Roxithromycin

Roxithromycin belongs to the macrolide family. It binds to the 50S subunit of the bacterial ribosome, the machine that makes the bacterium’s proteins. By binding there, it prevents the enzyme peptidyl transferase from lengthening the peptide chain being translated: protein synthesis stops, and the bacterium can no longer multiply.

Its action is described as bacteriostatic, because it blocks the growth of bacteria rather than destroying them outright; at high concentrations, it can become bactericidal. It also reaches bacteria that develop inside cells, such as Legionella pneumophila, whose treatment is helped by its good penetration into the body’s tissues and fluids.

Roxithromycin is used to treat infections caused by bacteria that are sensitive to its action. It is indicated for infections of the upper and lower respiratory tract, in the ear, nose and throat area, in the skin and soft tissues, as well as in certain genital infections.

The choice of antibiotic depends on the germ involved and its sensitivity. The reference pharmacological review confirms its favourable pharmacokinetic properties and its good spread into plasma, tissues and biological fluids, which explains its use in these infections caused by sensitive germs.

Roxithromycin is absorbed very rapidly, and its absorption is better when taken before a meal, on an empty stomach. Its plasma half-life is long for a macrolide, around 12 to 15 hours, with an average of about 14.6 hours in one study. This duration allows a dose to be taken once or twice a day, often 150 mg twice a day.

Taking the doses regularly maintains an effective concentration of the medicine against the bacterium. Treatment continues for the whole prescribed duration, even when symptoms improve before the end: stopping it on your own too soon exposes you to a relapse and encourages resistance. Any change is decided with the doctor or pharmacist.

Roxithromycin is generally well tolerated. In an analysis of 2,917 adults, of whom 2,519 were treated with 150 mg twice a day across 17 studies, adverse effects possibly or probably linked to the treatment were noted in 4.1% of patients, that is 120 out of 2,917, and in 3.1% of elderly subjects. The most frequent are digestive: nausea, upper abdominal pain, diarrhoea and vomiting. These symptoms are partly explained by the action of macrolides on motilin, a hormone that stimulates the movement of the digestive tract.

Less frequent effects exist, such as headaches or dizziness, and others that are rarer: skin rashes, abnormalities in liver tests, altered taste or smell. The incidence of treatment-related liver test abnormalities remained low in the tolerance evaluation in adults. A systematic review of 52 randomised trials, involving more than 10,000 participants, found no deaths linked to the macrolides and tetracyclines studied, with rates of serious effects comparable to placebo and digestive disorders as the most frequent effect.

Macrolides have a tendency to prolong the QT interval and the QTc, a portion of the heart’s electrical cycle. This tendency is most marked for erythromycin and weakest for azithromycin, with roxithromycin sitting within this family. A QT that is too long can, in rare cases, encourage a rhythm disturbance called torsades de pointes.

Several factors increase this risk, including a low blood potassium, a hypokalaemia, a low magnesium, a hypomagnesaemia, and a hypocalcaemia. During rhythm management, potassium levels are kept between 4.5 and 5 mmol/L and magnesium levels are corrected. Keeping potassium and magnesium within normal ranges therefore limits the rhythm risk associated with medicines that prolong the QT.

Roxithromycin has a weaker affinity for cytochrome P450 than erythromycin, so it causes fewer interactions by this route. This ranking places macrolides according to their potential for interaction via CYP3A4: erythromycin is very prone to it, clarithromycin much less so, and azithromycin does not take part in it.

There is, however, a significant interaction with warfarin, an anticoagulant: roxithromycin can increase prothrombin time and INR, with cases of severe bleeding reported. When the two are combined, monitoring of INR is warranted. It can also increase theophylline concentrations, which invites taking this into account during monitoring.