Rifampicin: a new orally active rifamycin

Laser-induced vaporization mass spectrometry of rifamycins

The mass spectra of many rifamycins cannot be obtained by electron ionization (EI) owing to their thermal decomposition. When a laser beam is used to vaporize the sample through an optic fibre inserted in a hollow probe which reaches the sample cup, decomposition is minimized and the EI spectra show abundant molecular ions and fragments of structurally high diagnostic value. These ionic species are easily observed owing to the lack of chemical noise often present in soft ionization methods, such as direct liquid chemical ionization and fast atom bombardment.

A resonance Raman study on the interaction of rifampicin with Escherichia coli RNA polymerase

The technique of resonance Raman spectroscopy has been used to investigate the interaction of the antibiotic rifampicin with Escherichia coli RNA polymerase. Spectra were analyzed by generating the first derivative of each recorded spectrum using the Savitsky-Golay algorithm. The only band that shifted significantly in the resonance Raman spectrum of rifampicin upon the formation of the drug-core polymerase complex was the amide III band. It underwent an 8 cm-1 shift from 1306 cm-1 in aqueous solution to 1314 cm-1. A comparable shift was observed for the rifampicin-holoenzyme complex. Thus, the interaction of the sigma subunit with the core polymerase does not significantly alter the manner in which rifampicin interacts with RNA polymerase. The nature of this shift has been analyzed further by recording the resonance Raman spectrum of rifampicin in a variety of solvents with different hydrogen-bonding solvents (benzene and carbon disulfide) the amide III band was observed at approximately 1220 cm-1; in dimethyl sulfoxide, a weak hydrogen-bond acceptor, 1274 cm-1; in water, a strong hydrogen-bonding solvent, 1306 cm-1; and finally, in triethylamine, a stronger hydrogen-bonding solvent than water, it was observed at 1314 cm-1. Thus, as the hydrogen-bonding ability of the solvent increased, the amide III band shifted to higher frequency. Based on these results, the rifampicin binding site in RNA polymerase provides a stronger hydrogen-bonding environment for the amidic proton of rifampicin than is encountered when rifampicin is free in aqueous solution.

Inductive and repressive effects of rifampicin on rabbit liver microsomal cytochrome P-450

New Zealand White rabbits were treated with rifampicin at a dose of 50 mg/kg for 4 days. The total amount of microsomal hepatic cytochrome P-450 was not modified in treated, with respect to control, animals. However, further studies involving SDS-PAGE analysis, monooxygenase activity measurements and radial immunodiffusion assays indicated that rifampicin strongly affects the level of two P-450 isoenzymes. An LM3 form was induced; this form, apparently associated with erythromycine demethylase activity and hydroxylation of progesterone preferentially in position 6 beta, was shown to be immunologically and functionally different from LM3a and LM3b. On the other hand, an LM4 form, typically induced by beta-naphthoflavone, was repressed. The concomitant inductive/repressive effect of rifampicine on two cytochrome P-450 isoenzymes makes this drug a very atypical inducer, at least in the rabbit.

In vitro effect of rifampin on serum bilirubin determinations

An in vitro study demonstrated inerference with the total serum bilirubin assay by toxic rifampin levels. This interference was not observed with therapeutic rifampin levels.

Inhibition of influenza A virus replication by rifampicin and selenocystamine

The effects of selenocystamine, an inhibitor of influenza virus RNA-dependent RNA polymerase in vitro activity, in the antibiotic rifampicin were studied on influenza A/PR/8/34 (HON1) infection in embryonated eggs. Both drugs completely inhibited hemagglutinating and infective virus yields when added at relatively early times postinfection. Maximal inhibition was produced by apparently noncytotoxic concentrations of 50 microgram of selenocystamine, or of 400 microgram of rifampicin, per egg.

Effect of rifampicin on the infectivity of RNA bacteriophage f2

RNA bacteriophage f2, treated in vitro with rifampicin, loses infectivity dramatically. Rifampicin interacts with phage RNA, binding to a few specific sites. Inhibition of phage RNA infectivity occurs at 10-100 times lower molar excess of rifampicin than inhibition of infectivity of intact phage particles. Thus the phage capsid acts as a barrier, diminishing interaction of the drug with phage RNA.

Implication of rifampicin-quinone in the irreversible binding of rifampicin to macromolecules

1. When [3H]rifampicin is incubated with rat liver microsomes or rat liver homogenate, minor amounts are bound irreversibly to protein. This effect does not depend on the presence of NAD, NADH, NADP or NADPH. 2. Rifampicin is autoxidized at physiological pH. The product of autoxidation, rifampicin-quinone, if incubated with albumin, shows a much greater irreversible binding to the protein than the parent compound rifampicin. Hence it is concluded that rifampicin may bind irreversibly to proteins in a non-enzymic reaction after autoxidation to rifampicin-quinone. 3. Rifampicin-quinone also binds irreversibly to RNA and poly-L-lysine, if incubated with these compounds. This suggests that free amino groups of protein or RNA are involved in the binding. 4. 48 h after dosage of [3H]rifampicin (33 mg/kg) to rats, 29-2 +/- 4-1 (S.D.) pmol are bound irreversibly to 1 mg liver RNA, 15.8 +/- 8-1 pmol to 1 mg liver protein and 5-0 +/- 0-47 pmol to 1 mg protein in brain tissue. 5. Microsomal NADPH-cytochromcin-quinone to rifampicin. The KM of this reaction is 10(-4) M. Induction of the NADPH-cytochrome c reductase by pre-treatment of rats with 20 mg/kg rifampicin over 5 days results in a corresponding increase of increase of rifampicin-quinone reduction. 6. These results suggest that microsomal NADPH-cytochrome c reductase prevents accumulation of higher amounts of possibly toxic rifampicin-quinone by reduction to rifampicin.

Effect of rifampicin treatment on the metabolism of oestradiol and 17alpha-ethinyloestradiol by human liver microsomes

Liver biopsies were obtained from four patients treated with rifampicin 600 mg for 6-10 days. Hepatic microsomes were incubated with an NADPH-regenerating system and the substrates [2,4,6,7-3H] oestradiol, [6,7-3H] oestradiol, [2,4,6,7-3H] ethinyloestradiol and [6,7-3H] ethinyloestradiol. The hydroxylation rates of these steroids at the labelled positions of rings A and B were determined by measuring the transformation of tritium into HTO by the microsomal enzymes. Comparison with previously published data showed that treatment with rifampicin caused a fourfold increase in the rate of hydroxylation of oestradiol and ethinyloestradiol at positions C-2/C-4 of ring A and C-6/C-7 of ring B. The acceleration of oestrogen hydroxylation by rifampicin was paralleled by an increase in microsomal cytochrome P-450, and also by microsomal reduction of rifampicin-quinone, a reactive metabolite of rifampicin. The increased aromatic hydroxylation of oestradiol and ethinyloestradiol leads to enhancement of their irreversible binding to microsomal protein. The data provide an explanation for the diminished efficacy of oestrogens in contraceptive formulations given to patients under treatment with rifampicin.

Evaluation of rifamycin SV and rifampin kinetics in lactating ewes

Serum and milk concentrations of rifamycin SV and rifampin were determined in lactating ewes after a single intravenous injection, and pharmacokinetic parameters were evaluated by the two-compartment open-system model. Rifampin was distributed throughout a greater volume than rifamycin SV and was eliminated more slowly from the body. The concentrations of the two drugs, both lipophilic weak acids, in milk after intravenous or intramuscular injection were lower than in serum, but rifampin was detected in milk sooner and for longer periods than rifamycin SV. Under constant serum drug concentrations, the observed milk/serum ultrafiltrate concentrations ratios (0.19 to 0.29 for rifamycin SV, and 0.90 to 1.28 for rifampin) were close to the calculated ratios derived from the pH-pK passive diffusion concept.

Interaction of intraleukocytic bacteria and antibiotics

Bacteria that survive inside polymorphonuclear neutrophils (PMN) following phagocytosis are protected from the bactericidal action of most antibiotics. Two possible explanations are altered metabolism by intraleukocytic bacteria or failure of antibiotics to enter the phagosome. The oxygen consumption of intraleukocytic and extraleukocytic bacteria was measured as an index of bacterial metabolism. PMN respiration and bactericidal activity were suppressed with large doses of hydrocortisone and extraleukocytic bacterial oxygen consumption was abolished by the addition of lysostaphin. Intraleukocytic bacterial continued to consume oxygen suggesting that surviving ingested micro-organisms are metabolically active. Neither penicillin (which cannot kill intraleukocytic bacteria) nor rifampin (which can kill intraleukocytic bacteria) was bactericidal for staphylococci at 5 degrees C. Thus, rifampin is not uniquely able to kill "resting" bacteria.Intraleukocytic or extraleukocytic Staphylococcus aurens were incubated with [benzyl-(14)C]penicillin for 2 h at 37 degrees C. Live intraleukocytic bacteria bound only 13% as much penicillin as live bacteria incubated with killed PMN. To measure the penetration of antibiotics into PMN, [(14)C]rifampin and [(14)C]penicillin were measured in leukocyte pellets and in the supernatant fluid. The total water space in the pellets was quantitated using tritium water and the extracellular water space was measured using Na(235)SO(4). All penicillin associated with the cell pellet could be accounted for in extracellular water. Thus penicillin was completely excluded from the leukocytes. Rifampin was concentrated in the cell pellet 2.2 times when compared with the supernatant concentration. These studies suggest that a likely explanation for the survival of phagocytized bacteria in the presence of high concentrations of most antibiotics is the inability of the antibiotic to enter the phagocyte. Rifampin, which is highly lipid soluble, can enter leukocytes and kill intracellular bacteria.

Rifamycins: modulation of specific anti-poxviral activity by small substitutions on the piperazinyliminomethyl side chain

Rifamycin derivatives differing in the substitutent at the 4 position of the piperazinyliminomethyl side chain were tested for anti-poxviral activity. The effects of each derivative on wild-type vaccinia virus and on a mutant selected for resistance to rifampin were determined. Antiviral activity was measured in tissue culture by plaque inhibition, reduction in virus yield, and specific interruption of virus morphogenesis. Rifamycin derivatives containing H, ethyl, or propyl groups at the 4 position of the piperazinyliminomethyl side chain were much less active than rifampin, which has a methyl group at this position. Thus, minimal shortening or lengthening of the methyl piperazinyliminomethyl side chain of rifampin led to loss of specific antiviral activity. In contrast, the derivative containing an amino group at the 4 position of the piperazinyliminomethyl side chain had enhanced anti-poxviral activity.

Synthesis of trachoma agent proteins in emetine-treated cells

Trachoma agent develops in emetine-treated cells in the absence of host cell protein synthesis. The time course of protein synthesis throughout the trachoma developmental cycle and the effect of antibiotics on this process were investigated.

Effect of rifampin on the development of ribonucleic acid bacteriophage Q

The drug rifampin, when added at the time of infection, inhibits synthesis of the phage Qbeta. Both viral ribonucleic acids and viral proteins are made in nearly the same amount as in the absence of rifampin, but the rate of assembly into phage particles is low.

In vitro susceptibility of atypical mycobacteria to rifampin

Atypical mycobacteria (209 strains) were examined for susceptibility to rifampin by the proportion method by using Middlebrook 7H-10 agar. All strains of Mycobacterium kansasii and tap-water scotochromogens were inhibited by 0.25 to 1 mug of the drug per ml. Seventy-six per cent of M. scrofulaceum and 61% of M. intracellulare strains were susceptible to 4 mug/ml or less; 5% of the former and 8% of the latter were resistant to 16 mug/ml. All strains of M. gastri and M. triviale and most strains of M. terrae were sensitive to 1 to 4 mug/ml. Two strains of M. borstelense were both inhibited by 8 mug/ml. Nearly all strains of M. fortuitum were resistant to the drug. The results of this study suggest that rifampin may be a valuable agent for the treatment of many atypical mycobacterial infections.

Rifampicin inhibition of ribonucleic acid and protein synthesis in normal and ethylenediaminetetraacetic acid-treated Escherichia coli

The kinetics of ribonucleic acid (RNA) and protein synthesis in rifampicin-inhibited normal and ethylenediaminetetraacetic acid (EDTA)-treated Escherichia coli was measured. Approximately 200-fold higher external concentrations of rifampicin were needed to produce a level of inhibition in normal cells comparable to that observed in EDTA-treated cells. The rates of RNA and protein synthesis in both kinds of cells decreased exponentially, after an initial lag phase, at all rifampicin concentrations tested. The lag phase was longer and the final exponential slope less for protein synthesis than for RNA synthesis at a given rifampicin concentration. Below certain rifampicin concentrations, both the lag phase and the subsequent exponential decrease in the rates of RNA and protein synthesis were found to be rifampicin concentration dependent. At greater concentrations only the time of the lag phase was decreased by higher rifampicin concentrations, whereas the slope of the exponential decrease in the rates of RNA and protein synthesis was unaffected. In all cases, the exponential decrease continued to at least a 99.8% inhibition of the original rate of synthesis. These in vivo results are consistent with the mode of rifampicin action determined from in vitro studies; rifampicin prevents initiations of RNA polymerase on deoxyribonucleic acid, but not its propagation, by binding the enzyme essentially irreversibly. The results also indicate the size distribution of messenger RNA molecules in E. coli under our conditions.