Significant effects of tipranavir on platelet aggregation and thromboxane B2 formation in vitro and in vivo.

OBJECTIVES: In the past, bleeding events have been described for patients with haemophilia taking HIV-1 protease inhibitors. Recently, the FDA published a warning concerning intracranial haemorrhage in patients taking the HIV-1 protease inhibitor tipranavir co-administered with ritonavir. METHODS: We investigated (i) platelet aggregation in vivo in HIV-1-infected adult patients (n = 5) immediately before and 2 and 4 h after dosing of tipranavir/ritonavir 500/200 mg. To further characterize the effects, we then evaluated (ii) platelet aggregation and (iii) thromboxane B2 (TxB2) formation (ELISA) with increasing tipranavir concentrations (TPV(conc)) in vitro of up to 100,000 ng/mL. Platelet aggregation was stimulated either with 2 microM ADP (ADP) or 10 mg/L collagen (COL). TPV(conc) were measured with validated EPI-LC-MS/MS. Intraindividual comparisons of values at time points and TPV(conc), respectively, were carried out with repeated samples ANOVA. RESULTS: Platelet aggregation (mean, maximal light transmission A(max)) was significantly decreased in patients 4 h post-dose in collagen- (from 79.8% to 57.1%; P < 0.001) and in ADP-stimulated (from 58.5% to 54.0%; not significant) samples at a median (range) TPV(conc) of 62 500 ng/mL (22,990-67,500). These results could be reproduced in vitro at TPV(conc) 50,000 ng/mL (A(max)ADP/A(max)COL = 20.7/36.9%; P = 0.003/<0.001) and 100 000 ng/mL (A(max)ADP/A(max)COL = 14.5/17.1%; P < 0.001/<0.001). Median (range) TxB2 concentrations were reduced (P = 0.07) from 327 ng/mL (187-500) at baseline to 265 ng/mL (152-428) at 5000 ng/mL and were significantly reduced (P < 0.001) to 187 ng/mL (81-362) at a TPV(conc) of 50,000 ng/mL, respectively. CONCLUSIONS: Five HIV-1-infected patients on tipranavir-containing highly active antiretroviral therapy presented marked decreases in platelet aggregation. In vitro these effects were reproduced and decreased TxB2 formation was also demonstrated. Inhibition of platelet aggregation while receiving tipranavir treatment might contribute to increased risk of bleeding.

Platelet-leucocyte adhesion markers before and after the initiation of antiretroviral therapy with HIV protease inhibitors.

INTRODUCTION: Thromboembolic complications under antiretroviral therapy (ART) have been described in the past. In particular, the influence of protease inhibitors (PIs) on platelet activation and coagulation is currently under discussion. METHODS: HIV-1-infected, PI-naive adults (n = 18) were investigated before and 4 weeks after the start of the ART, consisting either of boosted PI regimens (n = 13) plus reverse transcriptase inhibitors (RTIs) or a double PI regimen (n = 5) without RTI co-medication. Administered PIs were saquinavir (n = 15), lopinavir (n = 4), fosamprenavir (n = 2) and atazanavir (n = 2). Platelet CD62P, CD40L (%+ cells) and PAC-1 binding [mean fluorescence intensity (MFI)] as well as monocyte CD11b (MFI) and monocyte-associated CD41 (%+ cells and MFI) expression were assessed by flow cytometry with or without platelet stimulation. To investigate the influence of platelets on coagulation, the endogenous thrombin potential (ETP) [render fluorescence units (RFI)] was determined. RESULTS: CD62P, PAC-1 binding and CD11b expression remained unchanged. In contrast, the mean+/-SD MFI of CD40L (from 18.2+/-9.0 to 25.5+/-10.4, P = 0.038) and CD41 (from 446.1+/-213.8 to 605.0+/-183.8, P = 0.010) as markers for increased platelet-leucocyte interaction increased significantly. The collagen-induced ETP time-to-peak was altered significantly from 23.8+/-11.4 to 17.0+/-4.2 min (P = 0.028), although the ETP RFI peak showed no evidence for increased procoagulatory capacity (47.1+/-18.6 to 57.3+/-19.9, P = 0.085). CONCLUSIONS: Effects of the evaluated PI HIV therapy on platelet function assessed under field conditions seem to be minor, not affecting all investigated parameters. We found no evidence for increased platelet activation under PI-containing ART. However, CD41 as a marker for increased platelet-leucocyte interaction and CD40L, which can contribute to atherosclerosis, increased significantly.

Tenofovir comedication does not impair the steady-state pharmacokinetics of ritonavir-boosted atazanavir in HIV-1-infected adults.

OBJECTIVE: Our objective was to evaluate the steady-state pharmacokinetics of ritonavir-boosted atazanavir when coadministered with tenofovir in HIV-1-infected adult patients. DESIGN: Forty adult HIV-1-infected patients received either atazanavir/ritonavir 300/100 mg once daily and nucleoside reverse transcriptase inhibitors with (n = 20) or without (n = 20) tenofovir-disoproxil fumarate (tenofovir-DF) 300 mg once daily. Twenty-four-hour pharmacokinetics were assessed after at least 2 weeks of therapy according to a standardised therapeutic drug monitoring protocol. METHODS: Atazanavir/ritonavir plasma concentrations were measured by liquid chromatography tandem mass spectrometry, and the geometric means of minimum and maximum concentrations (C(min), C(max)), the area under the time-concentration curve (AUC), half-life (t(1/2)) and total clearance (CL(tot)) were subject to a matched pairs-analysis. Patients' pairs were matched for gender, ethnicity, weight and Center for Disease Control and Prevention (CDC) status. RESULTS: The respective geometric means (90% CI) for atazanavir C(min), C(max) and AUC with tenfovir vs. without tenofovir were 405 (314-523) vs. 417 (304-572) ng/ml, 3,022 (2,493-3,664) vs. 2,817 (2,341-3,390) ng/ml and 34,822 (29,315-41,363) vs. 32,101 (26,206-39,321) ng x h/ml showing no significant differences between the groups. Atazanavir plasma concentrations measured at week 5 of therapy or later were lower than in the first 4 weeks (T-test for C(max), p = .080; AUC, p = .050 and CL(tot), p = .051). CONCLUSIONS: The coadministration of tenofovir-DF did not impair the plasma concentrations of ritonavir-boosted atazanavir in a pharmacokinetic analysis of patient pairs matched for gender, ethnicity, weight and CDC status.

A comparison of the steady-state pharmacokinetics of nevirapine in men, nonpregnant women and women in late pregnancy.

AIMS: To evaluate the pharmacokinetics of nevirapine and any possible influencing factors in pregnant women (n = 16), nonpregnant women (n = 13) and men (n = 14), who received nevirapine 200 mg twice daily together with nucleoside reverse transcriptase inhibitors. METHODS: Blood samples were taken for 12 h at steady state. Nevirapine concentrations were measured by liquid chromatography-tandem mass spectrometry. The influence of gender, age, body weight and comedication on minimum and maximum concentrations (C(min), C(max)), area under the concentration-time curve (AUC), total clearance (CL(tot)), half-life (t(1/2)) and volume of distribution (V(d)) was analysed by multivariate techniques. RESULTS: Mean [95% confidence interval (CI)]C(max), AUC(ss) and clearance were 5221 ng ml(-1) (4267, 6175), 50 789 ng (-1)h ml(-1) (43 453, 58 125) and 69.9 ml min(-1) for men, 5871 ng ml(-1) (4848, 6895), 57 045 ng h(-1) ml(-1) (45 997, 68 093) and 65.6 ml min(-1) for nonpregnant women and 4505 ng ml(-1) (3644, 5366), 44 579 ng h(-1) ml(-1) (36 564, 52 594) and 82.1 ml min(-1) for pregnant women. The differences between pregnant and nonpregnant women (% difference, 95% CI) in C(max) (-30.3; -28.5, -33.0), AUC(ss) (-28.0; - 25.8, - 29.5) and clearance (20.2; 26.6, 15.6) reached statistical significance (P = 0.010, P = 0.028 and P = 0.028, respectively). The multivariate analysis underscored the influence of bodyweight on the plasma exposure to nevirapine. CONCLUSIONS: Pregnant women exhibited an increased nevirapine clearance and comparably low plasma concentrations, whereas women with a low bodyweight achieved high plasma nevirapine concentrations. The large variability in nevirapine concentrations in women may lead to loss of efficacy and viral resistance, or drug toxicity, and therefore these patients should be monitored frequently.