Source: Υπουργείο Υγείας (CY) Revision Year: 2021 Publisher: Delorbis Pharmaceuticals Ltd., 17 Athinon Street, Ergates Industrial Area, 2643 Ergates, P.O. Box 28629, 2081 Lefkosia, Cyprus, European Union
Pharmacotherapeutic group: Antibacterial for systemic use, macrolide
ATC-Code: J01FA09
Clarithromycin is an antibiotic belonging to the macrolide antibiotic group. It exerts its antibacterial action by selectively binding to the 50s ribosomal sub-unit of susceptible bacteria preventing translocation of activated amino acids. It inhibits the intracellular protein synthesis of susceptible bacteria.
The 14-hydroxy metabolite of clarithromycin, a product of parent drug metabolism also has antimicrobial activity. The metabolite is less active than the parent compound for most organisms, including mycobacterium spp. An exception is Haemophilus influenza where the 14-hydroxy metabolite is two-fold more active than the parent compound.
Clarithromycin is usually active against the following organisms in vitro:
Gram-positive Bacteria: Staphylococcus aureus (methicillin susceptible); Streptococcus pyogenes (Group A beta-hemolytic streptococci); alpha-hemolytic streptococci (viridans group); Streptococcus (Diplococcus) pneumoniae; Streptococcus agalactiae; Listeria monocytogenes.
Gram-negative Bacteria: Haemophilus influenzae; Haemophilus parainfluenzae; Moraxella (Branhamella) catarrhalis; Neisseria gonorrhoeae; Legionella pneumophila; Bordetella pertussis; Helicobacter pylori; Campylobacter jejuni.
Mycoplasma: Mycoplasma pneumoniae; Ureaplasma urealyticum.
Other Organisms: Chlamydia trachomatis; Mycobacterium avium; Mycobacterium leprae.
Anaerobes: Macrolide-susceptible Bacteroides fragilis; Clostridium perfringens; Peptococcus species; Peptostreptococcus species; Propionibacterium acnes.
Clarithromycin has bactericidal activity against several bacterial strains. The organisms include Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Moraxella (Branhamella) catarrhalis, Neisseria gonorrhoeae, H. pylori and Campylobacter spp.
The following breakpoints have been established by the European Committee for Antimicrobial Susceptibility Testing (EUCAST).
Breakpoints (MIC, mg/L):
| Microorganism | Susceptible (≤) | Resistant (>) |
|---|---|---|
| Staphylococcus spp. | 1 mg/L | 2 mg/L |
| Streptococcus A, B, C and G | 0.25 mg/L | 0.5 mg/L |
| Streptococcus pneumonia | 0.25 mg/L | 0.5 mg/L |
| Viridans group streptococcus | IE | IE |
| Haemophilus spp. | 1 mg/L | 32 mg/L |
| Moraxella catarrhalis | 0.25 mg/L | 0.5 mg/L1 |
| Helicobacter pylori | 0.25 mg/L1 | 0.5 mg/L |
1 The breakpoints are based on epidemiological cut-off values (ECOFFs), which distinguish wild-type isolates from those with reduced susceptibility.
“IE” indicates that there is insufficient evidence that the species in question is a good target for therapy with the drug.
H. pylori is associated with acid peptic disease including duodenal ulcer and gastric ulcer in which about 95% and 80% of patients respectively are infected with the agent. H. pylori is also implicated as a major contribution factor in the development of gastric and ulcer recurrence in such patients.
Clarithromycin has been used in small numbers of patients in other treatment regimens. Possible kinetic interactions have not been fully investigated. These regimens include:
Clarithromycin plus tinidazole and omeprazole; clarithromycin plus tetracycline, bismuth subsalicylate and ranitidine; clarithromycin plus ranitidine alone.
Clinical studies using various different H. pylori eradication regimens have shown that eradication of H. pylori prevents ulcer recurrence.
Clarithromycin is rapidly and well absorbed from the gastro-intestinal tract after oral administration of clarithromycin tablets. The microbiologically active metabolite 14-hydroxyclarithromycin is formed by first pass metabolism.
Clarithromycin may be given without regard to meals as food does not affect the extent of bioavailability of clarithromycin tablets. Food does slightly delay the onset of absorption of clarithromycin and formation of the 14-hydroxymetabolite.
The pharmacokinetics of clarithromycin are non linear; however, steady-state is attained within 2 days of dosing. At 250 mg b.i.d. 15-20% of unchanged drug is excreted in the urine. With 500 mg b.i.d. daily dosing urinary excretion is greater (approximately 36%). The 14-hydroxyclarithromycin is the major urinary metabolite and accounts for 10-15% of the dose. Most of the remainder of the dose is eliminated in the faeces, primarily via the bile. 5-10% of the parent drug is recovered from the faeces.
When clarithromycin 500 mg is given three times daily, the clarithromycin plasma concentrations are increased with respect to the 500 mg twice daily dosage.
Clarithromycin provides tissue concentrations that are several times higher than the circulating drug levels. Increased levels have been found in both tonsillar and lung tissue. Clarithromycin is 80% bound to plasma proteins at therapeutic levels.
Clarithromycin also penetrates the gastric mucus. Levels of clarithromycin in gastric mucus and gastric tissue are higher when clarithromycin is co-administered with omeprazole than when clarithromycin is administered alone.
In acute mouse and rat studies, the median lethal dose was greater than the highest feasible dose for administration (5 g/kg).
In repeated dose studies, toxicity was related to dose, duration of treatment and species. Dogs were more sensitive than primates or rats. The major clinical signs at toxic doses included emesis, weakness, reduced food consumption and weight gain, salivation, dehydration and hyperactivity. In all species the liver was the primary target organ at toxic doses. Hepatotoxicity was detectable by early elevations of liver function tests. Discontinuation of the drug generally resulted in a return to or toward normal results. Other tissues less commonly affected included the stomach, thymus and other lymphoid tissues and the kidneys. At near therapeutic doses, conjunctival injection and lacrimation occurred only in dogs. At a massive dose of 400 mg/kg/day, some dogs and monkeys developed corneal opacities and/or oedema.
Studies performed in rats at oral doses up to 500 mg/kg/day (highest dose associated with overt renal toxicity) demonstrated no evidence for clarithromycin-related adverse effects on male fertility. This dose corresponds to a human equivalent dose (HED) of approximately 5 times the maximum recommended human dose (MRHD) on a mg/m² basis for a 60-kg individual.
Fertility and reproduction studies in female rats have shown that a daily dosage of 150 mg/kg/day (highest dose tested) caused no adverse effects on the oestrus cycle, fertility, parturition and number and viability of offspring. Oral teratogenicity studies in rats (Wistar and Sprague-Dawley), rabbits (New Zealand White) and cynomolgous monkeys failed to demonstrate any teratogenicity from clarithromycin at the highest doses tested up to 1.5, 2.4 and 1.5 times the MRHD on a mg/m² basis in the respective species. However, a similar study in Sprague-Dawley rats indicated a low (6%) incidence of cardiovascular abnormalities which appeared to be due to spontaneous expression of genetic changes. Two mouse studies revealed a variable incidence (3-30%) of cleft palate at ~5 times the MRHD on a mg/m² basis for a 60-kg individual. Embryonic loss was seen in monkeys but only at dose levels which were clearly toxic to the mothers.
© All content on this website, including data entry, data processing, decision support tools, "RxReasoner" logo and graphics, is the intellectual property of RxReasoner and is protected by copyright laws. Unauthorized reproduction or distribution of any part of this content without explicit written permission from RxReasoner is strictly prohibited. Any third-party content used on this site is acknowledged and utilized under fair use principles.
