The quinolones are a family of synthetic broad-spectrum antibiotics. The term quinolone(s) refers to potent synthetic chemotherapeutic antibacterials.
The first generation of the quinolones begins with the introduction of nalidixic acid in 1962 for treatment of urinary tract infections in humans. Nalidixic acid was discovered by George Lesher and coworkers in a distillate during an attempt at chloroquine synthesis.
They prevent bacterial DNA from unwinding and duplicating. (See Mechanism of Action later.)
Quinolones, in comparison to other antibiotic classes, have the highest risk of causing colonization with MRSA and Clostridium difficile. For this reason, a general avoidance of fluoroquinolones is recommended based on the available evidence and clinical guidelines. The majority of quinolones in clinical use belong to the subset fluoroquinolones, which have a fluorine atom attached to the central ring system, typically at the 6-position or C-7 position.
Since the introduction of nalidixic acid in 1962, more than 10,000 analogs have been synthesized, but only a handful have found their way into clinical practice.
Fluoroquinolone use for pneumonia is increasing, and with it so is bacterial resistance to fluoroquinolones. The majority of the prescribing of fluoroquinolones is inappropriate, with less than four percent of people prescribed quinolones being appropriate according to clinical guidelines. Clinical guidelines in Canada recommend fluoroquinolones only for outpatient treatment of pneumonia in a small number of patients, such as those with certain comorbid conditions, e.g., patients with a history of COPD, or those with recent use of antibiotics. For severe forms of community-acquired pneumonia, the fluoroquinolones are associated with improved treatment rates, but with no differences found in mortality between other antibiotic classes.
Fluoroquinolones are not recommended as first-line antibiotics for acute sinusitis, as this condition is usually self-limiting, and the risks outweigh the benefits in comparison to other antibiotic classes.
Antibiotics including fluoroquinolones can be effective in some cases of bronchitis. However, only about 5-10% of bronchitis cases are caused by a bacterial infection; most cases of bronchitis are caused by a viral infection and are self-limiting and resolve themselves in a few weeks. It has been recommended that antibiotics are limited in most cases to those whose symptoms fail to resolve on their own.
Fluoroquinolones are often used for genitourinary infections; in general they are recommended only after other antibiotic regimens have failed. However, for serious acute cases of pyelonephritis or bacterial prostatitis where the patient may need to be hospitalised, fluoroquinolones are recommended as first-line therapy. Prostatitis has been termed "the waste basket of clinical ignorance" by prominent Stanford University urologist Dr. Thomas Stamey. Campbell's Urology, the urologist's most authoritative reference text, identifies only about 5% of all patients with prostatitis as having bacterial prostatitis, which can be "cured" at least in the short term by antibiotics. In other words, 95% of men with prostatitis have little hope for a cure with antibiotics alone, since they do not actually have any identifiable bacterial infection.
The American Thoracic Society recommends fluoroquinolones not be used as a first-line agent, instead recommending macrolide or doxycycline as first-line agents. The Drug-Resistant Streptococcus pneumoniae Working Group recommends fluoroquinolones be used only after other antibiotic classes have been tried and failed, or in those with demonstrated drug-resistant Streptococcus pneumoniae. The Centers for Disease Control are concerned fluoroquinolones are being used as a "one-size-fits-all" treatment unnecessarily by doctors without considering suitability and differences due to age and other risk factors. Effective interventions have been recommended to reduce the excessive fluoroquinolone prescribing in the United States.
These adverse reactions are a class effect of all quinolones; however, certain quinolones are more strongly associated with increased toxicity to certain organs. For example, moxifloxacin carries a higher risk of QTc prolongation, and gatifloxacin has been most frequently linked to disturbed blood sugar levels, although all quinolones carry these risks. Some quinolones were withdrawn from the market because of these adverse events (for example, sparfloxacin was associated with phototoxicity and QTc prolongation, thrombocytopenia and nephritis were seen with tosufloxacin, and hepatotoxicity with trovafloxacin). Simultaneous use of corticosteroids is present in almost one-third of quinolone-associated tendon rupture. The risk of adverse events is further increased if the dosage is not properly adjusted, for example if there is renal insufficiency. Caution is required in patients with liver disease. Events that may occur in acute overdose are rare, and include renal failure and seizure.
Fluoroquinolones are considered high-risk antibiotics for the development of Clostridium difficile and MRSA infections. A previously rare strain of C. difficile that produces a more severe disease with increased levels of toxins is becoming epidemic, and may be connected to the use of fluoroquinolones. Fluoroquinolones are more strongly associated with C. difficile infections than other antibiotics, including clindamycin, third-generation cephalosporins, and beta lactamase inhibitors. One study found fluoroquinolones were responsible for 55% of C. difficile infections. The European Center for Disease Prevention and Control recommends fluoroquinolones and the antibiotic clindamycin should be avoided in clinical practice due to their high association with C. difficile, a potentially life-threatening super-infection. Some support and patient advocacy groups refer to these adverse events as "fluoroquinolone toxicity". Some people from these groups claim to have suffered serious long-term harm to their health from using fluoroquinolones. This has led to a class-action lawsuit by those harmed by the use of fluoroquinolones, as well as action by the consumer advocate group, Public Citizen. Partly as a result of the efforts of Public Citizen, the FDA ordered black box warnings on all fluoroquinolones, advising consumers of their possible toxic effects on tendons.
Various substitutions made to the quinoline ring resulted in the development of numerous fluoroquinolone drugs available today. Each substitution is associated with a number of specific adverse reactions, as well as increased activity against bacterial infections,
Quinolones inhibit the bacterial DNA gyrase or the topoisomerase II enzyme, thereby inhibiting DNA replication and transcription. Recent evidence has shown eukaryotic topoisomerase II is also a target for a variety of quinolone-based drugs. Thus far, most of the compounds that show high activity against the eukaryotic type II enzyme contain aromatic substituents at their C-7 positions.
Quinolones can enter cells easily via porins and, therefore, are often used to treat intracellular pathogens such as Legionella pneumophila and Mycoplasma pneumoniae. For many Gram-negative bacteria, DNA gyrase is the target, whereas topoisomerase IV is the target for many Gram-positive bacteria. It is believed eukaryotic cells do not contain DNA gyrase or topoisomerase IV. However, there is debate concerning whether the quinolones still have such an adverse effect on the DNA of healthy cells, in the manner described above, hence contributing to their adverse safety profile. This class has been shown to damage mitochondrial DNA.
Products containing multivalent cations, such as aluminum- or magnesium-containing antacids and products containing calcium, iron, or zinc, invariably result in marked reduction of oral absorption of fluoroquinolones.
Other drugs that interact with fluoroquinolones include antacids, sucralfate, probenecid, cimetidine, warfarin, antiviral agents, phenytoin, cyclosporine, rifampin, pyrazinamide, and cycloserine. This inhibition causes an increased level of, for example, antidepressants such as amitriptyline and imipramine, clozapine (an atypical antipsychotic), caffeine, olanzapine (an atypical antipsychotic), ropivacaine (a local anaesthetic), theophylline (a xanthine), and zolmitriptan (a serotonin receptor agonist). Widespread veterinary usage of quinolones, in particular in Europe, has been implicated.
Fluoroquinolones have been recommended to be reserved for the use in patients that are seriously ill and may soon require immediate hospitalization. Though considered to be very important and necessary drugs required to treat severe and life-threatening bacterial infections, the associated antibiotic misuse remains unchecked, which has contributed to the problem of bacterial resistance. The overuse of antibiotics such as happens with children suffering from otitis media has given rise to a breed of super bacteria that are resistant to antibiotics entirely.
For example, the use of the fluoroquinolones had increased threefold in an emergency room environment in the United States between 1995 and 2002, while the use of safer alternatives, such as macrolides, declined significantly. Fluoroquinolones had become the most commonly prescribed class of antibiotics to adults in 2002. Nearly half (42%) of these prescriptions were for conditions not approved by the FDA, such as acute bronchitis, otitis media, and acute upper respiratory tract infection, according to a study supported in part by the Agency for Healthcare Research and Quality. In addition, they are commonly prescribed for medical conditions, such as acute respiratory illness, that are usually caused by viral infections.
Within a recent study concerning the proper use of this class in the emergency room, 99% of these prescriptions were revealed to be in error. Out of the one hundred total patients studied, eighty-one received a fluoroquinolone for an inappropriate indication. Out of these cases, forty-three (53%) were judged to be inappropriate because another agent was considered first line, twenty-seven (33%) because there was no evidence of a bacterial infection to begin with (based on the documented evaluation), and eleven (14%) because of the need for such therapy was questionable. Of the nineteen patients who received a fluoroquinolone for an appropriate indication, only one patient of one hundred received both the correct dose and duration of therapy.
There are three known mechanisms of resistance. Some types of efflux pumps can act to decrease intracellular quinolone concentration. In Gram-negative bacteria, plasmid-mediated resistance genes produce proteins that can bind to DNA gyrase, protecting it from the action of quinolones. Finally, mutations at key sites in DNA gyrase or topoisomerase IV can decrease their binding affinity to quinolones, decreasing the drugs' effectiveness.
Adverse effects of fluoroquinolones can lead to patients attending hospital emergency rooms. Many of the important adverse effects of fluoroquinolones are widely underappreciated by physicians, and are often misdiagnosed as other medical or psychiatric conditions. Physicians typically fail to enquire about antibiotic use to explain with an acute presentation of new symptoms. The important adverse effects of fluoroquinolones include hypoglycemia or hyperglycemia, QTc prolongation, central nervous system toxicity, gastrointestinal, skin, musculoskeletal, cardiotoxicity, and respiratory effects, phototoxicity, tendinopathy, angioedema, and Clostridium difficile infections. A further factor that leads to misdiagnosis of quinolone adverse effects is that some symptoms can persist or occur for the first time quite some time after a course of quinolone has been finished, so inquiring about distant-past use of quinolones has been recommended. Quinolones are probably the worst offending antibiotic for causing C. difficile infections. Some of the adverse effects can present similar to acute dementia, confusion, and psychosis. Quinolones are a common cause of cerebral dysfunction, with neuropsychiatric disturbances being the most common quinolone adverse effects. One study found, of all drug classes prescribed by doctors including psychotropic drugs, fluoroquinolones were the most common cause of neuropsychiatric adverse effects.
The results of these pediatric trials indicated arthropathy occurred more frequently in patients that received ciprofloxacin (within these studies). The affected joints included the knees, elbows, ankles, hips, wrists, and shoulders of the pediatric patients. In one study, at six weeks arthropathy was seen in 9.3% of ciprofloxacin patients. These rates increased significantly after one year to 13.7% of the ciprofloxacin patients. Such arthropathy occurred more frequently in patients treated with ciprofloxacin than any other control drug, regardless of whether they received IV ciprofloxacin or the oral version of the drug. Ciprofloxacin patients reported more than one event and on more than one occasion when compared to the control patients. The overall incidence of adverse events at six weeks was 41% in those patients being treated with ciprofloxacin. Serious adverse events were seen in 7.5% of these patients and 3% of the patients discontinued the drug due to adverse events. Despite these results the FDA stated “[t]he data support updating the package insert to include safety; and treatment recommendations for pediatric patients between 1 and 17 years of age with complicated urinary tract infection or pyelonephritis.”
Within a 2005 memo, the FDA reviewed seventeen unique pediatric cases reported to the FDA during the thirteen-month period after the pediatric exclusivity for ciprofloxacin had been granted. During this period, there was one report of death, two of disability, and four of hospitalization. The disabilities involved the inability to walk (in a 12-year-old female patient) and the inability to run (in a 12-year-old male patient). The hospital admissions were for pseudomembranous colitis, pancytopenia, tendonitis, and Stevens Johnson syndrome. The female patient received five weeks of ciprofloxacin oral therapy at the recommended doses. Even though ciprofloxacin was discontinued, she could not stand or walk, and required a wheelchair one month later. These seventeen unique pediatric cases showed mostly hematological, musculoskeletal, allergic/hypersensitivity, and central nervous system adverse events. It does not appear this executive summary was ever released to the medical community.
The adverse drug reaction profile of ciprofloxacin and other fluoroquinolone drugs has spawned a grass-roots movement of those so affected to lobby for black box warnings and Dear Doctor letters as well as the petitioning of the FDA for the removal of some fluoroquinolone drugs from clinical practice.
At present, there are a significant number of cases pending before the United States District Court, District of Minnesota, involving the drug Levaquin. On June 13, 2008 a Judicial Panel On Multidistrict Litigation (MDL) granted the Plaintiffs’ motion to centralize individual and class-action lawsuits involving Levaquin in the District of Minnesota over objection of Defendants, Johnson and Johnson / Ortho McNeil.
Several class action lawsuits had been filed in regards to the adverse reactions suffered by those exposed to ciprofloxacin during the anthrax scare of 2001, as well.
Musculoskeletal disorders attributed to use of quinolone antibiotics were first reported in the medical literature in 1972, as an adverse reaction to nalidixic acid. Rheumatic disease after use of a fluoroquinolone (norfloxacin) was first reported eleven years later. In response to a 1995 letter published in the New England Journal of Medicine, representatives of the U.S. Food and Drug Administration (FDA) stated the agency would "update the labeling [package insert] for all marketed fluoroquinolones to include a warning about the possibility of tendon rupture."
By August 1996, the FDA had not taken action, and the consumer advocacy group Public Citizen filed a petition with the FDA, prompting the agency to act. Two months later, the FDA published an alert in the FDA Medical Bulletin and requested that fluoroquinolone package inserts be amended to include information on this risk.
Nine years later, in 2005, the Illinois Attorney General filed a second petition with the FDA again seeking black box warnings and "Dear Doctor" letters emphasizing the risk of tendon rupture; the FDA responded it had not yet been able to reach a decision on the matter. In 2006, Public Citizen, supported by the Illinois Attorney General, renewed its demand of ten years prior for black box warnings by filing a third petition requesting such changes be made. When the FDA failed to respond to these two petitions as required by law, Public Citizen, in January 2008, filed suit to compel the FDA to respond to their 2006 petition. On July 7, 2008 the FDA requested that the makers of systemic-use fluoroquinolones add a boxed warning regarding spontaneous tendon ruptures, and to develop a Medication Guide for patients. The package inserts for ciprofloxacin, Avelox (moxifloxacin), Proquin XR, Factive (gemifloxacin), Floxin (ofloxacin), Noroxin (norfloxacin) and Levaquin (levofloxacin) were amended on September 8, 2008 to include these new warnings. Bayer, which manufactures Cipro, Avelox and Proquin XR, issued a Dear Healthcare Professional letter on October 22 concerning these changes. Ortho-McNeil, the manufacturers of Levaquin, issued a similar letter in November. through the Health Care Notification Network, a registration-only website that distributes drug alerts to licensed healthcare professionals.
A review of the FDA website indicated the majority of the generic versions of the fluoroquinolones have not been updated to include this Boxed Warning as of September 2009. In addition, there are numerous reports that claim this information has not been disseminated to pharmacists, the name brand products continue to contain the previous labels that are absent of this warning, and the Medication Guide has not been made available to pharmicists or physicians for distribution.
In 2011, the FDA has added another boxed warning that says that fluoroquinolones due to their neuromuscular blocking activity may exacerbate muscle weakness in persons with myasthenia gravis. Serious adverse events, including deaths and requirement for ventilatory support, have been reported in this group of patients. Avoidance of fluoroquinolones in patients with known history of myasthenia gravis is advised.
Some researchers group these drugs by patent dates Some by a specific decade (i.e., '60s, '70s, '80s, etc.) Others by the various structural changes
The first generation is rarely used today. Nalidixic acid was added to the OEHHA Prop 65 list as a carcinogen on May 15, 1998. A number of the second-, third-, and fourth-generation drugs have been removed from clinical practice due to severe toxicity issues or discontinued by their manufacturers. The drugs most frequently prescribed today consist of Avelox (moxifloxacin), Cipro (ciprofloxacin), Levaquin (levofloxacin), and, to some extent, their generic equivalents.
ciprofloxacin (Zoxan, Ciprobay, Cipro, Ciproxin) enoxacin (Enroxil, Penetrex) ofloxacin (Floxin, Oxaldin, Tarivid)
This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
