Biomedical subjects

Lisa M Almond

Publications and source records attributed to Lisa M Almond.

4 recordsLinked to original sources

PubMed2005

Intracellular and plasma pharmacokinetics of efavirenz in HIV-infected individuals.

OBJECTIVES: The site of action of efavirenz is inside HIV-infected cells. Measurement of intracellular (IC) concentrations of efavirenz may therefore provide further understanding of therapeutic failure, especially where virological rebound occurs despite adequate plasma levels, and a lack of detectable viral resistance. Here, we determined IC and plasma pharmacokinetics of efavirenz and their relationship with plasma protein binding and P-glycoprotein (P-gp, an active drug efflux transporter) expression. PATIENTS AND METHODS: Venous blood samples from 10 HIV-infected patients receiving efavirenz (600 mg once a day plus two nucleoside reverse transcriptase inhibitors) were collected over the 24 h dosing interval. Plasma and peripheral blood mononuclear cells (PBMCs) were isolated. Plasma protein bound and unbound efavirenz were separated using ultrafiltration. IC (or cell-associated), total plasma and unbound plasma efavirenz levels were quantified using HPLC-UV. P-gp expression was measured by flow cytometry. Area under the concentration-time curves (AUC0-24) were then calculated using non-compartmental analyses and the IC accumulation expressed as a ratio of IC to plasma AUC0-24. RESULTS: The median (range) % unbound and IC accumulation ratio was 0.6% (0.4-1.5%) and 1.3 (0.7-3.3), respectively. There was a linear relationship between IC and total AUC0-24 (r2= 0.59, P = 0.01) but not unbound AUC0-24 (r2= 0.13, P = 0.75). An inverse correlation between IC AUC0-24 and % unbound was observed (r2= 41, P = 0.05). There was no relationship between IC AUC0-24 and P-gp expression on the cell surface (r2< 0.01, P = 0.98). CONCLUSIONS: There was a direct relationship between % bound efavirenz in plasma and IC accumulation implying that the IC accumulation of efavirenz is related to binding to IC proteins or other cellular constituents. Studies investigating the unbound concentration of antiretrovirals inside the cell are now required.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

Intracellular and plasma pharmacokinetics of nevirapine in human immunodeficiency virus-infected individuals.

BACKGROUND AND OBJECTIVE: Plasma concentrations of nevirapine have been linked to human immunodeficiency virus (HIV) treatment outcome. However, because the site of action of nevirapine is within HIV-infected cells, intracellular concentrations may better relate to antiviral exposure. Investigation of factors that alter the intracellular pharmacokinetics of nevirapine may also aid in our understanding of therapeutic failure. Our objective was to determine intracellular (or cell-associated) nevirapine concentrations over the full dosing interval and to relate protein binding and P-glycoprotein (P-gp) expression to intracellular exposure. METHODS: Plasma and peripheral blood mononuclear cells were isolated from blood samples taken from 10 HIV-infected patients at 0, 2, 4, 8, and 12 hours after dosing. Intracellular and plasma (total and unbound) concentrations were determined by liquid chromatography-tandem mass spectrometry, and the ratios of intracellular to total plasma exposure (area under the concentration-time curves) were calculated. P-gp expression was measured by flow cytometry. RESULTS: The median intracellular accumulation ratio was 0.005 (range, 0.001-0.054) and remained unchanged over the dosing interval. There was an association between higher plasma concentrations and lower cellular concentrations of nevirapine (total r(2) = 0.62, P = .007). There was no relationship between percent unbound nevirapine and intracellular nevirapine. There was a correlation between higher plasma nevirapine exposure and higher P-gp expression (r(2) = 0.77, P = .03), whereas intracellular nevirapine exposure decreased with higher P-gp expression (r(2) = 0.62, P = .01). CONCLUSIONS: The intracellular accumulation of nevirapine was low, did not change over the dosing interval, and was not related to protein binding. In this small study, cells with higher P-gp expression had lower cellular concentrations of nevirapine. Further studies are required to explore the influx and efflux transporter profile of this drug.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2004

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.

Alanine Transaminase↗

PubMed2002

Time-dependent changes in HIV nucleoside analogue phosphorylation and the effect of hydroxyurea.

BACKGROUND: Nucleoside analogues are activated to their triphosphates, which compete with endogenous deoxynucleoside triphosphate (dNTP) pools to inhibit HIV reverse transcriptase. Hydroxyurea has been administered with nucleoside analogues to modulate intracellular dNTP pools and thus the ratio of drug triphosphate:endogenous triphosphate. OBJECTIVES: To examine changes in drug activation over time and investigate the effects of hydroxyurea on intracellular phosphorylation of antiretroviral nucleoside analogues. PATIENTS: A total of 229 HIV-infected individuals receiving abacavir, lamivudine and zidovudine were randomly assigned to receive or not nevirapine and hydroxyurea. Twenty-four patients were recruited to an observational substudy measuring intracellular drug triphosphate and dNTP concentrations at 0, 2, 6, 12, 24 and 48 weeks. METHODS: Drugs were extracted from isolated peripheral blood mononuclear cells before analysis of endogenous dNTP and drug triphosphates by primer extension assays. RESULTS: Twenty-two out of 24 patients were followed to completion of the substudy. Hydroxyurea had no demonstrable effect on endogenous dNTP or drug triphosphate levels at any timepoint. However, the ratio of zidovudine triphosphate to endogenous deoxythymidine triphosphate was significantly increased with hydroxyurea. A significant decrease in lamivudine triphosphate (3TCTP) and the 3TCTP:endogenous deoxycytidine triphosphate ratio was seen over 48 weeks. In five patients who failed therapy in the first 24 weeks, significantly reduced 3TCTP was seen. CONCLUSION: Hydroxyurea does not affect measurable pools of endogenous nucleosides in vivo. Decreased lamivudine phosphorylation over time may provide a novel pharmacological explanation for the mechanism of resistance to this drug.

Adult↗