Drug-drug interactions and safety of linezolid, tedizolid, and other oxazolidinones.

INTRODUCTION: Oxazolidinones are synthetic antimicrobials with strong bacteriostatic activity against Gram-positive organisms. Recently, tedizolid phosphate was approved for clinical use becoming the second agent of this class after linezolid available in clinical practice. AREAS COVERED: Oxazolidinone pharmacology including structure-activity relationships, mode of action, pharmacokinetics, drug-drug interactions, and adverse drug reactions is reviewed. Furthermore, bacterial resistance, approved indications, use in paediatric populations, and tuberculosis treatment with oxazolidinones are discussed, and differences in indications and pharmacotoxicological properties between the two approved agents are elucidated. A MEDLINE PubMed search for articles published in English from January 1960 to June 2015 was completed using the terms: oxazolidinone, oxazolidinone-induced toxicity, oxazolidinone pharmacokinetics, serotonin syndrome, oxazolidinone drug-drug interactions, antituberculotic treatment. EXPERT OPINION: Linezolid illustrates an important antimicrobial in several Gram-positive infections especially when methicillin-resistant Staphylococcus aureus strains are involved. Myelosuppression and neuropathy are toxicities of high relevance particularly in case of prolonged treatment periods. The significance of linezolid in the treatment of extensively drug-resistant tuberculosis has to be further investigated. Tedizolid phosphate represents a welcome addition in our anti-infective arsenal, and future research will clarify its role in indications other than the already approved acute bacterial skin infections.

Ophthalmic drugs as part of polypharmacy in nursing home residents with glaucoma.

BACKGROUND: Glaucoma comprises age-related neurodegenerative diseases of retinal ganglion cells, the worldwide prevalence of which is increasing. Local pharmacotherapy is the primary treatment option, especially in the elderly. But this therapeutic approach may include risks for adverse drug effects and drug-drug interactions, of particular importance in frail nursing home resident populations. OBJECTIVE: The aim of the present study was to investigate anti-glaucoma pharmacotherapy in nursing home residents in the context of multi-morbidity and related systemic co-medication. METHODS: Data for 8,685 nursing home residents with 88,695 drug prescriptions were analysed according to diagnosis and local or systemic pharmacotherapy. Data were provided in anonymous form by a German public health insurance company. RESULTS: The study cohort was characterized by a mean age of 83.6 ± 7.3 years (range: 65-106 years), 21 % of nursing home residents were at least 90 years old and 83.7 % were women. For each nursing home resident, an average of 6.0 ± 3.3 different drugs were registered. A diagnosis of glaucoma was recorded in 520 (6.0 %) nursing home residents; all subjects had co-existing medical conditions. Dementia was a frequent co-morbidity, diagnosed in 51.7 % of nursing home residents with glaucoma. Anti-glaucoma drugs contributed to 0.5 % of all prescriptions and were prescribed to 341 nursing home residents. The most frequently used anti-glaucoma ophthalmics were ß-blockers (n = 219), followed by prostaglandin analogues (n = 101) and carbonic anhydrase inhibitors (n = 86). Local anti-glaucoma therapy was co-prescribed with a systemic pharmacotherapy in 338 nursing home residents. An ophthalmic agent was, on average, combined with 6.5 ± 3.2 prescriptions for systemic agents. Thus, 71.9 % of nursing home residents were prescribed ophthalmic ß-blockers and a concomitant antihypertensive medication; local and systemic ß-blockers were combined in 20.2 % of these patients. Co-treatment with cardiac glycosides or calcium antagonists was found in 13 % of nursing home residents prescribed ophthalmic parasympathomimetics, and in 14 % of those prescribed ophthalmic ß-blockers, with the potential for drug-drug interactions to influence cardiac function. CONCLUSIONS: Anti-glaucoma pharmacotherapy in nursing home residents is frequently prescribed in the context of polypharmacy. This may modify the efficacy and safety of local and systemic therapies. Therefore, individualized pharmacotherapy that integrates anti-glaucoma drug therapy into the overall treatment rationale in nursing home residents is necessary. However, to realize this concept, further clinical research in nursing home residents is warranted.

Resveratrol modulates interleukin-1ß-induced phosphatidylinositol 3-kinase and nuclear factor κB signaling pathways in human tenocytes.

Resveratrol, an activator of histone deacetylase Sirt-1, has been proposed to have beneficial health effects due to its antioxidant and anti-inflammatory properties. However, the mechanisms underlying the anti-inflammatory effects of resveratrol and the intracellular signaling pathways involved are poorly understood. An in vitro model of human tenocytes was used to examine the mechanism of resveratrol action on IL-1ß-mediated inflammatory signaling. Resveratrol suppressed IL-1ß-induced activation of NF-κB and PI3K in a dose- and time-dependent manner. Treatment with resveratrol enhanced the production of matrix components collagen types I and III, tenomodulin, and tenogenic transcription factor scleraxis, whereas it inhibited gene products involved in inflammation and apoptosis. IL-1ß-induced NF-κB and PI3K activation was inhibited by resveratrol or the inhibitors of PI3K (wortmannin), c-Src (PP1), and Akt (SH-5) through inhibition of IκB kinase, IκBα phosphorylation, and inhibition of nuclear translocation of NF-κB, suggesting that PI3K signaling pathway may be one of the signaling pathways inhibited by resveratrol to abrogate NF-κB activation. Inhibition of PI3K by wortmannin attenuated IL-1ß-induced Akt and p65 acetylation, suggesting that p65 is a downstream component of PI3K/Akt in these responses. The modulatory effects of resveratrol on IL-1ß-induced activation of NF-κB and PI3K were found to be mediated at least in part by the association between Sirt-1 and scleraxis and deacetylation of NF-κB and PI3K. Overall, these results demonstrate that activated Sirt-1 plays an essential role in the anti-inflammatory effects of resveratrol and this may be mediated at least in part through inhibition/deacetylation of PI3K and NF-κB.

Sirt-1 is required for the inhibition of apoptosis and inflammatory responses in human tenocytes.

Tendon overuse injuries and tendinitis are accompanied by catabolic processes and apoptosis of tenocytes. However, the precise molecular mechanisms of the destructive processes in tendon are not fully understood. Sirt-1, a nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase, has been linked to transcriptional silencing and appears to play a key role in inflammation. The purpose of this study was to examine whether down-regulation of Sirt-1 using antisense oligonucleotides (ASO) affects inflammatory and apoptotic signaling in tenocytes. Transient transfection of tenocytes with ASO against Sirt-1 induced expression of Bax and other proteins involved in apoptosis (cleaved caspase-3 and poly(ADP-ribose)polymerase), acetylation of tumor suppressor p53, and mitochondrial degradation. Interestingly, Sirt-1 was found to interact directly with p53. In contrast, Sirt-1 activator resveratrol inhibited interleukin-1ß (IL-1ß)- and nicotinamide-induced NF-κB activation and p65 acetylation and suppressed the activation of IκB-α kinase. Resveratrol also reversed the IL-1ß- or nicotinamide-induced up-regulation of various gene products that mediate inflammation (cyclooxygenase-2) and matrix degradation (matrix metalloproteinase-9) that are known to be regulated by NF-κB. Knockdown of Sirt-1 by using ASO abolished the inhibitory effects of resveratrol on inflammatory and apoptotic signaling including Akt activation and SCAX suppression. Down-regulation of histone deacetylase Sirt-1 by mRNA interference abrogated the effect of resveratrol on NF-κB suppression, thus highlighting the crucial homeostatic role of this enzyme. Overall, these results suggest for the first time that Sirt-1 can regulate p53 and NF-κB signaling via deacetylation, demonstrating a novel role for resveratrol in the treatment of tendinitis/tendinopathy.

Curcumin modulates nuclear factor kappaB (NF-kappaB)-mediated inflammation in human tenocytes in vitro: role of the phosphatidylinositol 3-kinase/Akt pathway.

Inflammatory processes play essential roles in the pathogenesis of tendinitis and tendinopathy. These events are accompanied by catabolic processes initiated by pro-inflammatory cytokines such as interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α). Pharmacological treatments for tendinitis are restricted to the use of non-steroidal anti-inflammatory drugs. Recent studies in various cell models have demonstrated that curcumin targets the NF-κB signaling pathway. However, its potential for the treatment of tendinitis has not been explored. Herein, we used an in vitro model of human tenocytes to study the mechanism of curcumin action on IL-1ß-mediated inflammatory signaling. Curcumin at concentrations of 5-20 µm inhibited IL-1ß-induced inflammation and apoptosis in cultures of human tenocytes. The anti-inflammatory effects of curcumin included down-regulation of gene products that mediate matrix degradation (matrix metalloproteinase-1, -9, and -13), prostanoid production (cyclooxygenase-2), apoptosis (Bax and activated caspase-3), and stimulation of cell survival (Bcl-2), all known to be regulated by NF-κB. Furthermore, curcumin suppressed IL-1ß-induced NF-κB activation via inhibition of phosphorylation and degradation of inhibitor of κBα, inhibition of inhibitor of κB-kinase activity, and inhibition of nuclear translocation of NF-κB. Furthermore, the effects of IL-1ß were abrogated by wortmannin, suggesting a role for the phosphatidylinositol 3-kinase (PI-3K) pathway in IL-1ß signaling. Curcumin suppressed IL-1ß-induced PI-3K p85/Akt activation and its association with IKK. These results demonstrate, for the first time, a potential role for curcumin in treating tendon inflammation through modulation of NF-κB signaling, which involves PI-3K/Akt and the tendon-specific transcription factor scleraxis in tenocytes.

A physiologically based toxicokinetic modelling approach to predict relevant concentrations for in vitro testing.

Our study was performed in the context of an in vitro primary hepatic cell culture as an alternative for the in vivo cancerogenic bioassay. The 29 substances which are to be used in the in vitro primary hepatic cell culture have been tested in 2-year bioassays and a 14-day short term study. The aim of this modelling study was to simulate the concentration--time profile of the compounds when given by the oral route at the doses tested in the previous studies taking into account the percentage of the dose absorbed. The model contained seven tissue compartments with uptake from the gastrointestinal tract into the portal vein. Because the primary hepatic cell culture is metabolically competent and the primary interest was to model the concentration in the portal vein, the hepatic vein and the systemic circulation (blood) in the beginning we did not include elimination. Partitioning between blood and tissues was calculated according to a published biologically based algorithm. The substances' kinetic profile differed according to their blood: tissue partitioning. Maximal concentrations in portal vein, hepatic vein and the blood depended mainly on the dose and the fraction absorbed which were the most critical parameters in this respect. Our study demonstrates an application of BPTK modelling for the purpose to simulate concentrations for planning the doses for an in vitro study. BPTK modelling seems to be a better approach than using data from in vitro studies on cytotoxicity.

Use of two validated in vitro tests to assess the embryotoxic potential of mycophenolic acid.

Mycophenolate mofetil is a widely used immunosuppressive drug that recently has been categorized as a human teratogen. Animal experiments indicate a teratogenic potential of the drug, but so far, it has not been studied in embryotoxicity in vitro assays. The aim of this study was to evaluate the in vitro embryotoxic potential of mycophenolic acid and investigate the ability of such tests to detect its embryotoxic potential. We used two validated assays: the rat whole embryo culture and the murine embryonic stem cell test. Rat embryos cultured from gestational day 9.5 for 48 h with the drug showed dysmorphogenic development already at a concentration of 250 microg mycophenolic acid/l medium. At concentrations of 750 microg/l and more, all rat embryos exhibited malformations. The main effects were defective yolk sac blood circulation, neural tube defects (open cranial neural pore), malformations of the head with missing eye anlagen and heart anomalies. Moreover, the exposed embryos showed a concentration-dependent decrease in protein content, crown-rump length, number of somites and morphological score. The murine embryonic stem cell test was slightly more sensitive. Proliferation and differentiation of the ES-D3-cells were significantly impaired at concentrations of 31 and 125 microg mycophenolic acid/l medium, respectively. In the differentiation assay, at a concentration of 125 microg mycophenolic acid/l medium and more, the number of wells with differentiated cardiomyocytes significantly decreased. Additionally, a cytotoxicity assay with balb/c 3T3 mouse fibroblasts was used to compare the proliferation and vitality of embryonic cells with adult cells. In the balb/c 3T3 cytotoxicity assay, the number of vital mouse fibroblasts significantly decreased at a mycophenolic acid concentration of 62 microg/l and more. In conclusion, by using the two validated in vitro tests, we showed that mycophenolic acid exhibits a pronounced embryotoxic potential at cytotoxic concentrations. This result from validated in vitro tests is of special interest, because it supports the use of the tests to detect human teratogens.

Investigation of the sensitising and cross-sensitising potential of textile dyes and beta-lactam antibiotics using a biphasic mice local lymph node assay.

We used a modified protocol of the murine local lymph node assay (LLNA) to study the cross-sensitising potential of (a) textile dye disperse yellow 3 and its metabolite 2-amino-p-cresol, (b) two antibiotics, penicillin G and cefotiam. The test substances were applied in a biphasic manner, i.e. first on the shaved skin of the back followed by application on the dorsal side of the ears after 2 weeks. The end-points analysed included thickness and weight of an ear-biopsy, weight and cell number of the draining lymph node, and lymphocyte cell surface markers analysed by flow-cytometry. Disperse yellow 3 and its metabolite significantly altered the various end-points at both the tested concentrations (0.5 and 1%), thus demonstrating the sensitising potential of the two substances. The cross-sensitisation study showed significant modulation in the tested variables in the treated group as compared to the control, signifying cross-sensitisation potential of the two substances. Penicillin G and cefotiam showed significant changes in various end-points, pointing towards their sensitising potential. However, even at 50% concentration of the beta-lactams no significant change in any end-point indicating absence of cross-reactivity of the antibiotics was noticed. We conclude that a biphasic, modified protocol of the LLNA is a suitable approach to test for a cross-reactivity potential of two related compounds.

Quinolone-induced arthropathy: an update focusing on new mechanistic and clinical data.

Quinolones possess favourable antibacterial and pharmacokinetic characteristics and are often used as anti-infective agents in adults. They are contraindicated in children and adolescents because they damage weight-bearing joints in juvenile animals. In addition, they possess a tendotoxic potential. Since ciprofloxacin has been used off-label for decades in children and adolescents, it is known today that no pronounced risks for arthropathies or tendinopathies exist in humans. Recently published clinical studies with gatifloxacin in children support this clinical experience. However, a low risk for joint disorders cannot be excluded and tendinopathies are a generally accepted rare adverse effect of quinolones at least in adults. Isolated case reports of arthralgia in children following quinolone therapy have been published and in studies with levofloxacin the incidence of musculoskeletal disorders was significantly greater in levofloxacin-treated patients than in control patients treated with comparator antibiotics. As a consequence, only life-threatening infections for which other antimicrobials cannot be used are possible indications for quinolones in children, for example the use of ciprofloxacin in cystic fibrosis patients with a bronchopulmonary exacerbation, chronic suppurative otitis media caused by Pseudomonas sp., complicated urinary tract infections and enteritis caused by invasive multidrug-resistant pathogens (e.g. Salmonella, Shigella).

A new dendritic cell type suitable as sentinel of contact allergens.

Establishing of alternatives to animal tests is ethically desirable and gains in importance in context of new European Union regulations such as REACH. We have refined our new in vitro assay for prediction of the sensitizing potency of xenobiotics. Monocytes cocultured with primary human keratinocytes develop to a novel class of in vitro generated dendritic cells after treatment with transforming growth factor beta and Interleukin-4 in serum-free medium. These dendritic cell-related cells (DCrc) are the key players in the loose-fit coculture-based sensitization assay (LCSA). Assay duration and cytokine consumption could be cut down without impairing the assay's functionality. DCrc showed a dose-dependent upregulation of CD86 after treatment with the contact allergens 2,4,6-trinitrobenzenesulfonic acid, the prohapten isoeugenol, and alpha-hexyl cinnamic aldehyde. The metal allergens nickel and cobalt could be detected by measuring Interleukin-6 and macrophage inflammatory protein 1-beta (MIP-1beta, CCL-4) in coculture supernatants. The irritant zinc elicited no reaction. Lipopolysaccharide produced upregulation of CD86, IL-6 and MIP-1beta. Determination of tolerable concentrations of an allergen in consumer products requires a widely accepted sharp quantitative assay. Animal-based assays do not meet this requirement. The LCSA provides dose-response information, thereby allowing prediction of the relative ability of a substance to induce sensitization.

[Chloracne after exposure to dioxin]. / Chlorakne nach Dioxin-exposition.

In 2004, the assumed "dioxin intoxication" of the presidential candidate and today's President of the Ukraine, Victor Yushchenko, gained considerable attention in the media. The politician exhibited pronounced skin changes compatible with chloracne, a characteristic sequela of an exposure to high doses of dioxin. Although this dermatologic disorder has been known for a long time, it is only during recent years that detailed knowledge regarding possible pathomechanisms has been gained. The probable underlying mechanisms of dioxin toxicity, with special emphasis on the development of chloracne, will be discussed in this review.

Diminished ciprofloxacin-induced chondrotoxicity by supplementation with magnesium and vitamin E in immature rats.

Quinolone-induced chondrotoxicity in juvenile rats and multiple other species has been demonstrated previously. Identical damages can be induced in immature rats by feeding them a magnesium-deficient diet. The objective of the present study was to investigate whether, in reverse, oral supplementation with magnesium, vitamin E, or both can diminish the typical quinolone-induced arthropathy in juvenile Wistar rats. Four groups of 12 (6 male, 6 female) 24-day-old Wistar rats were each fed either normal feed (group A), a vitamin E-enriched diet (group B), a magnesium-enriched diet (group C), or a diet enriched with both vitamin E and magnesium (group D) for 10 days. All rats received two subcutaneous ciprofloxacin doses of 600 mg/kg of body weight on postnatal day 32. Two days later, the rats were sacrificed and cartilage samples from knee joints were examined under a light microscope for the presence of typical quinolone-induced joint cartilage lesions. In addition, magnesium, calcium, and vitamin E concentrations in cartilage and plasma were determined. In the samples from rats fed a normal diet (group A), 17 quinolone-induced joint cartilage lesions were observed. In groups fed an enriched diet, the incidence of specific lesions (n) was significantly lower: group B, n = 10 (41% reduction compared to the incidence for group A; P < 0.05); group C, n = 6 (65% reduction; P < 0.01); and group D, n = 3 (82% reduction; P < 0.01). In comparison to the standard diet, diets with magnesium and vitamin E supplementation resulted in significantly higher magnesium and vitamin E concentrations in plasma and articular cartilage. Supplementation with magnesium and vitamin E alone or in combination may relevantly diminish joint cartilage lesions induced by quinolones in immature rats, with an additive effect of combined supplementation. The data further support the proposed pathomechanism of quinolone-induced arthropathy and the crucial role of magnesium in immature joint cartilage.

The in vitro effects of quinupristin/dalfopristin, erythromycin and levofloxacin at low concentrations on the expression of different cell adhesion molecules on the surface of endothelial cells (Eahy926).

OBJECTIVES: Infusion phlebitis is a common clinical problem associated with some antimicrobial agents. The pathomechanism of infusion phlebitis has not yet been elucidated, however, it has been proposed that chemical irritation of the endothelium leads to subsequent sterile inflammation with recruitment and migration of leukocytes. In the present study, cultured endothelial cells were exposed to antibiotics at clinically relevant concentrations to detect changes in various cell surface markers. METHODS: Cells from the endothelial hybrid cell line Eahy926 were exposed to quinupristin/dalfopristin, erythromycin and levofloxacin at increasing concentrations (3, 10, 30 and 100 mg/l) for 24 h. After washing, the cells were marked with monoclonal antibodies against different cell surface antigens (intercellular cell adhesion molecule-1 [ICAM-1], platelet-endothelial cell adhesion molecule-1 [PECAM-1], vascular cell adhesion molecule-1 [VCAM-1], E-selectin, L-selectin, CD34, alpha(2), alpha(5), beta(1) and beta(4) integrin chains and analysed by flow cytometry. For comparison, cells were either untreated or incubated with tumor necrosis factor alpha (TNF-alpha) at a concentration of 10 ng/ml and analysed for ICAM-1, VCAM-1 and E-selectin expression. RESULTS: There was an increase in ICAM-1 expression on endothelial cells with increasing concentrations of quinupristin/dalfopristin. VCAM-1, E-selectin, L-selectin and CD34 showed an excursive upregulation at the concentration of 100 mg/l only, while no consistent changes were observed for PECAM-1 and the integrins. Markedly less prominent changes in the expression of these adhesion molecules were seen with erythromycin while no relevant changes at all occurred with levofloxacin. The absolute change in ICAM-1 activation with quinupristin/dalfopristin at 100 mg/l (34.4%) was less pronounced than that observed after stimulation with TNF-alpha (>80%). CONCLUSIONS: The results of this study indicate that antibiotics with a high potential for local cytotoxicity may cause an inflammatory response by endothelial cells even at rather low concentrations. The increase in expression of cell surface markers involved in cell-cell interaction could be an important mechanism in the development of infusion phlebitis.

Developmental toxicity of polychlorinated biphenyls (PCBs): a systematic review of experimental data.

Experimental reproductive and developmental toxicity studies with polychlorinated biphenyls (PCBs) are reviewed in brief to determine their relevance for current environmental exposure of humans during the prenatal and postnatal developmental periods. Additional material is published in electronic form only, which contains graphic overviews on individual PCBs and various mixtures that are linked with the relevant citations. In this comprehensive article we focus on interactions of PCBs with biological substrates that could mediate adverse effects observed in experimental animals and in children, and the shortcomings of many of the animal studies available. A main point of criticism involves the relative lack of animal data on several of those persistent congeners, either as individual compounds or as environmentally relevant mixtures, which are currently used as a measure of human exposure. Experimental studies in animals are frequently conducted with commercial PCB mixtures, a test design that does not reflect the exposure situation in humans. Important improvements of animal experiments could be achieved by more complete reporting of litter data (pre- and post-natal losses, toxic signs in the dam and the offspring, birth weights and postnatal growth data), the inclusion of endpoints that have been found previously to be affected by PCBs, and measurements of internal exposure data.

Effects of 2,3,7,8-TCDD and PCB 126 on human thymic epithelial cells in vitro.

2,3,7,8-Tetrachloro-dibenzo- p-dioxin (TCDD) is a ubiquitously distributed xenobiotic. The adverse effects of TCDD on the mammalian immune system have been studied for decades, but it is still unclear whether TCDD has direct effects on T-lymphocytes or whether it acts via the thymic microenvironment. We have studied the effects of TCDD on primary cultures of human thymic epithelial cells (TEC) focusing on differentiation markers, integrins and adhesion molecules involved in cell-cell and in cell-matrix interactions. TEC were treated with TCDD at concentrations of 0.001, 0.01, 0.1, 1.0 or 10.0 nM or with 100 nM PCB 126 (3,3',4,4',5-pentachlorobiphenyl) for 3 days, and were then analysed by flow cytometry for expression of surface antigens using monoclonal antibodies against Hassall's bodies (TE-8, TE-16) or against surface structures such as CD29, CD49b, CD49e, CD49f, CD51, CD54, CD58, CD61 and CD106. At TCDD concentrations as low as 0.01 nM we found a significant increase in terminally differentiated, TE-16-positive TEC; at a ten-fold greater concentration the number of cells marked with the TE-8 antibody was also increased. With both markers the most pronounced effect (approximately +15%) was observed at 1 nM TCDD. An increase of cells expressing the integrin alpha-chains CD49b, CD49e and CD51 as well as CD54 was observed at concentrations of 0.1 nM TCDD or higher. The proportion of cells expressing CD106 or CD49f decreased significantly upon treatment with TCDD. No effects on the integrin beta-chains CD29 and CD61 could be detected. Overall, PCB 126 induced similar changes to TCDD. In summary, TCDD and a coplanar PCB induced terminal differentiation of human TEC along with changes of integrins and other adhesion molecules. These receptors and their interplay with the extracellular matrix have key functions in the maturation of T-lymphocytes and it is plausible that their alteration would be involved in TCDD-induced immunotoxicity.

Effects of the Des-F(6)-quinolone garenoxacin (BMS-284756), in comparison to those of ciprofloxacin and ofloxacin, on joint cartilage in immature rats.

We did not observe signs of chondrotoxicity in immature rats treated orally with garenoxacin (BMS-284756) at doses up to five times 600 mg/kg of body weight or with ciprofloxacin, whereas ofloxacin induced typical cartilage lesions. The peak plasma garenoxacin concentration was 25.5 mg/liter after administration of a dose of 600 mg/kg once daily for 5 days. Assuming that this model is predictive of human risk, BMS-284756 and ciprofloxacin should be more suitable for pediatric use than ofloxacin.

Clinical toxicological aspects of fluoroquinolones.

Reactions of the gastrointestinal tract and the central nervous system are the most often observed adverse effects during therapy with fluoroquinolones. Pathogenesis of the neurotoxic effects of fluoroquinolones could be related to the activation of the NMDA receptor. Animal experiments as well as clinical experience show that the cardiotoxic potentials of sparfloxacin and grepafloxacin are higher than those of the other fluoroquinolones: they cause QT prolongation at rather low doses thus increasing the risk for severe arrhythmia (torsades de pointes). Phototoxicity has been described for all quinolones, but derivatives with a halogen atom at position 8 show the highest potential for such reactions (e.g. clinafloxacin). Chondrotoxicity of quinolones can affect the articular cartilage and the epiphyseal growth plate in immature animals; the use of these drugs in pediatrics should be restricted to carefully selected indications (such as the use of ciprofloxacin in cystic fibrosis). Tendinitis and tendon ruptures can also be induced by quinolones. Overall, quinolones are as well tolerated as most other anti-microbial agents. However, their specific toxic potentials have to be considered when they are chosen for treatment of bacterial infections.

Synergistic effect of ofloxacin and magnesium deficiency on joint cartilage in immature rats.

Single high oral doses of fluoroquinolones (e.g., 1,200 mg of ofloxacin/kg of body weight) are chondrotoxic in juvenile rats. Characteristic cartilage lesions are detectable as early as 12 h after treatment. Since this dosing regimen does not reflect the therapeutic situation, we studied the effects of a 5- or 7-day treatment with ofloxacin at lower oral doses (10, 30, and 100 mg/kg twice a day [b.i.d.]) on joint cartilage in 4-week-old rats. We additionally investigated whether the effects of ofloxacin under these conditions are enhanced in animals kept on a magnesium-deficient diet during treatment. Knee joints were examined histologically. The concentrations of ofloxacin and magnesium were determined in plasma and cartilage. The lowest ofloxacin dose at which cartilage lesions occurred in animals on a standard diet was 100 mg/kg b.i.d. for 5 days. Peak plasma ofloxacin levels were approximately 10 mg/liter in these rats and thus were in the same range as the levels in the plasma of humans during therapy with high doses of ofloxacin. Treatment with 30 mg of ofloxacin/kg b.i.d. for 7 days caused no cartilage lesions in rats on a standard diet, but lesions did occur in 10 of 12 rats that were simultaneously fed a magnesium-deficient diet. Magnesium concentrations in bone, plasma, and cartilage from animals on an Mg(2+)-deficient diet were significantly lower than those in the controls. The concentration in plasma from animals on an Mg(2+)-deficient diet was 0.27 +/- 0.03 mmol/liter, whereas it was 0.88 +/- 0.08 mmol/liter in plasma from rats on a standard diet (means +/- standard deviations). Ofloxacin treatment did not change the total magnesium concentrations in tissues, as determined with ashed samples. The incidence of ofloxacin-induced lesions was higher in the magnesium-deficient animals, suggesting a synergistic effect. These results must be taken into account for a benefit-risk evaluation if ofloxacin is considered for use in the pediatric population.