In-vitro susceptibility of mycobacteria to ciprofloxacin

Targeting Multidrug Resistant Mycobacterium tuberculosis HtrA2 with Identical Chemical Entities of Fluoroquinolones

Tuberculosis is a highly communicable and chronic respiratory disease caused by pathogenic bacterium Mycobacterium tuberculosis. The drug - resistant species of Mycobacterium tuberculosis are tough to cure due to its resistant activity toward potential drugs. Available inhibitors of tuberculosis include few antimicrobial fluoroquinolone agents like ciprofloxacin, ofloxacin, and moxifloxacin to treat resistant Mycobacterium strains. Literature study elucidates that macromolecular target namely, HtrA2 of Mycobacterium tuberculosis play a dual role of protease and chaperone. These two activities are dependent on temperature, with low temperatures promoting the chaperone function and high temperatures promoting serine protease activity. Under normal physiological conditions HtrA2 acts as a quality control factor and promotes cell survival. In the present investigation, we screened fluoroquinolone such as ciprofloxacin, moxifloxacin and ofloxacin and their analogues based on better Docking score, absorption, distribution, metabolism and excretion screening and Lipinski's rule of 5, to find out their efficiency on resistant strain through in silico study. From the results observed, the analogues are suggested to be potent inhibitors of HtrA2 with sufficient scope for further exploration.

New antituberculous drugs in development

There have been no new antituberculous drugs since the introduction of rifampin in 1952. The collision of the HIV and tuberculosis (TB) epidemics in developing regions of the world together with the emergence of multidrug resistance and extensively drug-resistant strains of TB has emphasized the urgent need for newer antituberculous drugs. There is a need for drugs that are safe, effective against resistant strains, are able to shorten the course of treatment, are effective for latent TB infection, and that have minimal interactions with antiretroviral drugs. Drugs that are currently in phase 3 development are moxifloxacin and gatifloxacin. In phase 2 development are PA-824 and TMC207; and in phase 1 are SQ109, AZD5847, and linezolid. Nanotechnology holds future promise for targeted drug delivery. Immunotherapy such as new vaccines and vitamin D may serve as adjunctive treatment for prevention and active disease, together with shortening the course of treatment. Bringing newer and more effective antituberculous drugs to market is a global priority and the process must be accelerated.

Fluoroquinolone resistance in Mycobacterium tuberculosis isolates: associated genetic mutations and relationship to antimicrobial exposure

OBJECTIVES

We assessed the fluoroquinolone (FQ) susceptibility of clinical isolates of Mycobacterium tuberculosis in an endemic area. The genetic mutations responsible for FQ resistance were also evaluated.

METHODS

A total of 420 M. tuberculosis isolates during January 2004 to December 2005 were randomly selected. Data on the clinical characteristics of the patients were obtained from medical records. The MICs of ofloxacin, ciprofloxacin, levofloxacin and moxifloxacin were determined. Spoligotyping and sequencing of the gyrA and gyrB genes were performed for all isolates resistant to any tested FQ.

RESULTS

Of the 420 isolates, 52 (12.4%), 26 (6.2%), 26 (6.2%) and 30 (7.1%) were resistant to isoniazid, rifampicin, ethambutol and streptomycin, respectively. Multidrug resistance was found in 5.0% of isolates. For all tested FQs, the susceptibility rate was higher than 97%. Resistance to any first-line drug and isolation from a patient with prior anti-tuberculous treatment were correlated with FQ resistance. Multidrug resistance had the strongest correlation with FQ resistance (19% of isolates). Neither the previous use of FQs nor the duration of FQ exposure was correlated with the FQ susceptibility. Of the 14 FQ-resistant isolates, five (35.7%) had gyrA mutations (four D94G and one A90V) and another one (7.1%) had a gyrB mutation (N538D).

CONCLUSIONS

This study found FQ resistance in 3.3% of all clinical isolates of M. tuberculosis. FQ resistance was correlated with first-line drug resistance and prior anti-tuberculous treatment, suggesting the need for routine FQ susceptibility testing in patients with these characteristics.

New drugs for tuberculosis

In the last ten years, an unexpected resurgence of tuberculosis (TB) has occurred in industrialised countries; contributing factors are likely to include the spread of HIV infection and increasing waves of immigration. Moreover, multidrug resistant (MDR) strains of Mycobacterium tuberculosis are emerging, rendering older therapies largely ineffective. One approach to circumvent this situation has been the addition of antimicrobials with some in vitro antituberculosis activity, but which are marketed for other infections (particularly some quinolones and the combination of oxicillin-clavulanic acid), to current therapeutic regimens. New drugs, possibly acting on novel targets, are urgently required, as are more specific vaccines.

Fluoroquinolones, tuberculosis, and resistance

Although the fluoroquinolones are presently used to treat tuberculosis primarily in cases involving resistance or intolerance to first-line antituberculosis therapy, these drugs are potential first-line agents and are under study for this indication. However, there is concern about the development of fluoroquinolone resistance in Mycobacterium tuberculosis, particularly when administered as monotherapy or as the only active agent in a failing multidrug regimen. Treatment failures as well as relapses have been documented under such conditions. With increasing numbers of fluoroquinolone prescriptions and the expanded use of these broad-spectrum agents for many infections, the selective pressure of fluoroquinolone use results in the ready emergence of fluoroquinolone resistance in a diversity of organisms, including M tuberculosis. Among M tuberculosis, resistance is emerging and may herald a significant future threat to the long-term clinical utility of fluoroquinolones. Discussion and education regarding appropriate use are necessary to preserve the effectiveness of this antibiotic class against the hazard of growing resistance.

Fluoroquinolones and tuberculosis

Tuberculosis (TB) remains one of the main causes of morbidity worldwide, and the emergence of multi-drug resistant (MDR) Mycobacterium tuberculosis strains in some parts of the world has become a major concern. The decrease in activity of the major anti-TB drugs, such as isoniazid and rifampicin, is an important threat and alternative therapies are urgently required. The anti-TB activity of the fluoroquinolones has been under investigation since the 1980s. Many are active in vitro but only a few, including ofloxacin, ciprofloxacin, sparfloxacin, levofloxacin and lomefloxacin, have been clinically tested. Fluoroquinolones can be used in co-therapy with the available anti-TB drugs. However, the choice of fluoroquinolone should be based not only on the in vitro activity, but also on the long-term tolerance. Fluoroquinolones are novel anti-TB drugs to be used when a patient is infected with a MDR-TB strain.

Systemic antibiotic agents

Understanding the breadth of systemic antimicrobial agents available for use by the dermatologist and their associated side-effect profiles and drug interactions allows the clinician to offer patients optimal care in the management of cutaneous infectious disease.

Antimycobacterial activities of novel levofloxacin analogues

In order to investigate structure-activity relationships between antimycobacterial activities and basic substituents at the C-10 position of levofloxacin (LVFX), we synthesized a series of pyridobenzoxazine derivatives by replacement of the N-methylpiperazinyl group of LVFX with various basic substituents. A compound with a 3-aminopyrrolidinyl group had one-half the activity of LVFX against Mycobacterium avium, M. intracellulare, and M. tuberculosis. Mono- and dimethylation of the 3-amino moiety of the pyrrolidinyl group increased the activities against M. avium and M. intracellulare but not those against M. tuberculosis. On the other hand, dialkylation at the C-4 position of the 3-aminopyrrolidinyl group enhanced the activities against M. avium, M. intracellulare, and M. tuberculosis. Thus, introduction of an N-alkyl or a C-alkyl group(s) into the 3-aminopyrrolidinyl group may contribute to an increase in potency against M. avium, M. intracellulare, and/or M. tuberculosis, probably through elevation of the lipophilicity. However, among the compounds synthesized, compound VII, which was a 2,8-diazabicyclo[4.3.0]nonanyl derivative with relatively low lipophilicity, showed the most potent activity against mycobacterial species: the activity was 4- to 32-fold more potent than that of LVFX and two to four times as potent as that of gatifloxacin. These results suggested that an increase in the lipophilicity of LVFX analogues in part contributed to enhancement of antimycobacterial activities but that lipophilicity of the compound was not a critical factor affecting the potency.

Outcomes of patients with multidrug-resistant pulmonary tuberculosis treated with ofloxacin/levofloxacin-containing regimens

OBJECTIVE

To analyze outcomes of patients with multidrug-resistant tuberculosis (MDR-TB) treated with ofloxacin/levofloxacin-containing regimens.

MATERIALS AND METHODS

From February 1990 through June 1997, 63 MDR-TB patients (with bacillary resistance to at least isoniazid and rifampin in vitro) were analyzed retrospectively. Twenty-two patients (34.9%) had had no previous antituberculosis chemotherapy. Each patient received either ofloxacin (53) or levofloxacin (10) even though 13 patients had bacilli resistant to ofloxacin in vitro. The other accompanying drugs mainly included aminoglycosides, cycloserine, ethionamide/prothionamide, and pyrazinamide. Sputum smear and culture examinations for acid-fast bacilli (AFB) were performed monthly for the initial 6 months and then at 2- to 3-month intervals until the end of treatment. Comparison was made between clinical successes and failures using univariate and multiple logistic regression analyses for the following variables: age, sex, presence of cavitation, extent of disease, sputum smear positivity, in vitro resistance to ofloxacin, in vitro resistance to streptomycin and/or ethambutol, treatment adherence, and the number of drugs per regimen.

RESULTS

Fifty-one patients (81.0%) were cured, nine patients (14.3%) failed, and three patients (4.7%) died. For the entire group, the mean duration of treatment was 14.0 months, and the mean number of drugs was 4.7. Mean durations of chemotherapy in successful and failed patients were 14.5 and 14.2 months, respectively. Mean time for sputum smear and culture conversions were 1.7 and 2.1 months, respectively. Only cavitation, resistance to ofloxacin, and poor adherence were found to be variables independently associated with adverse outcomes (p < 0.05; odds ratios = 15.9, 13.5, 12.8, respectively). Negative sputum cultures after 2 and 3 months of therapy were 100% predictive of cure. Positive sputum cultures after 2 and 3 months were 52.3% and 84.6% predictive of failure, respectively. One patient (2.1%) relapsed after apparent cure. Twenty-five patients experienced adverse drug reactions, but only 12 of them needed drug modifications.

CONCLUSION

Most MDR-TB patients can be treated effectively with ofloxacin/levofloxacin-containing regimens. Presence of cavitation, resistance to ofloxacin in vitro, and poor adherence to therapy portend treatment failure. Monitoring monthly sputum culture for AFB in the initial months of chemotherapy helps predict clinical outcomes.

Comparison of topical antibiotics for treating Mycobacterium chelonae keratitis in a rabbit model

PURPOSE

To investigate the effect of topical amikacin (25 mg/ml), imipenem (25 mg/ml), ciprofloxacin (3 mg/ml), clarithromycin (20 mg/ml), amikacin combined with ciprofloxacin, amikacin combined with imipenem, and amikacin combined with clarithromycin on Mycobacterium chelonae keratitis.

METHODS

Ninety New Zealand albino rabbits were infected with a strain of M. chelonae for which minimum inhibitory concentration indicated in vitro sensitivity to the above antibiotics. The rabbits were treated for one or two weeks. The treatment efficacy was judged by the size of stromal infiltrate and quantitative culture of the infected corneas.

RESULTS

The size of the stromal infiltrate showed no significant difference in treated eyes compared to the untreated, control eyes. However, all treatments significantly reduced the number of organisms in treated eyes compared to untreated, control eyes (all p-values < 0.05). No significant difference in treatment efficacy was found between individual treatment groups. In none of the cases were organisms eliminated from the infected eyes, even after 2 weeks of treatment.

CONCLUSIONS

The results suggest that topical amikacin, imipenem, ciprofloxacin and clarithromycin had some therapeutic effect on M. chelonae keratitis; however, amikacin combined with imipenem, ciprofloxacin, and clarithromycin showed no increased efficacy over single agent therapy during 2 weeks of treatment. Long term treatment may be required to eradicate M. chelonae.

Topical ciprofloxacin for treating nontuberculous mycobacterial keratitis

OBJECTIVE

This study aimed to evaluate the clinical efficacy of topical ciprofloxacin for treating Mycobacterium fortuitum and Mycobacterium chelonae keratitis refractory to amikacin therapy.

DESIGN

A prospective clinical trial of topical ciprofloxacin treatment for nontuberculous mycobacterial keratitis was conducted.

PARTICIPANTS

Eleven patients with nontuberculous mycobacterial keratitis diagnosed from 1992 to 1996 were enrolled.

INTERVENTION

All 11 patients were treated initially with topical fortified amikacin, but only 2 patients responded. The other nine patients, four with M. fortuitum and five with M. chelonae keratitis, were refractory to amikacin therapy and received topical ciprofloxacin treatment. Bacterial culture and drug susceptibility tests using the broth microdilution method were performed on all 11 patients.

MAIN OUTCOME MEASURES

The clinical response to amikacin or ciprofloxacin treatment was judged by corneal re-epithelialization and density and/or size of corneal infiltrates.

RESULTS

M. chelonae isolates were more resistant to amikacin and ciprofloxacin than M. fortuitum isolates based on the in vitro susceptibility test. Clinically, three patients with M. fortuitum keratitis were responsive to ciprofloxacin therapy; however, only one patient with M. chelonae keratitis responded to the same therapy.

CONCLUSIONS

Topical ciprofloxacin offers a therapeutic alternative for nontuberculous mycobacterial keratitis, which was refractory to amikacin treatment. However, topical ciprofloxacin was more effective for treating M. fortuitum keratitis than for M. chelonae keratitis.

Antimicrobial agents for the dermatologist. II. Macrolides, fluoroquinolones, rifamycins, tetracyclines, trimethoprim-sulfamethoxazole, and clindamycin

This article is the second of a two-part series reviewing antimicrobial agents that are used by the dermatologist. In part I we reviewed beta-lactam antibiotics and related compounds. In this section we again emphasize some newer agents (macrolides, fluoroquinolones) as well as some of the more commonly employed older agents (rifamycins, tetracyclines, trimethoprim-sulfamethoxazole, and clindamycin.

Emergence of fluoroquinolone-resistant tuberculosis in New York City

22 patients infected with fluoroquinolone-resistant Mycobacterium tuberculosis in New York City were identified between January, 1991, and November, 1993. In 16 patients resistance arose as a result of inadequate or inappropriate treatment. 6 patients had primary infection with fluoroquinolone-resistant organisms; 5 acquired the organisms nosocomially. Seven distinct patterns of restriction-fragment length polymorphism were identified in isolates from 21 patients. Fluoroquinolones should be restricted to patients with multidrug-resistant disease or intolerance to other antituberculosis drugs. All patients with multidrug-resistant tuberculosis should be on directly observed therapy.

Comparative efficacy of topical ciprofloxacin for treating Mycobacterium fortuitum and Mycobacterium chelonae keratitis in an animal model

Mycobacterium fortuitum and M. chelonae are the two most common causes of nontuberculous mycobacterial keratitis, and they may be difficult to differentiate at diagnosis. Mycobacterium fortuitum is generally more sensitive to ciprofloxacin in vitro than is M. chelonae. Using a rabbit model, we compared the efficacy of topical ciprofloxacin (3 mg/ml) against M. chelonae keratitis to its efficacy against M. fortuitum keratitis. After four days of therapy, ciprofloxacin significantly reduced the number of both organisms in treated eyes compared to untreated control eyes (both P values < .001). Mean culture ratios (colony-forming units in treated eye divided by colony-forming units in untreated eye for each rabbit) were used to compare efficacy between groups. When all treated animals were considered, no significant difference was found between groups (P = .13). When outlier values were excluded, ciprofloxacin was more effective against M. fortuitum than M. chelonae (P = .01). When treated and untreated eyes were compared after therapy in the M. fortuitum group, ciprofloxacin treatment was associated with a reduction in mean stromal infiltrate area (P = .03) and in the tendency to form satellite lesions (P = .07). A clinical effect was not observed in the M. chelonae group. Although ciprofloxacin is effective against both organisms, it appears to be less effective against M. chelonae than M. fortuitum in vivo.

Comparison of topical antibiotics for treating Mycobacterium fortuitum keratitis in an animal model

The efficacy of three topical antibiotic treatments for Mycobacterium fortuitum (strain ATCC-6841) keratitis were compared in rabbits. Rabbits were treated with ciprofloxacin (3 mg/ml) or clarithromycin (20 mg/ml) or a combination of amikacin (100 mg/ml) and vancomycin (50 mg/ml). All three treatments significantly reduced the number of organisms in treated eyes compared to untreated, control eyes (all P values < .001). No significant difference in treatment efficacy was found between the three treatment groups (all P values > or = .48), although ciprofloxacin (3 mg/ml) was more effective than clarithromycin (20 mg/ml) after excluding outliers (P = .01). All treatments stabilized or reduced the size of stromal infiltrates after four days of therapy, whereas infiltrates continued to enlarge in untreated eyes. These results suggest that topical clarithromycin, topical ciprofloxacin, and combined amikacin and vancomycin may all be clinically useful for treating M. fortuitum keratitis. Both clarithromycin and ciprofloxacin were better tolerated than combined amikacin and vancomycin. This study supports the further development of clarithromycin, a new macrolide antibiotic, as a topical drug for treatment of M. fortuitum keratitis.

In vitro activity of DNA gyrase inhibitors, singly and in combination, against Mycobacterium avium complex

The in vitro activities of the DNA gyrase inhibitors ciprofloxacin, coumermycin, and novobiocin against 31 clinical isolates of Mycobacterium avium complex were studied using a microdilution technique. Minimal inhibitory concentrations (MICs) were determined in 4 days using Middlebrook 7H9 broth, and minimal bactericidal concentrations (MBCs) were determined by subculturing to Middlebrook 7H10 agar. MICs were: ciprofloxacin, 0.5-greater than 16 (mean, 4.1) micrograms/ml; novobiocin, 4-greater than 128 (mean, 54.7) micrograms/ml; and coumermycin, 2-greater than 16 (mean, 17.5) micrograms/ml. MBCs were usually more than two dilution steps higher than MICs. Checkerboard studies failed to reveal synergistic or antagonistic inhibitory activity of DNA gyrase-A and DNA gyrase-B inhibitors in vitro.

Post-surgical nasal cellulitis outbreak due to Mycobacterium chelonae

An outbreak of post-rhinoplasty nasal cellulitis due to Mycobacterium chelonae in a secondary care centre is described. A case-control study demonstrated that the use of inadequately sterilized surgical equipment in the Otorhinolaryngology Department was a risk factor. The causal organism was cultured from the equipment, from the surface of the operating theatre lamp, adhesive tape and from two of the hospital's general water tanks. Introduction of effective instrument sterilization methods, monitored with biological controls, the use of new air filters and cleansing and disinfection of hospital water tanks, were sufficient to control the outbreak. The antimicrobial susceptibilities of the causal organism were consistently different from those previously reported in M. chelonae.

Ciprofloxacin in patients with mycobacterial infections: experience in 15 patients

In vitro and animal investigations have demonstrated the antimycobacterial activity of some fluoroquinolones, including ciprofloxacin, but information regarding their clinical usefulness in mycobacterial infections is sparse. This article presents treatment results of 11 patients with tuberculosis and 4 with atypical mycobacterial infections. They were treated with combinations of ciprofloxacin and one or two other antituberculosis agents. Susceptibility of the infecting organisms to ciprofloxacin was determined in 14 of the 15 patients: in 12 of them, minimum inhibitory concentrations ranged between 0.31 and 1.25 micrograms/mL, suggesting a good level of activity. Serum concentrations of ciprofloxacin, sampled one hour after dosing and measured by a specific HPLC assay, revealed considerable variability (range 0.22-8.41 micrograms/mL). Serial plasma samples taken under controlled conditions suggested that a decreased rate of absorption was responsible for low one-hour concentrations in one of the subjects. Adverse reactions to ciprofloxacin were few and included nausea in four patients, crystalluria in one, and febrile reaction in another. A satisfactory response in terms of clinical and radiologic improvement, bacteriologic conversion, and absence of relapse was seen in 13 of the 14 patients who completed an adequate course of therapy. A controlled clinical trial of this promising antimycobacterial agent is needed.

A case of resistant tuberculosis

We report a case of multiple drug-resistant pulmonary tuberculosis, in which treatment with two second line chemotherapy regimens was inadequate. Despite in-vitro sensitivity to ciprofloxacin the patient remained sputum positive with Mycobacterium tuberculosis after 11 months.

MICs and MBCs of Win 57273 against Mycobacterium avium and M. tuberculosis

A new quinolone, Win 57273 [1-cyclopropyl-7-(2,6-dimethyl-4-pyridinyl)-6-fluoro-1,4-dihydro-4-oxo-3 - quinolonecarboxylic acid], synthesized by Sterling Research Group, was tested in vitro against Mycobacterium tuberculosis and Mycobacterium avium strains. The broth-determined MICs of this agent ranged from 1.0 to 4.0 micrograms/ml for M. tuberculosis strains and from 0.25 to 8.0 micrograms/ml for M. avium strains. A distinctive feature of this agent, in comparison with ofloxacin and ciprofloxacin, is its substantially greater activity at the low pHs. For M. avium strains, the MICs of Win 57273 were 2.0 micrograms/ml or less for 54.5% of strains at pH 6.8 and 85.5% of strains at pH 5.0. Win 57273 was more active than ciprofloxacin against M. avium strains, and this difference was very substantial for all M. avium strains at pH 5.0. Taking into account that the predominant locations of these organisms in vivo are within the phagosomes and phagolysosomes of macrophages, i.e., in acidic environments at pH 5.0 or lower, the greater activity of Win 57273 at low pH makes this quinolone especially promising for M. avium infection. The bactericidal activity of Win 57273 for M. avium strains was the same as that of ciprofloxacin, with MBCs from 4.0 to 16.0 micrograms/ml.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Comparative antimycobacterial activities of difloxacin, temafloxacin, enoxacin, pefloxacin, reference fluoroquinolones, and a new macrolide, clarithromycin

The activities of fluoroquinolones and a new macrolide against 30 clinical isolates of Mycobacterium tuberculosis were determined in vitro by agar diffusion. In order of relative potencies against M. tuberculosis, temafloxacin (MIC for 90% of isolates [MIC90], 2.3 micrograms/ml) was at least as active as the reference quinolones ofloxacin (MIC90, 2.4 micrograms/ml) and ciprofloxacin (MIC90, 4.3 micrograms/ml). Less active were difloxacin (MIC90, 4.7 micrograms/ml), pefloxacin (MIC90, 6.7 micrograms/ml), and enoxacin (MIC90, 8.3 micrograms/ml). The macrolide clarithromycin was more potent than erythromycin but less potent than the fluoroquinolones. Our results suggest that the newer fluoroquinolones and clarithromycin should be included with ciprofloxacin and ofloxacin in pharmacokinetic studies that may lead to trials in human subjects with mycobacterial infections.

In vitro activity of ciprofloxacin in combination with standard antituberculous drugs against mycobacterium tuberculosis

Chequer-board titrations show that the in vitro activity of ciprofloxacin against Mycobacterium tuberculosis is independent of that of streptomycin, isoniazid, ethambutol and pyrazinamide and confirm that there is antagonism between ciprofloxacin and rifampicin.

Ciprofloxacin: chemistry, mechanism of action, resistance, antimicrobial spectrum, pharmacokinetics, clinical trials, and adverse reactions

Ciprofloxacin, considered a benchmark when comparing new fluoroquinolones, shares with these agents a common mechanism of action: inhibition of DNA gyrase. While ciprofloxacin demonstrated a fairly good activity against gram-positive bacteria, it is against gram-negative organisms that it proved to be more potent than other fluoroquinolones. It is the most active quinolone against Pseudomonas aeruginosa, with MIC90s on the order of 0.5 micrograms/ml. When given orally, ciprofloxacin exhibited 70% bioavailability and attained peak serum levels ranging between 1.5 and 2.9 micrograms/ml after a single 500-mg dose. Nineteen percent of an oral dose was excreted as metabolites in both urine and feces. In most cases, body fluids and tissue concentrations equaled or exceeded those in concurrent serum samples. In clinical trials, oral and intravenous ciprofloxacin yielded similar clinical and bacteriologic results compared to standard therapy in a wide array of systemic infections, including lower and upper urinary tract infections; gonococcal urethritis; skin, skin structure, and bone infections; and respiratory tract and gastrointestinal tract infections. Major benefits with the oral form of this quinolone are expected in chronic pyelonephritis and bone infections, and in pulmonary exacerbations in patients with cystic fibrosis. Emergence of ciprofloxacin-resistant microorganisms has been noted in clinical practice, primarily Pseudomonas aeruginosa and Staphylococcus aureus. The most frequent side effects are related to the gastrointestinal tract; but attention should be given to adverse central nervous system effects.

Bacteriostatic and bactericidal activity of ciprofloxacin and ofloxacin against Mycobacterium tuberculosis and Mycobacterium avium complex

MICs of ciprofloxacin were lower than MICs of ofloxacin for both M. tuberculosis and M. avium complex strains. The MICs of both drugs for 41 M. tuberculosis strains were in a narrow range, and significantly lower than the achievable serum concentrations. The MICs of ciprofloxacin for 46 M. avium strains were in a wide range, and in only 28% were the broth-determined MICs of ciprofloxacin within the same range as for M. tuberculosis and lower than the achievable serum level. When compared with the concentrations achievable in macrophages, the broth-determined MICs of ciprofloxacin were lower than this level for 61% of M. avium strains. Both drugs were bactericidal against M. tuberculosis and M. avium, with a low MIC/MBC ratio.

In vitro activity of four fluoroquinolones against eighty-six isolates of mycobacteria

The in vitro activity of pefloxacin, norfloxacin, ofloxacin and ciprofloxacin against 86 strains of mycobacteria was evaluated by broth dilution. While Mycobacterium avium, Mycobacterium scrofulaceum and Mycobacterium chelonae were resistant to all four antibacterials, the susceptibility of the other species, Mycobacterium tuberculosis, Mycobacterium kansasii, Mycobacterium xenopi and Mycobacterium fortuitum, depended on the antibiotic. Ofloxacin and ciprofloxacin (MIC90: 0.5 - 2 mg/l) were more active than pefloxacin and norfloxacin (MIC90: 2 - 16 mg/l).

In vitro activity of ciprofloxacin and ofloxacin against the Mycobacterium avium-intracellulare complex

The in vitro activity of ciprofloxacin and ofloxacin against strains of Mycobacterium avium-intracellulare complex were studied by the standard 1% proportion method. Thirty-eight of 100 strains (30%) were inhibited by ciprofloxacin at 2 micrograms/ml and 11 of 30 strains (37%) were inhibited by ofloxacin at 8 microm/ml. Patients having these more susceptible isolates may potentially benefit from therapy with these agents [corrected].

Failure of doxycycline treatment in aquarium-associated Mycobacterium marinum infections

Two cases of aquarium-associated Mycobacterium marinum infections are described. Neither was cured by the initial therapy consisting of surgical excision followed by doxycycline treatment. Both strains of M. marinum were shown to be resistant to doxycycline. In one patient the lesions were subsequently healed with cotrimoxazole. The other patient, a 12-year-old girl with sporotrichoid spread of the lesions on the lower arm, failed to respond satisfactorily to a combination of rifampicin and ethambutol despite favourable effect in vitro of both drugs. Nine months after the initial treatment, the infection was finally cured with renewed surgery followed by additional chemotherapy with rifampicin and ethambutol. No signs of immunological disorder could be detected in the patient. Increased awareness of the possibility of tetracycline resistance of M. marinum is advocated. A combination of adequate chemotherapy and surgical intervention may be required at least in complicated cases.

Differentiation of Mycobacterium chelonei from M. fortuitum by ciprofloxacin susceptibility

Seventy-five strains of Mycobacterium fortuitum were inhibited by 3.0 mg/l ciprofloxacin but 36 strains of M. chelonei were resistant. The results correlated well with those obtained by the nitratase test. The ciprofloxacin sensitivity test is a useful supplement to the tests used to identify these two species.