Doxycycline, an antibiotic for the papulo-pustular form of rosacea.

Stage III of rosacea is characterised by the emergence of red bumps (papules) or pus-filled bumps (pustules), or even both (papulopustules), relating to the inflammatory form. However, doxycycline is an antibiotic from the tetracycline family. It helps to alleviate and limit the development of pustules and papules associated with this stage of rosacea, but not the redness or telangiectasias.

Doxycycline is a second-generation tetracycline, exhibiting superior pharmacokinetic properties and less toxicity than first-generation tetracyclines (chlortetracycline). This antibiotic also helps to improve the quality of life of those affected. Indeed, facial imperfections often cause anxiety. Seeing them disappear helps to regain self-confidence and reduces stress.

Doxycycline exhibits an anti-inflammatory effect. This antibiotic reduces the levels of pro-inflammatory cytokines, such as IL-1β, IL-6, and TNF-α, through its action on the pro-inflammatory signalling pathway NF-KB, which decreases inflammation and acne-like lesions associated with rosacea.

Doxycycline is taken orally. Generally, for patients over 15 years old, the dosage of doxycycline in the context of a treatment for rosacea is 100 mg once a day. Depending on the patient's weight (kg), the recommendations tend towards 4 mg/kg once a day. It is advised to not exceed three months of treatment.

It is recommended to administer the medication at least one hour before bedtime during a meal, with a sufficient amount of water. It should not be taken while lying down. The intake of doxycycline should be done after consulting a doctor. It is also necessary to adhere to the prescribed dosage, as well as the duration of the treatment depending on your case.

It is also recommended to avoid direct exposure to the sun or UV radiation, due to the risks of photosensitisation posed by doxycycline. Studies suggest that the energy from UV rays would trigger the generation of an excited singlet oxygen by doxycycline, which induces the oxidation of lipids and proteins in cell membranes, resulting in skin damage.

Several side effects have been linked to the intake of doxycycline, due to its significant penetration into various organs. Here are some potential effects.

• Dermatological effects: Maculopapular rash, photosensitisation, skin hyperpigmentation, pruritus, urticaria;

• Haematological Effects: Haemolytic Anaemia;

• Hepatological Effects: Liver failure, hepatitis (due to its accumulation in the liver during its excretion);

• Immuno-allergic effects: Anaphylactic shock, Quincke's oedema;

• Metabolic effects: Anorexia, dysphagia;

• Digestive Effects: Vomiting, gastric ulcer, nausea, abdominal pain, diarrhoea, gastritis; These effects may be due to the (low) penetration of doxycycline into the small intestine in its free drug form, which can influence digestion.

• Nervous Effects: Headache, intracranial hypertension; particularly due to the penetration of the drug into the cerebrospinal fluid.

• Cardiovascular effects: Tachycardia, pericarditis,

• ENT Effects: Tinnitus, glossitis.

The treatment must be discontinued in the event of a severe skin reaction. If you experience one or more of these effects after taking the medication, or if you have any doubts, consult your doctor.

Doxycycline is contraindicated in children under eight years old (due to tooth discolouration, enamel dysplasia and potential bone deformities related to the accumulation of doxycycline on the bones and teeth, by forming a calcium complex), in breastfeeding women (due to the presence of doxycycline in breast milk, which can lead to abnormalities in the child's tooth development) and pregnant women during the last six months of pregnancy (due to the risk of discolouration and malformation of the foetus's teeth), and in people hypersensitive to cyclines. Its use is also prohibited for people taking retinoids and other cyclines.

As a precaution, it is advisable to avoid its use for pregnant women during the first three months of pregnancy, for individuals suffering from liver disease, Lyme disease, severe myasthenia, gastroesophageal reflux and spirochaetosis, for subjects who have used expired medication and for individuals currently undergoing hepatotoxic treatment, due to the previously mentioned potential effects of doxycycline on the liver.

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• Doxycycline SANDOZ. VIDAL (2022).