A pharmacokinetic study of intermittent rifabutin dosing with a combination of ritonavir and saquinavir in patients infected with human immunodeficiency virus

A drug interaction study investigating the effect of Rifabutin on the pharmacokinetics of Maraviroc in healthy subjects

Effects of steady-state rifabutin on the pharmacokinetics of steady-state maraviroc were investigated in fourteen healthy adult female and male volunteers. Maraviroc 300 mg twice daily (BID) was given orally with food for fifteen days. On day six, rifabutin 300 mg once daily (QD, P.O.) was added to the regimen. Formal pharmacokinetic (PK) sampling was performed on days five and fifteen. Individual plasma drug concentration-time data for maraviroc, and rifabutin on day fifteen, were obtained using validated High Performance Liquid Chromatography (HPLC) tandem Mass Spectrometry (MS/MS). Rifabutin steady state exposure was comparable to data in the literature. Maraviroc area under the curve (AUC) and minimum plasma concentration (C_last or C_min) were reduced by 17% and 30% respectively when co-administered with rifabutin. No unexpected or serious adverse eventsoccurred. Based on the reduced exposure of maraviroc observed in this study, increasing the dose of maraviroc may be studied to normalize its moderately reduced exposure following rifabutin co-administration, a moderate inducer of CYP3A4.

Critical Review: What Dose of Rifabutin Is Recommended With Antiretroviral Therapy?

Since the advent of combination antiretroviral therapy to successfully treat HIV infection, drug-drug interactions (DDIs) have become a significant problem as many antiretrovirals (ARVs) are metabolized in the liver. Antituberculous therapy traditionally includes rifamycins, particularly rifampicin. Rifabutin (RBT) has shown similar efficacy as rifampicin but induces CYP3A4 to a lesser degree and is less likely to have DDIs with ARVs. We identified 14 DDI pharmacokinetic studies on HIV monoinfected and HIV-tuberculosis coinfected individuals, and the remaining studies were healthy volunteer studies. Although RBT may be coadministered with most nonnucleoside reverse transcriptase inhibitors, identifying the optimal dose with ritonavir-boosted or cobicistat-boosted protease inhibitors is challenging because of concern about adverse effects with increased RBT exposure. Limited healthy volunteer studies on other ARV drug classes and RBT suggest that dose modification may be unnecessary. The paucity of data assessing clinical tuberculosis endpoints concurrently with RBT and ARV pharmacokinetics limits evidence-based recommendations on the optimal dose of RBT within available ARV drug classes.

Population pharmacokinetic drug-drug interaction pooled analysis of existing data for rifabutin and HIV PIs

OBJECTIVES

Extensive but fragmented data from existing studies were used to describe the drug-drug interaction between rifabutin and HIV PIs and predict doses achieving recommended therapeutic exposure for rifabutin in patients with HIV-associated TB, with concurrently administered PIs.

METHODS

Individual-level data from 13 published studies were pooled and a population analysis approach was used to develop a pharmacokinetic model for rifabutin, its main active metabolite 25-O-desacetyl rifabutin (des-rifabutin) and drug-drug interaction with PIs in healthy volunteers and patients who had HIV and TB (TB/HIV).

RESULTS

Key parameters of rifabutin affected by drug-drug interaction in TB/HIV were clearance to routes other than des-rifabutin (reduced by 76%-100%), formation of the metabolite (increased by 224% in patients), volume of distribution (increased by 606%) and distribution to the peripheral compartment (reduced by 47%). For des-rifabutin, clearance was reduced by 35%-76% and volume of distribution increased by 67%-240% in TB/HIV. These changes resulted in overall increased exposure to rifabutin in TB/HIV patients by 210% because of the effects of PIs and 280% with ritonavir-boosted PIs.

CONCLUSIONS

Given together with non-boosted or ritonavir-boosted PIs, rifabutin at 150 mg once daily results in similar or higher exposure compared with rifabutin at 300 mg once daily without concomitant PIs and may achieve peak concentrations within an acceptable therapeutic range. Although 300 mg of rifabutin every 3 days with boosted PI achieves an average equivalent exposure, intermittent doses of rifamycins are not supported by current guidelines.

Influence of Panax ginseng on the steady state pharmacokinetic profile of lopinavir-ritonavir in healthy volunteers

STUDY OBJECTIVE

Panax ginseng has been shown in preclinical studies to modulate cytochrome P450 enzymes involved in the metabolism of HIV protease inhibitors. Therefore, the purpose of this study was to determine the influence of P. ginseng on the pharmacokinetics of the HIV protease inhibitor combination lopinavir-ritonavir (LPV-r) in healthy volunteers.

DESIGN

Single-sequence, open-label, single-center pharmacokinetic investigation.

SETTING

Government health care facility.

SUBJECTS

Twelve healthy human volunteers.

MEASUREMENTS AND MAIN RESULTS

Twelve healthy volunteers received LPV-r (400-100 mg) twice/day for 29.5 days. On day 15 of LPV-r administration, serial blood samples were collected over 12 hours for determination of lopinavir and ritonavir concentrations. On study day 16, subjects began taking P. ginseng 500 mg twice/day, which they continued for 2 weeks in combination with LPV-r. On day 30 of LPV-r administration, serial blood samples were again collected over 12 hours for determination of lopinavir and ritonavir concentrations. Lopinavir and ritonavir pharmacokinetic parameter values were determined using noncompartmental methods, and preadministration and postadministration ginseng values were compared using a Student t test, where p<0.05 was accepted as statistically significant.

CONCLUSION

Neither lopinavir nor ritonavir steady-state pharmacokinetics were altered by 2 weeks of P. ginseng administration to healthy human volunteers. Thus, a clinically significant interaction between P. ginseng and LPV-r is unlikely to occur in HIV-infected patients who choose to take these agents concurrently. It is also unlikely that P. ginseng will interact with other ritonavir-boosted protease inhibitor combinations, although confirmatory data are necessary.

Determination of rifabutin dosing regimen when administered in combination with ritonavir-boosted atazanavir

OBJECTIVES

Treatment of HIV/tuberculosis (TB) co-infected patients is complex due to drug-drug interactions for these chronic diseases. This study evaluates an intermittent dosing regimen for rifabutin when it is co-administered with ritonavir-boosted atazanavir.

PATIENTS AND METHODS

A randomized, multiple-dose, parallel-group study was conducted in healthy subjects and these subjects received a daily dose of rifabutin 150 mg (n = 15, reference group) or a twice weekly dose with atazanavir 300 mg/ritonavir 100 mg once daily (n = 18, test group). Serial blood samples were collected at steady-state for pharmacokinetic analysis. Modelling and simulation techniques were utilized, integrating data across several healthy subject studies. This study is known as Study AI424-360 and is registered with ClinicalTrials.gov, number NCT00646776.

RESULTS

The pharmacokinetic parameters (C(max), AUC(24avg) and C(min)) for rifabutin (149%, 48% and 40% increase, respectively) and 25-O-desacteyl rifabutin (6.77-, 9.90- and 10.45-fold increases, respectively) were both increased when rifabutin was co-administered with atazanavir/ritonavir than rifabutin 150 mg once daily alone. The study was stopped because subjects experienced more severe declines in neutrophil counts when rifabutin was given with atazanavir/ritonavir than alone. A post-hoc simulation analysis showed that when rifabutin 150 mg was given three times weekly with atazanavir/ritonavir, the average daily exposure of rifabutin was comparable to rifabutin 300 mg once daily, a dose necessary for reducing rifamycin resistance in HIV/TB co-infected patients.

CONCLUSIONS

The benefits to HIV/TB co-infected patients receiving rifabutin 150 mg three times weekly or every other day may outweigh the risks of neutropenia observed here in non-HIV-infected subjects, provided that patients on combination therapy will be closely monitored for safety and tolerability.

Echinacea purpurea significantly induces cytochrome P450 3A activity but does not alter lopinavir-ritonavir exposure in healthy subjects

STUDY OBJECTIVE

. To determine the influence of Echinacea purpurea on the pharmacokinetics of lopinavir-ritonavir and on cytochrome P450 (CYP) 3A and P-glycoprotein activity by using the probe substrates midazolam and fexofenadine, respectively.

DESIGN

Open-label, single-sequence pharmacokinetic study.

SETTING

Outpatient clinic in a federal government research center.

SUBJECTS

Thirteen healthy volunteers (eight men, five women).

INTERVENTION

Subjects received lopinavir 400 mg-ritonavir 100 mg twice/day with meals for 29.5 days. On day 16, subjects received E. purpurea 500 mg 3 times/day for 28 days: 14 days in combination with lopinavir-ritonavir and 14 days of E. purpurea alone. In order to assess CYP3A and P-glycoprotein activity, subjects received single oral doses of midazolam 8 mg and fexofenadine 120 mg, respectively, before and after the 28 days of E. purpurea.

MEASUREMENTS AND MAIN RESULTS

On days 15 and 30 of lopinavir-ritonavir administration (before and after E. purpurea administration, respectively), serial blood samples were collected over 12 hours to determine lopinavir and ritonavir concentrations and subsequent pharmacokinetic parameters by using noncompartmental methods. Neither lopinavir nor ritonavir pharmacokinetics were significantly altered by 14 days of E. purpurea coadministration. The post-echinacea: pre-echinacea geometric mean ratios (GMRs) for lopinavir area under the concentration-time curve (AUC) from 0-12 hours and for maximum concentration were 0.96 (90% confidence interval [CI] 0.83-1.10, p=0.82) and 1.00 (90% CI 0.88-1.12, p=0.72), respectively. Conversely, GMRs for midazolam AUC from time zero extrapolated to infinity and oral clearance were 0.73 (90% CI 0.61-0.85, p=0.008) and 1.37 (90% CI 1.10-1.63, p=0.02), respectively. Fexofenadine pharmacokinetics did not significantly differ before and after E. purpurea administration (p>0.05).

CONCLUSION

Echinacea purpurea induced CYP3A activity but did not alter lopinavir concentrations, most likely due to the presence of the potent CYP3A inhibitor, ritonavir. Echinacea purpurea is unlikely to alter the pharmacokinetics of ritonavir-boosted protease inhibitors but may cause modest decreases in plasma concentrations of other CYP3A substrates.

Interaction studies of tipranavir-ritonavir with clarithromycin, fluconazole, and rifabutin in healthy volunteers

Three separate controlled, two-period studies with healthy volunteers assessed the pharmacokinetic interactions between tipranavir-ritonavir (TPV/r) in a 500/200-mg dose and 500 mg of clarithromycin (CLR), 100 mg of fluconazole (FCZ), or 150 mg of rifabutin (RFB). The CLR study was conducted with 24 subjects. The geometric mean ratios (GMR) and 90% confidence intervals (90% CI; given in parentheses) of the areas under the concentration-time curve (AUC), the maximum concentrations of the drugs in serum (C(max)), and the concentrations in serum at 12 h postdose (Cp12h) for multiple-dose TPV/r and multiple-dose CLR, indicating the effect of TPV/r on the CLR parameters, were 1.19 (1.04-1.37), 0.95 (0.83-1.09), and 1.68 (1.42-1.98), respectively. The formation of the metabolite 14-OH-CLR was decreased by 95% in the presence of TPV, and the TPV AUC increased 66% compared to that for human immunodeficiency virus (HIV)-negative historical controls. The FCZ study was conducted with 20 subjects. The GMR (and 90% CI) of the AUC, C(max), and Cp24h, indicating the effect of multiple-dose TPV/r on the multiple-dose FCZ parameters, were 0.92 (0.88-0.95), 0.94 (0.91-0.98), and 0.89 (0.85-0.92), respectively. The TPV AUC increased by 50% compared to that for HIV-negative historical controls. The RFB study was conducted with 24 subjects. The GMR (and 90% CI) of the AUC, C(max), and Cp12h for multiple-dose TPV/r and single-dose RFB, indicating the effect of TPV/r on the RFB parameters, were 2.90 (2.59-3.26), 1.70 (1.49-1.94), and 2.14 (1.90-2.41), respectively. The GMR (and 90% CI) of the AUC, C(max), and Cp12h of TPV/r and RFB with 25-O-desacetyl-RFB were 4.33 (3.86-4.86), 1.86 (1.63-2.12), and 2.76 (2.44-3.12), respectively. Coadministration of TPV with a single dose of RFB resulted in a 16% increase in the TPV Cp12h compared to that for TPV alone. In the general population, no dose adjustments are necessary for the combination of TPV/r and CLR or FCZ. Combining TPV/r with RFB should be done with caution, while toxicity and RFB drug levels should be monitored. Study medications were generally well-tolerated in these studies.

Nontuberculous mycobacterial infections

CONTEXT

Nontuberculous mycobacteria include numerous acid-fast bacilli species, many of which have only recently been recognized as pathogenic. The diagnosis of mycobacterial disease is based on a combination of clinical features, microbiologic data, radiographic findings, and histopathologic studies.

OBJECTIVE

To provide an overview of the clinical and pathologic aspects of nontuberculous mycobacteria infection, including diagnostic laboratory methods, classification, epidemiology, clinical presentation, and treatment.

DATA SOURCES

Review of the pertinent literature and published methodologies.

CONCLUSIONS

Nontuberculous mycobacteria include numerous acid-fast bacilli species, many of which are potentially pathogenic, and are classified according to the Runyon system based on growth rates and pigment production. Their slow growth hinders cultures, which require special medium and prolonged incubation. Although such methods are still used, newer nucleic acid-based technologies (polymerase chain reaction and hybridization assays) can rapidly detect and speciate some mycobacteria--most notably, distinguishing Mycobacterium tuberculosis from other species. Infections caused by these organisms can present as a variety of clinical syndromes, not only in immunocompromised patients but also in immunocompetent hosts. Most common among these are chronic pulmonary infections, superficial lymphadenitis, soft tissue and osteoarticular infections, and disseminated disease. Treatment of nontuberculous mycobacterial infections is difficult, requiring extended courses of multidrug therapy with or without adjunctive surgical intervention.

Effect of Ginkgo biloba extract on lopinavir, midazolam and fexofenadine pharmacokinetics in healthy subjects

OBJECTIVE

Animal and in vitro data suggest that Ginkgo biloba extract (GBE) may modulate CYP3A4 activity. As such, GBE may alter the exposure of HIV protease inhibitors metabolized by CYP3A4. It is also possible that GBE could alter protease inhibitor pharmacokinetics (PK) secondary to modulation of P-glycoprotein (P-gp). The primary objective of the study was to evaluate the effect of GBE on the exposure of lopinavir in healthy volunteers administered lopinavir/ritonavir. Secondary objectives were to compare ritonavir exposure pre- and post-GBE, and assess the effect of GBE on single doses of probe drugs midazolam and fexofenadine.

METHODS

This open-label study evaluated the effect of 2 weeks of standardized GBE administration on the steady-state exposure of lopinavir and ritonavir in 14 healthy volunteers administered lopinavir/ritonavir to steady-state. In addition, single oral doses of probe drugs midazolam and fexofenadine were administered prior to and after 4 weeks of GBE (following washout of lopinavir/ritonavir) to assess the influence of GBE on CYP3A and P-gp activity, respectively.

RESULTS

Lopinavir, ritonavir and fexofenadine exposures were not significantly affected by GBE administration. However, GBE decreased midazolam AUC(0-infinity) and C(max) by 34% (p = 0.03) and 31% (p = 0.03), respectively, relative to baseline. In general, lopinavir/ritonavir and GBE were well tolerated. Abnormal laboratory results included mild elevations in hepatic enzymes, cholesterol and triglycerides, and mild-to-moderate increases in total bilirubin.

CONCLUSIONS

Our results suggest that GBE induces CYP3A metabolism, as assessed by a decrease in midazolam concentrations. However, there was no change in the exposure of lopinavir, likely due to ritonavir's potent inhibition of CYP3A4. Thus, GBE appears unlikely to reduce the exposure of ritonavir-boosted protease inhibitors, while concentrations of unboosted protease inhibitors may be affected. Limitations to our study include the single sequence design and the evaluation of a ritonavir-boosted protease inhibitor exclusively.

Outcomes of dosage adjustments used to manage antiretroviral drug interactions

Dosage adjustments are often used to manage HIV drug interactions, but little is known about their clinical significance. We examined patients from the Ontario HIV Cohort Study to assess the effects of dosage adjustments on plasma viral load. A significant reduction (0.67 log10 copies/mL) in viral load was associated with adjustments to manage efavirenz-based interactions (95% confidence interval, -1.33 to -0.01) but was not observed after adjustments to manage rifabutin-based (difference in viral load, 0.03 log10 copies/mL; 95% confidence interval, -0.71 to 0.77) or nevirapine-based interactions (difference in viral load, 0.09 log10 copies/mL; 95% confidence interval, -0.83 to 1.01).

Saquinavir: a review of its use in boosted regimens for treating HIV infection

Protease inhibitor boosting involves concurrent administration of a protease inhibitor, such as saquinavir, plus a potent inhibitor of cytochrome P450 (CYP) 3A4, usually ritonavir in subtherapeutic doses. Since protease inhibitors are extensively metabolised by CYP3A4, this results in a marked increase in systemic exposure of saquinavir or other protease inhibitors boosted by ritonavir. As with traditional protease inhibitor regimens, boosted regimens are typically used in combination with nucleoside reverse transcriptase inhibitors (NRTIs). In protease inhibitor-experienced and -naive patients with HIV infection, twice-daily and once-daily boosted saquinavir regimens achieved good rates of viral suppression, improved CD4+ cell counts and were generally well tolerated in clinical trials. Encouraging results have also been reported in a number of small studies in heavily pretreated HIV-infected patients who received salvage therapy comprising double-boosted regimens of saquinavir plus lopinavir with subtherapeutic doses of ritonavir, along with other agents. The largest clinical trials have been multicentre, randomised comparisons of twice-daily boosted saquinavir versus twice-daily boosted indinavir (MaxCmin1) or lopinavir (MaxCmin2) regimens. In the MaxCmin1 study, >90% of patients in both groups had an undetectable viral load (<400 copies/mL) after 48 weeks of therapy in the on-treatment analysis. However, viral suppression was achieved in significantly more saquinavir than indinavir recipients in the intention-to-treat analysis, which appeared to be due to the significantly greater percentage of patients in the indinavir group who switched from randomised therapy because of adverse events. Interim 24-week results of the MaxCmin2 trial indicate that 90% of patients in both groups combined had plasma HIV RNA levels <400 copies/mL; final results at 48 weeks will report data separately for the boosted regimens of saquinavir and lopinavir.

CONCLUSION

Boosted protease inhibitor regimens (including two NRTIs) are recommended as a first-line option in current HIV treatment guidelines and are used extensively in clinical practice. The convenient administration schedule and good pharmacokinetic profile associated with boosted saquinavir regimens have the potential to increase adherence to therapy and improve antiretroviral effects through increased drug exposure. Twice-daily boosted saquinavir is one of the most extensively evaluated boosted protease inhibitor regimens and has been shown to have good efficacy on surrogate markers of HIV disease as well as significant tolerability advantages over boosted indinavir. Once-daily boosted saquinavir regimens may be most suitable for HIV-infected patients with busy lifestyles and those who would benefit from directly observed therapy.

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.

Drug-drug interactions in inmates treated for human immunodeficiency virus and Mycobacterium tuberculosis infection or disease: an institutional tuberculosis outbreak

The use of rifamycins is limited by drug interactions in human immunodeficiency virus (HIV)-infected persons who are receiving highly active antiretroviral therapy (HAART). During a tuberculosis (TB) outbreak at a prison housing HIV-infected inmates, rifabutin was used to treat 238 men (13 case patients and 225 contacts). Steady-state peak plasma rifabutin concentrations were obtained after rifabutin dosages were adjusted for men receiving single-interacting HAART (with either 1 protease inhibitor [PI] or efavirenz), multi-interacting HAART (with either 2 PIs or > or =1 PI with efavirenz), and for noninteracting HAART (>1 nucleoside reverse-transcriptase inhibitor or no HAART) without rifabutin dose adjustments. Low rifabutin concentrations occurred in 9% of those receiving noninteracting HAART, compared with 19% of those receiving single-interacting and 29% of those receiving multi-interacting HAART (chi2, 3.76; P=.05). Of 225 contacts treated with rifabutin-pyrazinamide, 158 (70%) completed treatment while incarcerated. Rifabutin-pyrazinamide therapy was difficult to implement, because of the need for dosage adjustments and expert clinical management.

Interaction between saquinavir soft-gel and rifabutin in patients infected with HIV

AIMS

To evaluate the potential pharmacokinetic interaction between the HIV protease inhibitor saquinavir and rifabutin.

METHODS

Fourteen HIV-infected patients provided full steady-state pharmacokinetic profiles following administration of rifabutin alone (300 mg once daily) or saquinavir soft-gel formulation (1200 mg three times daily) plus rifabutin (300 mg once daily) in this open label, partially randomized study.

RESULTS

Coadministration of saquinavir and rifabutin resulted in a reduction in saquinavir AUC(0,8 h) and C(max)(0,8 h) of 47% (95% CI 30, 60%) and 39% (95% CI 11, 59%), respectively. Rifabutin AUC(0,24 h) and C(max)(0,24 h) was increased by an average of 44% (95% CI 17, 78%) and 45% (95% CI 14, 85%), respectively. Saquinavir in combination with rifabutin was well tolerated. Gastrointestinal intolerance and asymptomatic increases in liver enzymes were the only adverse events of note.

CONCLUSIONS

Administration of rifabutin with saquinavir may decrease the efficacy of this HIV protease inhibitor.

Comparative pharmacokinetics and pharmacodynamics of the rifamycin antibacterials

The rifamycin antibacterials, rifampicin (rifampin), rifabutin and rifapentine, are uniquely potent in the treatment of patients with tuberculosis and chronic staphylococcal infections. Absorption is variably affected by food; the maximal concentration of rifampicin is decreased by food, whereas rifapentine absorption is increased in the presence of food. The rifamycins are well-known inducers of enzyme systems involved in the metabolism of many drugs, most notably those metabolised by cytochrome P450 (CYP) 3A. The relative potency of the rifamycins as CYP3A inducers is rifampin > rifapentine > rifabutin; rifabutin is also a CYP3A substrate. The antituberculosis activity of rifampicin is decreased by a modest dose reduction from 600 to 450mg. This somewhat surprising finding may be due to the binding of rifampicin to serum proteins, limiting free, active concentrations of the drug. However, increasing the administration interval (after the first 2 to 8 weeks of therapy) has little effect on the sterilising activity of rifampicin, suggesting that relatively brief exposures to a critical concentration of rifampicin are sufficient to kill intermittently metabolising mycobacterial populations. The high protein binding of rifapentine (97%) may explain the suboptimal efficacy of the currently recommended dose of this drug. The toxicity of rifampicin is related to dose and administration interval, with increasing rates of presumed hypersensitivity with higher doses combined with administration frequency of once weekly or less. Rifabutin toxicity is related to dose and concomitant use of CYP3A inhibitors. The rifamycins illustrate the complexity of predicting the pharmacodynamics of treatment of an intracellular pathogen with the capacity for dormancy.