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David J Back

Publications and source records attributed to David J Back.

At least 19 recordsLinked to original sources
PubMed2006

Pharmacologic optimization of protease inhibitors and nonnucleoside reverse transcriptase inhibitors (POPIN)--a randomized controlled trial of therapeutic drug monitoring and adherence support.

We evaluated the feasibility and effectiveness of therapeutic drug monitoring (TDM) and adherence support (collectively, AT) vs standard of care (SOC) in patients receiving HIV protease inhibitors (PIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs) within a nurse-led clinic. Primary end points were failure to achieve viral load of <50 copies/mL at 24 weeks, viral rebound, or development of treatment limiting toxicity. One hundred twenty-two patients (AT 63 and SOC 59) were followed-up every 12 weeks, for a median of 72 weeks. No difference was observed between arms in risk of reaching a study end point or between groups of patients with abnormal vs "therapeutic" drug concentrations. Interindividual variabilities (coefficient of variation) were the following: efavirenz, 77.5%; nevirapine, 74.5%; lopinavir, 73.4%; nelfinavir, 83.7%; indinavir, 80.8%; saquinavir, 112.4%. Intraindividual variabilities (median coefficient of variation) were the following: NNRTIs, approximately 25%; PIs, 48.4%. Despite persistently abnormal results in 26 of patients in the AT arm (38%), dosage adjustment was only undertaken in 9 patients (35%).A significant proportion of patients had drug concentrations outside the therapeutic range. The Pharmacologic Optimization of PIs and NNRTIs (POPIN) study confirms that TDM trials are complex to interpret and statistically underpowered, with effectiveness better assessed through the clinical utility of a TDM result, whether normal or abnormal. Although TDM of PIs and NNRTIs may be useful in selected patients, routine and unselected use is not supported by current evidence.

Adult↗
PubMed2006

Pharmacogenetics of HIV therapy.

Drug treatment in HIV disease is characterized by variable responses, in terms of both efficacy and toxicity. Both genetic and environmental factors are important determinants of this variability, although the relative contributions are unclear and likely to vary with different drugs. Many of the antiretrovirals are metabolized by polymorphically expressed enzymes (cytochrome P450, CYP450; glucuronyl transferase, GT) and/or transported by drug transporters (ABC and SLC families). Initial studies of antiretroviral efficacy have therefore focused on these genes. For example, it has recently been shown that a CYP2B6 genetic variant predicts higher plasma efavirenz exposure and possibly increased central nervous system toxicity. A large number of studies on ABCB1 genetics with antiretrovirals have also been undertaken; however, as in other therapeutic areas, the data have been contradictory, and currently, no firm conclusions can be reached on the effect of ABCB1 variability as a determinant of efficacy. Indeed, this highlights the need for validation of initial association studies in pharmacogenetic research. By contrast, the clearest association between genetic variants and response relates to the hypersensitivity reaction that occurs with abacavir. The identification that the major histocompatibility complex haplotype 57.1 acts as a strong genetic predisposing factor can be regarded as a prime example of how fundamental research can be translated into a pharmacogenetic test. Nevirapine hypersensitivity has also been related to an HLA gene (HLA-DRB1*0101) but the predictive value does not appear to be sufficient to implement in clinical practice. Much more work needs to be done to define the genetic factors determining response to antiretroviral agents. These studies need to be sufficiently powered and utilize a modern genotyping strategy. Most importantly, the phenotype needs to be carefully characterized. We also need to disseminate this information: a pivotal resource for this can be found at www.HIV-pharmacogenomics.org.

Anti-HIV Agents↗
PubMed2005

Assessment of adipokine expression and mitochondrial toxicity in HIV patients with lipoatrophy on stavudine- and zidovudine-containing regimens.

OBJECTIVES: Despite evidence for the role of adipokines such as adiponectin in the metabolic toxicities of protease inhibitor (PI)-treated patients, little is known about their role in nucleoside reverse transcriptase inhibitor (NRTI)-induced lipoatrophy (LA). We analyzed the relations between mitochondrial toxicity, adipokine expression, and clinical LA in peripheral blood mononuclear cells (PBMCs) and adipose samples from individuals treated with stavudine (d4T) or zidovudine (ZDV) in comparison to patients undergoing highly active antiretroviral therapy (HAART) as well as HIV-negative individuals. METHODS: In this cross-sectional analysis, we studied 18 PI-naive HIV-infected patients with LA treated with d4T (d4T+LA+ [n = 12]) or zidovudine (ZDV+LA+ [n = 6]) in comparison to HAART-treated patients with (HAART+LA+ [n = 8]) and without (HAART+LA- [n = 8]) LA as well as HIV-negative controls (n = 12). Adipose samples were assessed for protein and/or messenger RNA (mRNA) levels of adiponectin, tumor necrosis factor-alpha (TNFalpha), interleukin (IL)-6, and sterol regulatory element-binding protein (SREBP) 1a/c in all groups, whereas adipose and PBMC samples from the d4T+LA+, ZDV+LA+, and HIV-negative subgroups were assessed for mitochondrial DNA (mtDNA) depletion and cytochrome c-oxidase (COX) II/COX IV ratios. RESULTS: There was no change in mtDNA levels in adipose or PBMC samples in NRTI-treated patients with LA, although patients treated with d4T had reduced COX II/COX IV ratios in adipose and PBMC samples. Adipose tissue adiponectin mRNA and plasma levels were reduced in the d4T- and ZDV-treated patients regardless of the use of PIs. Tissue SREBP1c mRNA levels were also significantly reduced in both NRTI groups when compared with the HIV-negative controls. Significant reductions in SREBP1c levels were also evident with the HAART+LA+ group when compared with HAART+LA- controls. CONCLUSIONS: Patients with LA on d4T-based regimens show evidence of mitochondrial respiratory chain dysfunction, whereas the d4T- and ZDV-based regimens also demonstrated reduced SREBP1c and adiponectin levels, findings that have previously been shown with PIs.

Adiponectin↗
PubMed2005

Modulation of the intracellular accumulation of saquinavir in peripheral blood mononuclear cells by inhibitors of MRP1, MRP2, P-gp and BCRP.

BACKGROUND: The efflux transporters P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRP) and breast cancer resistance protein (BCRP) limit the accumulation of antiretrovirals in cell lines but it is more important to know whether the expression of these transporters in peripheral blood mononuclear cells (PBMC) impacts cellular drug concentrations. OBJECTIVES: To study the transport and accumulation of saquinavir (SQV) in PBMC and the effects of specific inhibitors of MRP1, MRP2, P-gp and BCRP. METHODS: Transport and accumulation of [H]-SQV was measured in PBMC in the absence or presence of specific and non-specific inhibitors of MRP1, MRP2, P-gp and BCRP. Flow cytometric, western blot and real-time PCR assays were used to examine the relative expression of the drug efflux transporters in the same batches of PBMC. RESULTS: MRP2 is present in PBMC. The expression of P-gp, MRP1, MRP2 (mRNA) and BCRP all displayed batch-to-batch variability. Specific and non-specific inhibitors of MRP1, P-gp and MRP2 significantly increased the baseline accumulation of SQV. Accumulation of SQV was not correlated with the expression of any single transporter. CONCLUSIONS: Multiple drug efflux transporters are important in the intracellular accumulation of SQV in PBMC. If drug efflux contributes towards virological failure, then all contributing transporters will need to be inhibited.

Blotting, Western↗
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

The pharmacology of antiretroviral nucleoside and nucleotide reverse transcriptase inhibitors: implications for once-daily dosing.

The trend toward once-daily dosing in HIV antiretroviral therapy is based on the association between adherence, treatment outcome, and patient preferences. Patients prefer simpler treatments, fewer pills, less frequent dosing, and no food restrictions. When a regimen meets a patient's preferences, the patient is more likely to be adherent, and with good adherence, the regimen is more likely to be effective. Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) have been a prime focus for developing once-daily therapies primarily because they form the backbone of most current regimens. Within the NRTI class, however, drugs differ in their pharmacokinetic properties, such as plasma and intracellular half-lives, and thus in their suitability for once-daily dosing. For example, newer NRTIs, such as tenofovir and emtricitabine, combine longer plasma half-lives with longer intracellular half-lives, prolonging exposure and the period of pharmacologic activity. Of equal importance, the clinical impact of systemic and intracellular interactions between concomitant drugs defines which once-daily drugs may be combined in once-daily regimens. To construct simplified and effective therapies for individual patients, clinicians require an understanding of the plasma and intracellular pharmacokinetic properties of NRTIs and how these properties determine a drug's appropriateness for once-daily dosing and placement within a once-daily regimen.

Drug Administration Schedule↗
PubMed2005

In vitro synergy and enhanced murine brain penetration of saquinavir coadministered with mefloquine.

Highly active antiretroviral therapy has substantially improved prognosis in human immunodeficiency virus (HIV). However, the integration of proviral DNA, development of viral resistance, and lack of permeability of drugs into sanctuary sites (e.g., brain and lymphocyte) are major limitations to current regimens. Previous studies have indicated that the antimalarial drug chloroquine (CQ) has antiviral efficacy and a synergism with HIV protease inhibitors. We have screened a panel of antimalarial compounds for activity against HIV-1 in vitro. A limited efficacy was observed for CQ, mefloquine (MQ), and mepacrine (MC). However, marked synergy was observed between MQ and saquinavir (SQV), but not CQ in U937 cells. Furthermore, enhancement of the antiviral activity of SQV and four other protease inhibitors (PIs) by MQ was observed in MT4 cells, indicating a class specific rather than a drug-specific phenomenon. We demonstrate that these observations are a result of inhibition of multiple drug efflux proteins by MQ and that MQ also displaces SQV from orosomucoid in vitro. Finally, coadministration of MQ and SQV in CD-1 mice dramatically altered the tissue distribution of SQV, resulting in a >3-fold and >2-fold increase in the tissue/blood ratio for brain and testis, respectively. This pharmacological enhancement of in vitro antiviral activity of PIs by MQ now warrants further examination in vivo.

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↗
PubMed2005

The implications of P-glycoprotein in HIV: friend or foe?

P-glycoprotein (P-gp), coded by the ABCB1 gene, has a wide tissue distribution. The drug transporter is known to limit the bioavailability of a plethora of drugs and xenobiotics including the human immunodeficiency virus (HIV) protease inhibitors. There remains a considerable degree of debate in the literature with respect to the role of ABCB1 polymorphisms in HIV-treatment outcome and some studies have also implicated antiretroviral drugs as inducers of P-gp. Recent evidence indicates a role for P-gp in the inhibition of viral infectivity and/or release and cellular relationships with other infection-related proteins (and cholesterol). It is becoming increasingly clear that future studies on P-gp in HIV should consider both pharmacological and virological issues.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

Altered adipokine response in murine 3T3-F442A adipocytes treated with protease inhibitors and nucleoside reverse transcriptase inhibitors.

BACKGROUND: Abnormal levels of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6 and adiponectin have been observed in HIV patients with lipodystrophy. However, because these patients have long drug and disease histories, it is unclear which drugs are responsible for these abnormalities. We have therefore investigated the effects of individual antiretrovirals on adipokine expression and adipogenesis using a murine cell line in vitro. METHODS: Differentiating murine 3T3-F442A adipocytes were incubated with 20 microM nucleoside reverse transcriptase inhibitors (NRTIs) zidovudine or stavudine, or protease inhibitors (PIs) indinavir, ritonavir, saquinavir or nelfinavir, in the presence and absence of rosiglitazone (10 microM). Adipogenesis was assessed using glycerol-3-phosphate dehydrogenase activity, while expression of TNF-alpha, IL-6 and adiponectin at protein and mRNA levels was assessed by ELISA and quantitative real-time PCR, respectively. RESULTS: Nelfinavir, ritonavir and saquinavir inhibited adipogenesis and up-regulated the expression of TNF-alpha and IL-6, but this effect was not seen with indinavir, zidovudine and stavudine. Adiponectin expression was significantly reduced in both NRTI- and PI-treated cells, although the most profound reductions were found with ritonavir and saquinavir. Co-incubation with rosiglitazone led to a partial attenuation of the change in TNF-alpha, IL-6 and adiponectin secretion. CONCLUSIONS: Our data suggest that the PIs nelfinavir, ritonavir and saquinavir have potent effects in inhibiting adipocyte differentiation whilst up-regulating TNF-alpha and IL-6 mRNA levels and decreasing adiponectin levels. These changes were partially attenuated by rosiglitazone. Taken together, the data show that antiretrovirals have complex effects on adipocyte function, which may be mediated by an altered adipokine response.

3T3 Cells↗
PubMed2004

Lopinavir/ritonavir combined with twice-daily 400 mg indinavir: pharmacokinetics and pharmacodynamics in blood, CSF and semen.

OBJECTIVES: To evaluate the steady-state blood plasma (BP), CSF and seminal plasma (SP) pharmacokinetics (PK) of twice-daily indinavir 400 mg and lopinavir/ritonavir. METHODS: Ten HIV-1-positive men on lopinavir/ritonavir participated in a PK study. PK sampling was performed before and 2 weeks after adding indinavir to lopinavir/ritonavir-containing regimens. BP, CSF and SP RNA levels, CD4 counts and blood chemistry were checked at baseline and 2 weeks after indinavir. RESULTS: At baseline: lopinavir parameters (n=10) in BP were within expected levels. Median lopinavir trough concentrations (n=5) in CSF and SP were below the limit of detection (BLD) (i.e. <10 ng/mL) and 248 ng/mL (range 96-2777), respectively. After indinavir: lopinavir C(max), C(min) and AUC(0-12) increased by 9%, 46% and 20%, respectively (P<0.32, P<0.32 and P<0.20). In two of four men lopinavir concentrations in CSF were detectable at 27 and 29 ng/mL. Median SP lopinavir concentration was 655 ng/mL (20-2734). Median indinavir PK parameters were C(max) 3365 ng/mL (range 2130-5194), C(min) 293 ng/mL (14-766), T(max) 2.25 h (1-3), AUC(0-12) 22452 ng/mL.h (11243-33661), and t(1/2) 2.8 h (1.4-3.7). Median indinavir concentrations in CSF and SP were 39 ng/mL (21-86) and 592 ng/mL (96-983). Two of eight men who initially had detectable BP viral load (VL) became BLD (<50 copies/mL) after the addition of indinavir, and in 2/4 men with low-level viraemia in SP (BPVL BLD) their SPVL became BLD after addition of indinavir. CONCLUSIONS: Adding indinavir 400 mg twice daily to lopinavir/ritonavir-containing regimens did not significantly alter the median lopinavir PK parameters. However, wide interpatient variability in lopinavir concentrations was seen. In contrast plasma indinavir levels were >80 ng/mL in seven of eight plasma samples, and all CSF and semen samples collected.

Adult↗
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↗
PubMed2004

Lopinavir protein binding in vivo through the 12-hour dosing interval.

Most protease inhibitors available for the treatment of human immunodeficiency virus (HIV) infection are highly bound to plasma proteins, mainly alpha-1 acid glycoprotein. Therapeutic drug monitoring (TDM) of total protease inhibitor (PI) concentrations has been increasing in the past few years; however, the pharmacological activity of the PIs is dependent on unbound drug entering cells harboring HIV. There is little information available on unbound drug concentrations of these drugs in vivo. The aim of the study was to measure unbound plasma concentrations of lopinavir (LPV) and to relate them to the total plasma concentrations to establish the unbound percentage in vivo during a full dosage interval. A pharmacokinetic study was performed in HIV-infected subjects (n = 23; median CD4 cell count = 290 x 10(6) cells x L(-1); viral load < 50 copies x mL(-1)) treated with a LPV/ritonavir (RTV)-containing regimen. Ultrafiltration was used to separate unbound LPV in all plasma samples (n = 115). Equilibrium dialysis was also used to compare with ultrafiltration measurements in 10/23 patients at baseline and 2 hours after drug intake. Total and unbound LPV concentrations were measured by a fully validated method using high-performance liquid chromatography-mass spectometry (HPLC-MS/MS). Based on a comparison of AUC(unbound)AUC(total), the mean (+/- SD) unbound percentage of LPV from all the samples studied (n = 115) was 0.92% (+/- 0.22) when measured with ultrafiltration and 1.32% (+/- 0.44) when equilibrium dialysis was used (n = 20), showing a higher drug recovery (P = 0.048). The unbound percentage of LPV was found to be significantly higher after 2 h than at baseline (P < 0.05 with both methods), suggesting a concentration-dependent binding of LPV that has not been observed in vitro. However, the clinical significance of such phenomena is still unclear.

Adult↗
PubMed2004

Functional correlation of P-glycoprotein expression and genotype with expression of the human immunodeficiency virus type 1 coreceptor CXCR4.

The aim of this study was to investigate the relationship between lymphocyte P-glycoprotein (P-gp) expression and genotype in vivo and the expression of lymphocyte receptors critical in the life cycle of human immunodeficiency virus type 1 (HIV-1), i.e., CD4, CCR5, and CXCR4. Using flow cytometry to quantify each membrane receptor/transporter, we demonstrate a highly significant correlation between P-gp protein expression and the expression of CXCR4 (rho = 0.874; P < 0.0001). Furthermore, confocal microscopy showed colocalized expression of CXCR4 and P-gp in the lymphocyte membrane. This significant relationship was also apparent at the mRNA level by use of reverse transcription-PCR (rho = 0.61; P < 0.005) and was present in both phytohemagglutinin-stimulated and unstimulated peripheral blood mononuclear cells. Genotypic analysis of the C3435T single-nucleotide polymorphism of P-gp confirmed significantly higher levels of P-gp in C (range, 2.45 to 11.00 relative fluorescence units [RFU])- than in T (range, 0.25 to 5.00 RFU)-homozygous individuals (P = 0.0088; 95% confidence interval [95% CI], 0.7 to 6.3 RFU). An equivalent association between CXCR4 levels and C (range, 12.7 to 44.1 RFU) versus T (range, 3 to 18.9 RFU) genotype was also demonstrated (P = 0.0019; 95% CI, 5.4 to 23.7). Functionally, although these correlates had no impact on HIV-1 production from either X4- or R5-tropic virus, expression correlated significantly with the activity of the HIV-1 protease inhibitor (PI) saquinavir for both P-gp (rho = 0.75; P = 0.0019) and CXCR4 (rho = 0.71; P = 0.0041). This study defines an association between P-gp (expression and genotype) and CXCR4 that may have implications for the selection of viral tropism and the access of drugs to protease for specific tropic types. The interplay between these two proteins may also influence the viral genotypes which escape effective chemotherapy and which therefore have the opportunity to evolve resistance to PIs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Effect of mycophenolate mofetil on the pharmacokinetics of antiretroviral drugs and on intracellular nucleoside triphosphate pools.

OBJECTIVE: To study the effect of mycophenolate mofetil therapy on the pharmacokinetic parameters of a number of antiretroviral drugs, on intracellular pools of deoxycytidine triphosphate (dCTP) and deoxyguanosine triphosphate (dGTP), and on intracellular concentrations of the triphosphate of lamivudine (3TCTP). DESIGN: Randomised pharmacokinetic study. PARTICIPANTS: Nineteen HIV-1-infected patients. METHODS: Antiretroviral-naive men starting treatment with didanosine 400 mg once daily, lamivudine 150 mg twice daily, abacavir 300 mg twice daily, indinavir 800 mg twice daily, ritonavir 100 mg twice daily and nevirapine 200 mg twice daily were randomised to a group with or without mycophenolate mofetil 500 mg twice daily. After 8 weeks of therapy, the plasma pharmacokinetic profiles of mycophenolic acid (the active metabolite of mycophenolate mofetil), abacavir, indinavir and nevirapine, and triphosphate concentrations (dCTP, dGTP and 3TCTP) in peripheral blood mononuclear cells, were determined. RESULTS: Nine of the 19 patients received mycophenolate mofetil. There was no difference in plasma clearance of indinavir or abacavir between the two groups. The clearance of nevirapine was higher in patients using mycophenolate mofetil (p = 0.04). In 12 patients, of whom five also received mycophenolate mofetil, intracellular triphosphates were measured. There was no significant difference in intracellular dCTP, dGTP or 3TCTP concentrations between the two groups. CONCLUSION: In this small cohort of patients, mycophenolate mofetil therapy reduced the plasma concentration of nevirapine but had no effect on plasma concentrations of indinavir and abacavir. There were no consistent effects of mycophenolic acid on the intracellular concentrations of dCTP, dGTP or 3TCTP.

Acquired Immunodeficiency Syndrome↗
PubMed2004

Intracellular and plasma pharmacokinetics of nelfinavir and M8 in HIV-infected patients: relationship with P-glycoprotein expression.

One of the targets of antiretroviral therapy is within cells infected with HIV. In order to improve therapeutic efficacy, it is therefore important that the intracellular pharmacokinetics of drugs, such as nelfinavir mesylate and its active metabolite M8, are studied in addition to plasma pharmacokinetics. Previously, the intracellular accumulation of protease inhibitors has been reported in vivo, displaying the following hierarchy: nelfinavir > saquinavir > ritonavir > indinavir. Multidrug resistance transporters, such as P-glycoprotein (P-gp), may result in a lower intracellular concentration of drug via an efflux mechanism, thus contributing to sanctuary site formation. The objective of this study was to determine concentrations of nelfinavir and M8 in plasma and peripheral blood mononuclear cells from HIV-infected patients, and to ascertain the relationship between intracellular accumulation and lymphocyte P-gp expression. Venous blood samples from 12 HIV-infected patients (viral load <50 copies/ml) receiving nelfinavir (1250 mg twice daily) and dual nucleoside reverse transcriptase inhibitor therapy were collected over a full dosage interval (0, 2, 4, 8 and 12 h). Plasma and intracellular (cell-associated) drug concentrations were measured by HPLC-MS/MS. Drug exposure in plasma and cells was expressed as the area under the concentration-time curve (AUC(0-12h)), derived from non-compartmental modelling. The ratio of intracellular AUC(0-12h)/total plasma AUC(0-12h) was calculated to determine cellular drug accumulation. P-gp expression on lymphocytes was determined by flow cytometry. The median (range) AUC(0-12h) of nelfinavir in plasma and cellular compartments was 21.8 mg x h x l(-1) (5.64-50.8) and 104.6 mg x h x l(-1) (23.1-265.7), respectively. Corresponding values for M8 in plasma and cells were 6.60 mg x h x l(-1) (2.16-17.3) and 19.6 mg x h x l(-1) (5.14-60.8). A ratio of plasma M8/plasma nelfinavir (AUC(0-12h)) and intracellular M8/intracellular nelfinavir (AUC(0-12h)) gave median values of 0.32 and 0.17, respectively. The cellular accumulations [median; (range)] of nelfinavir and M8 were 5.30 (2.28-16.2) and 2.32 (1.01-10.7), respectively. A significant correlation between plasma and intracellular nelfinavir minimum concentration (Cmin) (r2=0.34; P=0.049), but not between plasma and intracellular M8 Cmin was observed. C(0h) concentrations were higher than C(12h) for both nelfinavir and M8. No relationship was observed between nelfinavir or M8 accumulation and lymphocyte cell surface expression of P-gp. This study illustrates that intracellular concentrations were higher than plasma concentrations for both nelfinavir and M8, suggesting lymphocyte accumulation. The mechanism of differential intracellular accumulation of nelfinavir and M8 remains to be elucidated. It may be that affinities for influx transporters or fundamental drug characteristics play a major role in the greater accumulation of nelfinavir than M8.

ATP Binding Cassette Transporter, Subfamily B, Mem↗