Clarithromycin

Clarithromycin belongs to the macrolide family. It binds selectively to the 50S ribosomal subunit of susceptible bacteria, the part of the cellular machinery that assembles proteins. By occupying this site, it prevents the translocation of activated amino acids and blocks bacterial protein synthesis. Deprived of its proteins, the bacterium can no longer multiply normally, which gives the body’s defenses time to regain the upper hand.

Its elimination half-life depends on the dose administered. It is roughly 3 to 4 hours at a dose of 250 mg every 12 hours, and lengthens to 5 to 7 hours at a dose of 500 mg every 8 to 12 hours. This non-linear pharmacokinetics explains why the doses are spread throughout the day, in order to maintain an active concentration against the bacteria.

Clarithromycin treats bacterial infections of the upper and lower respiratory tract, for example pharyngitis, sinusitis, bronchitis or pneumonia. It is also used for certain infections of the skin and soft tissues. The physician chooses it when a bacterium susceptible to this macrolide is responsible.

It is also used, in combination, in the eradication of Helicobacter pylori during peptic ulcer disease. In this indication, it does not act alone: it is part of a regimen that combines several medicines to eliminate the bacterium from the stomach. The choice of antibiotic always depends on the targeted infection and on the patient’s profile.

The clarithromycin tablet is taken with or without food: food does not change the extent of its bioavailability. You can therefore take it at whatever time suits you, which helps you not to forget a dose. Regularity matters more than the meal: respecting the interval between doses maintains an effective concentration throughout the day.

An antibiotic is taken until the planned end, even if symptoms improve beforehand. Stopping too early leaves bacteria alive and promotes both relapse and resistance. If discomfort appears or a question arises, talk to your physician or pharmacist rather than stopping the treatment on your own.

The most frequent adverse effects mainly involve digestion. In the clinical trials of the tablet in adults, diarrhea (3%), nausea (3%), an abnormal taste or dysgeusia (3%), dyspepsia (2%), abdominal pain or discomfort (2%) and headache (2%) are observed. These disturbances are most often temporary and disappear when the treatment is stopped.

The European summary of product characteristics classes diarrhea, vomiting, dyspepsia, nausea and abdominal pain among the very common effects, that is at least one patient in ten. Dysgeusia, headache and insomnia appear as common, meaning at least one case in a hundred and fewer than one in ten. A metallic taste in the mouth is thus a well-known nuisance of this macrolide.

Clarithromycin has been associated with a prolongation of the QT interval, a feature of the electrocardiogram, and with rare cases of arrhythmia. Cases of torsades de pointes, a serious rhythm disorder, have been reported after marketing. This cardiac risk remains rare, but it guides the precautions surrounding the treatment.

For this reason, clarithromycin must not be administered in the presence of an electrolyte disturbance, that is hypokalemia or hypomagnesemia. A lack of potassium or magnesium in the blood indeed increases the risk of QT prolongation. A correct status of these two minerals therefore contributes to the cardiac safety of the treatment, which places food in the foreground.

Clarithromycin inhibits the liver enzyme CYP3A, which breaks down many medicines. A medicine metabolized mainly by this route can see its concentration rise, which increases or prolongs its effects, whether desired or unwanted. Its combination with lovastatin or simvastatin is contraindicated, because of the risk of myopathy and rhabdomyolysis. The combination with colchicine is also contraindicated: life-threatening, sometimes fatal, interactions have been reported.

Other combinations call for close monitoring. With warfarin, clarithromycin exposes to a risk of serious hemorrhage and to a rise in the INR and prothrombin time, which requires a check of coagulation. With oral antidiabetics or insulin, it can cause significant hypoglycemia, hence blood glucose monitoring. Always tell the physician about all the medicines you take before starting the treatment.