Ciprofloxacin and sparfloxacin penetration into human brain tissue and their activity as antagonists of GABAA receptor of rat vagus nerve

Long-term toxicity of fluoroquinolones: a comprehensive review

Fluoroquinolones (FQs) are highly potent bactericidal antibiotics with broad-spectrum activity against Gram-negative/positive bacteria. The Food and Drug Administration (FDA) anticipated the presence of a long-lasting incapacity of Fluoroquinolone Associated Toxicity (FQAT), which is not officially documented yet. This review aimed to précis the existing information on FQA long-term toxicity, such as cardiotoxicity, aortic aneurysm, tendon rupture, nephrotoxicity, hepatotoxicity, peripheral neuropathy, vagus nervous dysfunction, reactive oxygen species (ROS), phototoxicity, glucose hemostasis, and central nervous system (CNS) toxicity. We are focused on the CNS toxicity of FQs, either due to the direct action of the FQs on CNS receptors or by other drug co-administration, including nonsteroidal anti-inflammatory disease (NSAIDs) and theophylline. Due to the nature of the R7 side chain, FQs containing unsubstituted 7-piperazine and 7-pyrrolidine have the most significant effect. The gamma-aminobutyric acid-A (GABAA) receptor and CNS effects are inhibited through at least three possible mechanisms. Firstly, by the pharmacological action of the quinolone directly. Secondly, FQ-NSAIDs interact pharmacodynamically in which the interaction between the FQ and a receptor is significantly altered by the presence of another drug that interacts with the same receptor. An example may be the interaction between NSAIDs and some FQs. Thirdly, a pharmacokinetic drug-drug interaction leads to a higher concentration of quinolone or the other drug. An example may be the interaction between theophylline and benzodiazepines with some FQs.

A New Criterion for Fluoroquinolone-Associated Disability Diagnosis: Functional Gastrointestinal Disorders

Background and Objectives: Fluoroquinolones (FQs) are a broad-spectrum class of antibiotics routinely prescribed for common bacterial infections despite recent recommendations to use them only for life-threatening cases. In addition to their antimicrobial properties, FQs act in the central nervous system as GABAA receptor inhibitors, which could potentially affect functionality of the vagus nerve at the forefront of gastrointestinal (GI) tract function. Alterations in neural control of digestion have been shown to be linked to Functional Gastrointestinal Disorders (FGIDs), which are usually diagnosed based on self-reported symptoms. The aim of this study was to assess the incidence of FGIDs following FQ use. Materials and Methods: Self-reports from the FDA Adverse Event Reporting System were analyzed together with ~300 survey responses from a social network derived sample to the Bowel Disease Questionnaire. Results: The results of this study suggested that six different FQs are associated with a wide range of GI symptoms not currently reported in the drugs’ labels. The responses from the survey suggested that ~70% of FQ users scored positive for FGID, with no positive correlation between drug type, duration of administration, dosage and frequency of administration. Conclusions: This study showed that GI disorders other than nausea, vomiting and diarrhea are more common than currently reported on the drug labels, and that FGIDs are possibly a common consequence of FQ use even after single use.

Fluoroquinolones-Associated Disability: It Is Not All in Your Head

Fluoroquinolones (FQs) are a broad class of antibiotics typically prescribed for bacterial infections, including infections for which their use is discouraged. The FDA has proposed the existence of a permanent disability (Fluoroquinolone Associated Disability; FQAD), which is yet to be formally recognized. Previous studies suggest that FQs act as selective GABAA receptor inhibitors, preventing the binding of GABA in the central nervous system. GABA is a key regulator of the vagus nerve, involved in the control of gastrointestinal (GI) function. Indeed, GABA is released from the Nucleus of the Tractus Solitarius (NTS) to the Dorsal Motor Nucleus of the vagus (DMV) to tonically regulate vagal activity. The purpose of this review is to summarize the current knowledge on FQs in the context of the vagus nerve and examine how these drugs could lead to dysregulated signaling to the GI tract. Since there is sufficient evidence to suggest that GABA transmission is hindered by FQs, it is reasonable to postulate that the vagal circuit could be compromised at the NTS-DMV synapse after FQ use, possibly leading to the development of permanent GI disorders in FQAD.

Ciprofloxacin-induces free radical production in rat cerebral microsomes

In the presence of ciprofloxacin (CPFX), free radical adduct formation was demonstrated in rat cerebral microsomes using a spin trap α-(4-pyridyl-1-oxide)-N-tert-butyl-nitrone by electron spin resonance spectroscopy. Active microsomes, dihydronicotinamide-adenine dinucleotide phosphate, and ciprofloxacin were necessary for the formation of a spin trap/radical adduct. Adduct formation increased dose-dependently at 0.5-1 mM CPFX concentration for 180 min, and 0.3-1 mM concentration level for 240 min. The addition of SKF 525A, ZnCl₂ or desferrioxamine to the incubation system caused complete inhibition of the radical formation. However, pretreatment of microsomal system with superoxide dismutase (SOD) did not induce any protective effect. Induction of lipid peroxidation, and depletion of thiol levels by CPFX were also shown in the system. These results strongly suggested that CPFX produces free radical(s) in the cerebral microsomes of rats.

Relationship Between Fluoroquinolone Structure and Neurotoxicity Revealed by Zebrafish Neurobehavior

Central nervous system side effects are one of the most frequently reported adverse reactions of fluoroquinolones (FQs). However, the mechanism is not fully understood. In this study, zebrafish ( Danio rerio) were used as a model system. We quantified neurobehavior by recording indicators with automated video-tracking and used liquid chromatography-tandem mass spectrometry to detect drug absorption in vivo. We studied embryotoxicity and effects on zebrafish locomotor activity of 17 typical FQs. In addition, we calculated the stable conformation of typical FQs in aqueous conditions. The relationships between structure, neurotoxicity, and embryotoxicity were analyzed. The results indicate: (1) The effects of FQs on zebrafish neurobehavior can be divided into four categories. Type I has no significant influence on locomotor activity. Type II suppresses locomotor activity. Type III inhibits at low concentration and stimulates at high concentration. Type IV stimulates and then suppresses (biphasic response). (2) Structural modifications of FQs can change toxicity properties in zebrafish. Cleavage of the C-7 piperazinyl structure decreases neurotoxicity but enhances embryotoxicity. The C-3 decarboxyl formation and 5-NH₂ derivatives might enhance embryotoxicity and neurotoxicity. (3) There are two toxic functional groups. The piperazinyl structure at position C-7 (toxic functional group I) can cause primary reactions which may be by the inhibition of γ-aminobutyric acid receptors, and the nucleus containing a carboxyl group at position 3 (toxic functional group II) might cause a reaction secondary to the effect of toxic functional group I and reverse its effects.

A whole-body physiologically based pharmacokinetic (WB-PBPK) model of ciprofloxacin: a step towards predicting bacterial killing at sites of infection

The purpose of this study was to develop a whole-body physiologically based pharmacokinetic (WB-PBPK) model for ciprofloxacin for ICU patients, based on only plasma concentration data. In a next step, tissue and organ concentration time profiles in patients were predicted using the developed model. The WB-PBPK model was built using a non-linear mixed effects approach based on data from 102 adult intensive care unit patients. Tissue to plasma distribution coefficients (Kp) were available from the literature and used as informative priors. The developed WB-PBPK model successfully characterized both the typical trends and variability of the available ciprofloxacin plasma concentration data. The WB-PBPK model was thereafter combined with a pharmacokinetic-pharmacodynamic (PKPD) model, developed based on in vitro time-kill data of ciprofloxacin and Escherichia coli to illustrate the potential of this type of approach to predict the time-course of bacterial killing at different sites of infection. The predicted unbound concentration-time profile in extracellular tissue was driving the bacterial killing in the PKPD model and the rate and extent of take-over of mutant bacteria in different tissues were explored. The bacterial killing was predicted to be most efficient in lung and kidney, which correspond well to ciprofloxacin's indications pneumonia and urinary tract infections. Furthermore, a function based on available information on bacterial killing by the immune system in vivo was incorporated. This work demonstrates the development and application of a WB-PBPK-PD model to compare killing of bacteria with different antibiotic susceptibility, of value for drug development and the optimal use of antibiotics .

Toxic effects of methylmercury, arsanilic acid and danofloxacin on the differentiation of mouse embryonic stem cells into neural cells

This study was performed to assess the neurotoxic effects of methylmercury, arsanilic acid and danofloxacin by quantification of neural-specific proteins in vitro. Quantitation of the protein markers during 14 days of differentiation indicated that the mouse ESCs were completely differentiated into neural cells by Day 8. The cells were treated with non-cytotoxic concentrations of three chemicals during differentiation. Low levels of exposure to methylmercury decreased the expression of GABAA-R and Nestin during the differentiating stage, and Nestin during the differentiated stage. In contrast, GFAP, Tuj1, and MAP2 expression was affected only by relatively high doses during both stages. Arsanilic acid affected the levels of GABAA-R and GFAP during the differentiated stage while the changes of Nestin and Tuj1 were greater during the differentiating stage. For the neural markers (except Nestin) expressed during both stages, danofloxacin affected protein levels at lower concentrations in the differentiated stage than the differentiating stage. Acetylcholinesterase activity was inhibited by relatively low concentrations of methylmercury and arsanilic acid during the differentiating stage while this activity was inhibited only by more than 40 μM of danofloxacin in the differentiated stage. Our results provide useful information about the different toxicities of chemicals and the impact on neural development.

Safety considerations of fluoroquinolones in the elderly: an update

The fluoroquinolones ciprofloxacin, levofloxacin, moxifloxacin and gemifloxacin are widely used for the treatment of various types of bacterial infections. Overall, these antibacterial agents can be considered safe and well tolerated drugs. Comparative studies have evaluated the use of quinolones in elderly and younger populations. Although age per se does not seem to decrease their tolerability, specific adverse effects of the quinolones must be considered when they are chosen for antibacterial treatment. Renal function declines consistently with age and doses of renally excreted quinolones (e.g. ofloxacin, levofloxacin, gatifloxacin) need to be adjusted if a clinically relevant reduction of creatinine clearance is identified. Reactions of the gastrointestinal tract, such as nausea, dyspepsia, vomiting or diarrhoea, are among the most often registered adverse drug reactions during therapy with fluoroquinolones. Treatment with a quinolone causes diarrhoea less frequently than treatment with other classes of antimicrobials. Conflicting data have been published with respect to the incidence of Clostridium difficile-associated diarrhoea in quinolone-treated patients. Hypersensitivity reactions, often manifested on the skin, occur less commonly during therapy with quinolones than, for example, during therapy with beta-lactam antibacterials. Adverse reactions of the CNS are of particular concern in the elderly population. Given the CNS excitatory effects of quinolones, elderly patients should be monitored carefully for such symptoms. It is likely that many signs of possible adverse reactions, such as confusion, weakness, loss of appetite, tremor or depression, are often mistakenly attributed to old age and remain unreported. Quinolones should be used with caution in patients with known or suspected CNS disorders that predispose to seizures (e.g. severe cerebral arteriosclerosis or epilepsy). Quinolones can cause QT interval prolongation. They should be avoided in patients with known prolongation of the QT interval, patients with uncorrected hypokalaemia or hypomagnesaemia and patients receiving class IA (e.g. quinidine, procainamide) or class III (e.g. amiodarone, sotalol) antiarrhythmic agents. Tendinitis and tendon ruptures are recognized as quinolone-induced adverse effects that can occur during treatment or as late as several months after treatment. Chronic renal diseases, concomitant use of corticosteroids and age >60 years are known risk factors for quinolone-induced tendopathies. Overall, the specific adverse-effect profile of quinolones must be considered when they are chosen for treatment of bacterial infections. Because of physiological changes in renal function and when certain co-morbidities are present, some special considerations are necessary when elderly patients are treated with these drugs.

Successful treatment of pituitary abscess with oral administration of sparfloxacin

Pituitary abscess is a rare infection and it is difficult to make the correct diagnosis. It is usually treated by a combination of surgical drainage and intravenous administration of antibiotics. We describe a 74-year-old woman with recurrent meningo-encephalitis due to pituitary abscess. The abscess increased in size in spite of the intravenous administration of panipenem/betamipron (PAPM/BP), clindamycin (CLDM) and chloramphenicol (CP). Finally she was successfully treated with oral administration of sparfloxacin (SPFX) without operation.

Cytotoxic effect of ciprofloxacin in primary culture of rat astrocytes and protection by Vitamin E

The aim of this study was to investigate the possible cytotoxic and oxidative stress inducing effects of ciprofloxacin (CPFX) on primary cultures of rat astrocytes. The cultured cells were incubated with various concentrations of CPFX (0.5-300mg/l), and cytotoxicity was determined by neutral red (NR) and MTT assays. Survival profile of cells was biphasic in NR assay: CPFX did not cause any alteration at any concentration for 7h, whereas < or =50mg/l concentrations induced significant cell proliferation in incubation periods of 24, 48, 72, and 96h. However, cell proliferation gradually decreased at higher concentrations, and 200 and 300mg/l of CPFX exposure was found to be significantly (p<0.05) cytotoxic at all time periods. With MTT assay, no alteration was noted for incubation period of 7h, as observed with NR assay. But, cell viability decreased with approximately > or =50mg/l CPFX exposure in all other time periods. Cell proliferation was only seen in 24h of incubation with 0.5 and 5mg/l CPFX. Vitamin E pretreatment of cell cultures were found to be providing complete protection against cytotoxicity of 300mg/l CPFX in 96h incubation when measured with both NR and MTT assays. The SOD pretreatment was partially protective with NR assay, but no protection was noted when measured with MTT. A significant enhancement of lipid peroxidation was observed with the cytotoxic concentration of the drug, but total glutathione content and catalase activity of cells did not change. The data obtained in this study suggest that, in accordance with our previous results with fibroblast cells, CPFX-induced cytotoxicity is related to oxidative stress. And the biphasic effect of CPFX possibly resulted from the complex dose-dependent relationships between reactive oxygen species, cell proliferation, and cell viability.

Ciprofloxacin‐Induced Glutathione Redox Status Alterations in Rat Tissues

The possible oxidative stress inducing effect of a fluoroquinolone (FQ) antibiotic, ciprofloxacin (CPFX), was investigated in rats measuring glutathione redox status. For this purpose, the drug was administered to rats as two different single doses (100 and 150 mg/kg, ip) or a repeated dose (500 mg/kg/d, ig, for 5d). Then, total and oxidized glutathione levels were determined in hepatic and cerebral tissues of the rats by an enzymatic cycling assay, and the glutathione redox status was calculated. The possible protective effects of vitamin E or allopurinol against CPFX-induced alterations on glutathione system have also been examined. Following both routes of administration of CPFX, the total glutathione content of the liver, but not of brain decreased significantly. The oxidized glutathione (GSSG) in the brain increased after single or repeated dose treatments, but only with repeated doses of CPFX in the liver. CPFX induced dose-dependent alterations in the glutathione redox status in both tissues. With single doses the effect was more pronounced in cerebral tissue, and with repeated ig doses it was significant in both tissues. Pretreatment of rats with vitamin E or allopurinol before the administration of CPFX provided marked protection against glutathione redox status alterations in both tissues. Our results, thus, indicate that CPFX treatment introduces an oxidative stress in cerebral and hepatic tissues of rat.

Fluoroquinolones in the elderly: safety considerations

Fluoroquinolones such as ciprofloxacin, levofloxacin, moxifloxacin and gatifloxacin are widely used for the treatment of bacterial infections. Fluoroquinolone-induced adverse effects have not been reported to occur with increased frequency in the elderly, but large trials comparing the tolerability in aged and young individuals are not available. Renal function declines consistently with age and recommendations for dosage changes of renally eliminated fluoroquinolones (ofloxacin, levofloxacin, gatifloxacin) are related to changes in kidney function rather than to age per se. However, during routine clinical work, creatinine clearance data are usually not available; thus it seems more practical to recommend dosage adjustment for elderly individuals in whom low creatinine clearance values can be expected. Reactions of the gastrointestinal tract are the most often observed adverse effects during therapy with fluoroquinolones; however, compared with many other antibacterials, fluoroquinolones are less frequently associated with diarrhoea. Similarly, hypersensitivity reactions, as observed during therapy with penicillins and other beta-lactam agents, occur more rarely during fluoroquinolone therapy. Adverse reactions of the CNS are of particular concern for the elderly population. Elderly patients with impairments of the CNS (e.g. epilepsy, pronounced arteriosclerosis) should be treated with fluoroquinolones only under close supervision. Probably, many signs of possible adverse reactions such as confusion, weakness, loss of appetite, tremor or depression are often mistakenly attributed to old age and remain unreported. Fluoroquinolones can cause QT interval prolongation. Therefore, they should be avoided in patients with known prolongation of the QT interval, patients with uncorrected hypokalaemia or hypomagnesaemia and patients receiving class IA (e.g. quinidine, procainamide) or class III (e.g. amiodarone, sotalol) antiarrhythmic agents. Chondrotoxicity of fluoroquinolones, as observed in immature animals, has led to restricted use in paediatric patients, but there is no indication that similar effects could occur in joint cartilage of adults. Tendinitis and tendon ruptures have occurred in rare cases as late as several months after treatment with some fluoroquinolones. Chronic renal diseases, concomitant use of corticosteroids and age over 60 years have been recognised as risk factors for fluoroquinolone-induced tendon disorders. Overall, the widely used fluoroquinolones discussed in this review are generally well tolerated. Nevertheless, as with all drugs, their specific adverse effect profiles must be considered when they are chosen for treatment of bacterial infections. Because of physiological changes in renal function and in case of certain comorbidities, some special considerations are necessary when fluoroquinolones are used to treat elderly patients.

Inhibition by fluoroquinolones of K(+) currents in rat dissociated hippocampal neurons

The effects of four fluoroquinolones (sparfloxacin, fleroxacin, ofloxacin and levofloxacin) on K(+) currents were investigated in pyramidal neurons acutely isolated from rat hippocampus, to evaluate their relative potencies for inhibiting these channels. Using patch-clamp electrophysiological techniques, we found that all four compounds inhibited the delayed rectifier K(+) current (I(K)), but with different potencies. Sparfloxacin was the most potent compound, displaying an IC(50) value of 6.44 x 10(-4) M, followed by fleroxacin, ofloxacin and levofloxacin, their IC(50) values being 7.09 x 10(-3), 8.42 x 10(-3) and 1.10 x 10(-2) M, respectively. In contrast, the fast transient K(+) current (I(A)) was blocked only by sparfloxacin (IC(50)=2.86 x 10(-3) M) and fleroxacin (IC(50)=4.38 x 10(-3) M), but not by ofloxacin and levofloxacin even at concentrations up to 1 mM. The K(+) current inhibition was reversible after washout of the compounds. Further study is needed to clarify the possible involvement of this novel action in the adverse effects of fluoroquinolones in the central nervous system (CNS).

Penetration of rufloxacin into the cerebrospinal fluid in patients with inflamed and uninflamed meninges

Forty-four patients scheduled for lumbar puncture (LP) were recruited to determine the level of penetration of orally administered rufloxacin into cerebrospinal fluid (CSF). The patients were divided into three clinical groups: those with normal CSF (groups A(1d) and A(7d)), those with aseptic meningitis (group B), and those with bacterial meningitis (group C). Members of group A(1d) received a single 400-mg rufloxacin dose, while group A(7d), B, and C constituents had a multiple-dose regimen (one 400-mg dose, followed by one 200-mg dose daily for 6 days). LP was performed on group A(1d) members 5 h after they had received treatment, while for group A(7d) it was undertaken 5 h after administration of the last dose. For group B, LP was performed 5 h after the first and the last doses, whereas for group C it was undertaken after the first, fourth, and last doses. Concentrations of rufloxacin in simultaneously collected CSF and plasma samples were determined. Mean CSF/plasma rufloxacin concentration ratios ranged from 0.57 to 0.84, depending on the study group. A higher, but not statistically significant, degree of penetration into CSF was observed in patients with bacterial meningitis than in those with normal CSF or aseptic meningitis. These data indicate that rufloxacin diffuses efficiently into the CSF of patients with either inflamed or uninflamed meninges.

Comparative tolerability of the newer fluoroquinolone antibacterials

The most common adverse effects of the fluoroquinolones involve the gastrointestinal tract, skin and CNS, and are mainly mild and reversible. Of the gastrointestinal events, nausea and vomiting are the most common. Mild hepatic reactions are a class effect, usually presenting as mild transaminase level increases without clinical symptoms. However, postmarketing surveillance has revealed significant hepatotoxicity with trovafloxacin. It is not currently known whether the severe reactions to trovafloxacin are specific to that agent or simply represent an extreme of an emerging class effect. The enormous worldwide usage of, and extensive published adverse effect data on the other fluoroquinolones and naphthyridones suggests the former. In perspective, rare but serious hepatotoxicity has been reported with other fluoroquinolones and the overall incidence of trovafloxacin hepatotoxicity is not dissimilar to that reported with flucloxacillin and amoxicillin-clavulanic acid. CNS reactions vary in severity and include dizziness, convulsions (notably with lomefloxacin) and psychoses. Fluoroquinolones differ in their pro-convulsive activity, relating to their differing potential as gamma-aminobutyric acid antagonists and binding to the N-methyl-D-aspartate receptor. The basis for the increased seizure potential following the coadministration of nonsteroidal anti-inflammatory drugs with certain fluoroquinolones is not fully understood. Fluoroquinolone phototoxicity, caused by the generation of toxic free oxygen species under exposure to UVA radiation, is significantly more common with 8-halogenated compounds. Certain patient groups, e.g. patients with cystic fibrosis, are predisposed to this adverse effect. Murine photocarcinogenicity has been demonstrated with lomefloxacin, but no such effects have been reported in humans. Prolongation of the QTc interval is also a class effect, although cardiac arrhythmias have only been linked with sparfloxacin. Among the newer fluoroquinolones, clinically significant cardiac events are rare or absent but possible interactions in patients receiving other drugs capable of causi ng QT prolongation should be anticipated. Tendinitis and rupture, usually of the Achilles tendon, are rare, class-effects of fluoroquinolones, most frequently reported with pefloxacin. Predisposing factors include aging, corticosteroid use, renal disease, haemodialysis and transplantation. Use of fluoroquinolones in paediatric patients remains contentious. However, accruing human data suggest that restrictions on paediatric use imposed because of fluoroquinolone-induced cartilage damage in juvenile animals, may soon be relaxed. Data from over 1700 children in the UK failed to disclose arthropathy and extensive paediatric use of norfloxacin in Japan and ciprofloxacin in developing countries has been free of articular effects.

Potential interactions of the extended-spectrum fluoroquinolones with the CNS

The new generation fluoroquinolones -- sparfloxacin, levofloxacin, grepafloxacin and trovafloxacin -- have been designed to respond to the clinical need for extended antimicrobial cover in the face of increasing global microbial resistance. Their main focus is in the treatment of respiratory infections, particularly those acquired in the community. CNS adverse effects, such as dizziness and headache, are known to occur relatively commonly with some fluoroquinolones and are not, in general, well tolerated by patients. The structural component of the fluoroquinolone molecule believed to be responsible for improved gram-positive activity is also believed to be implicated in the production of CNS adverse effects, including those arising from drug interactions with theophylline and NSAIDs. Inhibition of brain gamma-aminobutyric acid (GABA) receptor binding appears to be a strong indicator of CNS activity, though N-methyl-D-aspartate receptor binding has also been implicated. In accordance with the results of these predictive studies, clinical trials have found sparfloxacin, levofloxacin and grepafloxacin to be associated with a low incidence of CNS events. Trovafloxacin has been found to be associated with a higher incidence of CNS events (particularly lightheadedness and dizziness) than the other 3 agents. Ongoing and future clinical studies will help to define the usefulness of the predictive models, as well as reveal the full CNS adverse event profile of these and other investigational fluoroquinolones.

Gyrase mutations in laboratory-selected, fluoroquinolone-resistant mutants of Mycobacterium tuberculosis H37Ra

To characterize mechanisms of resistance to fluoroquinolones by Mycobacterium tuberculosis, mutants of strain H37Ra were selected in vitro with ofloxacin. Their quinolone resistance-determining regions for gyrA and gyrB were amplified and sequenced to identify mutations in gyrase A or B. Three types of mutants were obtained: (i) one mutant (TKp1) had no mutations in gyrA or gyrB; (ii) mutants that had single missense mutations in gyrA, and (iii) mutants that had two missense mutations resulting in either two altered gyrase A residues or an altered residue in both gyrases A and B. The TKp1 mutant had slightly reduced levels of uptake of [14C]norfloxacin, which was associated with two- to fourfold increases in the MICs of ofloxacin, ciprofloxacin, and sparfloxacin. Gyrase mutations caused a much greater increase in the MICs of fluoroquinolones. For mutants with single gyrA mutations, the increases in the MICs were 4- to 16-fold, and for mutants with double gyrase mutations, the MICs were increased 32-fold or more compared with those for the parent. A gyrA mutation in TKp1 secondary mutants was associated with 32- to 128-fold increases in the MICs of ofloxacin and ciprofloxacin compared with the MICs for H37Ra and an eight-fold increase in the MIC of sparfloxacin. Sparfloxacin was the most active fluoroquinolone tested. No sparfloxacin-resistant single-step mutants were selected at concentrations of > 2.5 micrograms/ml, and high-level resistance (i.e., MIC, > and = 5 micrograms/ml) was associated with two gyrase mutations. Mutations in gyrB and possibly altered levels of intracellular accumulation of drug are two additional mechanisms that may be used by M. tuberculosis in the development of fluoroquinolone resistance. Because sparfloxacin is more active in vitro and selection of resistance appears to be less likely to occur, it may have important advantage over ofloxacin or ciprofloxacin for the treatment of tuberculosis.

Tolerability of fluoroquinolone antibiotics. Past, present and future

New fluoroquinolones have been in clinical use for 10 years and have an excellent record of safety and tolerance. The main elements of their adverse reaction profile were predictable from human experience with precursor naphthyridines and quinolones, and from toxicological studies in animals. Thus gastrointestinal reactions (1 to 5%), skin disturbances (less than 2.5%) and central nervous system (CNS) effects (usually around 1 to 2%) were anticipated. Individual group members exhibit particular properties in relation to their chemical structures, for example the phototoxicity associated with 8-halogenation of the nucleus and found to be a particular problem with lomefloxacin and sparfloxacin. Other members, for example ofloxacin, are linked to a higher than usual incidence of CNS reactions and psychological disturbance. However, despite increasing usage, none of the present group have been implicated in joint damage in children, which had been a major concern following reports of this effect in juvenile animals in chronic toxicity studies. Furthermore, intravenous formulations appear to have no associated increase in toxicity. Crystalluria with associated renal damage, originally thought likely to limit intravenous dosage, has not proved to be a problem in humans. Clinically significant interactions may occur but, as with those involving various NSAIDs and potentially leading to convulsions, they have been defined and are thus avoidable. Postmarketing surveillance studies and prescription event monitoring have largely confirmed the limited adverse reaction profile defined during clinical trials. However, some unexpected reactions have appeared after launch, most notably the episodes of haemolysis, renal failure and hypoglycaemia which led to the withdrawal of temafloxacin. These effects have not been observed with other fluoroquinolones. However, severe tendinitis appears to be a group effect, albeit rare, and anaphylactoid reactions have been reported with several of the fluoroquinolone group, often in AIDS patients. The new fluoroquinolones are essentially a well tolerated group of antibacterials, the benefits of which clearly outweigh their disadvantages in a wide range of indications. Clinical efficacy has been a larger determinant of which members have succeeded in the marketplace than potential toxicity. However, the lesser potential for adverse effects of some of the class, e.g. norfloxacin, ofloxacin and ciprofloxacin, has undoubtedly led to their more widespread use. For others, e.g. enoxacin, limited clinical utility and a perception of increased toxicity have resulted in sidelining. There remains the potential for development of safer and yet more active fluoroquinolones via chemical manipulation both of the nucleus and the side chain substituents.

Fluoroquinolone toxicities. An update

The main types of adverse effects associated with quinolones are uncommon and reversible and vary in frequency among different agents. Phototoxicity appears more frequent with lomefloxacin than with some other quinolones. Three mechanisms have been proposed to explain the neurotoxic effects, including rare proconvulsant activity, associated with quinolone therapy. Arthropathy remains a dilemma for paediatricians deciding whether to use quinolones in growing children. Importantly, the experience with temafloxacin, which has now been withdrawn from the market, emphasises the need for thorough postmarketing surveillance. Nonetheless, it should be remembered that the fluoroquinolones as a group are effective and very well tolerated antimicrobial drugs.