Persistence of nevirapine exposure during the postpartum period after intrapartum single-dose nevirapine in addition to zidovudine prophylaxis for the prevention of mother-to-child transmission of HIV-1

OBJECTIVE

To determine nevirapine (NVP) plasma levels during the postpartum period after a single intrapartum NVP dose for the prevention of mother-to-child transmission.

METHODS

Plasma samples at delivery and during days 8 to 45 postpartum were obtained from HIV-infected Thai women who received an intrapartum NVP dose in the Perinatal HIV Prevention Clinical Trial-2 (PHPT-2) for the prevention of perinatal HIV transmission. These data were combined with NVP concentration data from 2 phase 1 studies of NVP for a population analysis.

RESULTS

The median NVP level fell to 68 ng/mL (range: <50-228, n = 43) 8 to 14 days after dosing and to 51 ng/mL (range: <50-166, n = 25) between 15 and 21 days. During the second and third weeks postpartum, NVP levels were below the limit of quantitation in 23% and 44% of samples, respectively. Between 21 and 45 days, no sample had a quantifiable NVP concentration. A simulation derived from the population analysis predicts that NVP concentration falls to less than 10 ng/mL in 5% of women by 11 days, in 50% of women by 17.5 days, and in 95% of women by 28 days.

CONCLUSIONS

Significant NVP concentrations remained for up to 20 days in these Thai women. To ensure that coverage is maintained until NVP concentrations fall to nonsuppressive levels, 1 month of additional antiretroviral treatment after delivery should be considered to prevent the emergence of resistant viruses.

Practical guidelines to interpret plasma concentrations of antiretroviral drugs

Several relationships have been reported between antiretroviral drug concentrations and the efficacy of treatment, and toxicity. Therefore, therapeutic drug monitoring (TDM) may be a valuable tool in improving the treatment of HIV-1-infected patients in daily practice. In this regard, several measures of exposure have been studied, e.g. trough and maximum concentrations, concentration ratios and the inhibitory quotient. However, it has not been unambiguously established which pharmacokinetic parameter should be monitored to maintain optimal viral suppression. Each pharmacokinetic parameter has its pros and cons. Many factors can affect the pharmacokinetics of antiretroviral agents, resulting in variability in plasma concentrations between and within patients. Therefore, plasma concentrations should be considered on several occasions. In addition, the interpretation of the drug concentration of a patient should be performed on an individual basis, taking into account the clinical condition of the patient. Important factors herewith are viral load, immunology, occurrence of adverse events, resistance pattern and comedication. In spite of the described constraints, the aim of this review is to provide a practical guide for TDM of antiretroviral agents. This article outlines pharmacokinetic target values for the HIV protease inhibitors amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir, and the non-nucleoside reverse transcriptase inhibitors efavirenz and nevirapine. Detailed advice is provided on how to interpret the results of TDM of these drugs.

Efavirenz Intoxication Due to Slow Hepatic Metabolism

We describe a human immunodeficiency virus-positive woman who presented with severe psychosis while she was receiving therapy with efavirenz. Her plasma efavirenz level was excessively high. Genetic investigation showed that she was homozygous for the CYP2B6 G516T allele, resulting in slow hepatic metabolism. After the dosage of efavirenz was lowered, all neuropsychiatric symptoms subsided.

Simultaneous determination of the HIV nucleoside analogue reverse transcriptase inhibitors lamivudine, didanosine, stavudine, zidovudine and abacavir in human plasma by reversed phase high performance liquid chromatography

A reversed phase high performance liquid chromatography method was developed for the simultaneous quantitative determination of the nucleoside reverse transcriptase inhibitors (NRTIs) lamivudine, didanosine, stavudine, zidovudine and abacavir in plasma. The method involved solid-phase extraction with Oasis MAX cartridges from plasma, followed by high performance liquid chromatography with a SymmetryShield RP 18 column and ultraviolet detection set at a wavelength of 260 nm. The assay was validated over the concentration range of 0.015-5 mg/l for all five NRTIs. The average accuracies for the assay were 92-102%, inter- and intra-day coefficients of variation (CV) were <2.5% and extraction recoveries were higher than 97%. This method proved to be simple, accurate and precise, and is currently in use in our laboratory for the quantitative analysis of NRTIs in plasma.

Automated, fast, and sensitive quantification of drugs in human plasma by LC/LC-MS: quantification of 6 protease inhibitors and 3 nonnucleoside transcriptase inhibitors

An analytic assay based on automated sample preparation and liquid chromatography (LC) coupled with electrospray mass spectrometry (ESI-MS) was developed for the quantification of 6 protease inhibitors (PIs) and 3 nonnucleoside reverse transcriptase inhibitors (NNRTIs). The 6 PIs, amprenavir, indinavir, ritonavir, lopinavir, nelfinavir, and saquinavir, as well as the three NNRTIs, nevirapine, efavirenz, and delavirdine, require a succinct analysis technique for therapeutic drug monitoring in HIV/AIDS patients. After protein precipitation, samples were loaded on a C8, 10 x 4-mm extraction column, washed, and, after activation of the column-switching valve, backflushed onto the 30 x 2.1 mm C8 analytic column. [M+H] ions were detected in the selected ion mode. A nonlinear fit (y(-1) = a + b/x, all r2 > 0.999) for amprenavir, indinavir, ritonavir, lopinavir, nelfinavir, and saquinavir and a linear fit (y = ax + b, all r2 > 0.999) for nevirapine, efavirenz, and delavirdine led to best regression. Absolute recoveries were as follows: PIs > 81%; NNRTIs > 76%. Interday and intraday precision were <12.5% for the PIs and <11.7% for the NNRTIs. Interday and intraday accuracy were <12.2% for the PIs and <14.9% for the NNRTIs. Limits of quantification were 20, 40, 50, 40, 40, 20, and 100 microg/L for amprenavir, indinavir, ritonavir, lopinavir, nelfinavir, saquinavir, and the NNRTIs, respectively. The assay allows fast analysis of patient samples for therapeutic drug monitoring (TDM) and has successfully been used for TDM and pharmacokinetic drug-drug interactions studies.

Variations of CYP3A activity induced by antiretroviral treatment in HIV-1 infected patients

OBJECTIVE

To measure the in vivo variations of CYP3A activity induced by anti-HIV drugs in human immunodeficiency virus (HIV)1-positive patients.

METHODS

A low oral dose of midazolam (MID) (0.075 mg) was given to the patients and the 30-min total 1-OH midazolam (1-OHMID)/MID ratio was determined. Patients were phenotyped either before the introduction of antiretroviral treatments (control group, 90 patients) or after a variable period of antiretroviral treatment (56 patients). Twenty-one subjects underwent multiple phenotyping tests (before and during the course of the treatment).

RESULTS

The median MID ratio was 3.51 in the control group (range 0.20-14.6). It was 5-fold higher in the group with efavirenz (28 patients; median, range: 16.0, 3.81-367; P < 0.0001), 13-fold lower with nelfinavir (18 patients; 0.27, 0.06-36.3; P < 0.0001), 17-fold lower with efavirenz + ritonavir (three patients; 0.21, 0.05-0.47; P = 0.006), 50-fold lower with ritonavir (four patients; 0.07, 0.06-0.17; P = 0.0007), and 7-fold lower with nevirapine + (ritonavir or nelfinavir or grapefruit juice) (three patients; 0.48, 0.03-1.83; P = 0.03). CYP3A activity was lower in the efavirenz + ritonavir group (P = 0.01) and in the ritonavir group (P = 0.04) than in the nelfinavir group, although already strongly inhibited in the latter.

CONCLUSION

The low-dose MID phenotyping test was successfully used to measure the in vivo variations of CYP3A activity induced by antiretroviral drugs. Efavirenz strongly induces CYP3A activity, while ritonavir almost completely inhibits it. Nelfinavir strongly decreases CYP3A activity, but to a lesser extent than ritonavir. The inhibition of CYP3A by ritonavir or nelfinavir offsets the inductive effects of efavirenz or nevirapine administered concomitantly. Finally, no induction of CYP3A activity was noticeable after long-term administration of ritonavir at low dosages (200 mg/day b.i.d.) or of nelfinavir at standard dosages (2,500 mg/day b.i.d.).

The pharmacokinetics of nelfinavir and M8 during pregnancy and post partum

OBJECTIVE

The objective of this study was to explore the pharmacokinetics of nelfinavir and its active metabolite hydroxy-t-butylamidenelfinavir (M8) during pregnancy and post partum.

METHODS

Eleven human immunodeficiency virus type 1-infected pregnant women receiving 1250 mg nelfinavir twice daily were enrolled. Pharmacokinetics of nelfinavir and M8 were assessed over a 12-hour period during pregnancy (median, 32 weeks' gestation; range, 31-36 weeks) and post partum (median, 8 weeks post partum; range, 6-15 weeks). Drug concentrations were analyzed by HPLC coupled to tandem mass spectroscopy, and pharmacokinetic parameters were calculated by use of noncompartmental methods.

RESULTS

The median area under the plasma concentration-time curve from 0 to 12 hours (AUC 0-12), the maximal plasma concentration (C max), and the concentration at the end of the dosing interval (C 12) for nelfinavir post partum were 33.5 h . microg/mL, 5.80 microg/mL, and 1.40 microg/mL, respectively. The values for the geometric mean ratio (GMR) (third trimester/post partum) for the nelfinavir AUC 0-12 , C max , and C 12 were 0.76 (90% confidence interval [CI], 0.54-1.06), 0.81 (90% CI, 0.57-1.15), and 0.43 (90% CI, 0.25-0.76), respectively. The GMR values for the M8 AUC 0-12 , C max , and C 12 were 0.32 (90% CI, 0.18-0.55), 0.31 (90% CI, 0.19-0.51), and 0.30 (90% CI, 0.14-0.64), respectively. The median ratio values of the AUC 0-12 of M8 and nelfinavir (M8/nelfinavir) during the third trimester and post partum were 11% and 27%, respectively (GMR, 0.42 [90% CI, 0.33-0.53]).

CONCLUSIONS

Nelfinavir exposure was reduced during pregnancy, and the reduction was statistically significant for C 12 . M8 concentrations were about 70% lower during pregnancy compared with post partum, suggesting either induction of hepatic cytochrome P450 (CYP) 3A4 or inhibition of CYP2C19, or both, during pregnancy. Because 8 of 11 women had subtherapeutic nelfinavir trough concentrations during pregnancy, the safety and efficacy of therapeutic drug monitoring should be investigated.

SPECIES DIFFERENCES IN THE DISPOSITION OF THE CCR5 ANTAGONIST, UK-427,857, A NEW POTENTIAL TREATMENT FOR HIV

UK-427,857 (4, 4-difluoro-N-[(1S)-3-[exo-3-(3-isopropyl-5-methyl-4H-1,2,4-triazol-4-yl)-8-azabicyclo[3.2.1]oct-8-yl]-1-phenylpropyl]cyclohexanecarboxamide) is a novel CCR5 antagonist undergoing investigation for use in the treatment of human immunodeficiency virus (HIV) infection. Pharmacokinetic and metabolism studies have been performed in mouse, rat, dog, and human after single and multiple administration by oral and intravenous routes. The compound has physicochemical properties that are borderline for good pharmacokinetics, being moderately lipophilic (log D(7.4) 2.1) and basic (pK(a) 7.3), possessing a number of H-bonding functionalities, and with a molecular weight of 514. The compound was incompletely absorbed in rat (approximately 20-30%) but well absorbed in dog (>70%). Based on in vitro studies in Caco-2 cells, UK-427,857 has relatively poor membrane permeability, and transcellular flux is enhanced in the presence of inhibitors of P-glycoprotein. Further evidence for the involvement of P-glycoprotein in restricting the oral absorption of UK-427,857 was obtained in P-glycoprotein null mice (mdr1a/mdr1b knockout). In these animals, AUC after oral administration was 3-fold higher than in control animals. In oral dose escalation studies in humans, the compound demonstrated nonlinear pharmacokinetics, with increased dose-normalized exposure with increased dose size, consistent with saturation of P-glycoprotein. The oral dose-exposure relationship of UK-427,857 in humans was not reflected in either rat or dog. In animal species and humans, UK-427,857 undergoes some metabolism, with parent compound the major component present in the systemic circulation and excreta. Elimination of radioactive dose was primarily via the feces. In rat, parent compound was secreted via bile and directly into the gastrointestinal tract. Metabolites were products of oxidative metabolism and showed a high degree of structural consistency across species.

Nevirapine and efavirenz pharmacokinetics and covariate analysis in the 2NN study

OBJECTIVE

The aim of this 2NN pharmacokinetic substudy was to investigate the population pharmacokinetics of nevirapine and efavirenz.

METHODS

Treatment-naive, HIV-1-infected patients received nevirapine (once or twice daily), efavirenz or a combination with lamivudine and stavudine. Blood samples were collected on day 3 and weeks 1, 2, 4, 24 and 48. Using non-linear mixed effects modelling, pharmacokinetics of nevirapine and efavirenz and factors involved in the inter-individual variability were investigated.

RESULTS

Clearance of nevirapine in the induction phase (<14 days) and at steady state (>28 days) were 2.02 I/h and 2.81 I/h, respectively. Volume of distribution and absorption rate constant were 77.0 l and 1.66 h(-1), respectively. Clearance of nevirapine was lower in females (13.8%) and in patients with hepatitis B (19.5%). Patients from South America and Western countries had higher clearance of nevirapine compared with Thai and South African patients. The clearances of efavirenz in the induction phase and at steady state were 7.95 l/h and 8.82 l/h, respectively. The volume of distribution and absorption rate constant were 4181 and 0.287 h(-1), respectively. Concomitant use of nevirapine increased clearance of efavirenz (43%). Patients from Thailand had lower clearance than the rest of the population.

CONCLUSIONS

The population pharmacokinetics of nevirapine and efavirenz were assessed in the 2NN trial. For both drugs, an induction phase was distinguished from the steady-state phase. Gender, hepatitis B and geographical region were involved in the variability of the pharmacokinetics of nevirapine. Region and concomitantly used nevirapine were determinants of the pharmacokinetics of efavirenz.

Population Pharmacokinetics of Efavirenz in an Unselected Cohort of HIV-1-Infected Individuals

OBJECTIVE

The aim of this study was to characterise the population pharmacokinetics of efavirenz in a representative patient population and to identify patient characteristics influencing the pharmacokinetics of efavirenz, with the ultimate goal of further developing techniques that can be applied to optimise therapeutic drug monitoring of antiretroviral agents.

METHODS

Ambulatory HIV-1-infected patients using an efavirenz-containing regimen were included. During regular visits, blood samples were collected for efavirenz plasma concentrations and clinical chemistry parameters. Concentrations of efavirenz were quantitatively assessed by a validated high-performance liquid chromatographic with ultraviolet detection method. Using nonlinear mixed-effect modelling (NONMEM), the pharmacokinetics of efavirenz were described. Disposition of efavirenz was described by a two-compartment model and absorption was modelled using a chain of three transition compartments. Apparent clearance (CL/F), volume of distribution after oral administration (V(d)/F), intercompartmental clearance, the peripheral volume of distribution and the intercompartmental transition rate constant (k(tr)) were estimated. Furthermore, interindividual, interoccasion and residual variability were estimated. The influence of patient characteristics on the pharmacokinetic parameters of efavirenz was explored.

RESULTS

From 172 patients, 40 full pharmacokinetic curves and 315 efavirenz plasma concentrations at a single timepoint were available, resulting in a database of 1009 efavirenz plasma concentrations. CL/F, V(d)/F, and k(tr) were 11.7 L/h (4.3% relative standard error [RSE]), 189L (14.6% RSE) and 3.07 h(-1) (11.2% RSE), respectively. Residual variability in the model was composed of 0.14 mg/L additive error and 8.85% proportional error. Asian race and baseline total bilirubin (TBR) increased the relative bioavailability of efavirenz by 56% and 57%, respectively. No significant covariates were found for CL/F or V(d)/F.

CONCLUSION

The pharmacokinetic parameters of efavirenz were adequately described with the developed population pharmacokinetic model. Asian race and baseline TBR were found to be significantly correlated with the bioavailability of efavirenz. The described model will be an essential tool in further optimisation of efavirenz-containing antiretroviral therapy, e.g. by the use of Bayesian estimation of individual pharmacokinetic parameters.

Role of the inhibitory quotient in HIV therapy

A systemic review is presented of all studies that have evaluated the inhibitory quotient (IQ). The IQ is defined as the ratio between (trough) drug concentration and level of drug resistance of the HIV isolate. From the studies presented, it can be concluded that for protease inhibitors (PIs) and efavirenz, the phenotypic IQ is associated with virological response. The genotypic IQ (GIQ) for PIs was also demonstrated to be associated with virological response. An intrinsic limitation of the GIQ is that it is only applicable for PIs, of which resistance is based on the cumulative effect of mutations. As the IQ can be modified by adjustment of the drug dosage, it may be of clinical value. Its application in patient care should therefore be further investigated.

Are adverse events of nevirapine and efavirenz related to plasma concentrations?

OBJECTIVE

The relationships between adverse events (AEs) and plasma concentrations of nevirapine (NVP) and efavirenz (EFV) were investigated as part of the large, international, randomized 2NN study.

METHODS

Treatment-naive, HIV-1-infected patients received NVP (once or twice daily), EFV or their combination, each in combination with lamivudine and stavudine. Blood samples were collected on day 3 and weeks 1, 2, 4, 24 and 48. Concentrations of NVP and EFV were quantitatively assessed by a validated HPLC assay. Individual Bayesian estimates of the area under the plasma concentration-time curve over 24 h (AUC24h), and minimum and maximum plasma concentrations (Cmin and Cmax) as measures for drug exposure of NVP and EFV, were generated using a previously developed population pharmacokinetic model. Pharmacokinetic parameters were compared for patients with and without central nervous system (CNS) and psychiatric AEs, hepatic events, liver enzyme elevations (LEEs) and rash. Furthermore, it was investigated whether a clear cut-off for a pharmacokinetic parameter could be identified above which the incidence of AEs was clearly increased. AEs were also related to demographic parameters and baseline characteristics.

RESULTS

In total, from 1077 patients, NVP (3024 samples) and EFV (1694 samples) plasma concentrations and AE data (825 observations) were available. For all patients Cmin, Cmax and AUC24h were determined. When corrected for known covariates of gender, CD4 cell count at baseline, region, hepatitis coinfection and possible interactions between these factors, no significant associations between AEs and any tested exposure parameter of NVP was observed. Also, no target Cmin value, above which patients were at increased risk for AEs, could be established. On the other hand, geographical region, hepatitis coinfection, CD4 cell count and gender were found to be significantly related with the incidence of CNS and psychiatric AEs, hepatic events, LEEs and rash during the treatment with NVP. The occurrence of elevated liver enzymes during the first 6 weeks in the EFV-containing arm was significantly (P = 0.036) correlated to the exposure of EFV (Cmin). Only hepatitis coinfection impacted on LEEs during the first 6 weeks of treatment. With an EFV Cmin above 2.18 mg/l during the induction phase, patients were 4.4 (range 1.3-15.5) times more at risk for elevated liver enzymes. No other correlations between AEs and EFV pharmacokinetics or patient characteristics could be identified.

CONCLUSIONS

Pharmacokinetic parameters of NVP did not have a relationship to AEs in the 2NN trial when corrected for known covariates. The value of periodical drug monitoring of NVP as a way to prevent toxicity is therefore limited. Treating physicians should instead focus on factors that are more predictive of AEs (gender, CD4 count and hepatitis coinfection). High EFV Cmin levels resulted in elevated liver enzyme values during the first 6 weeks of treatment. Regular measurement of EFV levels and liver enzymes at the start of therapy may therefore be advised.

Saquinavir 500 mg film-coated tablets demonstrate bioequivalence to saquinavir 200 mg hard capsules when boosted with twice-daily ritonavir in healthy volunteers

OBJECTIVE

To establish the bioequivalence of a 500 mg film-coated tablet of saquinavir mesylate (FCT SQV) to the 200 mg hard-capsule saquinavir mesylate (HC SQV), both boosted with ritonavir and administered under fed conditions.

METHODS

We carried out a multi-centre, open-label, randomized, two-sequence, four-period, two-treatment, replicated crossover study in 93 healthy men and 7 healthy women. Individuals were randomly assigned to receive sequential single doses of saquinavir in one of two treatment sequences: ABAB or BABA. Individuals received 100 mg ritonavir twice daily for 24 days. On days 14,17, 20 and 23, study participants took 1000 mg of HC SQV (five 200 mg capsules, treatment A) or FCT SQV (two 500 mg tablets, treatment B) with a high-fat, high-calorie breakfast, and pharmacokinetic analyses were carried out over the next 24 hours. Area under the saquinavir concentration-time curve (AUC0-alpha), maximum saquinavir plasma concentration (Cmax), time to Cmax and terminal half-life were calculated. The relative bioavailability of FCT SOV versus HC SQV was calculated as the ratio of the respective estimated mean saquinavir AUC0-alpha and Cmax. The calculation was based on an ANOVA including the factors site, sex, sequence, period, treatment and study participant to the log-transformed parameters log(AUC0-alpha) and log(Cmax); the relative bioavailability and the 90% confidence intervals (CIs) were estimated using the treatment contrasts of the ANOVA. Bioequivalence was concluded as for both parameters, AUC0-alpha and Cmax, the 90% CIs for the relative bioavailability were entirely included in the reference region [0.80-1.25].

RESULTS

Saquinavir plasma concentration-time profiles for the two formulations were similar. Geometric mean AUC0-alpha and Cmax values were clearly increased for FCT SQV (26 826 versus 24 430 h*ng/ml; and 3644 versus 3064 ng/ml, respectively); ratios of mean exposures were estimated to be 1.10 for AUC0-alpha and 1.19 for Cmax of saquinavir. However, the corresponding two-sided 90% CIs (1.04-1.16 and 1.14-1.25, respectively) all fell within the limits set for equivalence (0.80, 1.25). The adverse event profile for FCT SQV was similar to that for HC SQV.

CONCLUSION

The new 500 mg FCT SQV formulation is bioequivalent to the 200 mg HC SQV formulation, at the dose of 1000 mg, in combination with 100 mg ritonavir under fed conditions. The 500 mg FCT SQV formulation reduces pill count for boosted saquinavir (SQV/r) from six capsules to three tablets twice daily. This may increase patient acceptability of SQV/r, particularly in less treatment-experienced patients.

Effects of valproic acid coadministration on plasma efavirenz and lopinavir concentrations in human immunodeficiency virus-infected adults

Valproic acid (VPA) has the potential to benefit patients suffering from human immunodeficiency virus (HIV)-associated cognitive impairment. The purpose of this study was to determine if VPA affects the plasma concentration of efavirenz (EFV) or lopinavir. HIV type 1 (HIV-1)-infected patients receiving EFV or lopinavir-ritonavir (LPV/r) had 9 or 10 blood samples drawn over 8 to 24 h of a dosing interval at steady state before and after receiving 250 mg of VPA twice daily for 7 days. VPA blood samples drawn before (C(0)) and 8 h after the morning dose (8 h) were compared to blood samples from a group of HIV-1-infected subjects who were taking either combined nucleoside reverse transcriptase inhibitors alone or had discontinued antiretroviral therapy. Pharmacokinetic parameters were calculated by noncompartmental analysis, and tests of bioequivalence were based on 90% confidence intervals (CIs) for ratios or differences. The geometric mean ratio (GMR) (90% CI) of the areas under the concentration-time curve from 0 to 24 h (AUC(0-24)s) of EFV (n = 11) with and without VPA was 1.00 (0.85, 1.17). The GMR (90% CI) of the AUC(0-8)s of LPV (n = 8) with and without VPA was 1.38 (0.98, 1.94). The differences (90% CI) in mean C(0) and 8-h VPA concentrations versus the control (n = 11) were -1.0 (-9.4, 7.4) microg/ml and -2.1 (-11.1, 6.9) microg/ml for EFV (n = 10) and -5.0 (-13.2, 3.3) microg/ml and -6.7 (-17.6, 4.2) microg/ml for LPV/r (n = 11), respectively. EFV administration alone is bioequivalent to EFV and VPA coadministration. LPV concentrations tended to be higher when the drug was combined with VPA. Results of VPA comparisons fail to raise concern that coadministration with EFV or LPV/r will significantly influence trough concentrations of VPA.

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.

Effectiveness and tolerability of a once-daily amprenavir/ritonavir-containing highly active antiretroviral therapy regimen in antiretroviral-naïve patients at risk for nonadherence: 48-week results after 24 weeks of directly observed therapy

OBJECTIVES

To determine the safety and effectiveness of a once-daily highly active antiretroviral therapy (HAART) regimen in patients at risk for poor adherence using directly observed therapy (DOT) for 24 weeks followed by weekly phone contact for another 24 weeks.

METHODS

A prospective, open-label pilot study was carried out. Antiretroviral-naïve patients with advanced HIV disease were treated with once-daily amprenavir 1200 mg, ritonavir 200 mg, didanosine 400 mg and lamivudine 300 mg. After 24 weeks, DOT was substituted by weekly phone contact. Measurements of viral load and CD4 cell count, and safety laboratory measurements, were taken regularly for 48 weeks.

RESULTS

Twenty-two patients were enrolled in the study, of whom 19 completed at least 4 weeks of treatment. Seventeen patients completed 24 weeks and 13 completed 48 weeks. None discontinued treatment as a result of adverse events. The median baseline HIV viral load was 5.29 log(10) HIV-1 RNA copies/mL and the median CD4 cell count was 20 cells/microL. At weeks 24 and 48, 74% of the patients had viral loads <400 copies/mL. At 48 weeks, the median decrease in viral load from baseline was 3.06 log(10) copies/mL, and the median increase in CD4 cell count was 118 cells/microL. The median trough plasma amprenavir concentrations at weeks 1 and 24 were 1.87 and 1.42 microg/mL, respectively.

CONCLUSIONS

This study suggests that DOT followed by weekly patient contact results in good treatment outcome in this challenging population. The median trough plasma amprenavir concentrations were above the effective concentration of drug that resulted in 90% inhibition of viral load in vivo (EC(90)) for wild-type HIV.

GENOPHAR: a randomized study of plasma drug measurements in association with genotypic resistance testing and expert advice to optimize therapy in patients failing antiretroviral therapy

OBJECTIVES

To evaluate the benefits of therapeutic drug monitoring (TDM) in association with genotypic resistance testing and expert advice to optimize therapy in multiexperienced patients infected with HIV-1.

METHODS

Patients with a viral load>1000 HIV-1 RNA copies/mL and an unchanged antiretroviral therapy regimen over the last 3 months were randomized into two groups: a genotypic group (G) and a geno-pharmacological group (GP). Treatment was selected by an expert committee according to genotypic resistance testing (the G and GP groups) and TDM (the GP group) at week 4. Treatment could be modified at each visit according to toxicity, poor virological response and TDM. Results of TDM were withheld from the G group until week 12. The primary endpoint of the study was the percentage of patients with viral load<200 copies/mL at week 12.

RESULTS

A total of 134 patients were randomized in the study, with 67 in each group, and included in the intent-to-treat (ITT) analysis. At baseline, median values were as follows: viral load (log(10) copies/mL): G=4.1, GP=4.0; CD4 cell count (cells/microL): G=292, GP=294; and number of prior drugs: G=7, GP=8. The median number of resistance mutations was five in the G group [nucleoside reverse transcriptase inhibitors (NRTIs)=three; non-nucleoside reverse transcriptase inhibitors (NNRTIs)=one; protease inhibitors (PI)=one] and seven in the GP group (NRTI=four; NNRTI=two; PI=one). At week 8, treatment was adjusted according to the TDM in 13 of the 67 patients in the GP group (19%). By ITT missing equal failure analysis at week 12, and after only one intervention according to plasma concentration results, a viral load<200 copies/mL was achieved in 30 of the 67 patients (45%) in the G group and in 29 of the 67 patients (43%) in the GP group (not significant). In the multivariate analysis, only prior exposure to at least two PIs at baseline gave a poor response to subsequent antiretroviral therapy. At week 24, a viral load<200 copies/mL was achieved in 35 of the 67 patients (52%) in the G group and in 40 of the 67 patients (60%) in the GP group.

CONCLUSIONS

A statistically significant benefit of using TDM was not found in this short-term study where patients appeared to be adherent. However, combining genotypic resistance testing with the use of an expert committee to monitor subsequent therapy individually in patients with multiple resistance mutations was associated with high antiviral efficacy.

Lopinavir plasma levels in salvage regimes by a population of highly active antiretroviral therapy-treated HIV-1-positive patients

Increased lopinavir (LPV) exposure obtained in vivo through combination with low-dose ritonavir may overcome a certain grade of resistance but not all. We sought to analyze LPV variability and possible risk factors. LPV trough plasma concentrations were determined by high-performance liquid chromatography after 1, 4, and 12 weeks from salvage regimens and tested in both univariate and multivariate regression analyses with age, gender, weight, risk factors for HIV acquisition, hepatitis C virus reactivity, hepatitis B surface antigen positivity, baseline aspartate transferase (AST) or alanine transferase (ALT) levels, creatinine, non-nucleoside reverse transcriptase inhibitors (NNRTIs) or tenofovir as concomitant drugs, and NNRTIs administered in the previous regimen. Fifty-six patients were included into the study. Among them, 8 of 56 (14.3%) at week 1, 12 of 56 (21.4%) at week 4, and 9 of 56 (16.1%) at week 12 had suboptimal LPV plasma concentrations, defined as trough concentration less than 4 microg/mL. No correlation was found between LPV trough concentrations and assessed variables. In conclusion, pharmacokinetic variability and low LPV concentrations have been found, supporting the use of therapeutic drug monitoring in those starting this drug.

Therapeutic drug monitoring of antiretroviral agents scenario

The efficacy of antiretroviral treatment (ART) may be limited by pharmacological factors. Dose-response relationship exists for many antiretroviral agents, and failure to maintain adequate concentrations may allow the development of viral resistance, thereby decreasing the probability of response of current and subsequent therapies. Fixed dosage of antiretroviral agents may result in different systemic and intracellular concentrations of drugs (interindividual variability). Therapeutic drug monitoring (TDM) consists of individualising dosages with the aim of maximising the efficacy of treatment while minimising its toxicity. The combination of pharmacokinetic-pharmacodynamic relationships for antiretroviral therapy and the presence of a wide interpatient variability in drug exposure support the application of TDM in HIV-infected individuals. Prospective clinical trials assessing the clinical usefulness of this strategy have shown contradictory results, pointing out the need to consider different issues when performing TDM of ART. Pharmacological and resistance data should be combined in one parameter (inhibitory quotient) in antiretroviral-experienced patients. Protease inhibitors exhibit a moderate to high degree of binding to plasma proteins, and in vitro inhibitory concentrations need to be corrected by this factor. The best method to individualize the dosage regimen has not been identified yet. Finally, participation of different laboratories in external cross-validation programmes is crucial to ensure that results are accurate.

Serum lamivudine levels in the presence of a lamivudine-resistant HBV mutant

BACKGROUND/AIMS

Lamivudine efficiently inhibits hepatitis B virus replication and has been used to treat hepatitis B virus recurrence after orthotopic liver transplantation. Although effective, its use is hampered by viral breakthrough due to the appearance of hepatitis B virus drug-resistant strains. Aims of this work were to evaluate the inter- and intra-individual variations of lamivudine serum levels and the effects on the drug levels of the lamivudine-resistant hepatitis B virus mutant infection.

METHODS

Serum lamivudine concentration was measured by high-performance liquid chromatography. Polymerase chain reaction analysis and sequencing analysis of the reverse transcriptase area of the polymerase was performed on each sample using specific primers. A polymerase chain reaction-enzyme-linked immunosorbent assay was used to differentiate between wild-type hepatitis B virus and lamivudine-resistant hepatitis B virus strain.

RESULTS

Lamivudine serum levels presented minor inter- and intra-individual fluctuations along time, with an important increase at the time of the hepatitis flare-up due to the hepatitis B virus mutant presence. When the wild-type hepatitis B virus briefly reappeared as a mixed population, the titre of lamivudine dropped to below the detection level.

CONCLUSIONS

While lamivudine serum levels appears stable when the anti-viral efficacy is fully achieved, important fluctuations are present according to the type of viral population, with a considerable decrease possibly due to the presence of the wild-type virus.

Improving HIV Infection Management Using Antiretroviral Plasma Drug Levels Monitoring: A Clinicians Point of View

Due to genetic and environmental factors, there are wide inter-patient differences when measuring drug exposure to a standard dose. If there is a relationship between drug exposure and efficacy or toxicity, this inter-patient variability carries various risks to develop toxicity or failure. Therapeutic drug monitoring is an attempt to adjust the dose to obtain a level within a therapeutic range consisting in a minimum plasma concentration needed to be efficacious and a maximum plasma concentration not to exceed to avoid toxicity. Many studies have shown a relationship between various pharmacokinetic parameters and drug toxicity or efficacy for HIV protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Therapeutic drug monitoring (TDM) proves to be a useful tool to assess adherence, to investigate drug-drug interactions between antiretroviral (ARV) drugs or with co-medications, to prevent some ARV drug toxicities, to adjust the dosage in particular populations, and to increase ARV efficacy of some drugs in naive patients. The integration of virological and pharmacological parameters, using inhibitory quotients, looks promising to improve therapy in ARV-experienced patients. Effective and non-toxic target concentrations will be determined for all present and future antiretroviral drugs covering the extended spectrum of naive patients to multiple failures. In this article, we review the rationale of TDM for antiretroviral drugs, the retrospective and prospective studies assessing plasma drug concentrations in relation with antiretroviral toxicity or efficacy, and the actually recommended or proposed indications for TDM. We also highlight the benefits and limits of this tool as an adjunct in the care of HIV-infected patients.

Efavirenz plasma concentrations in HIV-infected patients: inter- and intraindividual variability and clinical effects

Efavirenz is a drug subject to extensive metabolism, mainly by the cytochrome P-450 isoenzyme CYP2B6, known to exhibit extensive interindividual variability. The aim of the present study was 2-fold: to investigate the relationship between plasma concentration and clinical effects of efavirenz and to investigate the extent of the inter- and intraindividual variability of the plasma concentration measurements. From an open clinic, 68 HIV-positive patients on efavirenz-containing treatment were recruited. From each patient 1 to 5 samples were collected; 43 had more than 1 sample taken. Most samples were taken 10-24 hours after the latest dose. Efavirenz was analyzed by high-performance liquid chromatography with UV detection. The data were analyzed by the variance component model analysis of variance. Efavirenz concentrations were reproducible, and intraindividual variability constituted only 16% of the total variance. Thus, 84% of the variance was attributed to interindividual variability. The incidence of primary treatment failure was related to low plasma concentrations with a geometric mean concentration of 6.1 micromol/L compared with 8.7 micromol/L in those responding to therapy (P < 0.05). If a cutoff of 7 micromol/L is used, 10 of 13 failing to respond were below this level compared with 15 of 45 in those responding. It is concluded that efavirenz plasma concentration measurement gives reproducible results predictive of primary treatment failure. A lower bound for the therapeutic level of 7 micromol/L is proposed, and data from other authors suggests that an upper level of 13 micromol/L may be applied.

Determination of abacavir in human plasma by high-performance liquid chromatography with ultraviolet detection and the analytical error function

A rapid and simple high-performance liquid chromatography method has been developed for the determination of the HIV-1 reverse transcriptase inhibitor abacavir in human plasma. It included a single liquid-liquid extraction procedure with a mixture of ethyl acetate-diethyl ether prior to reversed-phase chromatography on a C18 column and C18 precolumn insert. Ultraviolet detection was set at 285 nm. The mobile phase consisted of water-acetonitrile (83:17, v/v) and the flow rate was kept at 1 mL/min. The total run time for a single analysis was 10 min. The method has been validated over the range 50-2500 ng/mL. The assay was linear over the entire concentration range (r2 = 0.9993). Intra- and inter-day precision and accuracy were less than 8.1 and -5.2%, respectively. The extraction recovery was greater than 94.3%. Abacavir was stable under the relevant storage conditions tested. After the validation, the analytical error function was established as standard deviation (SD; ng/mL) = -1.072 + 0.037C (C = theoretical concentration value). The method developed and its associated analytical error function will be suitable for pharmacokinetic studies and monitoring of HIV-1 patients.

Pharmacokinetics and Pharmacodynamics of Methadone Enantiomers After Coadministration with Amprenavir in Opioid-Dependent Subjects

STUDY OBJECTIVE

To investigate the steady-state pharmacokinetics of methadone enantiomers when coadministered with amprenavir.

DESIGN

Prospective, open-label, within-subject pharmacokinetic study.

SETTING

University research center.

SUBJECTS

Nineteen opioid-dependent, methadone-maintained, healthy individuals were enrolled.

INTERVENTION

On study day 1, subjects received their usual once-daily dose of methadone alone. On study days 2-11, they received the same once-daily methadone dose plus amprenavir 1200 mg twice/day. Serial blood samples were collected over 24 hours on study days 1 and 11 for measurement of plasma R- and S-methadone, and over 12 hours on day 11 for serum amprenavir concentrations.

MEASUREMENTS AND MAIN RESULTS

Standard pharmacokinetic parameters were determined from the concentrations and compared between the two treatments (methadone alone vs methadone with amprenavir). Subjects served as their own control for methadone comparisons, and amprenavir comparisons were made by using a historic control group (38 healthy men). Opioid-effect measures were assessed throughout the study. Coadministration of amprenavir with methadone resulted in a 3-4-hour delay in plasma R- and S-methadone enantiomer peak concentrations at steady state (Cmax-ss). The active R-methadone enantiomer area under the plasma concentration-time curve during a dosing interval (AUCt-ss, Cmax-ss, and the minimum plasma concentration at steady state (Cmin-ss) were decreased by 13%, 25%, and 21%, respectively, after coadministration of methadone and amprenavir. The inactive S-enantiomer AUCt-ss, Cmax-ss, and Cmin-ss were decreased by 40%, 48%, and 52%, respectively. No clinically significant changes were noted in opioid pharmacodynamic effects, and there was no evidence of opioid withdrawal. No methadone dosage was changed in any subject.

CONCLUSION

No a priori adjustment in methadone dosage is required during coadministration with amprenavir as there is only a small effect on R-methadone exposure and no evidence of opioid withdrawal.

Follow-up measurements of Nevirapine plasma levels over a prolonged period

Over a period of more than four years of treatment, 177 Nevirapine plasma levels were taken from 27 patients. The values showed a high inter-patient variability and a lower intra-patient variability. Differences in body weight turned out to be the main reason for inter-patient variability. Treatment over a prolonged period did not result in any change in plasma concentrations. Adjusting dosage by means of therapeutic drug monitoring would appear to be a reasonable way of maximising patient benefit from treatment.

Development of a fluorescent microplate assay for determining cyanovirin-N levels in plasma

A sensitive immunosorbent competition assay was developed for quantitation of the anti-HIV protein cyanovirin-N (CV-N) in plasma using a 96-well plate format and a fluorescent endpoint. The assay is based on the binding of CV-N in plasma to plate-bound anti-CV-N antibodies, followed by removal of the plasma and addition of europium-labeled CV-N (Eu3+ -CV-N) to compete for the remaining antibody sites. Detection by addition of a dissociative fluorescence enhancement solution and time-resolved fluorescence measurements allowed correlation to the concentration of the native CV-N in plasma. A linear detection range of 1-100 nM (r2>0.99) was obtained for CV-N in mouse plasma. This assay was then utilized for analysis of plasma levels of CV-N samples following subcutaneous injection of CV-N into mice. The results of these studies confirmed the reliability and sensitivity of this assay and the feasibility of its use for pharmacokinetic studies in a variety of species.

Homozygous CYP2B6 *6 (Q172H and K262R) correlates with high plasma efavirenz concentrations in HIV-1 patients treated with standard efavirenz-containing regimens

Efavirenz (EFV) is metabolized by cytochrome P450 2B6 (CYP2B6) in the liver. We analyzed the genotypes of CYP2B6 and their contribution to plasma EFV concentrations in 35 EFV-treated patients in International Medical Center of Japan. The mean plasma EFV concentration of patients with CYP2B6 *6/*6 (Q172H and K262R) (25.4+/-7.5 microM, +/-SD, n = 2) was significantly higher than that of patients with genotypes *6 heterozygote (9.9+/-3.3 microM, n = 10) or without alleles *6 (8.0+/-2.6 microM, n = 23) (p < 0.0001). To confirm our result, we further analyzed nine patients (three with high EFV concentrations and arbitrarily selected six with normal EFV concentrations) treated in Osaka National Hospital, and it resulted that the only three patients with the high concentrations were the *6/*6 holder. EFV dose could be decreased in those patients harboring the genotype to reduce toxicity with compromising potency, representing the first step of the Tailor-Made therapy of HIV-1 infection.

Race Is Not Associated with Nevirapine Pharmacokinetics

The effect of race on the pharmacokinetics of nevirapine was investigated in a nonselected population. Included patients were ambulatory HIV-1-infected patients from the outpatient clinics of the Academic Medical Center and the Slotervaart Hospital, Amsterdam, The Netherlands. All patients were using nevirapine as part of their antiretroviral regimen and had at least one plasma concentration available for analysis. From the included patients, gender, age, race, hepatitis C status, baseline ASAT value, and body weight were obtained. The nonlinear mixed-effect modeling program (NONMEM) version V 1.1 was used for all analyses. Population pharmacokinetic parameters [clearance (CL/F), volume of distribution (V/F), absorption rate constant (ka)] and interindividual (IIV) and interoccasion variability (IOV) were estimated. The influence of race on the CL/F of nevirapine was tested as Negroid race versus the other races, Asian race versus the other races, and the Negroid and the Asian races as separate variables versus the Caucasian race. A database of 1732 nevirapine plasma concentrations of 383 HIV-1-infected individuals collected during 1186 outpatient clinic visits was available for this analysis. The conclusion of this study is that race is not associated with the pharmacokinetics of nevirapine, and thus requires no dose adaptations.

Therapeutic drug monitoring for patients with HIV infection: Children's National Medical Center, Washington DC experience

This paper provides a brief overview of therapeutic drug monitoring (TDM) in patients with HIV infection. The manuscipt not only focuses on an update on TDM in HIV infection but also provides the latest information on tandem mass spectrometric methods for antiretroviral drug quantification. Also discussed are the preliminary new and original data on free antiretroviral drug measurement in both plasma and saliva.

Therapeutic drug monitoring in children with HIV/AIDS

In this paper we present an overview on the use of TDM in the treatment of HIV-1-infected children. The processes of growth and development have a significant impact on drug metabolism. The use of TDM makes it possible to optimize plasma drug concentrations of antiretroviral drugs. This is important when one considers that the levels of viral suppression and drug toxicity in adults and children are associated with the plasma concentration of PIs and NNRTIs. Indeed, in clinical practice the use of TDM in the treatment of HIV-1-infected children has favorable results. However, there is a serious shortage of population reference values of antiretroviral medication in children. Targeting plasma drug levels in children to adult reference values may be insufficient because of the unique features of HIV infection in children. Apart from its primary function for dose optimization, TDM can also be used as a tool to assess adherence to antiviral medication. One should, however, be cautious to base assumptions on plasma levels alone because aberrant plasma levels may also be the result of other factors such as changes in nutritional habits, drug-drug interactions, or changing gastric motility. We conclude that TDM is a useful tool in the treatment of HIV-1-infected children. Additional data are needed to establish child-specific reference values and to assess the optimal method of TDM.

Integrase inhibitors and cellular immunity suppress retroviral replication in rhesus macaques

We describe the efficacy of L-870812, an inhibitor of HIV-1 and SIV integrase, in rhesus macaques infected with the simian-human immunodeficiency virus (SHIV) 89.6P. When initiated before CD4 cell depletion, L-870812 therapy mediated a sustained suppression of viremia, preserving CD4 levels and permitting the induction of virus-specific cellular immunity. L-870812 was also active in chronic infection; however, the magnitude and durability of the effect varied in conjunction with the pretreatment immune response and viral load. These studies demonstrate integrase inhibitor activity in vivo and suggest that cellular immunity facilitates chemotherapeutic efficacy in retroviral infections.

The relationship between nevirapine plasma concentrations and abnormal liver function tests

Abnormal liver function tests are frequently observed in HIV-infected individuals receiving nevirapine (NVP). Here we investigate the relationship between total and unbound plasma concentrations of NVP and the liver enzymes alanine aminotransferase (ALT) and gamma-glutamyl transferase (gammaGT). HIV-infected individuals [n = 85, 22 female, 34 hepatitis C or B virus (HCV or HBV(+))] receiving NVP (200 mg bd; median duration 66 weeks, range 3-189) and two nucleoside reverse transcriptase inhibitors (NRTIs) were enrolled into this study. Blood samples were taken at C(trough) (12 hr postdose) for measurement of NVP and liver function tests (ALT and gammaGT). Plasma protein bound and unbound drug was separated using ultrafiltration and NVP concentrations quantified using HPLC-MS/MS. A linear relationship was observed between total and unbound NVP C(trough) (r(2) = 0.77, p < 0.0001). Patients with elevated ALT (>37 IU/liter; n = 31) had higher NVP unbound C(trough) than those with ALT within the normal range (median 2268 vs. 1694 ng/ml, p = 0.04) but there was no difference in total C(trough). Logistic regression revealed no association between higher NVP C(trough) and ALT elevations. Significantly higher NVP total and unbound C(trough) were observed in patients with increased gammaGT (>40 IU/liter; n = 63; total 6747 vs. 4530 ng/ml, p = 0.001; unbound 2113 vs. 1557 ng/ml, p = 0.03). Significantly higher unbound NVP C(trough) was observed in HCV/HBV(+) (median 2275 vs. 1726 ng/ml, p = 0.02) and on bivariate analysis, higher NVP C(trough) was associated with HCV/HBV coinfection (chi(2) = 4.228; p = 0.04). Overall we found no strong association between NVP concentrations and hepatotoxicity. Although in this study NVP was well tolerated in HCV/HBV coinfected patients, higher plasma concentrations were observed.

METABOLISM AND EXCRETION OF CAPRAVIRINE, A NEW NON-NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITOR, ALONE AND IN COMBINATION WITH RITONAVIR IN HEALTHY VOLUNTEERS

Metabolism and disposition of capravirine, a new non-nucleoside reverse transcriptase inhibitor, were studied in healthy male volunteers who were randomly divided into two groups (A and B) with five subjects in each group. Group A received a single oral dose of [(14)C]capravirine (1400 mg) and group B received multiple oral doses of ritonavir (100 mg), followed by a single oral dose of [(14)C]capravirine (1400 mg). Mean total recoveries of radioactivity for groups A and B were 86.3% and 79.0%, respectively, with a mean cumulative recovery in urine comparable with that in feces for both groups. Excretion of unchanged capravirine was negligible in urine and low in feces for both groups. The results suggest that capravirine was well absorbed, with metabolism as the principal mechanism of clearance. Capravirine underwent extensive metabolism to a variety of metabolites via oxygenations (mono-, di-, tri-, and tetra-) representing the predominant pathway, glucuronidation, and sulfation in humans. No useful plasma profiles of group A were obtained due to extremely low levels of plasma radioactivity. Analysis of group B plasma indicated that unchanged capravirine was the major radiochemical component, with three monooxygenated products and a glucuronide of capravirine as the major circulating metabolites. Nineteen metabolites were identified using liquid chromatography-multistage ion-trap mass spectrometry methodologies. In summary, coadministration of low-dose ritonavir (a potent CYP3A4 inhibitor) drastically decreased the levels of sequential oxygenated metabolites and markedly increased the levels of the parent drug and primary oxygenated metabolites overall in plasma, urine, and feces.

A Proof‐of‐Concept Study of Short‐Cycle Intermittent Antiretroviral Therapy with a Once‐Daily Regimen of Didanosine, Lamivudine, and Efavirenz for the Treatment of Chronic HIV Infection

BACKGROUND

We previously demonstrated that short-cycle structured intermittent therapy (SIT; 7 days without therapy followed by 7 days with antiretroviral therapy [ART]) with a ritonavir-boosted, indinavir-based, twice-daily regimen maintained suppression of plasma HIV viremia while reducing serum levels of lipids. Adherence to such a regimen may be problematic for certain patients.

METHODS

Eight patients with a history of receiving combination ART that maintained suppression of plasma HIV RNA to <50 copies/mL received a once-daily SIT regimen of didanosine, lamivudine, and efavirenz.

RESULTS

For 7 patients, suppression of plasma HIV RNA to <50 copies/mL was maintained for 60-84 weeks. Four patients with adequate samples had no evidence for an increase in plasma viremia for up to 72 weeks, by use of an assay with a limit of detection of <1 copy/mL. The lack of rebound viremia may be the result of the persistence of efavirenz in plasma on day 7 of the no-therapy period, as was detected in 7 of 7 patients. There was no significant change in CD4(+) T cell counts or serum hepatic transaminase or lipid levels.

CONCLUSION

A once-daily short-cycle SIT regimen maintained suppression of plasma HIV RNA while preserving CD4(+) T cell counts. Such a regimen may have importance in resource-limited settings where the monetary cost of continuous ART is prohibitive.

Diarrhea and reduced levels of antiretroviral drugs: improvement with glutamine or alanyl-glutamine in a randomized controlled trial in northeast Brazil

The effects of therapy with glutamine and alanyl-glutamine on diarrhea and antiretroviral drug levels in patients with acquired immune deficiency syndrome (AIDS) were examined in a randomized, double-blinded, placebo-controlled study in northeast Brazil. Patients with AIDS and with diarrhea and/or wasting were randomized into 4 groups to determine the efficacy of glutamine or high- or low-dose alanyl-glutamine given for 7 days, compared with isonitrogenous glycine given to control subjects. All patients in whom baseline antiretroviral drug levels were determined had low levels 2 h after dosing. Gastrointestinal symptom scores improved with receipt of high-dose alanyl-glutamine (P<.05) or glutamine (P<.01). Antiretroviral drug levels increased in patients given alanyl-glutamine (P=.02) or glutamine (P=.03) by 113% (P=.02) and 14% (P=.01), respectively. Antiretroviral drug resistance mutations were common in all groups. The dose-related efficacy of alanyl-glutamine and glutamine in treating diarrhea and in increasing antiretroviral drug levels shows that these supplements may help to improve therapy for patients with AIDS who have diarrhea and/or wasting in developing, tropical areas.

No relationship between high nevirapine plasma concentration and hepatotoxicity in HIV-1-infected patients naive of antiretroviral treatment or switched from protease inhibitors

OBJECTIVE

A prospective population pharmacokinetic study of nevirapine (NVP) was performed to test the relationship between hepatotoxicity and NVP trough plasma concentration and to identify which covariates could influence NVP pharmacokinetics.

METHODS

All patients [77 HIV-1 (human immunodeficiency virus type 1)-infected patients (128 samples)] were either on first-line antiretroviral therapy or switched from successful therapy containing protease inhibitor. Population pharmacokinetic parameters were estimated by a non-linear mixed-effect modelling method. Hepatotoxicity was evaluated by ASAT (aspartate aminotransferase) plasma level.

RESULTS

No correlation was found between high NVP trough plasma concentration and high ASAT level or the increase of ASAT level on NVP therapy. Age and Caucasian race were found to be significant covariates of NVP clearance (Cl/F). Population pharmacokinetic parameters (rate absorption constant=1.04 h(-1); Cl/F=3.31 h(-1); apparent volume of distribution=92 l) are consistent with previous studies.

CONCLUSION

High NVP trough plasma concentrations are not correlated with hepatotoxicity in our population. NVP clearance is decreased in the elderly patients, suggesting a potential increase of NVP plasma level and the interest of therapeutic drug monitoring for this population.

Design, Synthesis, Anti-HIV Activities, and Metabolic Stabilities of Alkenyldiarylmethane (ADAM) Non-nucleoside Reverse Transcriptase Inhibitors

The alkenyldiarylmethane (ADAM) HIV-1 non-nucleoside reverse transcriptase inhibitors (NNRTIs) are effective anti-HIV agents in cell culture. However, the potential clinical utility of the ADAMs is expected to be limited by the presence of methyl ester moieties that are likely to be metabolized by nonspecific esterases in blood plasma to biologically inactive carboxylic acid derivatives. The present investigation was therefore undertaken to investigate the anti-HIV activities of the ADAMs versus HIV-1(IIIB) and HIV-2(ROD) in MT-4 cells and the stabilities of the biologically active ADAMs in rat plasma. The ADAMs displayed a wide range of metabolic stabilities in rat plasma, with half-lives ranging from 0.9 to 76.6 min. A wide assortment of structural modifications was tolerated, with 18 of the 32 compounds tested displaying EC(50) values between 0.3 and 3.7 microM versus HIV-1(IIIB) in MT-4 cells, 3 compounds in the EC(50) = 13.2-35.4 microM range, and the remaining compounds inactive. Consistent with the mechanism of action of the ADAMs as NNRTIs, they were inactive or displayed comparatively low activity versus HIV-2(ROD). The replacement of the two aromatic methyl ester substituents in one of the most active ADAMs (EC(50) = 0.6 microM) with two methyl thioester groups resulted in an increase in plasma half-life from 5.8 to 55.3 min, while maintaining the antiviral potency at the EC(50) = 1.8 microM level. At the same time, the bis(thioester) modification was less cytotoxic to uninfected MT-4 cells, with a CC(50) of >224 microM versus 160 microM for the parent compound.

Resistance and replication capacity assays: clinical utility and interpretation

Resistance testing has emerged as an important tool for antiretroviral management. Research continues to refine phenotypic susceptibility cut-offs and genotypic interpretation schemes that relate resistance mutations with antiretroviral drug effectiveness. Highly sensitive phenotypic assays have allowed for the recognition of drug hypersusceptibility in HIV, and other studies have related hypersusceptibility to resistance mutations; efforts are ongoing to use what is known about hypersusceptibility to optimize the benefits of antiretroviral therapy. Resistance-associated mutations in several viral genes result in viruses that exhibit reduced replication capacity; assays to measure replication capacity are being developed that may, in the future, be useful in guiding therapy to improve treatment outcomes. This article summarizes a presentation given by Richard H. Haubrich, MD, at the International AIDS Society-USA Sacramento course in November 2003.

Stereospecific chemical and enzymatic stability of phosphoramidate triester prodrugs of d4T in vitro

The phosphoramidate triester prodrug approach is widely used to deliver nucleotide forms of nucleoside analogues into target cells. We investigated the stereoselective stability of a series of prodrugs of the anti-HIV agent 2',3'-didehydro-2',3'-dideoxythymidine (d4T). Chemical stability was evaluated in phosphate buffer at pH values of biological relevance (i.e. pH 2.0, 4.6, 7.4). Enzymatic stability was tested in human plasma, in Caco-2 cell homogenates and monolayers and in rat liver. The compounds were relatively stable to chemical hydrolysis. Between 50 and 70% of unchanged prodrug was recovered after 16h incubation in human plasma, with no stereoselective preference for phosphate diastereoisomers. The p-OMe phenyl derivative, however, was an exception and only 5% of one diastereoisomer was recovered. In Caco-2 cells the stability and stereoselectivity largely depended on the experimental conditions: high enzymatic activity and stereoselectivity was observed in cell homogenates, but not in monolayers. In rat liver S9 fractions the stability profile was similar to that in Caco-2 cells and carboxyl ester cleavage appeared to be the sole mechanism of degradation in both media. The large and unpredictable differences in stereoselective metabolic rate of the pronucleotide series here presented suggest that in vivo circulating levels of intact prodrug could exert profoundly different activity or toxicity due to preferential body distribution of one diastereoisomeric form.

Quality assurance program for clinical measurement of antiretrovirals: AIDS clinical trials group proficiency testing program for pediatric and adult pharmacology laboratories

Clinical trials designed to compare antiretroviral regimens, investigate therapeutic drug monitoring, or measure pharmacometrics often include protease inhibitors (PIs), nonnucleoside reverse transcriptase inhibitors (NNRTIs), and nucleoside reverse transcriptase inhibitors, requiring the measurement of these antiretrovirals in plasma. Within the adult and pediatric AIDS Clinical Trials Group (ACTG), a network of Pharmacology Support Laboratories (PSLs) is a component of the group laboratory infrastructure and conducts these types of pharmacologic assays. The adult ACTG has developed a comprehensive quality assurance program for the conduct of clinical pharmacology protocols, one component of which is the antiretroviral proficiency testing (PT) program that has been implemented between the adult and pediatric pharmacology laboratories of the ACTG. PT testing samples were prepared and distributed in July 2001, February 2002, and July 2002. High, medium, and low concentrations of PIs (indinavir, saquinavir, amprenavir, lopinavir, ritonavir, and nelfinavir) and NNRTIs (nevirapine and efavirenz) were added to drug-free EDTA plasma and distributed, on dry ice, to eight ACTG PSLs. One testing laboratory used liquid chromatography-tandem mass spectrometry, and seven used high-performance liquid chromatography-UV analysis. A result was considered acceptable if it was within 20% deviation of the assigned concentration. For all concentrations of PIs evaluated, 96% of samples tested (430 of 448 measurements) met the acceptance criteria. For both NNRTIs, 100% of samples tested (140 of 140 measurements) met the acceptance criteria. In conclusion, the PT program results presented demonstrate excellent interlaboratory agreement for all antiretrovirals tested and provide support for the merger of plasma concentration data among laboratories for large clinical trials.

Pharmacokinetics and safety of GW433908 and ritonavir, with and without efavirenz, in healthy volunteers

OBJECTIVE

To evaluate the safety and pharmacokinetic interaction between GW433908, ritonavir (RTV), and efavirenz (EFV).

METHODS

In period 1, subjects received either a once daily (QD) regimen of GW433908 1395 mg + RTV 200 mg (Study 1) or a twice daily (bid) regimen of GW433908 700 mg + RTV 100 mg (Study 2) for 14 days. In period 2, subjects received EFV 600 mg QD with either the same GW433908 + RTV regimen as in period 1 (arm 1) or with a GW433908 + RTV regimen that included an additional 100 mg of RTV (arm 2) for 14 days. Amprenavir (APV) pharmacokinetic sampling and safety assessments were performed on the last day of each period.

RESULTS

Plasma APV exposure was not significantly altered when EFV was coadministered with GW433908 700 mg twice daily (BID) + RTV 100 mg BID. Plasma APV exposure was decreased when EFV was coadministered with GW433908 1395 mg QD + RTV 200 mg QD. However, administration of EFV with GW433908 1395 mg QD + RTV 300 mg QD (i.e., adding an extra 100 mg of RTV) was able to negate this interaction. Adverse events were consistent with prior data for each of the separate agents.

CONCLUSION

When EFV is coadministered with the GW433908 700 mg + RTV 100 mg BID regimen, no dosage adjustment is recommended. However, when EFV is coadministered with the GW433908 1400 mg + RTV 200 mg QD regimen, an increase to RTV 300 mg QD is needed to maintain plasma APV exposure.

Evaluation of clinical pharmacist interventions on drug interactions in outpatient pharmaceutical HIV-care

OBJECTIVE

To evaluate the usefulness of intervention in drug interactions of antiretroviral drugs with coadministered agents by a clinical pharmacist in outpatient HIV-treatment.

METHODS

The study design included two intervention arms (A and B), which were both preceded by a control observation period. In arm A, a complete list of the currently used drugs, extracted from pharmacy records was provided to the treating physician. In arm B the same list was provided but with a notification when a drug interaction was present and an advice how to handle this. The infectious disease specialist obtained the information before the patient's visit to the outpatient clinic (time point 0). Three months prior (time point -3) and 3 months after (time point +3) the intervention, pharmacy records were also screened for drug interactions. The number of drug interactions (total and per patient) was determined at the three different time points (-3, 0, +3). In addition, drug interactions encountered at time points -3 and 0 were checked for their presence at time points 0 and +3, respectively, for both intervention arms.

RESULTS

Arms A and B included 115 and 105 patients, respectively. Patient characteristics of both intervention arms were similar at time point 0. The number of interactions and the number of patients with interactions were similar in both intervention arms at time point 0. There were 42 and 40 potential drug interactions in 30 and 24 patients in arms A and B, respectively. The reduction in the number of interactions per patient over time and after intervention was small but significant, and was equal in both intervention arms. The advice of the clinical pharmacist had thus no additional value.

CONCLUSION

Both interventions were effective in reducing the number of drug interactions per patient. The advice of a clinical pharmacist was, however, redundant in the studied setting.

Assessment of cetirizine, an antihistamine, to prevent cutaneous reactions to nevirapine therapy: results of the viramune-zyrtec double-blind, placebo-controlled trial

We conducted a 12-week, multicenter, randomized, double-blind, placebo-controlled trial of cetirizine to assess the ability of antihistamines to prevent nevirapine-associated rash in patients infected with human immunodeficiency virus type 1. Patients initiating treatment with nevirapine were randomized to receive either cetirizine, 10 mg q.d. (104 patients), or placebo (96 patients) during the first 6 weeks of therapy. Rash occurred in 22 (11%) of 200 patients; 10 (9.6%) were in the cetirizine group and 12 (12.5%) were in the placebo group (odds ratio [OR], 0.75; 95% confidence interval [CI], 0.31-1.81; P=.5). Five of 22 rashes were cases of hypersensitivity syndrome. The rate of nevirapine discontinuation due to rash was similar in the 2 groups (7.7% and 6.25% in the cetirizine and placebo groups, respectively; P=.4). Multivariate analysis showed no treatment-group effect but indicated that age >40 years (OR, 3.83; 95% CI, 1.4-10.46; P=.008) was associated with an increased risk of rash. Cetirizine has no preventive effect on nevirapine-associated rash.

Differential diffusions of indinavir and lopinavir in genital secretions of human immunodeficiency virus-infected women

Plasma and cervicovaginal secretion (CVS) samples were collected from 19 human immunodeficiency virus type 1-infected women on lopinavir- or indinavir-containing regimens. Lopinavir and indinavir were detectable in 29 and 93% of CVS samples, respectively, a finding that may be ascribed to these drugs' differences in protein binding and pK(a). The relationship between lopinavir and indinavir pharmacodynamics and viral evolution in the female genital tract should be assessed over time.

Determination of ddATP levels in human immunodeficiency virus-infected patients treated with dideoxyinosine

Clinical failures of the highly active antiretroviral therapy could result from inefficient intracellular concentrations of antiviral drugs. The determination of drug contents in target cells of each patient would be useful in clinical investigations and trials. The purpose of this work was to quantify the intracellular concentration of ddATP, the active metabolite of dideoxyinosine (ddI), in peripheral blood mononuclear cells (PBMCs) of human immunodeficiency virus (HIV)-infected patients treated with ddI. We have raised antibodies against ddA-citrate, a stable isostere of ddATP selected on the basis of its structural and electronic analogies with ddATP. The anti-ddA-citrate antibodies recognized ddATP and ddA with nanomolar affinities and cross-reacted neither with any of the nucleotide reverse transcriptase inhibitors used in HIV therapy nor with their phosphorylated metabolites. The three phosphorylated metabolites of ddI (ddAMP, ddADP, and ddATP) were purified by anion exchange chromatography and the amount of each metabolite was determined by radioimmunoassay with or without prior phosphatase treatment. The intracellular levels of the three ddI metabolites were measured both in an in vitro model and in PBMCs of HIV-infected patients under ddI treatment. The possibility to measure intracellular levels of ddATP from small blood samples of HIV-infected patients treated with ddI could be exploited to develop individual therapeutic monitoring.

Detection of nevirapine in plasma using thin-layer chromatography

BACKGROUND

Nevirapine (NVP) is widely prescribed in resource-poor settings to pregnant women for treatment and prevention of HIV infection. High rates of misreported adherence, however, have compelled clinicians to find alternative methods to ensure systemic drug exposure. This report describes a fast, inexpensive thin-layer chromatography (TLC) method to detect the presence of NVP in human plasma.

METHODS

Human plasma was spiked with various concentrations of NVP. NVP was subsequently isolated using solid-phase extraction and visualized with TLC. Clinical samples with NVP concentrations predetermined by high-performance liquid chromatography were used to validate the TLC method.

RESULTS

NVP was detected at concentrations as low as 60 ng/mL. The lower limit of detection was set at 100 ng/mL due to the clear spot definition at this concentration. The turnaround time for assay results averages several hours, and costs associated with the assay are considerably below standard drug quantitation techniques.

CONCLUSION

TLC provides a rapid, sensitive, and economical tool to qualitatively measure NVP in plasma. This method offers clinicians in resource-poor settings an alternative approach for measuring adherence, particularly in developing-world regions where NVP use is common and there is an immediate need to prevent mother-to-child HIV transmission.

Development and validation of a reversed-phase liquid chromatographic method for analysis of D4T (Stavudine) in rat plasma

An improved and simplified high-performance liquid chromatographic (HPLC) method at UV detection 265 nm is presented for the determination of d4T in rat plasma. The mobile phase consists of methanol-distilled water-acetic acid in the 23:77:0.2 (v/v) ratio. Quantification is achieved by the peak-area ratio method with reference to the internal standard. This paper presents linearity, accuracy, precision, limit of quantification and limit of detection, specificity-selectivity and sample stability data. Based on the intra and inter-day validation, all coefficients of variation (CV) were found less than 15%. The assay is sufficiently rapid and sensitive and was applied in a pharmacokinetic study in rats.