Pharmacokinetics and biotransformation of rifamycins in the body of experimental animals]

The study on distribution of 14C-rifampicin and 14C-rifamycin S in experimental animals after intramuscular administration of the drugs showed that concentrations of rifampicin in the organs and blood were higher than those of rifamycin S. Biotransformation products of both antibiotics, such as 25-deacetylrifampicin, N-oxide of rifampicin, 3-phormylrifamycin SV, rifamycin SV and others were found in the liver, kidneys, bile and urine. No products of the antibiotic metabolism were found in the blood, lungs and spleen.     

Bromide kinetics and distribution in the rat. I

Biological half-lives of bromine in 15 different organs and tissues of the rat, in addition to the whole-body half-life, were determined by measuring the radioactive concentration of 82Br-bromide in samples of tissues collected at the time intervals of 12-396 h from animals that continuously (up to 17 d) received 82Br-labeled bromide in their drinking water. The half-life values, calculated from the experimental data by the method of gradual estimates of the parameters in question with the SPSS statistical program, ranged from 94.3+/-14.6 h in the thyroid gland to 235.0+/-88.9 h in liver. In most of the studied tissues, the biological half-lives of bromine were shorter than in the whole body, in which it equaled 197.8+/-22.2 h. Significant correlation between the values of the steady-state concentration of bromide and of the biological half-life was found for most tissues (except for liver). The steady-state concentrations of 82Br in tissues are probably proportional to the magnitude of bromide space, and, consequently, of chloride space.     

Lung specific stealth liposomes as antitubercular drug carriers in guinea pigs

The problem of patient non-compliance in the management of tuberculosis (TB) can be overcome by reducing the dosing frequency of antitubercular drugs (ATD) employing drug carriers. This study reports on the intravenous (iv) administration of lung specific stealth liposomes encapsulating ATD (rifampicin and isoniazid in combination) to guinea pigs and the detailed pharmacokinetic/chemotherapeutic studies. Following a single iv administration of liposomal drugs, the latter were found to exhibit sustained therapeutic levels in plasma for 96-168 hr with half-lives of 24-70 hr, mean residence time (MRT) of 35-81 hr and organ drug levels up to day 7. The relative bioavailability (as compared to oral free drugs) was increased by 5.4-8.9 folds, whereas the absolute bioavailability (as compared to iv free drugs) was increased by 2.9-4.2 folds. Weekly therapy with liposomal ATD for 6 weeks produced equivalent clearance of Mycobacterium tuberculosis from organs as did daily therapy with oral free drugs. Hence, intravenous liposomal ATD offer the therapeutic advantage of reducing the dosing frequency and improving the patient compliance in the management of TB.     

Chromosomal aberrations in tuberculosis patients before and after treatment with short-term chemotherapy

Cytogenetic effects of 4 common anti-tubercular drugs, isoniazid (H), streptomycin (S), rifampicin (R) and pyrazinamide (Z), in 3 different combinations (2 SHRZ, 2 HRZ and 2 H2R2Z2) were evaluated in the lymphocytes of tuberculosis patients undergoing chemotherapy, in order to estimate their mutagenic potential in combination. All 3 regimens showed an increased frequency of chromosomal aberrations after treatment compared to before treatment. These findings are of significance in the treatment of tuberculosis, as the drugs in question are observed to be mutagenic/clastogenic.     

Oral poly(lactide-co-glycolide) nanoparticle based antituberculosis drug delivery: toxicological and chemotherapeutic implications

The present study reports on the detailed toxicological and chemotherapeutic evaluation of antituberculosis drug loaded nanoparticles in mice. A single oral dose administration of poly(lactide-co-glycolide) (PLG, a synthetic polymer) nanoparticles containing rifampicin+isoniazid+pyrazinamide+ethambutol could maintain drug levels in various tissues for 9-10 days and did not elicit any adverse response even when administered at several fold higher than the recommended therapeutic dose. However, dosing with conventional free drugs at the equivalent higher doses was lethal. Despite multiple oral dosing with the formulation at every 10th day, no toxicity was observed on the completion of subacute (28 days) or chronic (90 days) toxicity studies based on survival, gross pathology, histopathology, blood biochemistry and hematology. In mice harboring a high mycobacterial load (mimicking human tuberculosis), two independent chemotherapeutic regimens, i.e. 5 doses of PLG nanoparticles encapsulating (rifampicin+isoniazid+pyrazinamide+ethambutol) administered 10 days apart, or 2 doses of the 4-drug formulation followed by 3 doses of 2-drug formulation (rifampicin+isoniazid) resulted in undetectable bacilli. Further, the efficacy was comparable to 46 daily doses of oral free drugs. Therefore, the experimental evidence suggests that PLG nanoparticle-based antituberculosis drug delivery system is safe and well suited for prolonged and intermittent oral chemotherapy.     

Bacteriostatic and bactericidal activity of antituberculosis drugs against Mycobacterium tuberculosis, Mycobacterium avium-Mycobacterium intracellulare complex and Mycobacterium kansasii in different growth phases.

Bacteriostatic and bactericidal activities of rifampicin, isoniazid, streptomycin, enviomycin and ethambutol against Mycobacterium tuberculosis, Mycobacterium avium--M. intracellulare complex and Mycobacterium kansasii were studied in different growth phases. Bacteriostatic activities of the drugs were similar in different growth phases, except isoniazid. M. tuberculosis was much less susceptible to isoniazid in the lag phase than in the log and the stationary phases. In contrast, bactericidal activity was influenced by the growth phase. M. tuberculosis was killed by isoniazid, streptomycin and rifampicin. The bactericidal activity of isoniazid was strongest. The bactericidal activity of isoniazid and streptomycin was most marked in the log phase. M. avium complex and M. kansasii resisted the bactericidal activity, but some strains of M. avium complex were killed by streptomycin and enviomycin, and the activities of these two drugs were most marked in the lag phase.     

A novel solid dosage form of rifampicin and isoniazid with improved functionality

The aim of the present investigation was to develop a novel dosage form of rifampicin and isoniazid to minimize degradation of rifampicin in acidic medium and to modulate the release of rifampicin in the stomach and isoniazid in the intestine. Gastroretentive tablets of rifampicin (150 mg) were prepared by the wet granulation method using hydroxypropyl methylcellulose, calcium carbonate, and polyethylene glycol 4000. The granules and tablets of rifampicin were characterized. Hard gelatin capsules (size 4) containing a compacted mass of isoniazid (150 mg) and dicalcium phosphate (75 mg) were enteric coated. Two tablets of rifampicin and 1 capsule (size 4) of isoniazid were put into a hard gelatin capsule (size 00). The in vitro drug release and in vitro drug degradation studies were performed. Rifampicin was released over 4 hours by zero-order kinetics from the novel dosage form. More than 90% of isoniazid was released in alkaline medium in 30 minutes. The results of dissolution studies with the US Pharmacopeia XXIII method revealed that a substantial amount of rifampicin was degraded from the immediate release capsule containing rifampicin and isoniazid powder owing to drug accumulation in the dissolution vessel and also to the presence of isoniazid. The degradation of rifampicin to 3-formyl rifampicin SV (3FRSV) was arrested (3.6%–4.8% degradation of rifampicin at 4 hours) because of the minimization of physical contact between the 2 drugs and controlled release of rifampicin in acidic medium in the modified Rossett-Rice apparatus. This study concludes that the problem of rifampicin degradation can be alleviated to a certain extent by this novel dosage form. Published: August 24, 2007     

Pharmacokinetic study of rifampicin in the body of pregnant animals]

The study on distribution of 14C-rifampicin administered intramuscularly to pregnent animals showed that its concentrations in the blood, liver, kidneys, lungs and other organs did not practically change from those in nonpregnant animals. The concentration of 14C-rifampicin in the fetus organs was much lower than that in the organs of the adult animals. The liver and kidneys of the pregnant animals, as well as the fetus though to a less extent had a capacity for metabolism of 14C-rifampicin. The following products of biotransformation were detected: N-oxide of rifampicin, 25-deacetylrifampicin, 3-formylrifamycin SV and rifamycin SV.     

Activity of 7-methyljuglone in combination with antituberculous drugs against Mycobacterium tuberculosis

The recent increase in the incidence of tuberculosis with the emergence of multidrug-resistant (MDR) cases has lead to the search for new drugs that are effective against MDR strains of Mycobacterium tuberculosis and can augment the potential of existing drugs against tuberculosis. In the present study, we investigated the activities of a naphthoquinone, 7-methyljuglone, isolated from the roots of Euclea natalensis alone and in combination with other antituberculous drugs against extracellular and intracellular M. tuberculosis. Combinations of 7-methyljuglone with isoniazid or rifampicin resulted in a four to six-fold reduction in the minimum inhibitory concentration of each compound. Fractional inhibitory concentration (FIC) indexes obtained were 0.2 and 0.5, respectively, for rifampicin and isoniazid, suggesting a synergistic interaction between 7-methyljuglone and these anti-TB drugs. The ability of 7-methyljuglone to enhance the activity of isoniazid and rifampicin against both extracellular and intracellular organisms suggests that 7-methyljuglone may serve as a promising compound for development as an anti-tuberculous agent.     

High Isoniazid Resistance Rates in Rifampicin Susceptible Mycobacterium tuberculosis Pulmonary Isolates from Pakistan

Background

Rapid new diagnostic methods (including Xpert MTB/RIF assay) use rifampicin resistance as a surrogate marker for multidrug resistant tuberculosis. Patients infected with rifampicin susceptible strains are prescribed first line anti-tuberculosis therapy. The roll out of such methods raises a concern that strains with resistance to other first line anti-tuberculosis drugs including isoniazid will be missed and inappropriate treatment given. To evaluate implications of using such methods review of resistance data from high burden settings such as ours is essential.

Objective

To determine resistance to first line anti-tuberculosis drugs amongst rifampicin susceptible pulmonary Mycobacterium tuberculosis (MTB) isolates from Pakistan.

Materials and Methods

Data of pulmonary Mycobacterium tuberculosis strains isolated in Aga Khan University Hospital (AKUH) laboratory (2009–2011) was retrospectively analyzed. Antimicrobial susceptibility profile of rifampicin susceptible isolates was evaluated for resistance to isoniazid, pyrazinamide, ethambutol, and streptomycin.

Results

Pulmonary specimens submitted to AKUH from 2009 to 2011 yielded 7738 strains of Mycobacterium tuberculosis. These included 54% (n 4183) rifampicin susceptible and 46% (n: 3555) rifampicin resistant strains. Analysis of rifampicin susceptible strains showed resistance to at least one of the first line drugs in 27% (n:1133) of isolates. Overall isoniazid resistance was 15.5% (n: 649), with an isoniazid mono-resistance rate of 4% (n: 174). Combined resistance to isoniazid, pyrazinamide, and ethambutol was noted in 1% (n: 40), while resistance to isoniazid, pyrazinamide, ethambutol, and streptomycin was observed in 1.7% (n: 70) of strains.

Conclusions

Our data suggests that techniques (including Xpert MTB/RIF assay) relying on rifampicin susceptibility as an indicator for initiating first line therapy will not detect patients infected with MTB strains resistant to other first line drugs (including isoniazid). The roll out of these techniques must therefore be accompanied by strict monitoring ensuring early resistance detection to increase chances of improved patient outcomes.     

Kinetic characteristics and toxic effects of benzalkonium chloride following intravascular and oral administration in rats

Kinetic characteristics and toxic effects of benzalkonium chloride (BZK) following injection via jugular vein (JV), femoral artery (FA) and oral administration (PO) were experimentally investigated using rats. The BZK concentrations in blood and tissues (lung, liver and kidney) were determined by high-performance liquid chromatography with solid phase extraction. Toxic doses of 15 and 250 mg/kg of BZK were used for intravascular (JV and FA) and PO administration, respectively. The fatal effects appeared soon after the dose in JV-rats, while delayed in FA- or PO-rats. The blood BZK concentrations and the elimination half-lives were similar between JV- and FA-rats, while the distribution of BZK in tissues was slightly different. In PO administration, the rats that aspirated BZK into their lungs had some symptoms, while the rats that did not aspirate BZK appeared to be normal. The BZK concentrations in blood and tissues were significantly higher in the aspirated PO-rats. The toxic degree of BZK was correlated with the BZK concentration in orally dosed rats. Lung and kidney had higher BZK concentrations compared to blood or liver, and they could be the target organs of BZK.Keyword: Benzalkonium chloride     

Prevalence,Risk Factors,and Treatment Outcomes of Isoniazid- and Rifampicin- Mono-Resistant Pulmonary Tuberculosis in Lima,Peru

BackgroundIsoniazid and rifampicin are the two most efficacious first-line agents for tuberculosis (TB) treatment. We assessed the prevalence of isoniazid and rifampicin mono-resistance, associated risk factors, and the association of mono-resistance on treatment outcomes.MethodsA prospective, observational cohort study enrolled adults with a first episode of smear-positive pulmonary TB from 34 health facilities in a northern district of Lima, Peru, from March 2010 through December 2011. Participants were interviewed and a sputum sample was cultured on Löwenstein-Jensen (LJ) media. Drug susceptibility testing was performed using the proportion method. Medication regimens were documented for each patient. Our primary outcomes were treatment outcome at the end of treatment. The secondary outcome included recurrent episodes among cured patients within two years after completion of the treatment.ResultsOf 1292 patients enrolled, 1039 (80%) were culture-positive. From this subpopulation, isoniazid mono-resistance was present in 85 (8%) patients and rifampicin mono-resistance was present in 24 (2%) patients. In the multivariate logistic regression model, isoniazid mono-resistance was associated with illicit drug use (adjusted odds ratio (aOR) = 2.10; 95% confidence interval (CI): 1.1–4.1), and rifampicin mono-resistance was associated with HIV infection (aOR = 9.43; 95%CI: 1.9–47.8). Isoniazid mono-resistant patients had a higher risk of poor treatment outcomes including treatment failure (2/85, 2%, p-value<0.01) and death (4/85, 5%, p<0.02). Rifampicin mono-resistant patients had a higher risk of death (2/24, 8%, p<0.01).ConclusionA high prevalence of isoniazid and rifampicin mono-resistance was found among TB patients in our low HIV burden setting which were similar to regions with high HIV burden. Patients with isoniazid and rifampicin mono-resistance had an increased risk of poor treatment outcomes.     

Pharmacokinetics of Isoniazid,Pyrazinamide, and Ethambutol in Newly Diagnosed Pulmonary TB Patients in Tanzania

Exposure to lower-than-therapeutic levels of anti-tuberculosis drugs is likely to cause selection of resistant strains of Mycobacterium tuberculosis and treatment failure. The first-line anti-tuberculosis (TB) regimen consists of rifampicin, isoniazid, pyrazinamide, and ethambutol, and correct management reduces risk of TB relapse and development of drug resistance. In this study we aimed to investigate the effect of standard of care plus nutritional supplementation versus standard care on the pharmacokinetics of isoniazid, pyrazinamide and ethambutol among sputum smear positive TB patients with and without HIV. In a clinical trial in 100 Tanzanian TB patients, with or without HIV infection, drug concentrations were determined at 1 week and 2 months post initiation of anti-TB medication. Data was analysed using population pharmacokinetic modelling. The effect of body size was described using allometric scaling, and the effects of nutritional supplementation, HIV, age, sex, CD4+ count, weight-adjusted dose, NAT2 genotype, and time on TB treatment were investigated. The kinetics of all drugs was well characterised using first-order elimination and transit compartment absorption, with isoniazid and ethambutol described by two-compartment disposition models, and pyrazinamide by a one-compartment model. Patients with a slow NAT2 genotype had higher isoniazid exposure and a lower estimate of oral clearance (15.5 L/h) than rapid/intermediate NAT2 genotype (26.1 L/h). Pyrazinamide clearance had an estimated typical value of 3.32 L/h, and it was found to increase with time on treatment, with a 16.3% increase after the first 2 months of anti-TB treatment. The typical clearance of ethambutol was estimated to be 40.7 L/h, and was found to decrease with age, at a rate of 1.41% per year. Neither HIV status nor nutritional supplementations were found to affect the pharmacokinetics of these drugs in our cohort of patients.     

Molecular genotyping of Mycobacterium tuberculosis strains isolated from patients in the Samara region by the restriction DNA fragment length polymorphism

The typing of 106 M. tuberculosis (MBT) strains isolated from patients in the Samara region by the restriction DNA fragment length polymorphism (RFLP) IS6110 revealed that most of the strains (71.7%) belonged to the W family, 5 MBT strains (4.7%) belonged to the AI family, one culture was the mixture of two strains, AI and W. In addition, 24 MBT strains (22.6%) classified with other genotypes were detected. The analysis of the sensitivity of the MBT strains to rifampicin and isoniazid, with the method of absolute concentrations and by point mutations, demonstrated that 29 MBT strains (27.3%) were sensitive to rifampicin and isoniazid and 56 MBT strains (52.9%) were resistant to rifampicin and isoniazid simultaneously. Among the MBT strains of different RFLP families, strains both sensitive and resistant to these two preparations could be detected, but strains with multiple drug resistance prevailed in the W family (61.8%).     

Apoptosis-inducing action of antituberculosis drugs of the main group in vitro

The influence of the main antituberculosis drugs (isoniazid, rifampicin, ethambutol) on in vitro apoptosis of peripheral blood lymphocytes from patients with pulmonary tuberculosis was researched. It was shown that all the investigated drugs induced apoptotic death of the lymphocytes in vitro, that could result in disturbance of antigen-specific response formation in pulmonary tuberculosis.     

Detection of mutations associated with multidrug-resistant Mycobacterium tuberculosis clinical isolates

Antimicrobial resistance was studied in 100 Mycobacterium tuberculosis strains selected randomly from sputum cultures of newly diagnosed tuberculosis patients. Resistance of the isolates to rifampicin, isoniazid, and ethambutol was tested by both drug susceptibility testing (DST) and allele-specific PCR (AS-PCR). A total of 19 (19%) isolates were found resistant to at least one of the antituberculosis drugs investigated by PCR compared with 14 (14%) resistant isolates detected by DST. Eleven mutations were detected by AS-PCR in the rpoB gene (codons 516, 526, and 531), associated with rifampicin resistance, a marker of multidrug-resistant tuberculosis (MDR-TB), 14 mutations in the katG gene codon 315 that confers resistance to isoniazid, and nine mutations in the embB gene codon 306 that confers resistance to ethambutol. Mutations in the six multidrug-resistant isolates were confirmed by DNA sequencing. Results were compared with phenotypic DST data. Nineteen different mutation types to at least one of the drugs were found; six isolates (6%) were classified as MDR-TB, defined as resistance to at least rifampicin and isoniazid. The rates of concordance of the PCR with the phenotypic susceptibility test were 71.4, 54.5, and 44.4 for isoniazid, rifampicin, and ethambutol, respectively. These results highlight the importance of molecular epidemiology studies of tuberculosis in understudied regions with a tuberculosis burden to uncover the true prevalence of the MDR-TB.     

Rifampicin reduces effectiveness and bioavailability of prednisolone.

Rifampicin is an inducer of hepatic drug metabolising enzymes. This results in interactions with several drugs including oral anticoagulants, hypoglycaemics, and contraceptives. Concurrent treatment with prednisolone and rifampicin is given when tuberculosis coexists with a disease that is sensitive to steroids, when the diagnosis is uncertain, or occasionally in the treatment of severe tuberculosis. Two patients with respiratory disease were treated with both drugs: their condition improved considerably after rifampicin was withdrawn. Seven patients were then studied to assess the effect of rifampicin on the pharmacokinetics of prednisolone. Overall, rifampicin increased the plasma clearance of prednisolone by 45% and reduced the amount of drug available to the tissues (area under the plasma concentration time curve) by 66%. The effectiveness of prednisolone may be considerably reduced when rifampicin and prednisolone are used in combination.     

Potentially Serious Side Effects of High-dose Twice-weekly Rifampicin

Daily rifampicin in a single dose of 600 mg, combined with other drugs, usually streptomycin and isoniazid, was given to 49 patients for three months. It was planned to continue for another 15 months with twice-weekly rifampicin 1,200 mg plus isoniazid 900 mg, but the high incidence of side effects led to cessation of the intermittent regimen when only two patients had completed 18 months.Though there was no serious problem with daily treatment 11 patients (22%) were unable to continue rifampicin on the intermittent regimen. In 8 (16%) a pyrexial syndrome occurred. In one of these patients there was also temporary renal failure, and in another precipitous thrombocytopenia led to epistaxis and bleeding into the tongue and lips. Symptomless thrombocytopenia developed in two other patients, making three cases (6%) of thrombocytopenia in all.In 16 (33%) of the 49 patients antibodies to rifampicin were detected in the blood. Side effects occurred in 9 (56%) of these, including the three developing thrombocytopenia, but in only 2 (6%) of the 33 patients with no antibodies detected. This association of toxic reactions with antibodies is highly significant (P<0·001).     

Determination of rifampicin, desacetylrifampicin, isoniazid and acetylisoniazid by high-performance liquid chromatography: Application to human serum extracts, polymorphonucleocytes and alveolar macrophages

A method for the determination of rifampicin, desacetylrifampicin, isoniazid, and acetylisoniazid by high-performance liquid chromatography and using the same extract of the same sample is reported. After protein precipitation and extraction of these antituberculous drugs, two reversed-phase chromatographies were necessary. The technique was applied to serum extracts, polymorphonucleocytes and alveolar macrophages from patients treated for tuberculosis.     

Contribution of efflux to the emergence of isoniazid and multidrug resistance in Mycobacterium tuberculosis

Multidrug resistant (MDR) tuberculosis is caused by Mycobacterium tuberculosis resistant to isoniazid and rifampicin, the two most effective drugs used in tuberculosis therapy. Here, we investigated the mechanism by which resistance towards isoniazid develops and how overexpression of efflux pumps favors accumulation of mutations in isoniazid targets, thus establishing a MDR phenotype. The study was based on the in vitro induction of an isoniazid resistant phenotype by prolonged serial exposure of M. tuberculosis strains to the critical concentration of isoniazid employed for determination of drug susceptibility testing in clinical isolates. Results show that susceptible and rifampicin monoresistant strains exposed to this concentration become resistant to isoniazid after three weeks; and that resistance observed for the majority of these strains could be reduced by means of efflux pumps inhibitors. RT-qPCR assessment of efflux pump genes expression showed overexpression of all tested genes. Enhanced real-time efflux of ethidium bromide, a common efflux pump substrate, was also observed, showing a clear relation between overexpression of the genes and increased efflux pump function. Further exposure to isoniazid resulted in the selection and stabilization of spontaneous mutations and deletions in the katG gene along with sustained increased efflux activity. Together, results demonstrate the relevance of efflux pumps as one of the factors of isoniazid resistance in M. tuberculosis. These results support the hypothesis that activity of efflux pumps allows the maintenance of an isoniazid resistant population in a sub-optimally treated patient from which isoniazid genetically resistant mutants emerge. Therefore, the use of inhibitors of efflux should be considered in the development of new therapeutic strategies for preventing the emergence of MDR-TB during treatment.