Transport of pefloxacin across the bacterial cytoplasmic membrane in quinolone-susceptible Staphylococcus aureus

Binding to phospholipids, uptake by simple diffusion, and an energy-dependent, carrier-mediated efflux are thought to characterize interactions between fluoroquinolones and bacterial cytoplasmic membranes. Here, we have found that an endogenous active efflux is unlikely in quinolone-susceptible Staphylococcus aureus. The protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP), increased pefloxacin uptake in different membrane systems under conditions which excluded carrier-mediated transport, i.e., in bacterial cells at 4 degrees C and in protein-free phosphatidylglycerol liposomes. When plotted as a function of outer pH, the CCCP effect, both in S. aureus cells and in phosphatidylglycerol liposomes, correlated with pefloxacin labeling of everted S. aureus membrane vesicles, with all three profiles showing maximal effect at an acidic pH. So the CCCP effect may result not from inhibition of the proton motive force, as previously thought, but rather from acidification of the intramembrane space by the protonophore, leading to enhanced binding of the positive pefloxacin species to the inner leaflet of the bilayer. Moreover, antistaphylococcal potency and uptake profiles of pefloxacin in S. aureus and phosphatidylglycerol liposomes, assayed as a function of outer pH, peaked at a neutral pH. These observations suggest that zwitterionic and positive quinolone species are responsible for diffusion through and binding to the cytoplasmic membrane, respectively.

Pharmacokinetics of paracetamol in the neonate and infant after administration of propacetamol chlorhydrate

The pharmacokinetic parameters of paracetamol were studied after 15 min intravenous infusion of 15 mg/kg of propacetamol (Prodafalgan) in 5 neonates aged less than 10 days and 7 infants aged between 1 and 12 months. Blood was sampled at 0, 0.5, 2 and 6 h after the first intravenous infusion of propacetamol. The infants aged less than 10 days had higher plasma concentrations of paracetamol, a longer half-life (3.5 vs. 2.1 h) and a lower plasma clearance (0.149 vs. 0.365 l/h/kg) than the older children. Dose simulations were performed on the basis of individual data of each child in order to obtain steady-state plasma concentrations between 4 and 18 mg/l permitting the best antipyretic effect for each child. In infants aged less than 10 days a 15 mg/kg dose of propacetamol four times a day (i.e. 30 mg/kg/day paracetamol) is sufficient, corresponding to the dosage recommended by the French pharmacopoeia. On the other hand, double the dosage, nearer to the American dosage, is necessary for children aged over 10 days.

Deposition of amphotericin B aerosols in pulmonary aspergilloma

The aim of the present study was to characterize amphotericin B aerosols nebulized by ultrasonic and jet nebulizers and to study their deposition and pharmacokinetics in patients with pulmonary mycetoma. The aerodynamic behaviour and pulmonary deposition of amphotericin B particles were measured using a direct isotopic method based on stable labelling of the drug with 99mTc. Each nebulizer was bench tested for inhaled mass and particle size distribution. Three patients suffering from pulmonary aspergilloma were enrolled for a 4 week clinical study. They received 5 mg of amphotericin B daily delivered by either Fisoneb or DP100 (ultrasonic) or Respirgard II (jet) nebulizers. Deposition of radiolabelled amphotericin B was measured once with each nebulizer using a gamma-camera. In two patients, amphotericin B serum concentration was monitored over a 330 min period after the nebulization had been completed. Inhaled masses of the three nebulizers, assessed as % of labelled drug caught in inspiratory filter in duplicate experiments, were: 5.8 and 3.6% for Respirgard II; 26.5 and 28.3% with Fisoneb; 5.9 and 6.3% for DP100. Mass median aerodynamic diameter (mean +/- SD) results were: 0.28 +/- 0.04 micron with Respirgard II; 4.82 +/- 0.78 microns with Fisoneb; and 2.27 +/- 1.14 microns with DP100. Because of larger particles and significantly greater inhaled mass, Fisoneb delivered more amphotericin B to the central airways, the lung periphery and in the mycetoma lung regions. Amphotericin B serum concentrations correlated with pulmonary deposition and remained below 25 ng.mL-1. No untoward effects were reported by the patients during the 4 week trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of protein D2 and lipopolysaccharide in diffusion of quinolones through the outer membrane of Pseudomonas aeruginosa

Routes of quinolone permeation in Pseudomonas aeruginosa were investigated by using sparfloxacin as a prototype compound. [14C]sparfloxacin cell labeling was 13 to 28% lower in three protein D2-deficient mutants resistant to imipenem than in their imipenem-susceptible counterparts. In four impermeability-type quinolone-resistant strains isolated from pefloxacin-treated animals, we observed two- to fourfold-greater resistance to imipenem, reduced protein D2 expression in the outer membrane according to Western blotting (immunoblotting), and 25 to 29% decreased cell labeling with imipenem. In a protein D2-producing strain but not in its protein D2-deficient isogenic mutant, uptake of [14C]sparfloxacin was strongly inhibited by L-lysine and imipenem, which act as substrates for protein D2. Conversely, binding of [14C]imipenem in a porin D2-positive strain was reduced by sparfloxacin but not by the nonamphoteric quinolone nalidixic acid. Sparfloxacin, imipenem, and lysine possess a carboxyl group and a potentially protonated nitrogen separated from each other by 0.64 to 1.07 nm as calculated by computer. Hence, protein D2 may catalyze facilitated diffusion for sparfloxacin, as it does for imipenem. In addition, pefloxacin-selected isolates contained 41 to 113% more 3-deoxy-D-mannooctulosonic acid than their quinolone-susceptible counterparts, with MIC increases of 2- to 4-fold for WIN-57273 (n-octanol-phosphate buffer partition coefficient, 13.139), 4- to 8-fold for difloxacin (partition coefficient, 3.093) and sparfloxacin (partition coefficient, 0.431), and 8- to 16-fold for norfloxacin (partition coefficient, 0.059) and ciprofloxacin (partition coefficient, 0.056). Thus, we hypothetize that in quinolone-selected strains, increased amounts of lipopolysaccharide form a permeability barrier that acts preferentially against hydrophilic quinolones.

Newly documented antimicrobial activity of quinolones

The improved antimicrobial activity of newer fluoroquinolones and novel applications recently found for the drugs already marketed are reviewed. Several new compounds are more active against gram-positive bacteria than the presently marketed fluoroquinolones. WIN 57273, the most potent compound in vitro on a weight basis, is 16 to 128 times more active than ciprofloxacin against various staphylococci, streptococci, Enterococcus spp., Corynebacterium spp., Listeria monocytogenes and Bacillus spp. BMY 40062, PD 117558, PD 127391, sparfloxacin, temafloxacin and tosufloxacin also show enhanced in vitro efficacy against these species. These drugs also possess increased activity against various anaerobes, notably Clostridium perfringens, Clostridium difficile and the Bacteroides fragilis group. Mycobacterium tuberculosis, rapidly growing mycobacteria other than Mycobacterium chelonae, and Mycobacterium leprae are often susceptible to quinolones displaying bactericidal activity which is potentially useful for curing difficult-to-treat mycobacteriosis. In addition, a number of new products, notably those containing a cyclopropyl group, are more active than reference fluoroquinolones against Mycobacterium leprae. Sparfloxacin, BMY 40062 and WIN 57273 compare favorably with older fluoroquinolones in the killing of intracellular Legionella spp., and several of the newer compounds have greater antichlamydial potency. Improved antibacterial activity has also been found against Mycoplasma hominis, Ureaplasma urealyticum, Acinetobacter spp. and Pseudomonas maltophilia. By contrast, the newer quinolones have similar or less activity against Pseudomonas aeruginosa and Enterobacteriaceae. Recently, pefloxacin, ofloxacin and ciprofloxacin were found to be active against protozoa, including Plasmodium spp., Trypanosoma cruzi and Leishmania donovani, but not against Toxoplasma gondii. In the near future, more specific research testing unusual pathogens may lead to the identification of quinolones with more selective activity.

Nebulization and anti-Pseudomonas aeruginosa activity of colistin

Colistin aerosols are frequently administered to patients with cystic fibrosis. However, questions arise concerning the effect of both jet and ultrasonic nebulizers on the properties of the drug. The aim of this study was to characterize the anti-Pseudomonas aeruginosa (PA) activity of colistin after jet (Pari LL) and ultrasonic (DP100) nebulization. A bench study was performed by capturing the aerosols, determining the drug mass, and assessing its anti-PA activity. Because the inhaled mass of colistin had to be entirely recovered for the bacteriological study, it was assessed by isotopic methods, mixing the drug with a 99mTc-labelled tracer and demonstrating that 99mTc activity accurately predicted the mass of colistin. Colistin was extracted from the filters and its antibiotic activity was determined using the method employed for the study of the bacteriostatic and bactericidal power of serum on the ATCC 27853 PA strain. The postnebulization minimum inhibitory concentrations (MIC) were 1.9 micrograms.mL-1 with DP100 and 0.5 microgram.mL-1 with Pari LL. These values were less than two dilutions different from the 1 microgram.mL-1 MIC of non-nebulized colistin. We conclude that neither jet nebulization nor ultrasonic nebulization alter the antibiotic properties of colistin and that both systems can be used to nebulize colistin.

Buflomedil poisoning: five cases with cardiotoxicity

OBJECTIVE

To report cardiotoxicity of buflomedil.

SETTING

Medical intensive care unit of a university hospital.

PATIENTS

Five patients admitted to the hospital since 1985 for buflomedil poisoning. The amount ingested was known for only three patients (3-10.8 g).

RESULTS

The five young women were admitted to the hospital because of generalized seizures or myoclonic jerks. Cardiac arrest (asystole) occurred for two of them on admission, 1 and 3 h after ingestion. Electrocardiogram revealed atrio-ventricular and intraventricular conduction abnormalities, increased QT interval and flattened T wave, decreasing after sodium bicarbonate infusion in two cases. The patients received mechanical ventilation, gastric lavage, oral activated charcoal, and clonazepam or valproic acid for convulsions or myoclonic jerks. Epinephrine was administered for cardiac arrest. Sodium bicarbonate was infused in one patient on the basis of slightly prolonged QRS duration and in two patients due to cardiac arrest. Clinical outcome was good and without sequelae for all five patients after a few days in the intensive care unit.

CONCLUSION

Clinical and electrocardiographic symptomatology of buflomedil poisoning suggests direct cardiotoxicity, which could be related to possible sodium antagonist properties.

Oxidative polymorphism of dextromethorphan in a Burundi population

The wide availability, metabolism by the same cytochrome P450 as debrisoquine and, above all, the inocuity of dextromethorphan (DMP) favour the frequent choice of this drug as the test substance in determining oxidation phenotypes. 100 healthy Burundian volunteers (94 m and 6 f) in this study ingested 50 mg DMP bromhydrate, i.e. 38.5 mg of DMP base. Urine was collected for 8 h following the dose and TLC was used to analyse it. The method was particularly useful in view of its low cost, speed and the ease of applying it to a large study group. 5% of the Burundian subjects were poor metabolizers.

Usual and unusual antibacterial effects of quinolones

Recently documented antibacterial effects of quinolones are reviewed. DNA gyrase is most likely to be the primary target site for these agents. Quinolones rapidly kill susceptible bacteria; the mechanisms of the bactericidal activity, still poorly understood, probably involve new protein synthesis. Quinolones alter membrane integrity before cell death, leading to leakage of cytoplasmic constituents. In Gram-negative bacteria, quinolones act as chelating agents for outer membrane divalent cations, disorganizing the bacterial lipopolysaccharide layer and facilitating the further entry of quinolone molecules in a 'self-promoted' pathway. Quinolones inhibit plasmid replication and reduce the efficacy of plasmid conjugation. Subinhibitory concentrations of quinolones can interfere with bacterial virulence factors, such as bacterial adherence to the host cell, phagocytosis and production of enzymes implicated in virulence. Recent studies also indicate synergism of quinolones with oxacillin against methicillin-resistant staphylococci and describe improved activity of newer compounds against Gram-positive pathogens.

Herbicide: fatal ammonium thiocyanate and aminotriazole poisoning

OBJECTIVE

To describe fatal herbicide poisoning with Radoxone TL composed of aminotriazole and ammonium thiocyanate.

CASE REPORT

A 54-year-old man was hospitalized because of unexplained coma with myoclonic jerks and vascular collapse. Despite symptomatic treatment with mechanical ventilation and vascular filling, life-threatening shock occurred with oliguria, profound metabolic acidosis and cardiac arrest. Hyperchloremia (141 mmol/L) with reversed anion gap (-19) suggested interference with chloride measurement caused by halogens (Br,F,I) or other anions such as thiocyanate. Eventually a weed killer, Radoxone TL containing ammonium thiocyanate, was found at the patient's house. Thiocyanate and aminotriazole blood levels were 750 mg/L and 138 mg/L respectively more than 12 hours after ingestion. After prolonged cardiopulmonary resuscitation, continuous venovenous hemodiafiltration was performed. Despite hemodynamic recovery the patient died 48 hours later of postanoxic coma.

CONCLUSION

Aminotriazole, a systemic nonselective herbicide, is often associated with ammonium thiocyanate which enhances its activity. Experimental studies and previous fatal cases suggest a predominant toxicity of thiocyanate. Early diagnosis is important.

Relative beta-lactamase- and transpeptidase-inhibitory activities of the new quinolone WIN-57273 in Staphylococcus aureus

The new quinolone WIN-57273 was shown to inhibit Staphylococcus aureus beta-lactamase activity noncompetitively in vitro with an apparent Ki value of 0.5 mM. MICs of penicillin G for a highly quinolone-resistant, beta-lactamase-negative strain in the presence of exogenous beta-lactamase decreased considerably when subinhibitory concentrations of WIN-57273 were added. Furthermore, the attachment transpeptidase reaction, investigated on whole cells of S. aureus, was impeded by WIN-57273 concentrations of greater than or equal to 30 microM. While these interactions suggest a novel mechanism of action for this compound, they are probably not relevant to the overall antibacterial potency of WIN-57273.

[Methadone blood assay by the FPIA technique: application to the monitoring of patients in maintenance treatment to opiates]

A large inter-individual variability in methadone pharmacokinetics is observed in patients under maintenance treatment for major addiction to opiates. Therefore an individual dose titration of methadone is necessary, based on clinical response, i.e. symptoms of overdosage or withdrawal syndrome, but these symptoms are unspecific. However, a poor response to methadone treatment (asking for drug compliance) or the possibility of drug interactions may require the determination of methadone blood concentrations. Therapeutic drug monitoring (TDM) of those patients is performed using methadone trough blood concentrations measured by chromatography (GC or HPLC: reference methods) or by immunoassay, which gives more rapid results. A review of the literature led us to use the fluorescence polarisation immunoassay (FPIA technique) performed on a TDx-FLx analyzer. We confirmed the lack of "matrix effect" and FPIA was compared to GC-MS (gas chromatography-mass spectrometry) on patients samples. According to the literature, a methadone trough serum concentration target of 400 ng/mL is recommended; results under 100 ng/mL are considered as clinically ineffective, whereas methadone concentrations above 1000 ng/mL are frequently associated with drug toxicity. The linearity domain of the technique stays between 50 and 500 ng/mL, which is satisfactory. We describe some clinical cases from the Methadone Treatment Center of Tours (Centre Port-Bretagne), which showed that methadone blood concentration measurement may be helpful to achieve the optimal dose of methadone in each patient.

[A new molecule in antiparasitic therapy: alpha-difluoromethylornithine]

Alpha-difluoromethylornithine (DFMO) is a specific irreversible inhibitor of ornithine-decarboxylase (ODC), key enzyme in the biosynthesis of polyamines, physiological compounds involved in cell multiplication. Pharmacokinetic studies of the drug revealed good oral absorption, low metabolisation and mainly urinary excretion. Short half-life (3 hrs to 3 hrs 30) implicates daily repeated administrations. DFMO is well tolerated, side effects being reversible on discontinuing drug therapy. They chiefly include diarrheas, hematological perturbations (thrombocytopenia) and hear losses (high dosages). Experimental studies show best results on trypanosomes: curative action in mice infected with Trypanosoma brucei brucei. DFMO is effective too against infection with sporozoïtes of Plasmodium berghei. Early clinical observations in African patients with Trypanosoma brucei gambiense sleeping sickness show favorable results: efficacy in both stages of the disease, without significant toxicity. Further trials are required to define optimal therapeutic applications. By the way, DFMO already seems to be a promising alternative to conventional therapy of African trypanosomiasis, expecting other indications in the field of antiparasitic chemotherapy.

[Epidemiology of pediatric paracetamol poisoning (retrospective analysis of calls received by the Poison Control Center of Tours)]

The authors analysed 101 phone calls received in 3 years and 8 months at the Poison Control Center of Tours for paracetamol poisoning in children under 15 years of age. 70% of children were between 1 and 5 years old, 15% under 1 year and 15% over 5 years old. The kind of poisoning differ according to age: iatrogenic in 93% of cases under 1 year old (medication given by parents; error in dosage); accidental in 85% of cases between 1 and 5 years old and "willful" poisoning (43%) or accidental (36%) over 5 years old. The average quantity of ingested paracetamol was low (58mg/kg). The delay before phone call from an individual or a doctor was usually quite short. The neurologic or digestive signs were present in 12% of the children. The outcome was uneventful in all cases indicating that this form of poisoning is being in childrens.

[Onset of convulsive crises with theophylline therapy at therapeutic doses]

Six patients treated with theophylline, including five with advanced chronic obstructive pulmonary disease, developed generalized seizures with serum theophylline concentrations ranging from 7 to 21 mg/l. Cerebral computed tomographic scans showed a small sylvian infarction in one patient. In the other five patients nothing, except theophylline, could account for the seizures. There were no clinical signs of theophylline toxicity prior to the failures, all of which had a favourable outcome. Patients with acute exacerbations of chronic obstructive pulmonary disease seem to be prone to develop generalized seizures when treated with theophylline.

[Study of residual levels of delayed-action neuroleptics]

Pharmacokinetics of the depot antipsychotics are unclear and mainly depend on releasing from the depot site (according to a "flip-flop" model). Few data are available on residual plasma concentrations of those drugs. We have practiced 38 blood determinations among 15 patients treated by long-acting neuroleptics (10 by fluphenazine decanoate, 4 by flupentixol decanoate and 1 by pipotiazine palmitate). Radio Receptor Assay method was used (based on competition for dopamine receptors binding), with results expressed as chlorpromazine equivalents. They showed; a wide interindividual variability; considering each subject, intraindividual variability is attenuated; blood measurements are mainly higher than therapeutic ranges (especially for patients on fluphenazine decanoate). Those results might involve that some patients are overdosed, but other studies are needed in this way.

[Cholestatic hepatitis caused by ketoconazole]

The authors report a new Ketoconazole-induced hepatitis in which clinical, chemical and histological features show evidence of a cholestatic injury in a 62 yrs-old female recovering once therapy is stopped. In this case-report, delay of onset of the illness is very short for a 200 mg-a-day prescription and no feature leads towards an immune response. This, may be, means that Ketoconazole-induced hepatitis should be led by an idiosyncrasic mechanism. Even if fatal hepatitis are rare, prescriptors have to beware of this therapy.