Clarithromycin - A Review
Chief editor
DR T R RAMANUJAM M.D., C.MI.Biol (Lond)
|
INTRODUCTION CLINICAL PHARMACOKINETICS
CLINICAL EFFICACY ADVERSE EFFECTS & DRUG INTERACTIONS
CHOOSING HOOSING MACROLIDES
BRIIGHTER SIDE OF CLARITHROMYCIN CURRENT TRENDS IN MICROLIDE USE INTRODUCTION Macrolides have additional pharmacological actions not connected with their antimicrobial actions on the following receptors: Motility receptors in GIT, Which forms the basis for their use as prokinetic agents in diabetic gastroparesis. Efforts are underway to isolate a preparation without antimicrobial effect. CYP Receptor in the liver – By this effect with the exception of Azithromycin, Dirithromycin and spiramycin other Macrolides inhibit CYP3A isoenzyme and therefore involved in many clinically significant drug interactions and adverse effects. Ex: Interactions with theophylline, Digoxin, Oral anticoagulants, Terfinadine, Azole antifungals, Cisapride etc., Auditory Receptors _ as evidenced by the production of reversible hearing loss in AIDS patients receiving high doses. IV Erythromycin has the potential for causing hearing impairment. Agents like Rosamycin (micromonospora spp), and Flurithomycin are under investigation appear promising. Clarithromycin is a semi synthetic broad spectrum macrolide antimicrobial agent having not only bactericidal activity against some organisms by virtue of its synergism with its microbiologically active 14 OH metabolite but also by its Post Antibiotic Effect (PAE). Current Review focuses antimicrobial activity, Clinical pharmacokinetics, efficacy, tolerability & safety profiles, and pharmacoeconomic considerations of clarithromycin. The concluding topic of “Choosing Macrolides” has been added for the benefit of readers. ANTIMICROBIAL ACTIVITY
It is very active against agents causing atypical pneumonia like C.pneumoniae, M.pneumoniae and markedly active against L.pneumophiliae. Similar effects are also observed against S.aureus, S.pyogenes and all strains of S.pneumoniae and M.catarrhalis and with GOOD against gram positive anaerobes. With reference to H.influenzae clarithromycin has twice the activity of erythromycin ( c.f. Azithromycin has increased activity against gram negative organisms particularly H.influenzae, Enterobactericae, and unlike Erythromycin & Clarithromycin it has activity against Salmonellae, Sigellae and E.coli). Clarithromycin has very good activity against agents causing opportunistic infections in AIDS patients viz., MAC infection, Toxoplasmosis, Cryptosporidiosis. Clarithromycin is one of the second line drug in M.leprae ( along with minocycline). Recent studies have shown that clarithromycin is an effective agent against M.chelonae which causes disseminated cutaneous lesion and along with Omeprazole (Better Lansoprazole) clarithromycin is effective in eradication of H.pylori in patients with peptic ulcer. Very recent investigations revealed the high efficacy of clarithromycin against B.burgedorferi causing Lyme disease. It is also effective against Toxoplasmosis, and Cryptosporidiosis (c.f Spiramycin). Clarithromycin is acid stable rapidly and completely absorbed per orally to the extent of 100% and absolute bioavailability is 55% and is unaffected by food. Binding- 80% to Plasma alpha 1 acidic glycoprotein Hepatic metabolism & its 14 OH metabolite is pharmacologically active (synergistic activity renders it bactericidal). Clarithromycin inhibits the isoenzyme of Cyt P 450 viz., CYP3A family and thereby increase the concentrations of several drugs administered concurrently resulting in serious clinically significant drug interactions. The hepatic metabolism of clarithromycin is reduced in older patients with hepatic impairment and necessary dose adjustments have to be made., however, in mild hepatic dysfunction no dose adjustments need be necessary. Hepatic elimination constitutes about 60% and renal elimination about 37%. No dose adjustments is necessary unless creatinine clearance is < 30 ml/Mt. i.e., 1.8L/hr. Clarithromycin concentrations achieved in tissue exceed the plasma by;
3.1 : 1 Bronchial secretion Of particular note is the high concentration in the alveolar macrophages, Lung tissue and tonsillar tissue show high penetration of the drug into the respiratory tract cells, a feature that should enhance efficacy against typical and atypical pathogens which usually cause community acquired pneumonia ( CAP). Concentrations of both clarithromycin and its 14 OH metabolite (active) exceed MICs for most respiratory pathogens maintained longer in tissue than fluid and longer in fluid secretions than in plasma. Significant quantities of clarithromycin and its metabolites are excreted in breast milk of nursing mothers.
A Modified Release (MR) formulation of clarithromycin has been developed to increase the patient compliance and the elimination t ½ of clarithromycin and its metabolite is not altered although the peak concentrations may be delayed. 7.5mg/kg b.d I.V 500mg b.d diluted to 2mg/ml concentration in 250ml of dextrose or normal saline. CONCURRENT ADMINISTATION OF TERFINADINE OR ASTEMIZOLE OR CISAPRIDE IS CONTRAINDICATED . In Streptococcal pharyngitis In patients allergic to betalactams or intolerant to erythromycin , clarithromycin is the better choice since it has better activity that erythromycin (greater tolerability and less GIT manifestations) but is expensive. Sinusitis Most often the pathogens involved are S.pneumoniae, H.influenzae, and anaerobes and less often staphylo , S.pyogenes, M.catarrhalis. There is no clear advantage of newer macrolides over amoxycillin except in H.influenzae. Azithromycin has also been studied and found to be equiv. effective with clarithromycin and amoxycillins. Acute otitis media Organisms implicated are S.pneumoniae, H.influenzae, and M.catarrhalis. More recent trials suggest even shorter course of clarithromycin (5 days), Azithromycin (3days) are effective for acute otitis media. Alper et al showed that clarithromycin was more effective than amoxycillin in eradicating high-level penicillin resistant pneumococcci. Both clarithromycin and Azithromycin are suitable for acute otitis media. Chest infections Acute bronchitis is an inflammatory condition of tracheobronchial tree that is usually viral in origin; Rhinovirus, influenza, adenovirus, M.pneumoniae, C.pneumoniae, and M.catarrhalis may be seen in acute bronchitis. Role of secondary bacterial invasion by S.pneumoniae and H.influenzae is unclear. Therefore there is no clear benefit in treating acute bronchitis with antibiotics in patients who are otherwise healthy. Patients with underlying chronic disease, however, might benefit from antibiotics with improvement of symptoms. If antibiotics are used, a macrolide or a betalactam should be used. Erythromycin, Azithromycin and clarithromycin are all reasonable choices. In chronic bronchitis, a clinical syndrome characterized by cough and sputum production , the symptoms are most often directed to chronic bronchial irritation with inflammatory changes in the airways. For treatment of Acute Exacerbation of Chronic Bronchitis (AECB), Short-term antibiotic therapy is useful in patients with increased sputum production with purulence. Both clarithromycin and Azithromycin are reasonable choices alternative to cephalosporins. Community Acquired Pneumonia Treatment is empirical and newer macrolides are active against many major pathogens of Community Acquired Pneumoniae including S.pneumoniae, H.influenzae, M.pneumoniae, L.pneumophiliae, and C.pneumoniae. Clarithromycin is an ideal choice in case of pneumoccal pneumonia, H.influenzae and Legionellae pneumonia. Hammedani et al determined that clarithromycin was very effective in the treatment legionellair’s disease. Results of comparator trials have shown similar efficacy for clarithromycin and other antibacterial agents in treatment of community acquired pneumonia, Acute bronchitis, ACEB, sinusitis, pharyngitis and otitis media. Comparators include betalactams, with combination of clauvulanic acid, Penicillin V, Cefaclor, Cefuroxime axetil, Cefpodoxime, Ceftibuten, Cefixime, Erythromycin, Azithromycin, Dirithromycin, Roxithromycin, and Josamycin. The study revealed hat CLARITHROMYCIN produced better clinical success and bacterial eradication. Skin & soft tissue infection For most of the skin infections where erythromycin is indicated clarithromycin not only substitutes but produced better clinical eradication rates. In opportunistic infections associated with AIDS Recently clarithromycin has been considered to be an important agent prophylactically (single agent) in the treatment of preventive strategies of disseminated MAC in AIDS. Macrolides are especially attractive treatment options for MAC bacteremia in disseminated advances AIDS and thanks to the Excellent Tolerability (Clarithromycin in particular), ease of administration and lack of recognizable interactions by clarithromycin with anti HIV agents like protease inhibitors. Clarithromycin is one of the single agent in the long term prophylaxis against opportunistic MAC infection in AIDS patients. Chemoprophylaxis is one of the most effective preventive strategic agent in disseminated MAC disease and this strategy improves quality of life (QOL) and reduce the risk of death associated with this disease in AIDS patients. Antimicrobial spectrum of macrolides encompasses atypical mycobacteriae together with gram-positive bacteriae and even some protozoae while it has been shown that clarithromycin confers survival benefits compared with placebo. Prolonged per oral clarithromycin as a single agent (others Azithromycin & Rifabutin) in Chemoprophylaxis for disseminated MAC infection in AIDS. In contrast to Rifabutin , macrolides are associated with bacterial resistance and offer no protection against tuberculosis. Although Rifabutin, Azithromycin, and clarithromycin have similar effects as prophylactic agents in disseminated MAC infection in AIDS, Clarithromycin produced significant survival benefits. Clinically clarithromycin interacts with Rifabutin because of their hepatic enzyme effects. Clarithromycin demonstrated significant survival benefit over azithromycin and rifabutin. With clarithromycin, rifabutin there is increased incidences of uveitis (PCK Interaction) Efficacy Data Either clarithromycin or azithromycin can be used in preference to rifabutin and macrolides are less likely to interact with anti HIV protease inhibitors whereas emergence of resistance is lower with rifabutin and rifabutin prevents tuberculosis while macrolides cannot. Mycobacterium Chelonae is noted for antimicrobial resistance, with limited and potential toxic therapeutic options. clarithromycin is much more active than erythromycin or azithromycin against M.chelonae and has been used successfully as monotherapy for the treatment of disseminated cutaneous disease. Mycobacterium leprea – Clarithromycin alone or in combination with minocycline is highly beneficial in M.leprae. NEITHER CLARITHROMYCIN NOR AZITHROMYCIN HAS ANY EFFECT ON M. TUBERCULOSIS OTHER INFECTIONS Urogenital infections with C.trachomatis both azithromycin and clarithromycin are very effective. Azithromycin is preferable and is given as a single dose of 1 H which is curative. H.pylori infections, Clarithromycin is preferred over azithromycin since the latter may manifest high level of post therapy resistance. Clarithromycin acts slowly and exhibit synergy with omeprazole and Lansoprazole and enhance H pylori eradication rapidly and moreover clarithromycin with Omeprazole show beneficial interaction for rapid synergistic efficacy. T.gondii infection and in Cryptosporidiosis associated with AIDS, clarithromycin in combination with pyrimethamine is effective.
In Lyme disease, a most common tick borne infection with arthritis caused by B.burgedorferi, clarithromycin produced significant results in recent studies (Azithromycin is also effective) Interactions of clinical significance are Clarithromycin (Primary drug):
Therapeutic drug monitoring is necessary and if needed dose adjustments Omeprazole increase clarithromycin absorption resulting in increasing concentration of both clarithromycin & omeprazole (beneficial interaction viz., rapid eradication of H.pylori because of synergy).
Clarithromycin X Digoxin = digoxin concentration. Monitor digoxin. PHARMACOECONOMIC CONSIDERATIONS
This becomes highly essential when it comes to using an expensive agent like Clarithromycin. In various studies in US clarithromycin appeared to be cost effective especially in patients in whom IV macrolides have been switched to per oral clarithromycin formulations known as sequential or swotching therapy. Even in out patient settings, considerable cost reductions are seen with clarithromycin on comparing with cephalosporins and amoxycillins. In clinical settings clarithromycin is the drug of choice and /or alternative drug of choice, local acquisition cost, prevalent pattern of pathogens and treatment methods need to be considered in assessing the cost. Clarithromycin and azithromycin have better activity against H.influenzae, M.catarhalis, especially in the treatment of community acquired pneumonia and acute exacerbations of chronic bronchitis. Clarithromycin is highly effective for treatment and prophylaxis of MAC (disseminated) infection in AIDS patients while Azithromycin is effective in prophylaxis alone. Clarithromycin exhibits good activity against Gram Positive anaerobes, C.trachomatis, M.catarrhalis, L.pneumophiliae, H.influenzae and H.parainfluenzae, B.bdgedorferi, H.pylori, MAC, M.chelonae. Clarithromycin is the drug of choice in H.pylori along with omeprazole in rapid eradication either in 3 or 4-drug regimen. Azithromycin is the drug of choice in C.trachomatis, and gi en as single dose 1 G curative (Long plasma half life for azithromycin viz., 245-96 hrs). Unlike clarithromycin azithromycin does not affect CYP isoenzymes and there is no drug interaction.
Dirithromytcin is similar to Erythromycin in antibacterial activity Poor against H.influenzae but exhibit good activity against several strains of H.pylori.
Recent trials have demonstrated activity of clarithromycin against B>burgdorferi. Roxithromycin is less effective than erythromycin well absorbed but food decreases absorption – usual dose is 150mg bd or 300mg/day. Spiramycin (16membered macrolide from Str. aumbofauceus) is similar to erythromycin. A combination preparation with metronidazole is available for amebiasis. Spiramycin has no embryo toxicity, no teratogenecity, no mutagenecity and found to be active against Legionellirs, Toxoplasmosi, Chlamydiae and certain anaerobes (except B.fragilis and fusobacterium). Spirmaycin exhibits very poor or no penetration into CNS. Major indications of spiramycin include
Toxoplasmosis in pregnancy
It has good activity against many respiratory pathogens causing atypical pneumonia specifically very effective against L.pneumophiliae etc.,
(1) Improvement in immune function Claritheomycin has consistent p.o absorption with good oral bioavailability exhibiting high concentrations in lung, tonsils, nasal tissue, middle ear, and WBCs etc.,
No need for adjustment of dosage in older patients and with mild hepatic impairment and renal impairment (except in Creatinine 30ml/mt) Clarithromycin has greater activity against T.gondii when combined with pyrimethammine although secondary to cotrimoxazole Clarithromycin has excellent activity against M.chelonae as mono-therapy in this refractory disseminated infection Recent studies have clearly shown that clarithromycin is highly effective against B.burgdorferi the tick borne Lyme disease and associated arthritis. Clarithromycin produced better clinical success and bacteriological eradication rate in chest infections like Acute bronchitis, Acute Exacerbation of Chronic Bronchitis (AECB), Community acquired pneumonia, otitis media etc.,
Clarithromycin is an important second line drug in leprosy and given in combination with minocycline. Theophylline, cyclosporin, tacrolimus, carbamazepine, digoxin, Rifamycins necesitasting therapeutic drug monitoring and dose adjustments.
Clarithromycin X Oral anticoagulants = serious bleeding diathesis
Clarithromycin X Terfinadine,astemizole,Cisapride = cardia arrhythmias leading to torsade de pointes etc., Rheumatoid arthritis, Myocardial infarction (Acute coronary syndrome) both of which have infectious origin where infection act as a precipitating factor for inflammatory changes. Recently Azithromycin and Doxycycline combination are being tried by NIH for rheumatoid arthritis . The role of antibiotics in MI is based on the fact that patholgoical examination of coronary plaque have revealed infection associated with C.pneumoniae, H.pylori, Herpes viridae etc., and CMV associated transplant vasculopathy. Recent pilot studies and controlled trials have demonstrated that macrolide anti microbial treatment against M.pneumoniae reduced the risk of recurrent coronary events.
Recently ROXI trials are underway in Acute Coronary Syndrome associated with QT syndrome. |