Determination of rifabutin in human plasma by high-performance liquid chromatography with ultraviolet detection

Therapeutic implications of nano-encapsulated rifabutin, azithromycin & ethambutol against experimental Mycobacterium avium infection in mice

Background & objectives

Mycobacterium avium causes atypical infection in both immunocompetent and immunocompromised individuals. Conventional chemotherapy for M. avium infection is not efficient due to lengthy course of treatment and drug-associated toxic side effects. The present study was aimed at reducing dosing frequency of antimicrobial regimen consisting of azithromycin (AZM), rifabutin (RBT) and ethambutol (EMB) by encapsulation of drugs in nanoparticles (NPs) in experimental M. avium infection in mice.

Methods

Poly (DL-lactide-co-glycolide) NPs containing anti-M. avium drugs were prepared, characterized and studied for their pharmacokinetics and pharmacodynamics parameters. Drug-loaded NPs were further analyzed for their therapeutic efficacy against experimental M. avium infection in mice.

Results

Drug-loaded NPs were of size 227.3±16.4 for RBT, 334.35±11.7 for AZM and 509.85±20.5 for EMB with smooth surface morphology and negative zeta potential. AZM, EMB and RBT from NPs were detectable for 6, 4 and 5 days, respectively, in the mice plasma, whereas free drugs were cleared from mice circulation within 24 h. Chemotherapeutic effects of weekly administered drug-loaded NPs were equivalent to daily administered free drugs.

Interpretation & conclusions

Our findings showed that NPs gave sustained release of drugs inside plasma and organs, thus decreasing dosage frequency, and their weekly dosage had therapeutic efficacy equivalent to daily dosage of free drugs.

Simultaneous LC-MS-MS Determination of Lopinavir and Rifabutin in Human Plasma

Tuberculosis (TB) with human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome represents the most common infectious diseases worldwide. Anti-TB drugs are used concurrently with antiretroviral drug for treatment of TB-HIV co-morbidities. Due to lower risk of interaction with protease inhibitors, rifabutin is preferred over rifampicin in treatment of HIV and TB co-morbidity. A simple and specific liquid chromatography tandem mass spectrometry method was developed for quantification of rifabutin (RBT) and lopinavir (LPV) simultaneously in human plasma. Following extraction using 60% n-hexane in ethyl acetate, the processed samples were chromatographed on a Discovery HS C18 column (5 μm, 50 × 4.6 mm, id) using mobile phase [85% acetonitrile in ammonium acetate buffer (10 mM, pH 4.5)] at a flow rate of 0.7 mL/min. Mass spectrometric detection was performed in positive electrospray ionization mode using multiple reaction monitoring (RBT, m/z 847.7 → 815.4; LPV, m/z 629.6 → 447.4). Raloxifene and phenacetin were used as internal standards for RBT and LPV, respectively. Linearity was established in the range of 1-1,000 ng/mL and 0.5-10 µg/mL (R2 ≥ 0.99) for RBT and LPV, respectively. The recovery of LPV and RBT were always >90 and >50%, respectively. The precisions and accuracies were well within the acceptable limits of variation.

Rapid and sensitive quantitation of antibiotics in fermentations by electrospray mass spectrometry

Electrospray ionisation mass spectrometry (ESI-MS) has been used for the determination and quantitation of a broad range of 24 antibiotics, from groups including aminoglycosides, beta-lactams, tetracyclines, antifungals and glycopeptides. Spectra have been acquired for all 24 antibiotics derived from pure samples dissolved in acetonitrile/water, along with samples extracted from complex fermentation liquor. Quantitation was carried out by the detection of the protonated molecules, using time-scheduled single-ion monitoring (SIM). ESI-MS was used to detect and quantify to 5-microM levels. A one-step extraction of antibiotics with an organic solvent (methanol) was used for this rapid and simple procedure. Specificity is not matched by other methods and antibiotic analogues (e.g. the five forms of erythromycin) can be determined within minutes.

Effects of fluconazole and clarithromycin on rifabutin and 25-O-desacetylrifabutin pharmacokinetics

Ten human immunodeficiency virus-infected patients were given rifabutin in addition to fluconazole and clarithromycin. There was a 76% increase in the area under the concentration-time curve of rifabutin when either fluconazole or clarithromycin was given alone and a 152% increase when both drugs were given together with rifabutin. Patients should be monitored for adverse effects of rifabutin administered concomitantly with clarithromycin and/or fluconazole.

Specific high-performance liquid chromatography assay for determination of rifabutin plasma concentration following Extrelut column extraction

A specific, precise and accurate assay for determination of rifabutin in human plasma using Extrelut column extraction was developed and validated. Rifabutin concentrations were calculated with a standard curve ranging from 5 to 800 ng ml(-1). using a split-curve approach. Chromatographic peaks were separated by means of a 5 microm Symmetry Shield RP8 using a KH2PO4 (0.05 M) buffer-acetonitrile mobile phase. Detection wavelength was set at 275 nm. Chromatography was carried out at room temperature (20-25 degrees C). The limit of quantification was 5 ng ml(-1). The recovery was over 71%. The intra-day precision of the assay was 5, 7, and 1% while the inter-day precision was 11.2, 8.1, and 5.8% at concentrations of 30, 150 and 500 ng ml(-1), respectively. The accuracy ranged from 99 to 108%. Forty of the drugs most commonly administered to HIV-positive patients were found not to interfere with the assay. The assay has been used in a comparative study of rifabutin pharmacokinetics in HIV-positive patients with or without wasting syndrome. reserved.

Chromatography as an analytical tool for selected antibiotic classes: a reappraisal addressed to pharmacokinetic applications

The first antibiotic discovered, penicillin, appeared on the market just after the Second World War. Intensive research in subsequent years led to the discovery and development of cephalosporins, aminoglycosides, tetracyclines and rifamycin. The chemotherapeutic quinolones and the more recently discovered fluoroquinolones have added promising new therapeutic weapons to fight the microbial challenge. The major role pharmacokinetics has played in developing these compounds should be highlighted. Plasma concentration-time profiles and the therapeutic activity evoked by these compounds allow the therapeutic window, doses and dose turnovers to be appropriately defined as well as possible dose adjustment to be made in renal failure. The pharmacokinetics of antimicrobial agents were initially explored by using microbiological methods, but these lack specificity. The HPLC technique with UV, fluorometric, electrochemical and, in some cases, mass spectrometry detection has satisfactory solved the problem of antimicrobial agent assay for pharmacokinetic, bioavailability and bioequivalence purposes alike. Indeed, in these studies, plasma concentrations of the given analyte must be followed up for a period > or = 3 times the half-life, which calls for specific sensitive assays. In the review, the authors have described the analytical methods employed in the pharmacokinetics of antibiotics, including some chemotherapeutic agents which are used in medical practice as alternatives to antibiotics. The pharmacokinetic characteristics of each class of drugs are also briefly described, and some historical and chemical notes on the various classes are given.

Pharmacokinetic study of the interaction between rifabutin and delavirdine mesylate in HIV-1 infected patients

The oxidative metabolism of delavirdine, a non-nucleoside inhibitor of HIV-1 reverse transcriptase, is mediated in part by cytochrome P450 3A. The influence of rifabutin, an inducer of certain human cytochrome P450 isozymes, on the steady-state pharmacokinetics of delavirdine was investigated in 12 HIV-positive patients with CD4 counts ranging from 75 to 671/mm3. Both the control group (n = 5) and the rifabutin group (n = 7) received 400 mg delavirdine mesylate every 8 h for 30 days; subjects in the rifabutin group took a 300 mg, once-daily dose of rifabutin on study days 16-30. Harvested plasma from serial blood samples collected after dosing on days 15, 16, and 30 was assayed for delavirdine and its N-desalkyl metabolite concentrations using a reversed-phase HPLC method. Blood samples obtained on days 16 and 30 were also assayed for rifabutin by HPLC. Delavirdine mesylate alone or in combination with rifabutin was well-tolerated. On day 30, statistically significant differences between groups were observed for all delavirdine pharmacokinetic parameters (P < 0.046). After coadministration of rifabutin and delavirdine mesylate for 2 weeks, oral clearance of delavirdine increased five-fold, resulting in lower steady-state plasma delavirdine concentrations. Rifabutin pharmacokinetic parameters were similar to those previously reported. Concomitant use of delavirdine and rifabutin at the recommended dose for each drug is discouraged. Maintaining therapeutic concentrations of delavirdine in patients on both medications may require dose modification.