Pharmacokinetics of rifampicin, isoniazid & pyrazinamide during daily & intermittent dosing: A preliminary study.

Background & objectives: The National Tuberculosis (TB) Control Programme has transitioned from thrice-weekly to daily drug treatment regimens in India. This preliminary study was conceived to compare the pharmacokinetics of rifampicin (RMP), isoniazid (INH) and pyrazinamide (PZA) in TB patients being treated with daily and thrice weekly anti-TB treatment (ATT). Methods: This prospective observational study was undertaken in 49 newly diagnosed adult TB patients receiving either daily ATT (n=22) or thrice-weekly ATT (n=27). Plasma RMP, INH and PZA were estimated by high-performance liquid chromatography. Results: The peak concentration (Cmax) of RMP was significantly higher (RMP: 8.5 µg/ml vs. 5.5 µg/ml; P=0.003) and Cmax of INH was significantly lower (INH: 4.8 µg/ml vs. 10.9 µg/ml; P<0.001) in case of daily dosing compared to thrice-weekly ATT. Cmax of drugs and doses was significantly correlated. A higher proportion of patients had subtherapeutic RMP Cmax (8.0 µg/ml) during thrice-weekly compared to daily ATT (78% vs. 36%; P=0.004). Multiple linear regression analysis showed that Cmax of RMP was significantly influenced by the dosing rhythm, pulmonary TB and Cmax of INH and PZA by the mg/kg doses. Interpretation & conclusions: RMP concentrations were higher and INH concentrations were lower during daily ATT, suggesting that INH doses may need to be increased in case of a daily regimen. Larger studies are, however, required using higher INH doses when monitoring for adverse drug reactions and treatment outcomes.

Differential Culturability of Mycobacterium tuberculosis in Culture-Negative Sputum of Patients With Pulmonary Tuberculosis and in a Simulated Model of Dormancy.

Tuberculosis (TB) remains a leading killer among infectious diseases of humans worldwide. Delayed diagnosis is a crucial problem in global TB control programs. Bacteriological methods currently used to diagnose TB in endemic countries take up to 8 weeks, which poses a significant delay in starting antibiotic therapy. The presence of a heterogeneous population of Mycobacterium tuberculosis, the causative agent of TB, is among the reasons for delayed diagnosis by bacteriological methods. Previously, it has been shown that mycobacterial resuscitation-promoting factors (RPFs), a family of proteins secreted by actively growing bacteria into the media, are capable of activating the growth of dormant bacteria, thus enhancing the detection of bacilli in the sputum of confirmed TB cases. However, the variability in bacterial resuscitation by RPF in the sputum of suspected pulmonary TB cases that showed differential smear and/or culture positivity during diagnosis has not been fully explored. Here, we report the presence of non-replicating bacteria in the sputum of suspected TB cases that show differential growth response to RPF treatment. Using crude and recombinant RPF treatment, we show improved sensitivity and reduced time to detect bacilli in the sputum samples of smear-positive/culture-negative or smear-negative/culture-negative cases. We also report the phenotypic heterogeneity in the RPF responsiveness among Mtb strains using an in vitro dormancy model. Our findings have implications for improving the bacteriological diagnostic modalities currently used to diagnose TB in endemic countries.

Pharmacokinetics of rifabutin during atazanavir/ritonavir co-administration in HIV-infected TB patients.

BACKGROUND & OBJECTIVE: Rifabutin (RBT) is the rifamycin that is recommended to treat tuberculosis (TB) in HIV-infected individuals during combination antiretroviral therapy (ART) containing HIV protease inhibitors (PIs). We studied the pharmacokinetics of rifabutin at doses of 300 mg thrice weekly and 150 mg daily during concomitant atazanavir/ritonavir (ATZ/r) administration in adult HIV-infected TB patients treated in the Revised National TB Control Programme (RNTCP) in India. METHODS: This was a multi-centric study conducted in 45 adult HIV-infected TB patients, who were being treated for TB with a RBT-containing regimen and an antiretroviral treatment regimen with ATZ/r, at doses of 300 mg thrice-weekly (n = 36) or 150 mg daily (n = 9). Serial blood draws at pre-dosing and at 1, 2, 4, 6, 8, 12 and 24 hours after drug administration were done. Plasma RBT was estimated by high pressure liquid chromatography (HPLC). RESULTS: The peak concentration (Cmax) of both doses were within the therapeutic range (0.45-0.90 µg/ml) of RBT. Proportion of patients having Cmax above or below the therapeutic range and trough concentration (Cmin) below the minimum inhibitory concentration of RBT did not significantly differ between the two doses. TB treatment outcomes were also similar at both doses. CONCLUSIONS: This is the first and only study from India reporting on the pharmacokinetics of RBT at 300 mg thrice weekly and 150 mg daily doses. Both doses yielded similar plasma RBT concentrations, outcomes and were well tolerated. RBT can be administered at either doses during ATZ/r co-administration in HIV-infected patients with TB.

A selective and sensitive high performance liquid chromatography assay for the determination of cycloserine in human plasma.

BACKGROUND: Cycloserine (CYC) is a second line antitubercular drug that is used for the treatment of multidrug resistant tuberculosis (MDR-TB) along with other antitubercular agents and is often used in developing countries. Monitoring CYC levels in plasma could be useful in the clinical management of patients with MDR-TB. A high performance liquid chromatography method for the determination of CYC in human plasma was developed. METHODS: The method involved extraction of the sample using solid phase extraction cartridges and analysis of the extracted sample using a reverse phase T3 column (150mm) and detection at 240nm with Photo Diode Array (PDA) detector. The chromatogram was run for 15min at a flow rate of 0.4ml/min at 30°C. RESULTS AND CONCLUSION: The assay was specific for CYC and linear from 5.0 to 50.0µg/ml. The relative standard deviations of within- and between-day assays were less than 10%. Recovery of CYC ranged from 102% to 109%. The interference of other second line anti-TB drugs in the assay of CYC was ruled out. The assay spans the concentration range of clinical interest. The specificity and sensitivity of this assay makes it highly suitable for pharmacokinetic studies.

N-acetyltransferase gene polymorphisms & plasma isoniazid concentrations in patients with tuberculosis.

BACKGROUND & OBJECTIVES: Variations in the N-acetyltransferase (NAT2) gene among different populations could affect the metabolism and disposition of isoniazid (INH). This study was performed to genotype NAT2 gene polymorphisms in tuberculosis (TB) patients from Chennai, India, and compare plasma INH concentrations among the different genotypes. METHODS: Adult patients with TB treated in the Revised National TB Control Programme (RNTCP) in Chennai, Tamil Nadu, were genotyped for NAT2 gene polymorphism, and two-hour post-dosing INH concentrations were compared between the different genotypes. Plasma INH was determined by high-performance liquid chromatography. Genotyping of the NAT2 gene polymorphism was performed by real-time polymerase chain reaction method. RESULTS: Among the 326 patients genotyped, there were 189 (58%), 114 (35%) and 23 (7%) slow, intermediate and fast acetylators, respectively. The median two-hour INH concentrations in slow, intermediate and fast acetylators were 10.2, 8.1 and 4.1 µg/ml, respectively. The differences in INH concentrations among the three genotypes were significant (P<0.001). INTERPRETATION & CONCLUSIONS: Genotyping of TB patients from south India for NAT2 gene polymorphism revealed that 58 per cent of the study population comprised slow acetylators. Two-hour INH concentrations differed significantly among the three genotypes.

Drug Concentration Thresholds Predictive of Therapy Failure and Death in Children With Tuberculosis: Bread Crumb Trails in Random Forests.

BACKGROUND: The role of drug concentrations in clinical outcomes in children with tuberculosis is unclear. Target concentrations for dose optimization are unknown. METHODS: Plasma drug concentrations measured in Indian children with tuberculosis were modeled using compartmental pharmacokinetic analyses. The children were followed until end of therapy to ascertain therapy failure or death. An ensemble of artificial intelligence algorithms, including random forests, was used to identify predictors of clinical outcome from among 30 clinical, laboratory, and pharmacokinetic variables. RESULTS: Among the 143 children with known outcomes, there was high between-child variability of isoniazid, rifampin, and pyrazinamide concentrations: 110 (77%) completed therapy, 24 (17%) failed therapy, and 9 (6%) died. The main predictors of therapy failure or death were a pyrazinamide peak concentration <38.10 mg/L and rifampin peak concentration <3.01 mg/L. The relative risk of these poor outcomes below these peak concentration thresholds was 3.64 (95% confidence interval [CI], 2.28-5.83). Isoniazid had concentration-dependent antagonism with rifampin and pyrazinamide, with an adjusted odds ratio for therapy failure of 3.00 (95% CI, 2.08-4.33) in antagonism concentration range. In regard to death alone as an outcome, the same drug concentrations, plus z scores (indicators of malnutrition), and age <3 years, were highly ranked predictors. In children <3 years old, isoniazid 0- to 24-hour area under the concentration-time curve <11.95 mg/L × hour and/or rifampin peak <3.10 mg/L were the best predictors of therapy failure, with relative risk of 3.43 (95% CI, .99-11.82). CONCLUSIONS: We have identified new antibiotic target concentrations, which are potential biomarkers associated with treatment failure and death in children with tuberculosis.

SLCO1B1 gene polymorphisms do not influence plasma rifampicin concentrations in a South Indian population.

OBJECTIVE: To determine the effect of SLCO1B1 gene polymorphisms (rs11045819, rs4149032 and rs4149033) on rifampicin (RMP) concentrations in adult tuberculosis (TB) patients from south India. METHODS: We genotyped adult TB patients for three SLCO1B1 gene polymorphisms-rs11045819, rs4149032 and rs4149033-and compared 2-h post-dosing RMP concentrations of the different genotypes for each of the polymorphisms. Plasma RMP was determined using high-performance liquid chromatography. Genotyping was performed using direct sequencing. RESULTS: Among the 256 study patients, minor allele frequencies were respectively 0.01 (A), 0.46 (C) and 0.07 (A) for rs11045819, rs4149032 and rs4149033 polymorphisms; genotype distributions followed Hardy-Weinberg equilibrium. RMP concentrations did not significantly differ between the different genotypes of the three polymorphisms. CONCLUSION: This is the first study to show that rs11045819, rs4149032 and rs4149033 polymorphisms in the SLCO1B1 gene did not influence RMP concentrations in Indian patients.

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.

RMP exposure is lower in HIV-infected TB patients receiving intermittent than daily anti-tuberculosis treatment.

We compared the pharmacokinetics of rifampicin (RMP) during daily and intermittent (thrice weekly) anti-tuberculosis treatment in human immunodeficiency virus infected tuberculosis patients. Patients treated with a thrice-weekly regimen had significantly lower plasma peak concentration, area under the time concentration curve from 0 to 24 h and higher oral clearance of RMP than those treated with the daily regimen. The median values were respectively 3.7 and 6.4 µg/ml (P < 0.001), 20.7 and 29.4 µg/ml.h (P = 0.03) and 21.7 and 15.3 ml/min (P = 0.03).

Pharmacokinetics of rifabutin during atazanavir/ritonavir co-administration in HIV-infected TB patients in India.

SETTING: Rifabutin (RBT) is reported to be as effective as and to have less inducing effect on cytochrome P450 enzymes than rifampicin against tuberculosis (TB). The optimal dose of RBT during ritonavir (RTV) co-administration remains a matter of debate. OBJECTIVE: To study the pharmacokinetics of 150 mg RBT thrice weekly during concomitant atazanavir/RTV administration in human immunodeficiency virus (HIV) infected TB patients. METHODS: This observational study was conducted in 16 adult HIV-infected TB patients being treated for TB with an RBT-containing regimen and an antiretroviral therapy regimen with RTV; the dose of RBT was 150 mg thrice weekly. Serial blood draws were performed at pre-dosing and at 1, 2, 4, 6, 8, 12 and 24 h after the drug was administered. Plasma RBT was estimated using high-performance liquid chromatography. RESULTS AND CONCLUSIONS: Peak RBT concentration was below the lower therapeutic limit (<0.3 µg/ml) in seven patients, while 10 patients had trough concentrations below the minimal inhibitory concentration against Mycobacterium tuberculosis (0.06 µg/ml), suggesting that the RBT dosage may be inadequate. Prospective studies in different settings are required to arrive at the proper therapeutic dose for RBT to be used during co-administration with RTV.

Age, nutritional status and INH acetylator status affect pharmacokinetics of anti-tuberculosis drugs in children.

SETTING: The currently recommended dosages of rifampicin (RMP), isoniazid (INH), pyrazinamide (PZA) and ethambutol in children are extrapolated from adult pharmacokinetic studies, and have not been adequately evaluated in children. OBJECTIVE: To describe the pharmacokinetics of RMP, INH and PZA given thrice weekly in children with tuberculosis (TB), and to relate pharmacokinetics to treatment outcomes. METHODS: Eighty-four human immunodeficiency virus negative children with TB aged 1-12 years in Chennai and Madurai, India, were recruited. Phenotypic INH acetylator status was determined. Nutritional status was assessed using Z scores. During the intensive phase of anti-tuberculosis treatment, a complete pharmacokinetic study was performed after directly observed administration of drugs. At 2 and 6 months, drug levels were measured 2 h post-dose. Drug concentrations were measured using high performance liquid chromatography and pharmacokinetic variables were calculated. Multivariable regression analysis was performed to explore factors impacting drug levels and treatment outcomes. RESULTS AND CONCLUSIONS: Children aged <3 years had significantly lower RMP, INH and PZA concentrations than older children, and 90% of all children had sub-therapeutic RMP Cmax (<8 µg/ml). Age, nutritional status and INH acetylator status influenced drug levels. Peak RMP and INH concentrations were important determinants of treatment outcome. Recommendations for anti-tuberculosis treatment in children should take these factors into consideration.

Effect of rifampicin & isoniazid on the steady state pharmacokinetics of moxifloxacin.

BACKGROUND & OBJECTIVES: Moxifloxacin (MFX) is reported to have promising antimycobacterial activity, and has a potential to shorten tuberculosis (TB) treatment. We undertook this study to examine the influence of rifampicin (RMP) and isoniazid (INH) on the steady state pharmacokinetics of MFX individually in healthy individuals. METHODS: A baseline pharmacokinetic study of MFX (400 mg once daily) was conducted in 36 healthy adults and repeated after one week of daily MFX with either RMP (450/600 mg) (n = 18) or INH (300 mg) (n = 18). Plasma MFX concentrations were determined by a validated HPLC method. RESULTS: Plasma peak concentration and exposure of MFX was significantly lower and plasma clearance significantly higher when combined with RMP (P<0.001). The C max to MIC and AUC 0-12 to MIC ratios of MFX were significantly lower during concomitant RMP (P<0.001). INH had no significant effect on the pharmacokinetics of MFX. INTERPRETATION & CONCLUSIONS: Concomitant RMP administration caused a significant decrease in C max and AUC 0-12 of MFX, the mean decreases being 26 and 29 per cent, respectively. It is uncertain whether this decrease would affect the treatment efficacy of MFX. Prospective studies in TB patients are needed to correlate MFX pharmacokinetics with treatment outcomes.

Comparison of HPLC & spectrophotometric methods for estimation of antiretroviral drug content in pharmaceutical products.

BACKGROUND & OBJECTIVES: Simple and reliable methods to estimate drugs in pharmaceutical products are needed. In most cases, antiretroviral drug estimations are performed using a HPLC method, requiring expensive equipment and trained technicians. A relatively simple and accurate method to estimate antiretroviral drugs in pharmaceutical preparations is by spectrophotometric method, which is cheap and simple to use as compared to HPLC. We undertook this study to standardise methods for estimation of nevirapine (NVP), lamivudine (3TC) and stavudine (d4T) in single tablets/capsules by HPLC and spectrophotometry and to compare the content of these drugs determined by both these methods. METHODS: Twenty tablets/capsules of NVP, 3TC and d4T each were analysed for their drug content by HPLC and spectrophotometric methods. Suitably diluted drug solutions were run on HPLC fitted with a C18 column using UV detection at ambient temperature. The absorbance of the diluted drug solutions were read in a spectrophotometer at 300, 285 and 270 nm for NVP, 3TC and d4T respectively. Pure powders of the drugs were used to prepare calibration standards of known drug concentrations, which was set up with each assay. RESULTS: The inter-day variation (%) of standards for NVP, 3TC and d4T ranged from 2.5 to 6.7, 2.1 to 7.7 and 6.2 to 7.7, respectively by HPLC. The corresponding values by spectrophotometric method were 2.7 to 4.7, 4.2 to 7.2 and 3.8 to 6.0. The per cent variation between the HPLC and spectrophotometric methods ranged from 0.45 to 4.49 per cent, 0 to 4.98 per cent and 0.35 to 8.73 per cent for NVP, 3TC and d4T,respectively. CONCLUSIONS: The contents of NVP, 3TC and d4T in the tablets estimated by HPLC and spectrophotometric methods were similar, and the variation in the amount of these drugs estimated by HPLC and spectrophotometric methods was below 10 per cent. This suggests that the spectrophotometric method is as accurate as the HPLC method for estimation of NVP, 3TC and d4T in tablet/capsule. Hence laboratories that do not have HPLC equipment can also undertake these drug estimations using spectrophotometer.

Pharmacokinetics of lamivudine & stavudine in generic fixed-dose combinations in HIV-1 infected adults in India.

BACKGROUND & OBJECTIVES: Antiretroviral drug concentrations are important determinants of clinical response to a drug accounting for both toxicity and efficacy. Several factors such as age, ethnicity, body weight and patients' immune status may influence antiretroviral drug concentrations. The aim of the study was to determine the influence of immunological status, sex and body mass index on the steady state pharmacokinetics of lamivudine (3TC) and stavudine (d4T) in HIV-infected adults, who were undergoing treatment with generic fixed dose combinations (FDC) of these drugs in India. METHODS: Twenty seven HIV-1 infected patients receiving antiretroviral treatment (ART) for at least two weeks at the Government ART clinic at Tambaram, Chennai, took part in the study. Serial blood samples were collected predosing and at different time points after drug administration. Plasma 3TC and d4T levels were estimated by HPLC. RESULTS: The patients' immune status, sex or body mass index had no impact on the pharmacokinetics of 3TC. In the case of d4T, peak concentration was significantly lower in patients with CD4 cell counts < 200 cells/microl than those with > or = 200 cells/ microl (P < 0.05), but were within the therapeutic range. The mean CD4 cell counts increased from 101 cells/microl at initiation of ART to 366 cells/microl at 12 months of treatment. INTERPRETATION & CONCLUSIONS: Blood levels of 3TC and d4T drugs that are part of generic FDCs commonly used by HIV-infected individuals in India were within the therapeutic range and not influenced by nutritional or immune status. There was a significant improvement in CD4 cell counts over 12 months of treatment. Indian generic FDCs manufactured and used widely in the developing world provide effective concentrations of antiretroviral drugs.

Simple and rapid liquid chromatography method for determination of moxifloxacin in plasma.

A high performance liquid chromatographic method for determination of moxifloxacin in human plasma was developed. The method involved deproteinisation of the sample with perchloric acid and analysis of the supernatant using a reversed-phase C(18) column (150 mm) and fluorescence detection at an excitation wavelength of 290 nm and an emission wavelength of 460 nm. The assay was specific for moxifloxacin and linear from 0.125 to 10.0 microg/ml. The relative standard deviation of intra- and inter-day assays was lower than 10%. The average recovery of moxifloxacin from plasma was 101%. Due to its simplicity, the assay can be used for pharmacokinetic studies of moxifloxacin.

CYP2B6 G516T polymorphism but not rifampin coadministration influences steady-state pharmacokinetics of efavirenz in human immunodeficiency virus-infected patients in South India.

The dose of efavirenz during concomitant rifampin (RMP) administration is a matter of debate. We studied the influence of RMP coadministration on the steady-state pharmacokinetics of efavirenz in human immunodeficiency virus type 1 (HIV-1)-infected patients in South India. Fifty-seven HIV-tuberculosis (TB)-coinfected and 15 HIV-1-infected patients receiving combination antiretroviral therapy (CART) with an efavirenz (600 mg once daily)-containing regimen were recruited. HIV-TB-coinfected patients were receiving treatment with RMP-containing regimens. A complete pharmacokinetic study was conducted with 19 HIV-TB patients on two occasions (with and without RMP). Trough concentrations of efavirenz were measured in the remaining 38 patients during RMP coadministration. The 15 HIV-infected patients underwent complete pharmacokinetic sampling on one occasion. Plasma efavirenz was estimated by high-performance liquid chromatography, and genotyping of CYP2B6 G516T polymorphism was performed by sequencing. Peak and trough concentrations and exposure to efavirenz were significantly higher in TT than in GT and GG genotype patients (P < 0.001). Although RMP coadministration decreased the peak and trough concentrations and exposure to efavirenz by 17.8, 20.4, and 18.6%, respectively, the differences were not statistically significant. The trough concentration of efavirenz was subtherapeutic (less than 1.0 microg/ml) in 6 (8%) of 72 patients. In this South Indian population of HIV-infected patients, CYP2B6 G516T polymorphism but not RMP coadministration significantly influenced the pharmacokinetics of efavirenz; patients with the TT genotype had very high blood levels of efavirenz. While a small proportion of patients had subtherapeutic efavirenz levels, the clinical implications are uncertain, as all had good immunological responses to CART.

Urine levels of rifampicin & isoniazid in asymptomatic HIV-positive individuals.

BACKGROUND & OBJECTIVE: AIDS and its associated gastrointestinal complications may impair the absorption of anti-tuberculosis (TB) drugs. Impaired absorption of anti-TB drugs could lead to low drug exposure, which might contribute to acquired drug resistance and reduced effectiveness of anti-TB treatment. The aim of this study was to obtain information on the status of absorption of rifampicin (RMP) and isoniazid (INH) in asymptomatic HIV- positive individuals, who are less immunocompromised. The D-xylose absorption test was also carried out to assess the absorptive capacity of intestive. METHODS: The absorption of RMP, INH and D-xylose was studied in 15 asymptomatic HIV-positive individuals with CD4 cell counts>350 cells/mm3 and 16 healthy volunteers, after oral administration of single doses of RMP (450 mg), INH (300 mg) and D-xylose (5 g). Urine was collected up to 8 h after drug administration. Percentage dose of the drugs and their metabolites and D-xylose excreted in urine were calculated. RESULTS: A significant reduction in the urinary excretion of INH and D-xylose in HIV-positive persons compared to healthy volunteers was observed. The per cent dose of RMP and its metabolite, desacetyl RMP was also lower in HIV-positive persons compared to healthy volunteers, but this difference was not statistically significant. INTERPRETATION & CONCLUSION: Decreased urinary excretion of D-xylose and INH are suggestive of intestinal malabsorption in HIV-positive individuals. HIV infection could cause malabsorption of anti-TB drugs even at an early stage of the disease. The clinical implications of these findings need to be confirmed in larger studies.

Decreased bioavailability of rifampin and other antituberculosis drugs in patients with advanced human immunodeficiency virus disease.

We evaluated the effects of human immunodeficiency virus (HIV) disease on pharmacokinetics of antituberculosis medications by measuring concentrations of isoniazid and rifampin in blood and of pyrazinamide and ethambutol in urine. Peak concentration and exposure were reduced for rifampin, and rapid acetylators of isoniazid had lower drug levels. HIV and HIV-tuberculosis patients who have diarrhea and cryptosporidial infection exhibit decreased bioavailability of antituberculosis drugs.

Malabsorption of rifampin and isoniazid in HIV-infected patients with and without tuberculosis.

The absorption of rifampin, isoniazid, and D-xylose in patients with human immunodeficiency virus (HIV) infection and diarrhea, in patients with HIV infection and tuberculosis (TB), in patients with pulmonary TB alone, and in healthy subjects was studied. Percentage of dose of the drugs, their metabolites, and D-xylose excreted in urine were calculated. A significant reduction in the absorption of drugs and D-xylose in both the HIV infection/diarrhea and HIV infection/TB groups was observed (P<.05), and the correlation between them was significant. Our results indicate that patients with HIV infection and diarrhea and those with HIV infection and TB have malabsorption of rifampin and isoniazid.

Simple and rapid high-performance liquid chromatography method for the determination of ofloxacin concentrations in plasma and urine.

A high-performance liquid chromatographic method for the determination of ofloxacin in human plasma and urine was developed. The method involved deproteinisation of the sample with perchloric acid and analysis of the supernatant using a reversed-phase C18 column and fluorescence detection at an excitation wavelength of 290 nm and an emission wavelength of 460 nm. The assay was linear from 0.5 to 10.0 microg/ml. The relative standard deviation of intra- and inter-day assays was lower than 5%. The average recovery of ofloxacin from plasma was 93%. The method was evaluated in samples from healthy subjects whose drug levels were already measured by microbiological assay.