Clarithromycin

Clarithromycin is a macrolide antibiotic used to treat pharyngitis, tonsillitis, acute maxillary sinusitis, acute bacterial exacerbation of chronic bronchitis, pneumonia (especially atypical pneumonias associated with Chlamydia pneumoniae or TWAR), skin and skin structure infections. In addition, it is sometimes used to treat Legionellosis, Helicobacter pylori, and lyme disease.

Clarithromycin is available under several brand names, for example Crixan, Clarac, Biaxin, Klaricid, Klacid, Klaram, Klabax, Klacid, Claripen, Clarem, Claridar, Fromilid, Clacid, Clacee, Vikrol, Infex and Clariwin, Resclar.

History
Clarithromycin was invented by researchers at the Japanese drug company Taisho Pharmaceutical in the 1970s. The product emerged through efforts to develop a version of the antibiotic erythromycin that did not experience acid instability in the digestive tract, causing side effects, such as nausea and stomach ache. Taisho filed for patent protection for the drug around 1980 and subsequently introduced a branded version of its drug, called Clarith, to the Japanese market in 1991. In 1985 Taisho partnered with the American company Abbott Laboratories for the international rights, and Abbott also gained FDA approval for Biaxin in October 1991. The drug went generic in Europe in 2004 and in the US in mid-2005.

Antibacterial spectrum is the same as erythromycin but it is active against Mycobacterium avium complex MAV, M. leprae and atypical mycobacteria.

Mechanism of action
Clarithromycin prevents bacteria from growing by interfering with their protein synthesis. Clarithromycin binds to the subunit 50S of the bacterial ribosome and thus inhibits the translation of peptides. Clarithromycin has similar antimicrobial spectrum as erythromycin but is more effective against certain gram-negative bacteria, particularly Legionella pneumophila. Besides this bacteriostatic effect, clarithromycin also has bactericidal effect on certain strains such as Haemophilus influenzae, Streptococcus pneumoniae and Neisseria gonorrhoeae.

Pharmacokinetics
Unlike erythromycin, clarithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes. Due to the high concentration in phagocytes, clarithromycin is actively transported to the site of infection. During active phagocytosis, large concentrations of clarithromycin are released. The concentration of clarithromycin in the tissues can be over 10 times higher than in plasma. Highest concentrations were found in liver and lung tissue.

Metabolism
Clarithromycin has a fairly rapid first-pass hepatic metabolism. However, 14-hydroxy clarithromycin, clarithromycin's metabolite, is almost twice as active and has a half life of 7 hours compared to clarithromycin's 5. Clarithromycin and its metabolites main routes of elimination are urinary and biliary excretion. Of all the drugs in its class, clarithromycin has the best bioavailability at 50%, which makes it amenable to oral administration.

Side effects
Most common side-effects are gastrointestinal: Diarrhea, nausea, extreme irritability, abdominal pain and vomiting, facial swelling. Less common side-effects include headaches, hallucinations (auditory and visual), dizziness/motion sickness, rashes, alteration in senses of smell and taste, including a metallic taste that lasts the entire time one takes it. Dry mouth, panic and / or anxiety attacks and nightmares have also been reported albeit less frequently. In more serious cases it has been known to cause jaundice, cirrhosis, and kidney problems including renal failure. Uneven heartbeats, chest pain, and shortness of breath have also been reported while taking this drug.

Clarithromycin may cause false positives on urine drug screens for cocaine.

Adverse effects of clarithromycin in the central nervous system include dizziness, ototoxicity and headaches, but delirium and mania are also uncommon side effects.

When taken along with some statins, drugs used to reduce blood serum cholesterol levels, muscle pain may occur.

There is also the risk of oral candidiasis, due to the increased yeast production in the body from the antibiotics.

Special uses
According to a study performed by the Japanese manufacturer of clarithromycin, it was proved that it can be used in the treatment of asthma as it has an anti-inflammatory effect.

In the clarithromycin study, researchers led by Hideaki Amayasu, MD, of the Yokohama Rosai Hospital in Japan, randomized 17 subjects in double-blind fashion to 200 mg of clarithromycin or placebo twice daily for eight weeks. After a washout period of at least four weeks, the two groups of patients were then given the alternative treatment for eight weeks.

Before the study began, all patients had stable asthma, and all had been free from symptoms of respiratory infection for at least six weeks. None were smokers. Patients were permitted to use an inhaled ß-agonist for symptom control. However, those who used theophylline, antileukotriene agents, clarithromycin, or an anti-inflammatory agent (including oral or inhaled corticosteroids) were excluded from the study. During the study, the patients recorded their symptom severity once a week, using a 0 to 3 scale (0 indicated that a patient was asymptomatic on at least four days that week, and 3 indicated that a patient had had severe asthma attacks on more than four days and/or nocturnal asthma symptoms almost daily; 1 and 2 indicated intermediate levels of disease severity). In addition, they underwent laboratory testing as well as a methacholine challenge for evaluation of bronchial responsiveness.

Neither forced expiratory volume in one second (FEV1) nor forced vital capacity were affected by clarithromycin use. Thus, say the authors, it is unlikely that clarithromycin has a bronchodilating effect. However, symptoms (i.e., nocturnal cough, wheezing, and severity and frequency of asthma attacks) improved in 15 patients following clarithromycin use. "Overall, the symptom score decreased significantly after treatment with clarithromycin," the authors added. Blood and serum eosinophil counts and ECP levels also decreased; however, blood and sputum neutrophil levels remained unchanged.

Methacholine challenge caused airway obstruction in all patients at baseline and during the study. The amount of methacholine required to cause obstruction (PC20) was significantly greater when the patients received clarithromycin, however, suggesting lower airway hyperresponsiveness in this group. Yet no statistical association emerged between the increase in PC20 and the decrease in ECP levels during clarithromycin administration. "Although [the researchers] did not find a direct relationship between the changes in ECP concentrations and the changes in airway hyperresponsiveness, their study suggests that prolonged treatment with a macrolide may reduce the symptoms and bronchial hyperresponsiveness of asthma through an anti-inflammatory action," wrote Pedro C. Avila, MD, and Homer A. Boushey, MD, in an accompanying editorial.[3] Clarithromycin may also improve asthma symptoms by treating airway infection. Indeed, some studies of asthma patients have found evidence of chronic Chlamydia or Mycoplasma airway

Allergic symptoms include hallucinations, wheezing, hives, itching, swelling, spasms in the throat and breathing tubes, swelling of the face and neck, joint and muscle pain, difficulty breathing, fever and skin rashes, and lips blistering / scabbing. Rashes can range in severity, the most serious cases being toxic epidermal necrolysis and Stevens-Johnson syndrome.

Clarithromycin may also decrease the function of birth control pills and therefore an alternative birth control should be used.

Resistance
Many Gram positive microbes quickly develop resistance to clarithromycin after standard courses of treatment, most frequently via acquisition of the erm(B) gene, which confers high-level resistance to all macrolides.

Contraindications
Clarithromycin should be used with caution if the patient has liver or kidney disease, certain heart problems (e.g., QT prolongation or bradycardia), or an electrolyte imbalance (e.g., low potassium or magnesium levels). Many other drugs can interact with clarithromycin, which is why the doctor should be informed of any other drugs the patient is taking concomitantly. Clarithromycin is almost never used in HIV patients due to significant interaction with HIV drugs. Clarithromycin should not be used in pregnant patients.

Clarithromycin can also cause serotonin syndrome symptoms when taken in conjunction with Buspar.

Clarithromycin almost doubles the level of Carbamazepine in serum by reducing its clearance inducing toxic symptoms of Carbamazepine, including diplopia and nausea besides hyponatremia (reduced level of Sodium in serum). Research in many cases has shown a sharp increase in serum level of Carbamazepine in patients who were given Clarithromycin. Therefore, for epileptic patients taking carbamazepine, Clarithromycin should be better avoided.

Drugs using clarithromycin
In the United States generic clarithromycin is available from Andrx, Genpharm, Ivax, Ranbaxy Laboratories, Roxane, Sandoz, Teva and Wockhardt. It is also used as part of a combination therapy to treat Helicobacter pylori. In the Middle East it is available as Claridar, produced by Dar Al Dawa. In India, Acnesol-CL gel, containing 1% w/w Clarithromycin, marketed by Systopic, is used to treat acne vulgaris.

Potential increased mortality using clarithromycin
In the CLARICOR Trial, the use of short-term clarithromycin treatment correlated with an increased incidence of deaths which were classified as sudden cardiac deaths,.

Clarithromycin can cause liver disease.