective for NVP and its degradation products. Calibration curve was linear in the range of 8-48µg/ml and the method showed to be precise, accurate and robust for both NVP API and tablets, with detection and quantification limits of 0.092µg/ml and 0.174µg/ml, respectively.

Effect of system variables involved in packed column supercritical fluid chromatography of stavudine taken as model analyte using response surface methodology along with study of thermodynamic parameters.

A multifactor optimization technique is successfully applied to study the effect of simultaneously varying the system variables on feasibility of stavudine analysis by packed column supercritical fluid chromatography (PC-SFC). The effect of simultaneously varying the pressure, temperature and modifier concentration was studied to optimize the method in order to obtain excellent chromatographic figures of merit. The method is based on isocratic elution using methanol-modified supercritical carbon dioxide as the mobile phase at the flow rate of 3.0 ml/min through a JASCO Finepak SIL-5, ODS [C(18) (5 microm, 25 cm x 4.6 mm, i.d.)] column support using photodiode array detection. The optimal conditions were determined with the aid of the response surface methodology using 3(3) factorial designs. From the response surface graphs optimum regions were selected to be +1, -1, and +1 for temperature (60 degrees C), pressure (20 MPa) and percent modifier concentration (17.81%, v/v), respectively. Linearity dynamic range was found to be in the range of 2.0-150.0 microg/ml with significantly high value of correlation coefficient. The method was validated for precision, robustness and recovery to assess the viability of the established method. The chromatographic limit of detection and quantitation were 0.80 and 1.50 microg/ml respectively. The method has been successfully used to analyze commercial dosage form to assess the chromatographic performance of SFC system which was found to be 99.91%+/-1.62. The present work briefs the thermodynamic applications of PC-SFC with an emphasis on the results of stavudine. The foremost of such applications is the determination of solute diffusion coefficient in supercritical mobile phase by Taylor-Aris peak broadening technique.

Didanosine, lamivudine-emtricitabine and efavirenz as initial therapy in naive patients.

There are currently several suitable and different antiretroviral regimens to start highly active antiretroviral therapy (HAART), and many clinicians and patients prefer once-daily therapy. The efficacy and potency of efavirenz (EFV) has been established in many clinical trials and cohort studies; its pharmacokinetics, allowing for a convenient once-daily administration, make EFV one of the first agents to be included in once-daily regimens in naive patients. The two nucleoside reverse transcriptase inhibitors (NRTIs) accompanying the third drug have become the central skeleton, or the 'backbone' of the therapeutic scheme. Among the different NRTI pairs, a didanosine-lamivudine (3TC) or emtricitabine backbone for combination antiretroviral therapy may be a good option compared with any current NRTI-combinations due to its security, tolerance and once-daily dose. In this article, we review the advantages and drawbacks of didanosine-XTC-EFV as the initial regimen of HAART in HIV-infected patients.

Adherence, side effects and efficacy of stavudine plus lamivudine plus nelfinavir in treatment-experienced HIV-infected patients.

OBJECTIVES: To evaluate adherence, side effects and efficacy of a modality of highly active antiretroviral therapy (HAART) in HIV-infected patients. METHODS: In a cohort, prospective study, 65 previously treated patients received stavudine plus lamivudine plus nelfinavir. Fifty-three participants (81%) had a history of intravenous drug use. Patients were evaluated at 3-month intervals. The association of adherence with demographic variables, hepatitis C virus infection, number of stopped antiretroviral regimens, HIV RNA level, CD4 cell count, and adverse effects to drugs was assessed. RESULTS: After a median follow-up of 12 months, 30 participants (46%) showed adequate adherence in all visits. An association was observed between adherence and female sex: 18 of 47 men (38%) vs. 12 of 18 women (67%) presented adequate adherence in all visits (P=0. 0416). An association was also observed between adherence and low baseline HIV RNA level (P=0.0229). Discontinuation of treatment took place because of refusal to take medication in 11 participants (17%) and because of side effects in seven participants (11%). Undetectable HIV RNA level was achieved in 26 patients (40%) at 3 months and in lower percentages at months 6, 9 and 12. CONCLUSIONS: Overall adherence to the employed HAART regimen was poor. Female sex and low baseline HIV RNA were associated with better adherence. Refusal to take medications and side effects were the main reasons to stop therapy. At 3 months' follow-up, virological efficacy was achieved in 40% of patients.

Relationships between antiviral treatment effects and biphasic viral decay rates in modeling HIV dynamics.

Recently, potent combination antiviral therapies consisting of reverse transcriptase inhibitor (RTI) drugs and protease inhibitor (PI) drugs, have been developed which can rapidly suppress HIV below the limit of detection. Two phases of plasma viral decay after initiation of treatment have been observed in clinical studies. Some researchers have suggested that the viral decay rates may reflect the potency (efficacy) of antiviral therapies. In this paper we model the effect of RTI drugs and PI drugs as inhibition rates of cell infection and infectious virus production, respectively, based on the biological mechanisms of these two different types of drugs. Through rigorous mathematical derivation, we show that the two viral decay rates are monotone functions of the treatment effects of these antiviral therapies. We derive approximation formulas for the relationships between viral decay rates and treatment effects. Computer simulations show that the approximation formulas approximate the true values very well. These formulas may be used to study what factors really affect the viral decay rates. The results in this paper provide a theoretical justification for using both viral decay rates for evaluation of the treatment efficacy of antiviral therapies.