Limited sampling strategy for the estimation of systemic exposure to the protease inhibitor nelfinavir.

Therapeutic drug monitoring (TDM) of antiretroviral drugs has been proposed as a means of optimizing response to highly active antiretroviral therapy (HAART) in HIV infection because suboptimal exposure to these agents may lead to the development of resistant viral strains and subsequent therapeutic failure. The area under the curve (AUC), though considered to make the best estimate of total drug exposure, requires repeated blood sampling. The authors investigated the predictability of individual nelfinavir (NFV) concentrations at different time points for the AUC and tried to find the best sampling time for the abbreviated AUC to predict NFV total body exposure. A total of 99 NFV AUC0-12h values were measured in 99 patients receiving a 1250-mg oral dose twice a day. Venous blood samples were collected at baseline (predose, 0) and 1, 2, 3, 4, 5, 6, 8, and 12 hours postdose. A stepwise forward-selection, multiple-regression technique was chosen to assess the relative importance of single and combination concentration time points to predict the AUC calculated from the entire pharmacokinetic profile. Data were split into a development set and a validation set. The development set contained 49 randomly selected HIV patients. Of these, 22 HIV patients were coinfected with HCV, 7 with and 15 without cirrhosis. One-point predictors provided the lowest prediction precision, but predictive performance improved after the first 2 hours postdose. Plasma concentrations at 0 and 4 hours after the oral dose were most predictive if 2 variables were used in the regression equation. The AUC could be estimated from data for these 2 samples by using the following equation: AUC0-12 = 3.0 + 2.7 (C0) + 6.4 (C4), r = 92. The predictive performance of 2-point predictors at 0 and 4 hours (C0 + C4) was validated by comparing their ability to predict the full AUC in a validation set representative of HIV/HCV patients (n = 28) and HIV/HCV patients, with (n = 8) and without (n = 14) cirrhosis. The results showed a mean bias ranging from +2.7% in HIV/HCV patients to -6.0% in HCV coinfection with cirrhosis. The authors conclude that this result is clinically significant. The limited sampling strategy (LSS) described could be used in clinical practice for the easy assessment of the total exposure to NFV in HIV/HCV patients, both with and without cirrhosis.

Clinical pharmacokinetics of nelfinavir and its metabolite M8 in human immunodeficiency virus (HIV)-positive and HIV-hepatitis C virus-coinfected subjects.

In order to evaluate the potential risk of nelfinavir (NFV) accumulation in human immunodeficiency virus (HIV)-hepatitis C virus (HCV)-coinfected patients with liver disease, we investigated the concentrations of NFV and M8, the active metabolite of NFV, in plasma HIV-positive (HIV+) patients coinfected with HCV. A total of 119 HIV+ subjects were included in our study: 67 HIV+ patients, 32 HIV+ and HCV-positive (HCV+) patients without cirrhosis, and 20 HIV+ and HCV+ patients with cirrhosis. Most of the enrolled patients (chronically treated) were taking NFV at the standard dosage of 1,250 mg twice a day. To assay plasma NFV and M8 concentrations, patients underwent serial plasma samplings during the dosing interval at steady state. Plasma NFV and M8 concentrations were measured simultaneously by a high-performance liquid chromatography method with UV detection. The HIV+ and HCV+ patients with and without cirrhosis had significantly lower NFV oral clearances than the HIV+ and HCV-negative individuals (28 and 58% lower, respectively; P < 0.05), which translated into higher areas under the concentration-time curves for cirrhotic and noncirrhotic patients. The NFV absorption rate was significantly lower in cirrhotic patients, resulting in a longer time to the maximum concentration in serum. The mean ratios of the M8 concentration/NFV concentration were significantly lower (P < 0.05) in HIV+ and HCV+ subjects with cirrhosis (0.06 +/- 0.074) than in the subjects in the other two groups. The mean ratios for M8 and NFV were not statistically different between HIV+ and HCV-negative patients (0.16 +/- 0.13) and HIV+ and HCV+ patients without cirrhosis (0.24 +/- 0.17), but the interpatient variability was high. Our results indicate that the pharmacokinetics of NFV and M8 are altered in HIV+ and HCV+ patients, especially those with liver cirrhosis. Therefore, there may be a role for therapeutic drug monitoring in individualizing the NFV dosage in HIV-HCV-coinfected patients.