Michael Kurowski

Therapeutic drug monitoring in HIV infection: Current status and future directions

Background: Highly active antiretroviral therapy (HAART) can suppress viral replication and prolong patient life substantially. However, HAART can fail for a number of reasons, including incomplete adherence, pharmacokinetic factors and the emergence of resistance. Because the number of possible antiretroviral combinations is limited, the use of existing treatment options must be optimized. Whether the application of therapeutic drug monitoring (TDM) in routine clinical practice may help with this purpose remains a subject of debate. However, TDM has been introduced in some centres despite the lack of guidelines for optimal use of this test. Objective: In October 2000, a panel of experts met in Perugia, Italy, to discuss the key issues surrounding the introduction of TDM into routine clinical practice. The purpose of the meeting was to achieve a consensus among panel members on the following issues: (i) validity of data suggesting the utility of TDM in HAART; (ii) patient categories and clinical settings in which TDM may be of most benefit; (iii) target levels of antiretroviral agents; (iv) influence of covariables on target levels of drugs; (v) blood sampling and dosage adjustment strategies; and (vi) future research steps needed to elucidate issues regarding the applicability of TDM in clinical practice. Outcome: This report, which has been updated to include data published or presented at conferences up to the end of August 2001, summarizes the data presented and issues discussed at the meeting. This article will guide the reader through the data and discussions that have allowed the panel to formulate a series of position statements regarding the current status and future applications of TDM in antiretroviral therapy. These statements have been formulated to provide suggestions for the design of future TDM clinical trials, as well as to provide useful points of reflection for centres in which TDM is already in use.

Ertapenem Pharmacokinetics and Impact on Intestinal Microflora, in Comparison to Those of Ceftriaxone, after Multiple Dosing in Male and Female Volunteers

ABSTRACT The pharmacokinetics of ertapenem and ceftriaxone were investigated in an open, randomized, two-period crossover study after single- and multiple-dose administration in 10 healthy volunteers (five women and five men). Both antibiotics were administered intravenously once daily for 7 days at dosages of 1 g (ertapenem) and 2 g (ceftriaxone). The concentrations of the antibiotics in serum and urine were quantified by the agar well diffusion method bioassay and, in addition, for ertapenem only, by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). For ertapenem the maximum concentration of the drug in plasma (Cmax) was 256 mg/liter, the half-life was 20.7 h, and the area under the plasma concentration-time curve (AUC) was 830 mg · h/liter. The concentrations in fecal samples were (mean value) 37.2 and 32.7 mg/kg on day 4 and day 8, respectively. Ceftriaxone exhibited a mean Cmax of 315 mg/liter, a half-life of 7.6 h, and an AUC of 1,556 mg · h/liter. The mean concentrations in fecal samples were 153 and 258 mg/kg on day 4 and day 8, respectively. No accumulation of ertapenem or ceftriaxone was detected at steady state. A slightly but significantly decreased AUC for ertapenem was detected for the female volunteers. No serious adverse event was observed. Both antibiotics induced a marked decrease in the anaerobic microflora (4-log-unit decreases in lactobacilli, bifidobacteria, clostridia, and bacteroides) and Escherichia coli, whereas the number of enterococci increased (4 log units). A slight overgrowth of yeasts was observed with both regimens. In all cases the microflora returned to normal levels on days 21 to 35.

Atazanavir enhances saquinavir hard-gel concentrations in a ritonavir-boosted once-daily regimen

Objective: To determine the pharmacokinetics of saquinavir hard-gel capsules/ ritonavir/atazanavir co-administered once daily at 1600/100/300 mg in HIV-infected individuals. Methods: Eighteen patients receiving saquinavir/ritonavir switched to 1600/100 mg once daily a minimum of 3 days before the study. On study day 1, levels of saquinavir and ritonavir were determined over 24 h. Atazanavir (300 mg once daily) was then added to the regimen. On day 11, a pharmacokinetic analysis was performed. Atazanavir was discontinued on day 32. Drug concentrations were measured by high-pressure liquid chromatography–tandem mass spectrometry. Geometric mean ratios (GMR) and 95% confidence intervals (CI) were used to compare saquinavir and ritonavir pharmacokinetic parameters, with and without atazanavir. A safety analysis was performed at screening, days 1, 11, 32 and follow-up. Results: After the addition of atazanavir, statistically significant increases in saquinavir trough plasma concentration (Ctrough GMR, 95% CI 2.12, 1.72–3.50), maximum plasma concentration (Cmax 1.42, 1.24–1.94), area under the plasma concentration–time curve from 0–24 h (AUC0–24 1.60, 1.35–2.43) and ritonavir Cmax (1.58, 1.32–2.08), AUC0–24 (1.41, 1.22–1.74) were observed. The pharmacokinetics of atazanavir compared with those obtained in patients receiving atazanavir/ritonavir without saquinavir. Four patients developed scleral icterus and two jaundice. Total and unconjugated bilirubin increased approximately fivefold during atazanavir therapy. Conclusion: The addition of atazanavir to saquinavir/ritonavir increased saquinavir Ctrough, Cmax and AUC0–24 by 112, 42 and 60%. Ritonavir Cmax and AUC0–24 increased by 34 and 41%. The regimen was well tolerated, with no significant change in laboratory parameters, except for the occurrence of hyperbilirubinemia.

Antiviral efficacy, tolerability and pharmacokinetics of efavirenz in an unselected cohort of HIV-infected children

OBJECTIVES To obtain data on the pharmacokinetics of efavirenz in children in clinical practice. METHODS HIV-1-infected children received efavirenz capsules or tablets in accordance with manufacturers dosing recommendations. Plasma was collected at regular visits and analysed by HPLC. The therapeutic range of efavirenz was defined as 1.0-4.0 mg/L. RESULTS Thirty-three children were included. Median (range) age, body weight, dose and dose/kg were 8.2 (2.1-16.7) years, 24 (12-62) kg, 300 (200-800) mg and 13.3 (9.7-22.5) mg/kg, respectively. Median (range) efavirenz plasma concentration at first sampling was 2.8 (0.13-11.6) mg/L. Plasma concentrations were not dependent on age (P = 0.97) or dose/kg (P = 0.87). A total of 307 efavirenz plasma concentrations were determined. Forty-five samples (14.7%) contained >4.0 mg/L, and 27 samples (8.8%) contained <1.0 mg/L. Eight children (24%) reported persistent adverse events probably caused by efavirenz [concentration problems (5), sleep disorder (1), psychotic reaction (1) and seizure (1)]; six discontinued efavirenz for this reason. A non-significant trend existed towards a higher proportion of toxic efavirenz plasma concentrations (>4.0 mg/L) in subjects who reported efavirenz adverse events: 25.9% versus 12.8% (P = 0.23; t-test). Viral load was <50 copies/mL in all 27 subjects who continued efavirenz, despite occasional subtherapeutic efavirenz plasma concentrations in 12 children. The occasional subtherapeutic levels suggest that temporal non-adherence was present. CONCLUSIONS Efavirenz as part of highly active antiretroviral therapy was highly effective in children able to tolerate the drug. Therapeutic drug monitoring (TDM) as part of toxicity management may prevent discontinuation in a subset of patients. Temporal non-adherence occurs frequently. TDM may allow initiation of adherence interventions before viral load becomes detectable.

Placental transfer and pharmacokinetics of lopinavir and other protease inhibitors in combination with nevirapine at delivery.

Background:Antiretroviral combination therapies, including nevirapine (NVP) and protease inhibitors (PI), are increasingly used in the treatment and for the prophylaxis of vertical HIV-1 transmission in HIV-1 infected pregnant women. Objective:To determine pharmacokinetics and placental transfer of NVP and different PI in pregnancy we measured drug levels in maternal and foetal compartments at the day of delivery. Design and Methods:We conducted a prospective study in 40 eligible HIV-1 infected pregnant women who gave birth in our hospital. A pre-dose to 6 h post-dose steady-state pharmacokinetic analysis (n = 35) of the drugs on the day of the scheduled Caesarean section was performed. In addition cord blood and amniotic fluid drug levels were measured (n = 40). Results:In all women NVP plasma concentrations (n = 20) were below the recommended level. PI plasma concentrations (nelfinavir, n = 5; saquinavir, n = 3; lopinavir, n = 10; ritonavir, n = 13) were extremely variable. Cord blood and amniotic fluid drug levels suggested that NVP passes the placenta unrestricted whereas PI were detected in smaller concentrations in the foetal compartment. Conclusions:Because of the changed pharmacokinetics of antiretroviral drugs in pregnancy therapeutic drug monitoring could be important and dose adjustment should be considered. The minimal placental transfer of PI is desirable from the perspective that the foetus is protected from potentially teratogenic agents. However, it is not known if antiretroviral compounds in the foetal compartment contribute to the risk reduction of vertical HIV-1 transmission, and whether the property of missing placental transfer is in fact beneficial for the newborn.

Atovaquone maintenance therapy prevents reactivation of toxoplasmic encephalitis in a murine model of reactivated toxoplasmosis.

ABSTRACT Acute therapy with pyrimethamine plus sulfadiazine is the treatment of choice for reactivated toxoplasmic encephalitis (TE). Acute therapy is followed by lifelong maintenance therapy (secondary prophylaxis) with the same drugs at lower dosages. The use of pyrimethamine plus sulfadiazine is hampered by severe side effects including allergic reactions and hematotoxicity. Alternative treatment regimens with pyrimethamine plus clindamycin or other antiparasitic drugs are less efficacious. Atovaquone nanosuspensions show excellent therapeutic effects for “acute” intravenous (i.v.) treatment of reactivated TE in a murine model. In the present study, the therapeutic efficacy of atovaquone for oral “maintenance” therapy was investigated. Mice with a targeted mutation in the interferon regulatory factor 8 gene were latently infected with Toxoplasma gondii, developed reactivated TE, and received acute i.v. therapy with atovaquone nanosuspensions. Mice were then treated orally with atovaquone suspension or other antiparasitic drugs to prevent relapse of TE. Maintenance therapy with atovaquone at daily doses of 50 or 100 mg/kg (body weight) protected mice against reactivated TE and death. This maintenance treatment was superior to standard therapy with pyrimethamine plus sulfadiazine. The latter combination was superior to the combination of pyrimethamine plus clindamycin. Inflammatory changes in the brain parenchyma and meninges, as well as parasite numbers, in the brains of mice confirmed the therapeutic efficacy of atovaquone for maintenance therapy. Atovaquone was detectable in sera, brains, livers, and lungs of infected mice by high-performance liquid chromatography and/or mass spectrometry. In conclusion, atovaquone appears to be superior to the standard maintenance therapy regimens in a murine model of reactivated TE. The therapeutic efficacy of atovaquone for maintenance therapy against TE should be further investigated in clinical trials.

Saquinavir drug exposure is not impaired by the boosted double protease inhibitor combination of lopinavir/ ritonavir

Objective: To assess the pharmacokinetic interaction of saquinavir and lopinavir/ritonavir. Design: Patients from the Frankfurt HIV cohort with limited reverse transcriptase inhibitor (RTI) options received the protease inhibitor (PI) combination of saquinavir (soft-gel capsules, 1000 mg twice a day) plus lopinavir/ritonavir (400/100 mg twice a day), without RTI (LOPSAQ group). A control group received the same doses of saquinavir and ritonavir plus two to three RTI (RITSAQ group). A steady-state 12 h pharmacokinetic assessment was performed. Methods: Plasma levels of saquinavir, ritonavir and lopinavir were determined by liquid chromatography–tandem mass spectrophotometry. Minimum and maximum plasma concentrations (Cmin and Cmax), the clearance (Cltot) and the area under the concentration time curve (AUC) were calculated. Results: Data were collected from 45 patients (LOPSAQ) and 32 patients (RITSAQ). There was no significant difference between the groups for median saquinavir Cmin, Cmax, Cltot and AUC (LOPSAQ: 543 ng/ml, 2300 ng/ml, 1020 ml/min and 16 977 ng*h/ml; RITSAQ: 427 ng/ml, 2410 ng/ml, 1105 ml/min and 15 130 ng*h/ml). Median ritonavir Cmin, Cmax and AUC were lower, the Cltot was higher in the LOPSAQ group (78 ng/ml, 428 ng/ml and 2972 ng*h/ml, 551 ml/min) compared with RITSAQ (194 ng/ml, 683 ng/ml and 6506 ng*h/ml, 266 ml/min; P < 0.001). Lopinavir levels were similar to historical data. Conclusion: Effective plasma levels of both saquinavir and lopinavir can be achieved by the co-administration of saquinavir soft-gel capsules and lopinavir/ritonavir. This boosted double PI combination could be an effective option for patients with limited RTI options.

Persistence of nevirapine in breast milk and plasma of mothers and their children after single-dose administration

OBJECTIVES Nevirapine is widely used in the developing world for the prevention of mother-to-child transmission (PMTCT) of HIV. A single mutation in the HIV genome is sufficient to lead to significant nevirapine resistance. Persistence of low-level drug concentrations in body compartments can foster resistance formation. In this study, concentration-time courses of nevirapine after single-dose administration were analysed over an extended post-partum period. PATIENTS AND METHODS Breast milk and plasma samples of 62 HIV-positive Ugandan mother-child pairs who had received single-dose nevirapine were collected at delivery and 1, 2 and 6 weeks post-partum. Nevirapine concentrations were quantified by LC/tandem-mass-spectrometry using a quantification limit of 15 ng/mL, and a population pharmacokinetic (PK) analysis was performed. RESULTS Concentration-time profiles in breast milk, maternal plasma and child plasma showed similar shapes. At week 1, median nevirapine concentrations were 164 ng/mL in maternal plasma, 114 ng/mL in breast milk and 183 ng/mL in child plasma. The population PK model predicted nevirapine concentrations>10 ng/mL (IC50 for nevirapine) for 13 days in breast milk, 14 days in maternal plasma and 18 days in child plasma in 80% of the samples. CONCLUSIONS Nevirapine concentrations were present for 2-3 weeks in the three compartments. The concentrations are probably sufficiently high to protect most breastfed children from HIV transmission during the first 2 weeks. The long presence of slowly decreasing levels of nevirapine is likely to induce resistance formation. Post-natal addition of antiretrovirals for 1 week only, as recommended in the current PMTCT guidelines, will not suffice to avoid nevirapine resistance formation.

Nevirapine Significantly Reduces the Levels of Racemic Methadone and (R)-Methadone in Human Immunodeficiency Virus-Infected Patients

ABSTRACT Methadone is metabolized by various isoforms of the cytochrome P450 family, which can be induced by many drugs, including nevirapine. The objective of the present study was to determine the effects of coadministration of nevirapine and methadone on the dose-adjusted areas under the concentration-time curves (AUCs) of racemic and (R)-methadone. Twenty-five human immunodeficiency virus-infected subjects taking stable single daily doses of racemic methadone or (R)-methadone were included in this prospective, single-crossover trial. At the baseline, nevirapine was either started as part of a new regimen containing two nucleoside reverse transcriptase inhibitors (NRTIs) or added to an ongoing NRTI regimen. Patients could increase their methadone doses if withdrawal symptoms developed. Twelve-hour pharmacokinetic profiles were obtained before and 28 days after the start of nevirapine treatment. The total concentrations of methadone and its inactive metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), in serum were determined by liquid chromatography-tandem mass spectrometry. Among the 20 evaluable patients, coadministration of nevirapine significantly decreased the mean dose-adjusted AUC of methadone by 41%. AUC reductions were similar for patients taking racemic methadone (37%; n = 11) and (R)-methadone (44%; n = 9). AUC changes ranged from mild increases in three patients to decreases of up to 70%. Fourteen of 20 patients required additional methadone due to withdrawal symptoms. However, the median dose increase was only 15%, which was less than that which would have been expected from the pharmacokinetic data. The AUC of EDDP increased significantly, by 35%. Methadone dose adjustments are justified when methadone is coadministered with nevirapine. Due to extensive variability, the adjustments must be tailored to the individual patients needs.

Severe CNS side-effect and persistent high efavirenz plasma levels in a patient with HIV/HCV coinfection and liver cirrhosis

We describe an HIV/HCV coinfected patient with liver cirrhosis, who experienced severe CNS side-effects during efavirenz-based HIV therapy. Plasma levels of efavirenz were 10 times the upper limit and remained elevated (at twice the upper limit) 4 weeks after cessation of therapy. Efavirenz resistance (K103N) developed and was probably due to ‘functional’ monotherapy.