Richard Leff

Pamidronate Reduces Skeletal Morbidity in Women With Advanced Breast Cancer and Lytic Bone Lesions: A Randomized, Placebo-Controlled Trial

PURPOSE To assess whether pamidronate can reduce the frequency of skeletal morbidity in women with lytic bone metastases from breast cancer treated with hormone therapy. PATIENTS AND METHODS Three hundred seventy-two women with breast cancer who had at least one lytic bone lesion and who were receiving hormonal therapy were randomized to receive 90 mg of pamidronate or placebo as a 2-hour intravenous infusion given in double-blind fashion every 4 weeks for 24 cycles. Patients were evaluated for skeletal complications: pathologic fractures, spinal cord compression, irradiation of or surgery on bone, or hypercalcemia. The skeletal morbidity rate (the ratio of the number of skeletal complications to the time on trial) was the primary efficacy variable. Bone pain, use of analgesics, quality of life, performance status, bone tumor response, and biochemical parameters were also evaluated. RESULTS One hundred eighty-two patients who received pamidronate and 189 who received placebo were assessable. The skeletal morbidity rate was significantly reduced at 12, 18, and 24 cycles in patients treated with 90 mg of pamidronate (P = .028, .023, and .008, respectively). At 24 cycles, the proportion of patients having had any skeletal complication was 56% in the pamidronate group and 67% in the placebo group (P = .027). The time to the first skeletal complication was longer for patients receiving pamidronate than for those given placebo (P = .049). There was no statistical difference in survival or in objective bone response rate. Pamidronate was well tolerated. CONCLUSION Treatment with 90 mg of pamidronate as a 2-hour intravenous infusion every 4 weeks in addition to hormonal therapy significantly reduces skeletal morbidity from osteolytic metastases.

Multidrug-Resistant Tuberculosis Not Due to Noncompliance but to Between-Patient Pharmacokinetic Variability

BACKGROUND It is believed that nonadherence is the proximate cause of multidrug-resistant tuberculosis (MDR-tuberculosis) emergence. The level of nonadherence associated with emergence of MDR-tuberculosis is unknown. Performance of a randomized controlled trial in which some patients are randomized to nonadherence would be unethical; therefore, other study designs should be utilized. METHODS We performed hollow fiber studies for both bactericidal and sterilizing effect, with inoculum spiked with 0.5% rifampin- and isoniazid-resistant isogenic strains in some experiments. Standard therapy was administered daily for 28-56 days, with extents of nonadherence varying between 0% and 100%. Sizes of drug-resistant populations were compared using analysis of variance. We also explored the effect of pharmacokinetic variability on MDR-tuberculosis emergence using computer-aided clinical trial simulations of 10 000 Cape Town, South Africa, tuberculosis patients. RESULTS Therapy failure was only encountered at extents of nonadherence ≥60%. Surprisingly, isoniazid- and rifampin-resistant populations did not achieve ≥1% proportion in any experiment and did not achieve a higher proportion with nonadherence. However, clinical trial simulations demonstrated that approximately 1% of tuberculosis patients with perfect adherence would still develop MDR-tuberculosis due to pharmacokinetic variability alone. CONCLUSIONS These data, based on a preclinical model, demonstrate that nonadherence alone is not a sufficient condition for MDR-tuberculosis emergence.

Pharmacokinetics-Pharmacodynamics of Pyrazinamide in a Novel In Vitro Model of Tuberculosis for Sterilizing Effect: a Paradigm for Faster Assessment of New Antituberculosis Drugs

ABSTRACT There are currently renewed efforts to develop drugs that could shorten the duration of antituberculosis therapy. This is best achieved by optimizing the sterilizing effect. However, the current pathway for the development of new molecules with the potential to have a sterilizing effect is inefficient. We designed an in vitro pharmacokinetic-pharmacodynamic model in which Mycobacterium tuberculosis replicating slowly at pH 5.8 was exposed to pyrazinamide by use of the concentration-time profiles encountered in patients. The sterilizing effect rates and the time to the emergence of drug resistance were examined. Daily pyrazinamide dosing for 28 days accurately achieved (i) the pyrazinamide pharmacokinetic parameters, (ii) the lack of early bactericidal activity, (iii) a sterilizing effect rate of 0.10 log10 CFU/ml per day starting on day 6 of therapy, and (iv) a time to the emergence of resistance of the from 2 to 3 weeks of monotherapy encountered in patients with tuberculosis. Next, dose-scheduling studies were performed. The sterilizing effect was linked to the pyrazinamide ratio of the area under the concentration-time curve from 0 to 24 h (AUC0-24) to the MIC (r2 = 0.80 to 0.90), with 90% of the maximal effect being achieved by an AUC0-24/MIC of 209.08. Resistance suppression was associated with the percentage of time that the concentration persisted above the MIC (r2 = 0.73 to 0.91). Monte Carlo simulations of 10,000 patients demonstrated that the currently recommended pyrazinamide doses (15 to 30 mg/kg of body weight/day) achieved the AUC0-24/MIC of 209.08 in the epithelial lining fluid of only 15.1 to 53.3% of patients. Doses of >60 mg/kg per day performed better. Our vitro model for the sterilizing effect, together with Monte Carlo simulations, can be used for the faster identification of the clinical doses that are needed to achieve a sterilizing effect and that can then be studied in clinical trials.

Ribavirin Improves Early Responses to Peginterferon Through Improved Interferon Signaling

BACKGROUND & AIMS The therapeutic mechanisms of ribavirin for hepatitis C are unclear. Microarray analyses have shown that ribavirin increases induction of interferon-stimulated genes. We evaluated viral kinetics, serum cytokine expression, and viral mutagenesis during early stages of peginterferon therapy with and without ribavirin. METHODS Fifty patients with chronic hepatitis C virus (HCV) infection genotype 1 were randomly assigned to groups that were given peginterferon alpha-2a, with or without ribavirin, for 4 weeks; all patients then received an additional 44 weeks of combination therapy. First- and second-phase viral kinetics were evaluated. Serum levels of interferon-gamma-inducible protein-10 (IP10), monokine induced by interferon-gamma, and monocyte chemoattractant protein 1 were quantified as measures of the interferon-stimulated genes response. NS5A and NS5B were partially sequenced, and mutation rates were calculated. RESULTS The first-phase decrease in HCV RNA was similar between groups. Patients who received ribavirin had a more rapid second-phase decrease, compared with patients who did not receive ribavirin-particularly those with an adequate first-phase decrease (0.61 vs 0.35 log10 IU/mL/week; P = .018). At 12 hours, fold induction of serum IP10 was higher in patients given the combination therapy than those given peginterferon only (7.6- vs 3.8-fold; P = .01); however, the difference was greatest in patients with an adequate first-phase decrease in HCV RNA. IP10-induction correlated with first- and second-phase kinetics and with ribavirin serum concentrations on day 3. HCV mutation rates were similar between groups. CONCLUSIONS Ribavirin improves the kinetics of the early response to therapy in patients with an adequate initial response to peginterferon. Induction of interferon-stimulated cytokines correlates with viral kinetics following ribavirin therapy, suggesting that ribavirin promotes interferon signaling.

The Antibiotic-Resistance Arrow of Time: Efflux Pump Induction is a General First Step in the Evolution of Mycobacterial Drug-Resistance

ABSTRACT We hypothesize that low-level efflux pump expression is the first step in the development of high-level drug resistance in mycobacteria. We performed 28-day azithromycin dose-effect and dose-scheduling studies in our hollow-fiber model of disseminated Mycobacterium avium-M. intracellulare complex. Both microbial kill and resistance emergence were most closely linked to the within-macrophage area under the concentration-time curve (AUC)/MIC ratio. Quantitative PCR revealed that subtherapeutic azithromycin exposures over 3 days led to a 56-fold increase in expression of MAV_3306, which encodes a putative ABC transporter, and MAV_1406, which encodes a putative major facilitator superfamily pump, in M. avium. By day 7, a subpopulation of M. avium with low-level resistance was encountered and exhibited the classic inverted U curve versus AUC/MIC ratios. The resistance was abolished by an efflux pump inhibitor. While the maximal microbial kill started to decrease after day 7, a population with high-level azithromycin resistance appeared at day 28. This resistance could not be reversed by efflux pump inhibitors. Orthologs of pumps encoded by MAV_3306 and MAV_1406 were identified in Mycobacterium tuberculosis, Mycobacterium leprae, Mycobacterium marinum, Mycobacterium abscessus, and Mycobacterium ulcerans. All had highly conserved protein secondary structures. We propose that induction of several efflux pumps is the first step in a general pathway to drug resistance that eventually leads to high-level chromosomal-mutation-related resistance in mycobacteria as ordered events in an “antibiotic resistance arrow of time.”

Efflux-Pump—Derived Multiple Drug Resistance to Ethambutol Monotherapy in Mycobacterium tuberculosis and the Pharmacokinetics and Pharmacodynamics of Ethambutol

BACKGROUND Ethambutol is used for the treatment of tuberculosis in cases where there is isoniazid resistance. We examined the emergence of drug resistance to ethambutol monotherapy in pharmacokinetic-pharmacodynamic studies of a hollow-fiber system. METHODS Dose-effect and dose-scheduling studies were performed with ethambutol and log-phase growth Mycobacterium tuberculosis to identify exposures and schedules linked to optimal kill and resistance suppression. In one study, after 7 days of daily ethambutol, 300 mg isoniazid per day was administered to each system to determine its early bactericidal activity. RESULTS Efflux-pump blockage reduced the mutation frequency to ethambutol 64-fold. In dose-effect studies, ethambutol had a maximal early bactericidal activity of 0.22 log10 colony-forming units/mL/day, as is encountered in patients. By day 7, resistance to both ethambutol and isoniazid had increased. Previous exposure to ethambutol halted isoniazid early bactericidal activity. Daily therapy, as opposed to more intermittent therapy, was associated with the least proportion of efflux-pump-driven resistance, consistent with a time-driven effect. Microbial kill was best explained by the ratio of area under the concentration-time curve to minimum inhibitory concentration (r2 = 0.90). CONCLUSION The induction of an efflux pump that reduces the effect of multiple drugs provides an alternative pathway to sequential acquisition of mutations in the development of multiple drug resistance.

Treatment of Active Pulmonary Tuberculosis in Adults: Current Standards and Recent Advances: Insights from the Society of Infectious Diseases Pharmacists

Tuberculosis is a global pandemic, with 9 million new cases of the disease and approximately 2 million deaths each year. More than 98% of patients treated for tuberculosis in the United States between 1993 and 2007 had drug‐susceptible strains. The standard treatment regimen for drug‐susceptible tuberculosis has not changed in decades and was developed on the basis of empiric observations of different treatment regimens. Only recently has the veracity of the scientific basis for standard therapy been examined. The backbone of therapy is still isoniazid, rifampin, and pyrazinamide, although fluoroquinolones are being investigated as a replacement for isoniazid. Recent population pharmacokinetic studies have demonstrated the importance of individualized dosing of isoniazid, pyrazinamide, and rifampin. Isoniazid serum clearance differs depending on the patients number of N‐acetyltransferase 2 gene *4 (NAT2*4) alleles. Pyrazinamide serum clearance has been shown to increase with increases in body weight. Rifampins volume of distribution, clearance, and absorption have wide between‐patient and within‐patient variability. Microbial pharmacokinetic‐pharmacodynamic (PK‐PD) indexes and targets to optimize microbial killing and minimize resistance have been identified for rifampin, isoniazid, pyrazinamide, and the fluoroquinolones. These PK‐PD indexes suggest that different doses and dosing schedules than those currently recommended could optimize therapy and perhaps shorten duration of therapy. Efflux pump inhibition is also being investigated to enhance first‐line antituberculosis drug therapy. Comorbid conditions such as diabetes mellitus and genetically determined iron overload syndromes have been associated with significantly worse patient outcomes. Therapy for these and other patient groups needs further improvement. These patient factors, the covariates for pharmacokinetic variability, and PK‐PD factors suggest the need to individualize therapy for patients with tuberculosis in order to optimize outcomes and reduce the duration of therapy.

Ethambutol Optimal Clinical Dose and Susceptibility Breakpoint Identification by Use of a Novel Pharmacokinetic-Pharmacodynamic Model of Disseminated Intracellular Mycobacterium avium

ABSTRACT Ethambutol, together with a macrolide, is the backbone for treatment of disseminated Mycobacterium avium disease. However, at the standard dose of 15 mg/kg of body weight/day, ethambutol efficacy is limited. In addition, susceptibility breakpoints have consistently failed to predict clinical outcome. We performed dose-effect studies with extracellular M. avium as well as with bacilli within human macrophages. The maximal kill rate (Emax) for ethambutol against extracellular bacilli was 5.54 log10 CFU/ml, compared to 0.67 log10 CFU/ml for intracellular M. avium, after 7 days of exposure. Thus, extracellular assays demonstrated high efficacy. We created a hollow-fiber system model of intracellular M. avium and performed microbial pharmacokinetic-pharmacodynamic studies using pharmacokinetics similar to those of ethambutol for humans. The Emax in the systems was 0.79 log10 CFU/ml with 7 days of daily therapy, so the kill rates approximated those encountered in patients treated with ethambutol monotherapy. Ratio of peak concentration to MIC (Cmax/MIC) was linked to microbial kill rate. The Cmax/MIC ratio needed to achieve the 90% effective concentration (EC90) in serum was 1.23, with a calculated intramacrophage Cmax/MIC ratio of 13. In 10,000 patient Monte Carlo simulations, doses of 15, 50, and 75 mg/kg achieved the EC90 in 35.50%, 76.81%, and 86.12% of patients, respectively. Therefore, ethambutol doses of ≥50 mg/kg twice a week would be predicted to be better than current doses of 15 mg/kg for treatment of disseminated M. avium disease. New susceptibility breakpoints and critical concentrations of 1 to 2 mg/liter were identified for the determination of ethambutol-resistant M. avium in Middlebrook broth. Given that the modal MIC of clinical isolates is around 2 mg/liter, most isolates should be considered ethambutol resistant.

Pharmacokinetics of oseltamivir according to trimester of pregnancy

The purpose of this study was to determine pharmacokinetic parameters for oseltamivir in all trimesters of pregnancy. Thirty pregnant women, 10 per trimester, who were receiving oseltamivir phosphate (75 mg) were recruited to study first-dose pharmacokinetics. Plasma samples were obtained at 0, 0.5, 1, 2, 4, 8, and 12 hours after the first dose. Samples were analyzed for oseltamivir and oseltamivir carboxylate levels. With the use of a noncompartmental model, we estimated the area-under-the-curve, maximum concentration, time-to-maximum concentration, and half-life. There were no significant differences in the pharmacokinetics of oseltamivir by trimester, except for an increased half-life in the first trimester for oseltamivir phosphate and an increased maximum concentration in the third trimester for oseltamivir carboxylate. The levels of oseltamivir carboxylate that were observed were within the range that was needed to achieve inhibitory concentrations at 50% for pandemic H1N1. The pharmacokinetics of oseltamivir does not change significantly according to trimester of pregnancy.

Pharmacokinetic Mismatch Does Not Lead to Emergence of Isoniazid- or Rifampin-Resistant Mycobacterium tuberculosis but to Better Antimicrobial Effect: a New Paradigm for Antituberculosis Drug Scheduling

ABSTRACT Multidrug resistant-tuberculosis is a pressing problem. One of the major mechanisms proposed to lead to the emergence of drug resistance is pharmacokinetic mismatch. Stated as a falsifiable hypothesis, the greater the pharmacokinetic mismatch between rifampin and isoniazid, the higher the isoniazid- and rifampin-resistant subpopulation sizes become with time. To test this, we performed hollow-fiber-system studies for both bactericidal and sterilizing effects in experiments of up to 42 days. We mimicked pharmacokinetics of 600-mg/day rifampin and 300-mg/day isoniazid administered to patients. Rifampin was administered first, followed by isoniazid 0, 6, 12, and 24 h later. The treatment was for drug-susceptible Mycobacterium tuberculosis in some experiments and hollow fiber systems with inoculum preseeded with isoniazid- and rifampin-resistant isogenic Mycobacterium tuberculosis strains in others. Analysis of variance revealed that the 12-h and 24-h-mismatched regimens always killed better than the matched regimens during both bactericidal and sterilizing effects (P < 0.05). This means that either the order of scheduling or the sequential administration of drugs in combination therapy may lead to significant improvement in microbial killing. Rifampin-resistant and isoniazid-resistant subpopulations were not significantly higher with increased mismatching in numerous analysis-of-variance comparisons. Thus, the pharmacokinetic mismatch hypothesis was rejected. Instead, sequential administration of anti-tuberculosis (TB) drugs (i.e., deliberate mismatch) following particular schedules suggests a new paradigm for accelerating M. tuberculosis killing. We conclude that current efforts aimed at better pharmacokinetic matching to decrease M. tuberculosis resistance emergence are likely futile and counterproductive.