A review of low-dose ritonavir in protease inhibitor combination therapy.

The pharmacokinetics of protease inhibitors center around the microsomal enzyme cytochrome P-450 3A4. As a potent inhibitor of this enzyme, ritonavir can increase the bioavailability and half-life of coadministered protease inhibitors. Evidence suggests that increased exposure to protease inhibitors is clinically relevant. Antiretroviral treatment with low-dose ritonavir-boosted lopinavir, indinavir, and saquinavir has durable virological activity and shows impressive immune reconstitution. Although tolerable in most cases, gastrointestinal side effects, hepatotoxicity, and blood lipid abnormalities remain relevant issues. Additional study will elucidate the advantages and disadvantages of twice-daily, low-dose ritonavir-boosted regimens and determine whether once-daily regimens based on this principle will have a lasting role in clinical practice.

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.

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

AIM: Our primary aim was to evaluate the plasma exposures and safety of rifabutin and its active 25-O-desacetyl metabolite during concomitant therapy of intermittent rifabutin dosing regimens with a combination of ritonavir and saquinavir. METHODS: Twenty-four patients without mycobacterial infection who were human immunodeficiency virus seropositive and who were receiving 400 mg each of ritonavir and saquinavir twice daily participated in a 3-period, 2-group longitudinal pharmacokinetic study. Patients were equally randomized to receive 300 mg of rifabutin every 7 days (group 1) or 150 mg of rifabutin every 3 days (group 2) for 8 weeks. Blood samples were collected over the dosing intervals of the protease inhibitors at baseline (period 1) and of the 3 drugs after 4 weeks (period 2) and 8 weeks (period 3) for HPLC measurement of plasma concentrations of the 3 drugs and 25-O-desacetylrifabutin. RESULTS: Nineteen patients (group 1, n = 10; group 2, n = 9) completed the study. Five individuals withdrew from the study; 3 of them experienced side effects, and 2 were lost to follow-up. For combined groups, mean saquinavir and ritonavir overall (area under the concentration-time curve [AUC]) and peak (C(max)) plasma exposures averaged over periods 2 and 3 did not change significantly (8% to 19%; P > .05) compared with those in period 1 (90% confidence intervals, -7% to 26% for ritonavir and -2% to 38% for saquinavir). Rifabutin and metabolite AUC and C(max) exposures were stable over the 8 weeks, with intraindividual coefficients of variation of 12% to 19%. Oral clearance of rifabutin was similar in both groups (321 mL/min in group 2 versus 372 mL/min in group 1; P = .34). Rifabutin C(max) values were significantly lower in group 2 (310 ng/mL versus 496 ng/mL in group 1; P = .004). Rifabutin and metabolite predose levels were significantly higher in group 2 (rifabutin: 54 ng/mL versus 17 ng/mL; desacetyl rifabutin: 55 ng/mL versus 28 ng/mL; P < .002). CONCLUSIONS: Rifabutin exposures were similar at 4 and 8 weeks and had minimal effect on ritonavir and saquinavir exposures. Intermittent rifabutin dosing over 8 weeks provided a safe and manageable regimen for concurrent therapy with a combination of ritonavir and saquinavir.

An in vitro evaluation of human cytochrome P450 3A4 and P-glycoprotein inhibition by garlic.

PURPOSE: Garlic has been used as a flavouring agent, traditional medicine, and functional food to improve physical or mental well-being. Garlic and garlic products generally have been regarded as safe but a number of conflicting reports in the literature and confounding factors make it difficult to unequivocally establish the clinical efficacy and safety of these products either alone or in the presence of therapeutic products. A preliminary study was undertaken with fresh garlic and garlic products using the major cDNA-expressed human cytochrome P-450 isozymes associated with the metabolism of HIV/AIDS drugs, and purified P-glycoprotein (P-gp) cell membranes to ascertain the risk potential for generating interactions with therapeutic products. METHODS: A broad screening was undertaken with 10 garlic products (aged, odourless, oil, freeze-dried) and 3 varieties of fresh garlic bulbs (common, Elephant and Chinese), all purchased from local outlets, to examine their potential to affect human cytochrome P-450 2C9*1, 2C9*2, 2C19, 2D6, 3A4, 3A5 and 3A7 mediated-metabolism of marker substrates using an in vitro fluorometric microtiter plate assay. Four garlic products were screened for their potential to interact with P-gp using an in vitro colourmetric ATPase assay. RESULTS: Extracts of fresh garlic, different brands and lots of odourless garlic and representative samples of garlic oil, freeze dried garlic, and aged garlic exhibited an inhibitory effect on cytochrome P450 2C9*1, 2C19, 3A4, 3A5 and 3A7 mediated metabolism of a marker substrate. The activity of 2D6 mediated-metabolism was generally unaffected by garlic. Extracts of the fresh garlic stimulated CYP2C9*2 metabolism of the marker substrate. With the extracts tested, garlic had very low to moderate P-gp interaction as compared with the positive control verapamil. CONCLUSIONS: Our in vitro findings demonstrate that garlic components can affect cytochrome P-450 2C, 2D and 3A mediated-metabolism of the isoforms studied. The safety and efficacy of conventional therapeutic products metabolized by the affected isozymes, particularly those with a narrow therapeutic index, taken concomitantly with garlic needs to be examined further under clinical settings.

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.

Pharmacokinetic interaction between mefloquine and ritonavir in healthy volunteers.

AIMS: To evaluate the pharmacokinetic interaction between ritonavir and mefloquine. METHODS: Healthy volunteers participated in two separate, nonfasted, three-treatment, three-period, longitudinal pharmacokinetic studies. Study 1 (12 completed): ritonavir 200 mg twice daily for 7 days, 7 day washout, mefloquine 250 mg once daily for 3 days then once weekly for 4 weeks, ritonavir restarted for 7 days simultaneously with the last mefloquine dose. Study 2 (11 completed): ritonavir 200 mg single dose, mefloquine 250 mg once daily for 3 days then once weekly for 2 weeks, ritonavir single dose repeated 2 days after the last mefloquine dose. Erythromycin breath test (ERMBT) was administered with and without drug treatments in study 2. RESULTS: Study 1: Ritonavir caused less than 7% changes with high precision (90% CIs: -12% to 11%) in overall plasma exposure (AUC(0,168 h)) and peak concentration (Cmax) of mefloquine, its two enantiomers, and carboxylic acid metabolite, and in the metabolite/mefloquine and enantiomeric AUC ratios. Mefloquine significantly decreased steady-state ritonavir plasma AUC(0,12 h) by 31%, Cmax by 36%, and predose levels by 43%, and did not affect ritonavir binding to plasma proteins. Study 2: Mefloquine did not alter single-dose ritonavir pharmacokinetics. Less than 8% changes in AUC and Cmax were observed with high variability (90%CIs: -26% to 45%). Mefloquine had no effect on the ERMBT whereas ritonavir decreased activity by 98%. CONCLUSIONS: Ritonavir minimally affected mefloquine pharmacokinetics despite strong inhibition of CYP3A4 activity from a single 200 mg dose. Mefloquine had variable effects on ritonavir pharmacokinetics that were not explained by hepatic CYP3A4 activity or ritonavir protein binding.

Single and multiple dose pharmacokinetics of nelfinavir and CYP2C19 activity in human immunodeficiency virus-infected patients with chronic liver disease.

AIMS: To evaluate the single-dose and multiple-dose pharmacokinetics of nelfinavir and its active M8 metabolite in eight HIV-seropositive patients with liver disease, and to examine the relationship between CYP2C19 activity (genotype and plasma M8/nelfinavir metabolic ratio) and the severity of liver disease in these patients. METHODS: Nelfinavir was given as a single dose (500 or 750 mg) to patients beginning therapy and twice (500, 750 or 1000 mg) or three times (250 or 750 mg) daily during chronic therapy. Single-dose pharmacokinetic values were used to predict multiple-dose regimens. Peak and total plasma exposures between 2-4 microg ml-1 and 45-75 microg ml-1 h, respectively, and predose levels > 0.7 microg ml-1 were targeted for multidose nelfinavir. Genotype was determined by analysis for CYP2C19*1, CYP2C19*2, and CYP2C19*3. Individuals were grouped according to their genotype, molar M8/nelfinavir AUC ratio (low: < 0.1, intermediate: 0.1-0.3, high > 0.3), and Child-Pugh classification for severity of liver disease. RESULTS: Nelfinavir pharmacokinetics were characterized by wide interindividual variability, low clearance (181-496 ml min-1 70 kg-1, n = 7), and prolonged half-life (5-20 h, n = 7). M8/nelfinavir AUC ratio increased 58% (n = 4) and alpha 1-acid glycoprotein levels decreased up to 39% (n = 5) from single to multiple dosing. CYP2C19 activity was low (metabolic AUC ratio < 0.1) in four patients with moderate to severe liver disease even though they were genetically extensive CYP2C19 metabolizers (*1/*1 or *1/*2). Three patients required lower daily doses than the standard regimen of 750 mg every 8 h to achieve target concentrations and maintain virologic suppression at < 50 RNA copies ml-1 (up to 20 months). CONCLUSIONS: Acquired CYP2C19 deficiency from moderate or severe liver disease resulted in decreased M8 formation. Long-term HIV suppression is possible using low nelfinavir doses in patients with liver disease.

Patient-reported nonadherence to HAART is related to protease inhibitor levels.

OBJECTIVE: To compare self-reported nonadherence with antiretroviral therapy (ART) with predose plasma levels of protease inhibitor (PI). DESIGN: A cross-sectional study of consecutive patients from a university-based HIV clinic in Rome, Italy, was conducted. One hundred and forty HIV-infected patients were prescribed regimens containing ritonavir or indinavir. A patient questionnaire assessing knowledge of treatment regimen, adherence behavior, reasons for taking and missing therapy, factors influencing adherence, and health behaviors was administered. A predose PI plasma level was measured concurrently. RESULTS: By patient report, 12% missed at least one dose "yesterday," and 24% missed doses in the last 3 days; 14% had a predose plasma concentration below the assay limit of quantitation (2 ritonavir and 18 indinavir samples). Confusion, poor psychological well-being, long office wait, running out of drugs between visits, having relatives to remind the patient to take medication, children, and alteration of sense of taste were related to unquantifiable predose levels of PI. In multivariable analysis, reported nonadherence (odds ratio [OR], 15.8; 95% confidence interval [CI], 4.0-63.3) and confusion (OR, 9.9; 95% CI, 1.4-69.6) were related to unquantifiable predose levels of PI. CONCLUSION: Self-report of missing a dose of antiretroviral medication "yesterday" was related to an unmeasurable plasma PI level.

Decreased HIV-associated T cell apoptosis by HIV protease inhibitors.

Antiretroviral treatment of patients infected with HIV results in improvements in CD4+ T cell number. Emerging evidence suggests that some of the improvements in CD4+ T cell number that occur in response to protease inhibitor (PI) therapy may not be accounted for solely by enhanced viral suppression, implying that PI may directly affect T cell survival. Since HIV T cell depletion is associated with enhanced apoptosis, we analyzed the effect of PIs on T cell apoptosis. In vitro treatment of peripheral blood lymphocytes (PBLs) from HIV-infected but untreated patients with reverse transcriptase inhibitors (RTIs) does not alter apoptosis, whereas PI treatment rapidly reduces CD4+ and CD8+ T cell apoptosis. In contrast, PI treatment does not alter apoptosis in PBL blasts from HIV-negative patients, or in Jurkat T cells. Consistent with this observation, 8 days of PI therapy in HIV-infected patients does not significantly alter plasma viremia, yet results in significant inhibition of CD4+ and CD8+ T cell apoptosis. The inhibitory effects of PI on apoptosis have implications concerning the treatment of HIV and its pathogenesis.

Effect of ketoconazole on ritonavir and saquinavir concentrations in plasma and cerebrospinal fluid from patients infected with human immunodeficiency virus.

AIM: Our aim was to evaluate the effect of ketoconazole on ritonavir and saquinavir plasma and cerebrospinal fluid (CSF) concentrations. METHODS: Twelve patients who were human immunodeficiency virus-seropositive and who were receiving 400 mg of ritonavir and 400 mg of saquinavir twice daily completed a nonfasted, two-period, two-group, longitudinal pharmacokinetic study. Blood samples were collected over the daytime 12-hour dosing interval of the protease inhibitors at baseline (period 1, day 0) and after 10 days of coadministration of 200 mg (n = 6) or 400 mg (n = 6) of ketoconazole once daily (period 2, day 10). One set of paired CSF and blood samples was collected between 4 and 5 hours after the dose on both days. RESULTS: Ketoconazole significantly increased area under the plasma concentration-time curve, plasma concentration at 12 hours after the dose, and half-life of ritonavir by 29% (95% confidence interval (CI), 13%-46%), 62% (95% CI, 37%-92%), and 31% (95% CI, 13%-51%), respectively. Similar increases of 37% (95% CI, 4%-81%), 94% (95% CI, 41%-167%), and 38% (95% CI, 15%-66%), respectively, were observed for these parameters for saquinavir. Ketoconazole significantly elevated ritonavir CSF concentration by 178% (95% CI, 59%-385%), from 2.4 to 6.6 ng/mL, with no change in paired unbound plasma level (26 ng/mL); this led to a commensurate 181% increase (95% CI, 47%-437%) in CSF/plasma unbound ratio. All pharmacokinetic changes were unrelated to ketoconazole dose or plasma exposures. Corresponding changes for saquinavir CSF pharmacokinetics were insignificant (P > .06); saquinavir CSF levels were unmeasurable in 7 patients (<0.2 ng/mL). CONCLUSIONS: The disproportionate increase in CSF compared with plasma concentrations of ritonavir is consistent with ketoconazole inhibiting both drug efflux from CSF and systemic clearance.

Cerebrospinal fluid HIV RNA and drug levels with combination ritonavir and saquinavir.

UNLABELLED: Combination antiretroviral therapy with ritonavir and saquinavir has established potent and durable activity on plasma viremia. CNS HIV infection may be sequestered from drug therapy that does not penetrate the blood-brain barrier. Penetration of these protease inhibitors into the cerebrospinal fluid (CSF) and CSF HIV RNA levels on such therapy has not been well described. DESIGN/METHODS: In a cross-sectional study, 28 HIV1-infected study subjects were evaluated either before initiation of or before maximal response to ritonavir-saquinavir therapy, during maximal plasma virologic response, and after virologic failure. Simultaneous samples of plasma and cerebrospinal fluid were obtained from 24 study subjects to measure HIV RNA and protease inhibitor levels. RESULTS: Across the treatment groups, a strong correlation was found between plasma and CSF HIV RNA levels (r = 0.870; p < .001). In each study subject with plasma HIV RNA levels below assay limit (80 copies/ml), the CSF HIV RNA level was also below the limit of quantitation. Low levels of saquinavir (<2 ng/ml) and ritonavir (<25 ng/ml) in the CSF were observed, with a CSF:plasma drug concentration ratio of < or = 0.005 (0.5%) in all study subjects evaluated (n = 11). The plasma:CSF HIV RNA ratio was high before or early in treatment (median, 38; interquartile range [IQR], 13,97), but low (median, 0.29; IQR, 0.17, 7.5) in those failing therapy (group C, p < .001). CONCLUSIONS: CSF ritonavir and saquinavir levels are consistent with the estimated known fraction of unbound drug in plasma (<2%). Across these treatment response groups, suppression of plasma viremia can predict low CSF HIV RNA levels. This correlation may represent HIV RNA transport and equilibrium between CSF and plasma, or it may represent CNS anti-HIV activity of protease inhibitors. The low drug levels and inverted ratio of HIV RNA in the CSF compared with plasma early in plasma virologic breakthrough suggests CSF virologic failure may contribute to failure of plasma virologic response.

Induction of zidovudine glucuronidation and amination pathways by rifampicin in HIV-infected patients.

AIMS: The objective of the study was to determine the effect of multiple doses of rifampicin on the steady-state pharmacokinetics of zidovudine and its 5'-glucuronosyl (GZDV) and 3'-amino (AMT) metabolites. METHODS: Eight asymptomatic HIV-infected patients (seven male, one female) participated in this three-period longitudinal study. Each patient received zidovudine (200 mg every 8 h) for 14 days (period 1), followed by rifampicin (600 mg every 24 h) with zidovudine for 14 days (period 2), and then zidovudine alone for a further 14 days (period 3). Blood and urine samples were collected over 6 h on the last day of each period for measurements of zidovudine and GZDV by h.p.l.c.-u.v. and AMT by h.p.l.c.-m.s-m.s. RESULTS: Compared with zidovudine-alone values in period 1, 14 days of coadministration with rifampicin significantly increased zidovudine oral clearance (89%) and formation clearances to GZDV (100%) and AMT (82%). Correspondingly, there were decreases in maximum plasma concentration (43%), AUC (47%) and urine recovery (37%) of zidovudine. GZDV/zidovudine and AMT/zidovudine AUC ratios increased by 99% and 36%, respectively, despite a significant 29% decrease in AMT AUC. After stopping rifampicin for 14 days, values of these pharmacokinetic parameters returned to within 26% of baseline. Over the three periods AMT plasma levels were <18 ng ml-1 (n=6) and <40 ng ml-1 (n=2), and molar AMT/zidovudine AUC ratios ranged from 1.7% to 4.5%. CONCLUSIONS: Rifampicin induced zidovudine glucuronidation and amination pathways resulting in decreased plasma and urine exposures to zidovudine. AMT plasma exposure decreased because induction was more pronounced for the major GZDV metabolite. The magnitude of the residual inductive effect was minimal at 14 days after stopping rifampicin.

Reduced plasma concentrations of antituberculosis drugs in patients with HIV infection.

BACKGROUND: Reports suggest that antituberculosis drugs are malabsorbed in patients with advanced HIV disease. OBJECTIVE: To evaluate the pharmacokinetics of antituberculosis agents in HIV-seropositive patients at different stages of disease. DESIGN: Parallel study. SETTING: Two hospital outpatient clinics. PARTICIPANTS: 12 healthy volunteers, 12 patients with asymptomatic HIV disease, 12 patients with symptomatic HIV disease, and 12 patients with symptomatic HIV disease and diarrhea. MEASUREMENTS: Drug plasma concentrations were measured over 24 hours on day 4 of concurrent therapy. INTERVENTION: Oral isoniazid (300 mg/d), rifampin (600 mg/d), pyrazinamide (1000 mg/d), and ethambutol (1000 mg/d). RESULTS: Reduced total drug exposure to rifampin and pyrazinamide was associated with D-xylose malabsorption in persons with HIV infection or AIDS. Peak drug exposure to isoniazid was lower in patients with diarrhea. CONCLUSIONS: Reduced total drug exposure may be related to malabsorption in persons with HIV infection or AIDS.