Evaluating pediatric tuberculosis dosing guidelines: A model-based individual data pooled analysis.

BACKGROUND: The current World Health Organization (WHO) pediatric tuberculosis dosing guidelines lead to suboptimal drug exposures. Identifying factors altering the exposure of these drugs in children is essential for dose optimization. Pediatric pharmacokinetic studies are usually small, leading to high variability and uncertainty in pharmacokinetic results between studies. We pooled data from large pharmacokinetic studies to identify key covariates influencing drug exposure to optimize tuberculosis dosing in children. METHODS AND FINDINGS: We used nonlinear mixed-effects modeling to characterize the pharmacokinetics of rifampicin, isoniazid, and pyrazinamide, and investigated the association of human immunodeficiency virus (HIV), antiretroviral therapy (ART), drug formulation, age, and body size with their pharmacokinetics. Data from 387 children from South Africa, Zambia, Malawi, and India were available for analysis; 47% were female and 39% living with HIV (95% on ART). Median (range) age was 2.2 (0.2 to 15.0) years and weight 10.9 (3.2 to 59.3) kg. Body size (allometry) was used to scale clearance and volume of distribution of all 3 drugs. Age affected the bioavailability of rifampicin and isoniazid; at birth, children had 48.9% (95% confidence interval (CI) [36.0%, 61.8%]; p < 0.001) and 64.5% (95% CI [52.1%, 78.9%]; p < 0.001) of adult rifampicin and isoniazid bioavailability, respectively, and reached full adult bioavailability after 2 years of age for both drugs. Age also affected the clearance of all drugs (maturation), children reached 50% adult drug clearing capacity at around 3 months after birth and neared full maturation around 3 years of age. While HIV per se did not affect the pharmacokinetics of first-line tuberculosis drugs, rifampicin clearance was 22% lower (95% CI [13%, 28%]; p < 0.001) and pyrazinamide clearance was 49% higher (95% CI [39%, 57%]; p < 0.001) in children on lopinavir/ritonavir; isoniazid bioavailability was reduced by 39% (95% CI [32%, 45%]; p < 0.001) when simultaneously coadministered with lopinavir/ritonavir and was 37% lower (95% CI [22%, 52%]; p < 0.001) in children on efavirenz. Simulations of 2010 WHO-recommended pediatric tuberculosis doses revealed that, compared to adult values, rifampicin exposures are lower in most children, except those younger than 3 months, who experience relatively higher exposure for all drugs, due to immature clearance. Increasing the rifampicin doses in children older than 3 months by 75 mg for children weighing <25 kg and 150 mg for children weighing >25 kg could improve rifampicin exposures. Our analysis was limited by the differences in availability of covariates among the pooled studies. CONCLUSIONS: Children older than 3 months have lower rifampicin exposures than adults and increasing their dose by 75 or 150 mg could improve therapy. Altered exposures in children with HIV is most likely caused by concomitant ART and not HIV per se. The importance of the drug-drug interactions with lopinavir/ritonavir and efavirenz should be evaluated further and considered in future dosing guidance. TRIAL REGISTRATION: ClinicalTrials.gov registration numbers; NCT02348177, NCT01637558, ISRCTN63579542.

Effectiveness and Pharmacokinetic Exposures of First-Line Drugs Used to Treat Drug-Susceptible Tuberculosis in Children: A Systematic Review and Meta-Analysis.

BACKGROUND: Optimal doses of first-line drugs for treatment of drug-susceptible tuberculosis in children and young adolescents remain uncertain. We aimed to determine whether children treated using World Health Organization-recommended or higher doses of first-line drugs achieve successful outcomes and sufficient pharmacokinetic (PK) exposures. METHODS: Titles, abstracts, and full-text articles were screened. We searched PubMed, EMBASE, CENTRAL, and trial registries from 2010 to 2021. We included studies in children aged <18 years being treated for drug-susceptible tuberculosis with rifampicin (RIF), pyrazinamide, isoniazid, and ethambutol. Outcomes were treatment success rates and drug exposures. The protocol for the systematic review was preregistered in PROSPERO (no. CRD42021274222). RESULTS: Of 304 studies identified, 46 were eligible for full-text review, and 12 and 18 articles were included for the efficacy and PK analyses, respectively. Of 1830 children included in the efficacy analysis, 82% had favorable outcomes (range, 25%-95%). At World Health Organization-recommended doses, exposures to RIF, pyrazinamide, and ethambutol were lower in children than in adults. Children ≤6 years old have 35% lower areas under the concentration-time curve (AUCs) than older children (mean of 14.4 [95% CI 9.9-18.8] vs 22.0 [13.8-30.1] µg·h/mL) and children with human immunodeficiency virus (HIV) had 35% lower RIF AUCs than HIV-negative children (17.3 [11.4-23.2] vs 26.5 [21.3-31.7] µg·h/mL). Heterogeneity and small sample sizes were major limitations. CONCLUSIONS: There is large variability in outcomes, with an average of 82% favorable outcomes. Drug exposures are lower in children than in adults. Younger children and/or those with HIV are underexposed to RIF. Standardization of PK pediatric studies and individual patient data analysis with safety assessment are needed to inform optimal dosing.

Intracellular localisation of Mycobacterium tuberculosis affects efficacy of the antibiotic pyrazinamide.

To be effective, chemotherapy against tuberculosis (TB) must kill the intracellular population of the pathogen, Mycobacterium tuberculosis. However, how host cell microenvironments affect antibiotic accumulation and efficacy remains unclear. Here, we use correlative light, electron, and ion microscopy to investigate how various microenvironments within human macrophages affect the activity of pyrazinamide (PZA), a key antibiotic against TB. We show that PZA accumulates heterogeneously among individual bacteria in multiple host cell environments. Crucially, PZA accumulation and efficacy is maximal within acidified phagosomes. Bedaquiline, another antibiotic commonly used in combined TB therapy, enhances PZA accumulation via a host cell-mediated mechanism. Thus, intracellular localisation and specific microenvironments affect PZA accumulation and efficacy. Our results may explain the potent in vivo efficacy of PZA, compared to its modest in vitro activity, and its critical contribution to TB combination chemotherapy.

Alkylpyrazines from Coffee are Extensively Metabolized to Pyrazine Carboxylic Acids in the Human Body.

SCOPE: Coffee is a complex mixture of over 1000 compounds, including diverse heteroaromatic compounds such as alkylpyrazines. Little is known about the intake, metabolism, and bodily distribution of these compounds. Therefore, a human intervention study is conducted to investigate the excretion of alkylpyrazine metabolites in urine after the ingestion of brewed coffee containing alkylpyrazines. METHODS AND RESULTS: After consuming a diet without heat-processed food, ten volunteers consumed 500 mL of freshly brewed coffee prepared from coffee pads, providing intakes of 2-methylpyrazine (2-MeP), 2,5-dimethylpyrazine (2,5-DMeP), and 2,6-dimethylpyrazine (2,6-DMeP) amounting to 17.2, 4.4, and 4.9 µmol, respectively. These alkylpyrazines are metabolized into the corresponding pyrazine carboxylic acids, namely pyrazine-2-carboxylic acid (PA), 5-hydroxypyrazine-2-carboxylic acid (5-OHPA), 5-methylpyrazine-2-carboxylic acid (5-MePA), and 6-methylpyrazine-2-carboxylic acid (6-MePA). In total, 64% of the ingested 2-MeP is excreted as PA, as well as 26% as 5-OHPA, while 91% and 97% of the ingested 2,5-DMeP and 2,6-DMeP are recovered as 5-MePA and 6-MePA, respectively, in urine samples collected after coffee consumption. CONCLUSION: This study provides evidence that alkylpyrazines are rapidly metabolized into the corresponding carboxylic acids and excreted via urine by humans, which is consistent with earlier rodent studies.

Tuberculosis drugs' distribution and emergence of resistance in patient's lung lesions: A mechanistic model and tool for regimen and dose optimization.

BACKGROUND: The sites of mycobacterial infection in the lungs of tuberculosis (TB) patients have complex structures and poor vascularization, which obstructs drug distribution to these hard-to-reach and hard-to-treat disease sites, further leading to suboptimal drug concentrations, resulting in compromised TB treatment response and resistance development. Quantifying lesion-specific drug uptake and pharmacokinetics (PKs) in TB patients is necessary to optimize treatment regimens at all infection sites, to identify patients at risk, to improve existing regimens, and to advance development of novel regimens. Using drug-level data in plasma and from 9 distinct pulmonary lesion types (vascular, avascular, and mixed) obtained from 15 hard-to-treat TB patients who failed TB treatments and therefore underwent lung resection surgery, we quantified the distribution and the penetration of 7 major TB drugs at these sites, and we provide novel tools for treatment optimization. METHODS AND FINDINGS: A total of 329 plasma- and 1,362 tissue-specific drug concentrations from 9 distinct lung lesion types were obtained according to optimal PK sampling schema from 15 patients (10 men, 5 women, aged 23 to 58) undergoing lung resection surgery (clinical study NCT00816426 performed in South Korea between 9 June 2010 and 24 June 2014). Seven major TB drugs (rifampin [RIF], isoniazid [INH], linezolid [LZD], moxifloxacin [MFX], clofazimine [CFZ], pyrazinamide [PZA], and kanamycin [KAN]) were quantified. We developed and evaluated a site-of-action mechanistic PK model using nonlinear mixed effects methodology. We quantified population- and patient-specific lesion/plasma ratios (RPLs), dynamics, and variability of drug uptake into each lesion for each drug. CFZ and MFX had higher drug exposures in lesions compared to plasma (median RPL 2.37, range across lesions 1.26-22.03); RIF, PZA, and LZD showed moderate yet suboptimal lesion penetration (median RPL 0.61, range 0.21-2.4), while INH and KAN showed poor tissue penetration (median RPL 0.4, range 0.03-0.73). Stochastic PK/pharmacodynamic (PD) simulations were carried out to evaluate current regimen combinations and dosing guidelines in distinct patient strata. Patients receiving standard doses of RIF and INH, who are of the lower range of exposure distribution, spent substantial periods (>12 h/d) below effective concentrations in hard-to-treat lesions, such as caseous lesions and cavities. Standard doses of INH (300 mg) and KAN (1,000 mg) did not reach therapeutic thresholds in most lesions for a majority of the population. Drugs and doses that did reach target exposure in most subjects include 400 mg MFX and 100 mg CFZ. Patients with cavitary lesions, irrespective of drug choice, have an increased likelihood of subtherapeutic concentrations, leading to a higher risk of resistance acquisition while on treatment. A limitation of this study was the small sample size of 15 patients, performed in a unique study population of TB patients who failed treatment and underwent lung resection surgery. These results still need further exploration and validation in larger and more diverse cohorts. CONCLUSIONS: Our results suggest that the ability to reach and maintain therapeutic concentrations is both lesion and drug specific, indicating that stratifying patients based on disease extent, lesion types, and individual drug-susceptibility profiles may eventually be useful for guiding the selection of patient-tailored drug regimens and may lead to improved TB treatment outcomes. We provide a web-based tool to further explore this model and results at http://saviclab.org/tb-lesion/.

Predicting the Outcomes of New Short-Course Regimens for Multidrug-Resistant Tuberculosis Using Intrahost and Pharmacokinetic-Pharmacodynamic Modeling.

Short-course regimens for multidrug-resistant tuberculosis (MDR-TB) are urgently needed. Limited data suggest that the new drug bedaquiline (BDQ) may have the potential to shorten MDR-TB treatment to less than 6 months when used in conjunction with standard anti-TB drugs. However, the feasibility of BDQ in shortening MDR-TB treatment duration remains to be established. Mathematical modeling provides a platform to investigate different treatment regimens and predict their efficacy. We developed a mathematical model to capture the immune response to TB inside a human host environment. This model was then combined with a pharmacokinetic-pharmacodynamic model to simulate various short-course BDQ-containing regimens. Our modeling suggests that BDQ could reduce MDR-TB treatment duration to just 18 weeks (4 months) while still maintaining a very high treatment success rate (100% for daily BDQ for 2 weeks, or 95% for daily BDQ for 1 week during the intensive phase). The estimated time to bacterial clearance of these regimens ranges from 27 to 33 days. Our findings provide the justification for empirical evaluation of short-course BDQ-containing regimens. If short-course BDQ-containing regimens are found to improve outcomes, then we anticipate clear cost savings and a subsequent improvement in the efficiency of national TB programs.

Efficacy of pyrazinoic acid dry powder aerosols in resolving necrotic and non-necrotic granulomas in a guinea pig model of tuberculosis.

New therapeutic strategies are needed to treat drug resistant tuberculosis (TB) and to improve treatment for drug sensitive TB. Pyrazinamide (PZA) is a critical component of current first-line TB therapy. However, the rise in PZA-resistant TB cases jeopardizes the future utility of PZA. To address this problem, we used the guinea pig model of TB and tested the efficacy of an inhaled dry powder combination, referred to as Pyrazinoic acid/ester Dry Powder (PDP), which is comprised of pyrazinoic acid (POA), the active moiety of PZA, and pyrazinoic acid ester (PAE), which is a PZA analog. Both POA and PAE have the advantage of being able to act on PZA-resistant Mycobacterium tuberculosis. When used in combination with oral rifampicin (R), inhaled PDP had striking effects on tissue pathology. Effects were observed in lungs, the site of delivery, but also in the spleen and liver indicating both local and systemic effects of inhaled PDP. Tissue granulomas that harbor M. tuberculosis in a persistent state are a hallmark of TB and they pose a challenge for therapy. Compared to other treatments, which preferentially cleared non-necrotic granulomas, R+PDP reduced necrotic granulomas more effectively. The increased ability of R+PDP to act on more recalcitrant necrotic granulomas suggests a novel mechanism of action. The results presented in this report reveal the potential for developing therapies involving POA that are optimized to target necrotic as well as non-necrotic granulomas as a means of achieving more complete sterilization of M. tuberculosis bacilli and preventing disease relapse when therapy ends.

Chloroquine enhances the antimycobacterial activity of isoniazid and pyrazinamide by reversing inflammation-induced macrophage efflux.

Mycobacterium tuberculosis (MTB) is notorious for persisting within host macrophages. Efflux pumps decrease intracellular drug levels, thus fostering persistence of MTB during therapy. Isoniazid (INH) and pyrazinamide (PZA) are substrates of the efflux pump breast cancer resistance protein-1 (BCRP-1), which is inhibited by chloroquine (CQ). In this study, BCRP-1 was found to be expressed on macrophages of human origin and on foamy giant cells at the site of MTB infection. In the current in vitro study, interferon-gamma (IFNγ) increased the expression of BCRP-1 in macrophages derived from the human monocytic leukaemia cell line THP-1. Using a BCRP-1-specific fluorescent dye and radioactively labelled INH, it was demonstrated that efflux from macrophages increased upon activation with IFNγ. CQ was able to inhibit active efflux and augmented the intracellular concentrations both of INH and the dye. In agreement, CQ and specific inhibition of BCRP-1 increased the antimycobacterial activity of INH against intracellular MTB. Although PZA behaved differently, CQ had comparable advantageous effects on the intracellular pharmacokinetics and activity of PZA. The adjunctive effects of CQ on intracellular killing of MTB were measurable at concentrations achievable in humans at approved therapeutic doses. Therefore, CQ, a widely used and worldwide available drug, may potentiate the efficacy of standard MTB therapy against bacteria in the intracellular compartment.

Lung Tissue Concentrations of Pyrazinamide among Patients with Drug-Resistant Pulmonary Tuberculosis.

Improved knowledge regarding the tissue penetration of antituberculosis drugs may help optimize drug management. Patients with drug-resistant pulmonary tuberculosis undergoing adjunctive surgery were enrolled. Serial serum samples were collected, and microdialysis was performed using ex vivo lung tissue to measure pyrazinamide concentrations. Among 10 patients, the median pyrazinamide dose was 24.7 mg/kg of body weight. Imaging revealed predominant lung lesions as cavitary (n = 6 patients), mass-like (n = 3 patients), or consolidative (n = 1 patient). On histopathology examination, all tissue samples had necrosis; eight had a pH of ≤5.5. Tissue samples from two patients were positive for Mycobacterium tuberculosis by culture (pH 5.5 and 7.2). All 10 patients had maximal serum pyrazinamide concentrations within the recommended range of 20 to 60 µg/ml. The median lung tissue free pyrazinamide concentration was 20.96 µg/ml. The median tissue-to-serum pyrazinamide concentration ratio was 0.77 (range, 0.54 to 0.93). There was a significant inverse correlation between tissue pyrazinamide concentrations and the amounts of necrosis (R = -0.66, P = 0.04) and acid-fast bacilli (R = -0.75, P = 0.01) identified by histopathology. We found good penetration of pyrazinamide into lung tissue among patients with pulmonary tuberculosis with a variety of radiological lesion types. Our tissue pH results revealed that most lesions had a pH conducive to pyrazinamide activity. The tissue penetration of pyrazinamide highlights its importance in both drug-susceptible and drug-resistant antituberculosis treatment regimens.

Pharmacokinetics of thrice-weekly rifampicin, isoniazid and pyrazinamide in adult tuberculosis patients in India.

OBJECTIVE: To study the pharmacokinetics of rifampicin (RMP), isoniazid (INH) and pyrazinamide (PZA) in adult tuberculosis (TB) patients and examine factors that influence drug pharmacokinetics. METHODS: Adult TB patients (n = 101) receiving thrice-weekly anti-tuberculosis treatment in the Revised National TB Control Programme (RNTCP) were studied. The study was conducted at steady state after directly observed drug administration. RMP, INH and PZA concentrations were estimated using high-performance liquid chromatography and NAT2 genotyping by real-time polymerase chain reaction. RESULTS: RMP peak concentration (Cmax) was sub-therapeutic (<8 µg/ml) in 88% of the patients. The Cmax of RMP, INH and PZA at 2 h was observed in respectively 83.2%, 97.0% and 92.1% of the patients. The Cmax and area under the curve from 0 to 8 h (AUC0-8) of PZA was lower in TB patients with diabetes mellitus than in non-diabetics. Significant associations were observed between the Cmax and the AUC0-8 of RMP, INH and PZA with drug doses; RMP with category of treatment; INH with smoking, body mass index and N-acetyl transferase 2 genotype; and PZA with sex and smoking. CONCLUSIONS: Several risk factors for drug concentration variations were identified. Two-hour post-dosing drug concentrations mimicked Cmax. A high proportion of TB patients had RMP Cmax below the expected range, which is a matter of concern.

Pharmacokinetics of Rifampin, Isoniazid, Pyrazinamide, and Ethambutol in Infants Dosed According to Revised WHO-Recommended Treatment Guidelines.

There are limited pharmacokinetic data for use of the first-line antituberculosis drugs during infancy (<12 months of age), when drug disposition may differ. Intensive pharmacokinetic sampling was performed in infants routinely receiving antituberculosis treatment, including rifampin, isoniazid, pyrazinamide, and ethambutol, using World Health Organization-recommended doses. Regulatory-approved single-drug formulations, including two rifampin suspensions, were used on the sampling day. Assays were conducted using liquid chromatography-mass spectrometry; pharmacokinetic parameters were generated using noncompartmental analysis. Thirty-nine infants were studied; 14 (36%) had culture-confirmed tuberculosis. Fifteen (38%) were premature (<37 weeks gestation); 5 (13%) were HIV infected. The mean corrected age and weight were 6.6 months and 6.45 kg, respectively. The mean maximum plasma concentrations (Cmax) for rifampin, isoniazid, pyrazinamide, and ethambutol were 2.9, 7.9, 41.9, and 1.3 µg/ml, respectively (current recommended adult target concentrations: 8 to 24, 3 to 6, 20 to 50, and 2 to 6 µg/ml, respectively), and the mean areas under the concentration-time curves from 0 to 8 h (AUC0-8) were 12.1, 24.7, 239.4, and 5.1 µg · h/ml, respectively. After adjusting for age and weight, rifampin exposures for the two formulations used differed inCmax(geometric mean ratio [GMR],2.55; 95% confidence interval [CI], 1.47 to 4.41;P= 0.001) and AUC0-8(GMR, 2.52; 95% CI, 1.34 to 4.73;P= 0.005). HIV status was associated with lower pyrazinamideCmax(GMR, 0.85; 95% CI, 0.75 to 0.96;P= 0.013) and AUC0-8(GMR, 0.79; 95% CI, 0.69 to 0.90;P< 0.001) values. No other important differences were observed due to age, weight, prematurity, ethnicity, or gender. In summary, isoniazid and pyrazinamide concentrations in infants compared well with proposed adult target concentrations; ethambutol concentrations were lower but similar to previously reported pediatric studies. The low rifampin exposures require further investigation. (This study has been registered at ClinicalTrials.gov under registration no. NCT01637558.).

Isoniazid, rifampicin and pyrazinamide plasma concentrations 2 and 6 h post dose in patients with pulmonary tuberculosis.

BACKGROUND: Low concentrations of anti-tuberculosis drugs are related to drug resistance and treatment failure. OBJECTIVE: To determine the prevalence of low plasma concentrations of anti-tuberculosis drugs. METHODS: The study was performed among 60 pulmonary tuberculosis (TB) in-patients at a tertiary care university-affiliated hospital in Tehran, Iran. Drug samples were drawn 2 and 6 h post dose for isoniazid (INH), rifampicin (RMP) and pyrazinamide (PZA); related concentrations were determined using high-performance liquid chromatography. Plasma drug concentrations, duration of treatment, age, sex, liver enzyme levels, administered doses and smoking status were evaluated and recorded. RESULTS: Among 60 patients recruited to the study, the mean (±SD) age was 54.2 (±20.9) years; 39 were female. The median peak plasma concentrations (C(max)) of INH, RMP and PZA were respectively 2.5, 4.0 and 43.6 µg/ml; 81% of the patients had drug plasma concentrations lower than the target ranges for at least one administered drug. Respectively 49.1%, 92.5% and 8.7% of the patients had low concentrations of INH, RMP and PZA. CONCLUSION: The results indicate that RMP concentrations are below the reference range in most patients, while PZA is within the target range of the standard doses.

Pharmacokinetic evaluation of the penetration of antituberculosis agents in rabbit pulmonary lesions.

Standard antituberculosis (anti-TB) therapy requires the use of multiple drugs for a minimum of 6 months, with variable outcomes that are influenced by a number of microbiological, pathological, and clinical factors. This is despite the availability of antibiotics that have good activity against Mycobacterium tuberculosis in vitro and favorable pharmacokinetic profiles in plasma. However, little is known about the distribution of widely used antituberculous agents in the pulmonary lesions where the pathogen resides. The rabbit model of TB infection was used to explore the hypothesis that standard drugs have various abilities to penetrate lung tissue and lesions and that adequate drug levels are not consistently reached at the site of infection. Using noncompartmental and population pharmacokinetic approaches, we modeled the rate and extent of distribution of isoniazid, rifampin, pyrazinamide, and moxifloxacin in rabbit lung and lesions. Moxifloxacin reproducibly showed favorable partitioning into lung and granulomas, while the exposure of isoniazid, rifampin, and pyrazinamide in lesions was markedly lower than in plasma. The extent of penetration in lung and lesions followed different trends for each drug. All four agents distributed rapidly from plasma to tissue with equilibration half-lives of less than 1 min to an hour. The models adequately described the plasma concentrations and reasonably captured actual lesion concentrations. Though further refinement is needed to accurately predict the behavior of these drugs in human subjects, our results enable the integration of lesion-specific pharmacokinetic-pharmacodynamic (PK-PD) indices in clinical trial simulations and in in vitro PK-PD studies with M. tuberculosis.

Distribution of three antituberculous drugs and their metabolites in different parts of pathological vertebrae with spinal tuberculosis.

STUDY DESIGN: To detect drug concentration levels and metabolite using high-performance liquid chromatography. OBJECTIVE: To map concentration levels of three antituberculous drugs and two metabolites in the abnormal osseous tissues around the foci of patients with spinal tuberculosis. SUMMARY OF BACKGROUND DATA: Concentration levels of antituberculous drugs in the focus of spinal tuberculosis has been reported. However, the mapping of drugs distribution in different regions surrounding the foci of tuberculosis vertebrae remains unexplored, as well as the metabolite of the drugs. METHODS: Thirty-eight patients with spinal tuberculosis were assigned into sclerotic group (n = 13) and nonsclerotic group (n = 25) based on computed tomographic (CT) images. All patients received a chemotherapy 10 months with 2HRZE/8H(2)R(2)E(2). All patients received surgery after 4 weeks of chemotherapy. Samples of serum, ilium, and pathologic vertebral tissues, including the foci, sclerotic wall (if applicable), region I of abnormal osseous tissues (within 4 mm), and region II of abnormal osseous tissues (more than 4 mm) from the foci were collected during operation. Concentration levels and metabolite of three drugs were measured using high-performance liquid method for all samples. Differences of means within groups were evaluated by ANOVA and Dunnett post hoc. A significant levels was set at P < 0.05. RESULTS: Concentration levels of drugs varied greatly in different regions of spinal tuberculosis vertebrae. Concentration levels of isoniazid and rifampin were higher than the effective bactericidal concentration (EBC) level and that of pyrazinamide was five times of the minimal inhibitory concentration in the region II of abnormal osseous tissues and the ilium of nonsclerotic group. Three drugs achieved EBC in the region I of abnormal osseous tissues in the nonsclerotic group but not in the sclerotic group. Except pyrazinamide no drugs and their metabolite were identified in the foci of the sclerotic group, whereas there is trace of drugs and their metabolite in the foci of the nonsclerotic group. CONCLUSION: Three drugs resulted in an effective bactericidal concentration level in osseous tissues around the foci of spinal tuberculosis except the osseous tissues 4 mm surrounding the sclerotic wall. The results suggested that osseous tissues within 4 mm surrounding the sclerotic wall should be excised during the surgery.

Intestinal barrier function and serum concentrations of rifampin, isoniazid and pyrazinamide in patients with pulmonary tuberculosis

Intestinal barrier function and serum concentrations of rifampin, isoniazid and pyrazinamide were studied in healthy controls and patients with active pulmonary tuberculosis. A case-control study of 29 controls and 30 cases attending at the Health Center, July, 2004 to December, 2005 was conducted. The body mass index was significantly reduced in cases compared to controls (p < 0.001). The intestinal paracellular transport of lactulose was significantly (p = 0.019) reduced in cases compared to controls. The transcellular transport of mannitol and the lactulose:mannitol ratio were not significantly (p = 0.0698) reduced in cases compared to controls. Low serum concentrations of rifampin, isoniazid and pyrazinamide were observed in 81 percent (48/59), 92 percent (54/59) and 28 percent (12/59), respectively, in all individuals. The results demonstrated a marked decrease on intestinal paracellular transport in patients with active pulmonary tuberculosis and reduced serum concentrations of rifampin and isoniazid in both groups.

Measurement of the concentration of three antituberculosis drugs in the focus of spinal tuberculosis.

This is an experimental study on the distribution of antituberculosis drugs such as rifampin, isoniazid, and pyrazinamide in pathologic vertebrae of spinal tuberculosis in order to provide the regimen of chemotherapy and surgical treatment of spinal tuberculosis. The distribution of antituberculosis drugs in pathologic vertebral tissues matters greatly to the clinical effect of spinal tuberculosis' treatment. However, few pharmacokinetic studies and clinical reports about the concentrations of antituberculosis drugs in vertebral foci have been published so far. Twenty-four patients with spinal tuberculosis were divided into sclerotic group (n = 15) or non-sclerotic group (n = 9) according to radiographic features of lesion. All patients received chemotherapy with 2HRZ/2.5H(2)R(2)Z(2) for a duration of 4.5 months. Four weeks after chemotherapy all patients underwent surgery and the specimen of serum, ilium, and pathologic vertebral tissues, including sclerotic wall, subnormal osseous tissue, and foci were obtained during operation in 120-130 and 180-190 min after oral intake in the morning, respectively. The levels of three drugs in the specimen were measured using HPLC method. The concentration levels of isoniazid, rifampin and pyrazinamide varied greatly in different tissues of spinal tuberculosis, of which the bactericidal concentration values of isoniazid and rifampin and fivefold minimal inhibitory concentration (MICs) of pyrazinamide were found in subnormal vertebral bone and self-contrast ilium, the MICs of all drugs were found in sclerotic wall outside foci, and undetected level was found in foci inside the sclerotic wall. To patients without vertebral sclerotic wall around the foci, the isoniazid in foci was of bactericidal level and rifampin and pyrazinamide in foci corresponded to the MICs respectively. The sclerotic bone of affected vertebra plays an important role in blocking the antituberculosis drug's penetration into tuberculosis focus.

Drug diffusion through cystic fibrotic mucus: steady-state permeation, rheologic properties, and glycoprotein morphology.

One manifestation of cystic fibrosis (CF) is the presence of a viscid mucus secretion in the lungs. The clearance of this mucus is significantly slower than in "normals" due to uncoordinated beating of the cilia and the increased viscosity of the mucus. In these studies, the permeabilities of p-aminosalicylic acid, isoniazid, and pyrazinamide through unpurified CF respiratory mucus and through purified pig gastric mucus solutions were compared in order to evaluate the relative barrier properties of these mucus solutions. These model compounds, while not often used clinically in CF, are used in other pulmonary diseases and have the potential to be administered by inhalation delivery systems. Permeability studies were carried out in Side-Bi-Side diffusion cells fitted with a custom membrane holder capable of retaining the mucus solutions. Permeabilities through CF mucus solution and its fractions were compared to those measured through buffer and reconstituted purified pig gastric mucus. There were 28--75% decreases in drug permeability when pig gastric mucus was replaced by different CF mucus solutions. This indicates that optimal drug delivery directly to the lungs must take into account the decreased drug transport rate across diseased mucus in addition to drug loss due to binding to the glycoproteins or inefficient delivery via aerosolization. Transmission electron microscopy revealed minor differences in the glycoprotein strand structure between reconstituted pig gastric mucus and CF mucus primarily with regard to glycoprotein chain length and extent of branching. Similar viscoelastic behaviors between the CF gel fraction and synthetic CF mucus were observed. This model CF mucus system can simulate diseased mucus and can be utilized for in vitro studies to optimize drug permeability.

Activity and penetration of antituberculosis drugs in mouse peritoneal macrophages infected with Mycobacterium microti OV254.

The activities of some commonly used antituberculosis drugs were investigated within unstimulated peritoneal macrophages and in 7H-9 medium without Tween 80 using Mycobacterium microti OV254 as the target organism. In macrophage cultures, serial concentrations of isoniazid, rifampin, pyrazinamide, or streptomycin were added after a 2.5-h phagocytosis period. Viable counts were carried out at daily intervals for 5 or 6 days. The patterns of susceptibility to the four drugs were similar for M. microti and Mycobacterium tuberculosis. To ensure comparability with daily drug replacements in the macrophage experiments, the period of exposure to drugs in 7H-9 medium was kept to only 3 days. With in vitro culture at pH 6.4, drug penetration, measured as the ratio of MICs in macrophages to MICs in 7H-9 medium, was approximately 5 for isoniazid, 5 for rifampin, and 10 for streptomycin. With in vitro culture at pH 7.4, drug penetration was 100 for streptomycin, and at pH 5.6 it was 1 for pyrazinamide. Pyrazinamide was only bacteriostatic in macrophages but weakly bactericidal during the first day of exposure in vitro.