Variability in activity of hepatic CYP3A4 in patients infected with HIV

Drug-drug interactions between anti-retroviral therapies and drugs of abuse in HIV systems

INTRODUCTION

Substance abuse is a common problem among HIV-infected individuals. Importantly, addictions as well as moderate use of alcohol, smoking, or other illicit drugs have been identified as major reasons for non-adherence to antiretroviral therapy (ART) among HIV patients. The literature also suggests a decrease in the response to ART among HIV patients who use these substances, leading to failure to achieve optimal virological response and increased disease progression.

AREAS COVERED

This review discusses the challenges with adherence to ART as well as observed drug interactions and known toxicities with major drugs of abuse, such as alcohol, smoking, methamphetamine, cocaine, marijuana, and opioids. The lack of adherence and drug interactions potentially lead to decreased efficacy of ART drugs and increased ART, and drugs of abuse-mediated toxicity. As CYP is the common pathway in metabolizing both ART and drugs of abuse, we discuss the possible involvement of CYP pathways in such drug interactions.

EXPERT OPINION

We acknowledge that further studies focusing on common metabolic pathways involving CYP and advance research in this area would help to potentially develop novel/alternate interventions and drug dose/regimen adjustments to improve medication outcomes in HIV patients who consume drugs of abuse.

The role of therapeutic drug monitoring in the management of patients with human immunodeficiency virus infection

Therapeutic drug monitoring (TDM) is a well-established method to optimize dosing regimens in individual patients for drugs that are characterized by a narrow therapeutic range and large interindividual pharmacokinetic variability. For some antiretroviral drugs, mainly nonnucleoside reverse transcriptase inhibitors and protease inhibitors, TDM has been proposed as a means to improve the response in human immunodeficiency virus-infected patients. In contrast, nucleoside reverse transcriptase inhibitors do not show a predictable plasma concentration-response (toxicity, efficacy) relationship, and intracellular analyses are expensive. Therefore, TDM is generally not recommended for this class of drugs. TDM has been successfully applied in the clinical practice for certain antiretroviral drugs, but there are ongoing research efforts on the use and refinement of TDM for human immunodeficiency virus treatment, and convincing data from randomized trials are still needed. The best pharmacokinetic measures of drug exposure such as trough and peak concentrations or concentration ratios have not been unambiguously established.

The role of cytokines in the regulation of drug disposition: extended functional pleiotropism?

INTRODUCTION

Drug disposition, metabolism and drug-drug interactions are important considerations for most drugs. Cytokines are integral to the successful resolution of many diseases. Data are emerging on a role for cytokines in regulation of the expression and activity of drug transporters and drug metabolising enzymes. Investigation of the interaction between pharmacological and immunological responses is key to understanding the complex relationships involved in patient response to therapy.

AREAS COVERED

Evidence detailing the ability of cytokines to regulate drug disposition and metabolism is reviewed in the context of different cell and tissue types. The literature search undertaken provides an overview of the current understanding of the interrelationship between pharmacological and immunological factors which may influence successful drug therapy.

EXPERT OPINION

Dysregulation of cytokines and cytokine networks is a hallmark of a number of diseases such as HIV and cancer. The mechanisms by which the immune system can influence drug disposition are relatively understudied but recent work has highlighted the necessity for examining its impact on pharmacokinetics and pharmacodynamics. A more comprehensive approach in clinical studies will allow better determination of the impact of cytokines on drug disposition. In addition, determining the mechanisms that underpin the differential effects of cytokines across different cell types will clarify the responses reported in these studies.

Variability in drug metabolizing enzyme activity in HIV-infected patients

AIMS

To evaluate variability in cytochrome P450 (CYP) 1A2, CYP2D6, CYP3A, N-acetyltransferase 2 (NAT2), and xanthine oxidase (XO) activity in HIV-infected patients and compare this with data from uninfected, healthy volunteers.

METHODS

Ten HIV-infected men and seven women on medication affecting CYP enzyme activity were phenotyped four times over 2 months using caffeine, dextromethorphan, and midazolam. Urinary caffeine and dextromethorphan metabolite ratios were used to phenotype CYP1A2, NAT2, XO, and CYP2D6 activity and midazolam plasma clearance was used to phenotype CYP3A activity. Plasma and urine samples were analyzed by validated LC/UV or LC/MS methods for midazolam, caffeine, and dextromethorphan. Noncompartmental pharmacokinetics and nonparametric statistical analyses were performed, and the data compared with those of healthy volunteer historic controls.

RESULTS

Compared with age and sex-matched healthy volunteers, HIV-infected subjects had 18% lower hepatic CYP3A4 activity, 90% lower CYP2D6 activity, 53% lower NAT2 activity, and 22% higher XO activity. No significant difference was found in CYP1A2 activity. Additionally, 25% genotype-phenotype discordance in CYP2D6 activity was noted in HIV-infected subjects. Intraindividual variability in enzyme activity increased by 42-62% in HIV-infected patients for CYP1A2, NAT2, and XO, and decreased by 33% for CYP2D6. Interindividual variability in enzyme activity increased by 27-63% in HIV-infected subjects for CYP2D6, CYP1A2, and XO, and decreased by 38% for NAT2. Higher plasma TNFalpha concentrations correlated with lower CYP2D6 and CYP3A4 activity.

CONCLUSIONS

Infection with HIV or stage of HIV infection may alter Phase I and II drug metabolizing enzyme activity. HIV infection was related to an increase in variability of these drug-metabolizing enzymes. Altered metabolism may be a consequence of immune activation and cytokine exposure.

Design of antiretroviral drug interaction studies

PURPOSE OF REVIEW

Pharmacokinetic and/or pharmacodynamic drug interactions can occur as a result of treatment with antiretrovirals. Elucidating the mechanism, direction, and magnitude of an interaction, as well as its clinical impact, can be facilitated by proper study design. Two approaches may be considered: assessment based on full pharmacokinetic profiles within a conventional drug interaction trial, or a population pharmacokinetic analysis as a part of a larger trial. Consideration should be given to the population (i.e. healthy volunteer or HIV infected), dosing and administration of medications, and interpretation of findings. Dosing recommendations should be based on the clinical relevance of the interaction.

RECENT FINDINGS

Guidance documents on the conduct of clinical drug interaction study designs are summarized and applied to the design of antiretroviral drug interaction trials.

SUMMARY

Designing an antiretroviral drug interaction trial poses unique challenges, associated with the conditions and the drug combinations of the intended population. A rational study design can provide insights into antiretroviral pharmacology and allows the clinician to treat more effectively.

Drug-induced hepatotoxicity or drug-induced liver injury

Drug-induced hepatotoxicity is underreported and underestimated in the United States. It is an important cause of acute liver failure. Common classes of drugs causing drug-induced hepatotoxicity include antibiotics, lipid lowering agents, oral hypoglycemics, psychotropics, antiretrovirals, acetaminophen, and complementary and alternative medications. Hepatotoxic drugs often have a signature or pattern of liver injury including patterns of liver test abnormalities, latency of symptom onset, presence or absence of immune hypersensitivity, and the course of the reaction after drug withdrawal.

The impact of cytokines on the expression of drug transporters, cytochrome P450 enzymes and chemokine receptors in human PBMC

BACKGROUND AND PURPOSE

The function of transporters in peripheral blood mononuclear cells (PBMC) has been characterized, but less is known about cytochrome P450 (CYP) enzyme function in these cells. Given that cytokines are dysregulated in many diseases, the purpose of this work was to assess the impact of cytokines on the expression of CYPs, transporters and chemokine receptors in PBMC.

EXPERIMENTAL APPROACH

Human PBMC were incubated with cytokines for 48 h. ATP-binding cassette (ABC)B1, ABCC1, ABCC2, CYP2B6, CYP3A4, CXCR4 and CCR5 expression were measured by quantitative polymerase chain reaction and flow cytometry at 0, 4, 8, 24 and 48 h. Enzyme activity was assessed using fluorescent probes.

KEY RESULTS

We show here functional activity of CYP3A4 and CYP2B6 in PBMC. Furthermore, cytokines had a significant impact on the mRNA and protein expression of all proteins. For example, interleukin-2 (IL-2) had a marked impact on ABCB1 mRNA (% control 4745 +/- 11961) and protein (% control 200 +/- 57). Increases in drug efflux transporter expression, in response to cytokines, resulted in reduced cellular accumulation of digoxin [decrease of 17% and 26% for IL-2 and interferon-gamma (IFNgamma) respectively] and saquinavir (decrease of 28% and 30% for IL-2 and IFNgamma respectively). The degree to which drug transporter and chemokine receptor expression changed in response to cytokines was positively correlated (e.g. ABCB1 and CXCR4, r(2) = 0.545).

CONCLUSIONS AND IMPLICATIONS

These data have important implications for diseases in which cytokines are dysregulated and for which pharmacological intervention targets immune cells.

Minimal effect of MDR1 and CYP3A5 genetic polymorphisms on the pharmacokinetics of indinavir in HIV-infected patients

AIMS

The protease inhibitor indinavir is characterized by an important interindividual pharmacokinetic variability, which results from the actions of the metabolizing enzymes cytochrome P450 (CYP) 3A and the multidrug efflux pump P-glycoprotein (P-gp), encoded by MDR1. Using a population pharmacokinetic approach, we investigated the effect of several MDR1 and CYP3A5 polymorphisms on the pharmacokinetic parameters of indinavir in HIV-infected patients.

METHODS

Twenty-eight patients receiving indinavir alone or together with ritonavir were included. Indinavir pharmacokinetics were studied over a 12 h interval. Genetic polymorphisms were assessed by real-time PCR assays and direct sequencing for MDR1 and by PCR-SSCP analysis for CYP3A5.

RESULTS

The pharmacokinetics of indinavir were best described by a one-compartment model with first-order absorption. In the final model, the MDR1 C3435T genotype and ritonavir were identified as statistically significant covariates (P </= 0.001) for the absorption rate constant (95% confidence interval on the difference between CC and CT genotype 0.37, 5.53) and for clearance (95% confidence interval on the difference 5.8, 26.2), respectively. Patients with the CYP3A5*3/*3 genotype receiving indinavir alone had a 31% decrease in the indinavir clearance rate compared with patients carrying the CYP3A5*1/*3 genotype.

CONCLUSIONS

The MDR1 C3435T genotype affects the absorption constant of indinavir suggesting that P-gp may be implicated in its pharmacokinetic variability. Through its inhibition of CYP3A and P-gp, ritonavir could attenuate the pharmacokinetic variability linked to genetic differences, reducing significantly the interindividual variability of indinavir. However, genotyping MDR1 and/or CYP3A5 to optimize protease inhibitor boosted regimens does not seem clinically relevant.

Effect of widely used combinations of antiretroviral therapy on liver CYP3A4 activity in HIV-infected patients

AIMS

To evaluate the effects of combined antiretroviral drugs (HAART) on liver CYP3A4 activity using the [(14)C-N-methyl]-erythromycin breath test (ERMBT).

METHODS

HIV-infected patients (31 women, 30 men) with mean (+/- SD) age of 38 +/- 9 years were enrolled and underwent complete clinical and laboratory evaluation. Patients were divided into five groups and were treated with two nucleoside analogues (NAs) and one of the following: nelfinavir alone (n = 13), any ritonavir-boosted protease inhibitor with (n = 8) or without (n = 13) nevirapine, nevirapine alone (n = 15), or a third NA (n = 12). Three or four ERMBTs were performed 7 days prior to (D-7) and at the beginning of treatment (D0), D14 (only for patients taking nevirapine) and on D28.

RESULTS

Mean baseline liver CYP3A4 activity displayed high interindividual variability (47%) but low intraindividual variability (15%). Women had 30% higher ERMBT values than men [2.7 +/- 1.3 vs. 1.9 +/- 0.7; 95% confidence interval (CI) 20.5, 49.5; P = 0.003]. The ERMBT data correlated with body weight, alpha- and beta-globulins and alanin aminotransferases (0.10 < r(s) < 0.20; P < 0.01). Whereas nevirapine had no effect on liver CYP3A4 activity, nelfinavir-based and ritonavir-boosted drug regimens inhibited it by 69% (95% CI 64.7, 72.9; P = 0.005) and by 95% (95% CI 93.3, 96.7; P = 0.001), respectively.

CONCLUSION

Evaluation of the effect of HAART on liver CYP3A4 activity may aid in preventing inappropriate treatment regimens in HIV-infected patients.

Possible drug-metabolism interactions of medicinal herbs with antiretroviral agents

Herbal medicines are widely used by HIV patients. Several herbal medicines have been shown to interact with antiretroviral drugs, which might lead to drug failure. We have aimed to provide an overview of the modulating effects of Western and African herbal medicines on antiretroviral drug-metabolizing and transporting enzymes, focusing on potential herb-antiretroviral drug interactions. Echinacea, garlic, ginkgo, milk thistle, and St. John's wort have the potential to cause significant interactions. In vitro and in vivo animal studies also indicated other herbs with a potential for interactions; however, most evidence is based on in vitro studies. Further pharmacokinetic studies to unveil potential Western and especially African herb-antiretroviral drug interactions are urgently required, and the clinical significance of these interactions should be assessed.

Lack of sex-related differences in saquinavir pharmacokinetics in an HIV-seronegative cohort

AIMS

To examine the influence of sex on steady-state saquinavir pharmacokinetics in HIV-seronegative volunteers administered saquinavir without a concomitant protease inhibitor.

METHODS

Thirty-eight healthy volunteers (14 female) received saquinavir soft-gel capsules 1200 mg three times daily for 3 days to achieve steady-state conditions. Following administration of the 10th dose, blood was collected serially over 8 h for measurement of saquinavir plasma concentrations. Saquinavir pharmacokinetic parameter values were determined using noncompartmental methods and compared between males and females. CYP3A phenotype (using oral midazolam) and MDR-1 genotypes at positions 3435 and 2677 were determined for all subjects in order to characterize possible mechanisms for any observed sex-related differences.

RESULTS

There was no significant difference in saquinavir AUC(0-8) or any other pharmacokinetic parameter value between the sexes. These findings persisted after mathematically correcting for total body weight. The mean weight-normalized AUC(0-8) was 29.9 (95% confidence interval 15.5, 44.3) and 29.8 (18.6, 40.9) ng h(-1) ml(-1) kg(-1) for males and females, respectively. No significant difference in CYP3A phenotype was observed between the groups; likewise, the distribution of MDR-1 genotypes was similar for males and females.

CONCLUSION

In contrast to previous study findings, results from this investigation showed no difference in saquinavir pharmacokinetics between males and females. The discrepancy between our findings and those previously reported may be explained by the fact that we evaluated HIV-seronegative volunteers and administered saquinavir in the absence of concomitant protease inhibitors such as ritonavir. Caution must be exercised when extrapolating pharmacokinetic data from healthy volunteer studies (including sex-based pharmacokinetic differences) to HIV-infected populations or to patients receiving additional concurrent medications.

High variability of indinavir and nelfinavir pharmacokinetics in HIV-infected patients with a sustained virological response on highly active antiretroviral therapy

OBJECTIVES

To describe plasma concentrations of indinavir alone or combined with ritonavir, and of nelfinavir and its active metabolite M8, and to measure their variabilities in HIV-infected patients treated with a stable antiretroviral regimen and experiencing a sustained virological response for at least 12 months.

PATIENTS AND METHODS

In this prospective trial, blood samples were drawn during a 6-hour time interval between two doses at enrolment to assess protease inhibitor (PI) pharmacokinetic parameters, and 4 months later to assess plasma trough and peak concentrations. Safety and adherence assessments and laboratory data were collected during an 8-month period. PI pharmacokinetic characteristics were analysed using a non-compartmental approach. Inter- and intrapatient variabilities were estimated using a linear mixed-effect model. The impact of different covariates on plasma trough concentrations was investigated. Eighty-eight patients were analysed: 42 treated with indinavir and 46 with nelfinavir.

RESULTS

The interquartile range (IQR) of the plasma trough concentration corrected for the sampling time (Ccalc) was 116-374 microg/L for indinavir alone and 163-508 microg/L for indinavir/ritonavir. Ritonavir significantly increased indinavir elimination half-life and plasma exposure. For nelfinavir, the IQR of Ccalc was 896-2059 microg/L for three-times-daily administration and 998-2124 microg/L for twice-daily administration. Variabilities were high for both PIs. Intrapatient variability for indinavir alone (and indinavir + ritonavir) was 76% (107%) and interpatient variability was 58% (10%) in adherent patients. Intrapatient variability for nelfinavir three times daily (and twice daily) was 41% (74%) and interpatient variability was 62% (50%). Intrapatient variability was lowered in patients with a high adherence level.

CONCLUSION

Although performed in a homogeneous population, this study documented a high interpatient but also intrapatient variability of indinavir and nelfinavir pharmacokinetics, which should be taken into account when interpreting therapeutic drug monitoring. Once patients have reached a sustained virological response, plasma PI monitoring may have a limited impact.

Lack of In Vivo Correlation Between Indinavir and Saquinavir Exposure and Cytochrome P450 3A Phenotype as Assessed with Oral Midazolam as a Phenotype Probe

STUDY OBJECTIVE

To investigate a potential correlation between exposure to oral midazolam, a commonly used cytochrome P450 (CYP) 3A probe, and saquinavir and indinavir exposure.

DESIGN

Open-label, prospective, pharmacokinetic study.

SETTING

Outpatient research center.

SUBJECTS

Thirty-six healthy volunteers aged 22-50 years.

INTERVENTION

Subjects received a single oral dose of midazolam 8 mg; 4 hours later, blood was drawn to determine their serum midazolam concentrations. Midazolam phenotyping was followed by successive administration of the protease inhibitors indinavir and saquinavir, with blood sampling and pharmacokinetic analyses performed at steady state.

MEASUREMENTS AND MAIN RESULTS

Pharmacokinetic parameters of each protease inhibitor were evaluated to assess for a potential relationship with 4-hour concentrations of midazolam. No correlations between phenotype results for midazolam and any pharmacokinetic parameter for indinavir or saquinavir were identified (r(2)=0.00002-0.073). When the results were analyzed based on race, significant correlations were identified in five African-American subjects, including correlations between 4-hour midazolam levels and apparent oral clearance of saquinavir (r(2)=0.734, p=0.064), area under the plasma concentration-time curve from 0-8 hours (r(2)=0.914, p=0.011), minimum concentration (r(2)=0.857, p=0.024), and maximum concentration (r(2)=0.969, p=0.002). These findings for African-American subjects were not seen with indinavir. No correlation was found between indinavir and saquinavir pharmacokinetic parameters (r(2)=0.017-0.261).

CONCLUSION

Oral midazolam was not a useful probe for predicting saquinavir or indinavir exposure at steady state. Reasons for the lack of correlation likely included differences between midazolam and protease inhibitor P-glycoprotein specificity, differences in the relative contribution of CYP3A5-mediated metabolism, and/or variation in intestinal and hepatic CYP3A specificity. The strong correlation between midazolam phenotype and pharmacokinetic parameters for saquinavir in African-American subjects indicated a racial difference in one or more of these confounding variables.

Therapeutic Drug Monitoring and Human Immunodeficiency Virus (HIV) Antiretroviral Therapy

Treatment with antiretroviral drugs such as the HIV protease inhibitors and non-nucleoside reverse transcriptase inhibitors have contributed to the improvement of life of many HIV-infected patients in recent years, but antiretroviral therapy is not without problems. In some patients, treatment is not effective and suppression of viral replication is not achieved. Other patients experience toxicity and have to stop treatment or change to a less effective treatment. Several studies have demonstrated a relationship between plasma concentrations of the protease inhibitors and non-nucleoside reverse transcriptase inhibitors and viral suppression and toxicity. Therapeutic drug monitoring uses drug concentrations to individualize and optimise therapy by dosage adjustments and many clinicians have advocated for the use of therapeutic drug monitoring in HIV antiretroviral therapy. Evidence from a number of randomized clinical trials supports the use of therapeutic drug monitoring, but the studies have limitations and might not apply to all the antiretroviral drugs. However, the consensus is that certain patients are very likely to benefit from therapeutic drug monitoring. Additionally, the combination of therapeutic drug monitoring and genotypic or phenotypic resistance testing might further improve antiretroviral therapy.

Sexual risk behaviors and substance use among alcohol abusing HIV-positive men who have sex with men

An ethnically diverse sample (79.0% men of color) of HIV seropositive (HIV+) men who have sex with men (MSM) with alcohol use disorders from the New York City metropolitan area was recruited from a variety of settings frequented by such men. Data were collected using quantitative assessments and calendar based techniques at the baseline assessment of a longitudinal study assessing the relationship between alcohol and substance use and sexual risk behaviors as well as alcohol use and HIV disease progression. Data were selected on a sample of 253 HIV+ MSM (mean age = 38.55, SD = 6.73). Of these, the majority of participants (80.2%, n=203) reported engaging in sexual behaviors with casual partners. In terms of sexual behaviors that put partners at greatest risk for HIV transmission, unprotected anal insertive intercourse was most likely to occur with unknown status casual partners (46.8%, n=95) than with either HIV negative casual partners (19.2%, n=39) or with HIV+ casual partners (40.8%, n=83). Further, bivariate analyses indicated significant relationships between the use of several substances and sexual behaviors that put partners at greatest risk for HIV transmission, as well as a significant positive relationship between drinks per drinking day and viral load.

Variations of CYP3A activity induced by antiretroviral treatment in HIV-1 infected patients

OBJECTIVE

To measure the in vivo variations of CYP3A activity induced by anti-HIV drugs in human immunodeficiency virus (HIV)1-positive patients.

METHODS

A low oral dose of midazolam (MID) (0.075 mg) was given to the patients and the 30-min total 1-OH midazolam (1-OHMID)/MID ratio was determined. Patients were phenotyped either before the introduction of antiretroviral treatments (control group, 90 patients) or after a variable period of antiretroviral treatment (56 patients). Twenty-one subjects underwent multiple phenotyping tests (before and during the course of the treatment).

RESULTS

The median MID ratio was 3.51 in the control group (range 0.20-14.6). It was 5-fold higher in the group with efavirenz (28 patients; median, range: 16.0, 3.81-367; P < 0.0001), 13-fold lower with nelfinavir (18 patients; 0.27, 0.06-36.3; P < 0.0001), 17-fold lower with efavirenz + ritonavir (three patients; 0.21, 0.05-0.47; P = 0.006), 50-fold lower with ritonavir (four patients; 0.07, 0.06-0.17; P = 0.0007), and 7-fold lower with nevirapine + (ritonavir or nelfinavir or grapefruit juice) (three patients; 0.48, 0.03-1.83; P = 0.03). CYP3A activity was lower in the efavirenz + ritonavir group (P = 0.01) and in the ritonavir group (P = 0.04) than in the nelfinavir group, although already strongly inhibited in the latter.

CONCLUSION

The low-dose MID phenotyping test was successfully used to measure the in vivo variations of CYP3A activity induced by antiretroviral drugs. Efavirenz strongly induces CYP3A activity, while ritonavir almost completely inhibits it. Nelfinavir strongly decreases CYP3A activity, but to a lesser extent than ritonavir. The inhibition of CYP3A by ritonavir or nelfinavir offsets the inductive effects of efavirenz or nevirapine administered concomitantly. Finally, no induction of CYP3A activity was noticeable after long-term administration of ritonavir at low dosages (200 mg/day b.i.d.) or of nelfinavir at standard dosages (2,500 mg/day b.i.d.).

Pharmacokinetics of indinavir and ritonavir administered at 667 and 100 milligrams, respectively, every 12 hours compared with indinavir administered at 800 milligrams every 8 hours in human immunodeficiency virus-infected patients

Human immunodeficiency virus (HIV) patients on nucleoside or nucleotide reverse transcriptase inhibitors with HIV RNA at <1,000 copies/ml were randomized in an open-label study to administration of combined indinavir/ritonavir (IDV/RTV) at 667/100 mg every 12 h (q12h) or IDV alone at 800 mg q8h to determine the regimens' pharmacokinetics. On day 14, plasma IDV and RTV levels were determined over 24 h. Noncompartmental pharmacokinetics (minimum concentration of drug in serum [C(min)], area under the concentration-time curve from 0 to 24 h [AUC(0-24)], and maximum concentration of drug in serum [C(max)]) were expressed as geometric mean values with 90% confidence intervals (CI). The primary hypothesis was that the lower bound of the protocol-specified 90% CI for the geometric mean C(min) ratio of the combination compared to IDV alone regimen would be >/=2. Twenty-seven patients were enrolled, and 24 (15 male; average age, 42 years) completed the study. The C(min), AUC(0-24), and C(max) for IDV/RTV compared to IDV alone were 1,511 versus 250 nM, 119,557 versus 77,034 nM . h, and 10,428 versus 10,407 nM, respectively. Corresponding relationships for IDV/RTV compared to IDV alone were a 6.0-fold increase in C(min) (90% CI, 4.0, 9.3), an increase in AUC(0-24) (1.5-fold, 90% CI, 1.2, 2.0), and no increase in C(max). Adverse events were similar and generally mild, with no cases of nephrolithiasis. The geometric mean ratio of IDV C(min) for IDV/RTV compared to IDV was at least 2 by a lower bound of the 90% CI, satisfying the primary hypothesis. The C(max) was not increased, suggesting an IDV/RTV 667/100-mg toxicity profile may be similar to that of unboosted IDV.

CYP3A activity measured by the midazolam test is not related to 3435 C >T polymorphism in the multiple drug resistance transporter gene

A recent study with 69 Japanese liver transplants treated with tacrolimus found that the MDR13435 C >T polymorphism, but not the MDR12677 G >T polymorphism, was associated with differences in the intestinal expression level of CYP3A4 mRNA. In the present study, over 6 h, we measured the kinetics of a 75 microg oral dose of midazolam, a CYP3A substrate, in 21 healthy subjects genotyped for the MDR13435 C >T and 2677 G >T polymorphism. No statistically significant differences were found in the calculated pharmacokinetic parameters between the three 3435 C >T genotypes (TT, CT and CC group, respectively: Cmax (mean +/- SD: 0.30 +/- 0.08 ng/ml, 0.31 +/- 0.09 ng/ml and 0.31 +/- 0.11 ng/ml; Apparent clearance: 122 +/- 29 l/h, 156 +/- 92 l/h and 111 +/- 35 l/h; t1/2: 1.9 +/- 1.1 h, 1.6 +/- 0.90 h and 1.7 +/- 0.7 h). In addition, the 30-min 1'OH midazolam to midazolam ratio, a marker of CYP3A activity, determined in 74 HIV-positive patients before the introduction of antiretroviral treatment, was not significantly different between the three 3435 C >T genotypes (mean ratio +/- SD: 3.65 +/- 2.24, 4.22 +/- 3.49 and 4.24 +/- 2.03, in the TT, CT and CC groups, respectively). Similarly, no association was found between the MDR12677 G >T polymorphism and CYP3A activity in the healthy subjects or in the HIV-positive patients. The existence of a strong association between the activity of CYP3A and MDR13435 C >T and 2677 G >T polymorphisms appears unlikely, at least in Caucasian populations and/or in the absence of specific environmental factors.

Pharmacokinetic Interaction between Rifampin and the Combination of Indinavir and Low‐Dose Ritonavir in HIV‐Infected Patients

Rifampin is an important drug in the treatment of tuberculosis, but administration of rifampin in combination with protease inhibitors is complicated because of drug-drug interactions. A prospective, controlled, multiple-dose study involving 6 HIV-infected patients receiving a combination of indinavir (800 mg) and ritonavir (100 mg) twice a day was performed to evaluate whether the inducing effect of rifampin on the drug-metabolizing enzyme cytochrome P450 (CYP) 3A4 could be overcome by the inhibitory effect of ritonavir. Pharmacokinetic evaluations of steady-state concentrations of indinavir and ritonavir were performed before and after administration of rifampin (300 mg every day for 4 days). An 87% reduction (from 837 to 112 ng/mL) in median indinavir and a 94% reduction (from 431 to 27 ng/mL) in median ritonavir concentrations were seen 12 h after the last dose of rifampin was administered (P=.031). These results strongly indicate that the administration of rifampin with a combination of indinavir (800 mg) and ritonavir (100 mg) could lead to subtherapeutic concentrations of indinavir.

Subtherapeutic antiretroviral plasma concentrations in routine clinical outpatient HIV care

The objective of this study was to evaluate plasma concentrations of nonnucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) within several dosing schemes in a cohort of HIV-infected patients in routine clinical practice and to find possible explanations for subtherapeutic plasma concentrations. Patients were included if a PI or NNRTI was part of their antiretroviral regimen, at least one plasma concentration was obtained, and a complete medication overview from community pharmacy records was available. The study period was from January 1998 to September 2001. Each plasma concentration was related to median plasma concentrations of a pharmacokinetic reference curve, yielding a concentration ratio (CR). A cutoff CR was defined for each antiretroviral drug per specific regimen, discriminating between >or=therapeutic and subtherapeutic concentrations. For the patients with subtherapeutic concentrations, it was sorted out whether drug interactions, adverse events and self-reported symptoms, or nonadherence could be the cause of the lower than expected plasma concentration. Ninety-seven HIV-infected patients fulfilled the criteria. During the defined period, 1145 plasma concentrations were available (median, 11; interquartile range, 8-14). Three hundred fourteen (27.4%) plasma concentrations were classified subtherapeutic. Drug interactions (2; 0.6%), adverse events and self-reported symptoms (67; 21.3%), and nonadherence (14; 4.5%) could only partly explain the subtherapeutic drug levels. Consequently, a large number of the subtherapeutic plasma concentrations (73.6%) remained inexplicable. A high number of subtherapeutic plasma concentrations were observed. No clear causes were found; thus, corrective measures will be difficult to employ. Therefore, therapeutic drug monitoring (TDM) must maintain its crucial place in routine clinical care to be able to identify patients who need extra attention so that therapeutic plasma concentrations are achieved.

The [14C-N-methyl]-erythromycin breath test dosimetry complies with the French regulations for radiation safety

The [14C-N-methyl]-erythromycin breath test (14C-ERMBT) is one of the most valuable probes for liver cytochrome P450-3A4 activity in humans. In order to extend the use of this test in France, we herein provide safety data regarding either patient dosimetry or worker exposure to [14C-N-methyl]-erythromycin. In order to determine the maximum radiation exposure for patient and nuclear medicine technician following one intravenous 14C-ERMBT [111 kiloBequerel (kBq)], we have used the dosimetric data gathered in animal studies and extrapolated to humans using a weight-based method, approximate data provided by the French Society of Radioprotection and erythromycin pharmacokinetics in humans, considering always the worst conditions for the patient and worker exposure determination. The radioactivity administered to a patient after one 14C-ERMBT was equal to 108.8 kBq (i.e. 98% of the total radioactivity in the 14C-erythromycin vial) leading to a patient effective dose of 20 microsievert (microSv) and a maximum effective dose after 14CO2 inhalation by the exposed worker of 16 microSv compared with a mean individual annual effective dose from natural and artificial radioactivity exposure of 3500 microSv in France. The 14C-ERMBT is safe and complies with the European regulations regarding the administration of 14C-labelled compounds in humans. It can therefore be used in clinical research in France without any particular safety requirement.

Drug interactions between antiretroviral drugs and comedicated agents

HIV-infected individuals usually receive a wide variety of drugs in addition to their antiretroviral drug regimen. Since both non-nucleoside reverse transcriptase inhibitors and protease inhibitors are extensively metabolised by the cytochrome P450 system, there is a considerable potential for pharmacokinetic drug interactions when they are administered concomitantly with other drugs metabolised via the same pathway. In addition, protease inhibitors are substrates as well as inhibitors of the drug transporter P-glycoprotein, which also can result in pharmacokinetic drug interactions. The nucleoside reverse transcriptase inhibitors are predominantly excreted by the renal system and may also give rise to interactions. This review will discuss the pharmacokinetics of the different classes of antiretroviral drugs and the mechanisms by which drug interactions can occur. Furthermore, a literature overview of drug interactions is given, including the following items when available: coadministered agent and dosage, type of study that is performed to study the drug interaction, the subjects involved and, if specified, the type of subjects (healthy volunteers, HIV-infected individuals, sex), antiretroviral drug(s) and dosage, interaction mechanism, the effect and if possible the magnitude of interaction, comments, advice on what to do when the interaction occurs or how to avoid it, and references. This discussion of the different mechanisms of drug interactions, and the accompanying overview of data, will assist in providing optimal care to HIV-infected patients.

Virtual inhibitory quotient predicts response to ritonavir boosting of indinavir-based therapy in human immunodeficiency virus-infected patients with ongoing viremia

Depending on the degree of underlying resistance present, optimization of the pharmacokinetics of protease inhibitors may result in improved virologic suppression. Thirty-seven human immunodeficiency virus (HIV)-infected subjects who had chronic detectable viremia and who were receiving 800 mg of indinavir three times a day (TID) were switched to 400 mg of indinavir BID with 400 mg of ritonavir two times a day (BID) for 48 weeks. Full pharmacokinetic evaluations were obtained for 12 subjects before the switch and 3 weeks after the switch. Combination therapy increased the indinavir predose concentrations in plasma by 6.47-fold, increased the minimum concentration in serum by 3.41-fold, and reduced the maximum concentration in serum by 57% without significantly changing the area under the plasma concentration-time curve at 24 h. At week 3, 58% (21 of 36) of the subjects for whom postbaseline measurements were available achieved a viral load in plasma of <50 copies/ml or a reduction from the baseline load of > or =0.5 log(10) copies/ml. Of these subjects, 82% (14 of 17) whose viruses had three or fewer protease inhibitor mutations and 88% (14 of 16) whose viruses had an indinavir virtual phenotypic susceptibility test of more than sixfold less than that for the baseline isolate were considered virologic responders. The indinavir virtual inhibitory quotient, which is a function of baseline indinavir phenotypic resistance (estimated by virtual phenotype) and the indinavir predose concentration in plasma achieved with indinavir-ritonavir combination therapy, was the best predictor of a viral load reduction. Sixteen subjects discontinued the study by week 48 due to adverse events, predominantly related to hyperlipidemia. Pharmacokinetic intensification of indinavir-based therapy with ritonavir reduced the viral loads in subjects but added toxicity. The virtual inhibitory quotient, which incorporates both baseline viral resistance and the level of drug exposure in plasma, was superior to either baseline resistance or drug exposure alone in predicting the virologic response.

Pharmacokinetic interaction between nevirapine and rifampicin in HIV-infected patients with tuberculosis

To determine whether rifampicin reduces serum concentrations of nevirapine and whether nevirapine modifies serum concentrations of rifampicin, levels of these agents were determined at steady state by high-performance liquid chromatography in 10 HIV-infected patients with tuberculosis. The median area under the curve (AUC) 0-12h of nevirapine before and after rifampicin was 56.2 and 32.8 microg/ml per hour, respectively ( p =.04). This represents a 31% reduction in serum nevirapine concentrations. The C(max) decreased from 5.6 to 4.5 microg/ml ( p =.04), which represented a 36% reduction. A 21% decrease in the C(min) was not statistically significant. Exposure to rifampicin did not significantly differ between those patients who were receiving and were not receiving nevirapine. However, our study shows that rifampicin reduces serum exposure to nevirapine. The clinical implications for this reduction remain to be established. Given that the lowest trough serum concentration of nevirapine exceeded by more than 40 times the protein binding adjusted median infective dose (IC(50)) of wild-type HIV in all patients, we suggest that there is no need to increase nevirapine dosage when it is given with rifampicin.

Drugs and cardiotoxicity in HIV and AIDS

The advent of potent antiretroviral drugs in recent years has had an impressive impact on mortality and disease progression in HIV-infected patients, so that issues related to long-term effects of drugs are of growing importance. Hyperlipidemia, hyperglycemia, and lipodystrophy are increasingly described adverse effects of highly active antiretroviral therapy (HAART), in particular when protease inhibitors are used. Hyperlipidemia is strikingly associated with the use of most available protease inhibitors, with an estimated prevalence of up to 50%. Because of the short observation period and the small number of cardiovascular events, epidemiological evidence for an increased risk of coronary heart disease in HIV-infected patients treated with HAART is not adequate at present; however, it is likely that shortly more data will accumulate to quantify this risk. Before starting HAART and during treatment it is reasonable to evaluate all patients for traditional coronary risk factors, including lipid profile. Among the drugs that are currently used in HIV+ patients, antibacterials, antifungals, psychotropic drugs and anti-histamines have been associated with QT prolongation or torsade de pointe, a life-threatening ventricular arrhythmia. Among the risk factors that may precipitate an asymptomatic electrocardiographic abnormality into a dangerous arrhythmia is the concomitant use of drugs that share the CYP3A metabolic pathway. Since most protease inhibitors are potent inhibitors of CYP3A, clinicians should be aware of this potentially dangerous effect of HAART. Anthracyclines are potent cytotoxic antibiotics that have been widely used for the treatment of HIV-related neoplasms. Their cardiotoxicity is well known, ranging from benign and reversible arrhythmias to progressive severe cardiomyopathy. The increased survival and quality of life of HIV+ patients emphasize the importance of a high awareness of adverse drug-related cardiac effects.