Doxycycline: Formula, Presentation, Indications, Mechanism of Action, Dosage, Warnings and Contraindications

T is a drug with antibiotic properties and belongs to the group of tetracyclines.

Doxycycline can be used to treat multiple bacterial infections; it is the most common antibiotic prescribed by doctors for acne and rosacea.

It is a very effective treatment for inflammatory acne of moderate to severe intensity or for mild inflammatory acne that is not improving with other medicines.

It is also used in the case of sexually transmitted diseases.

Chemical formula

  • C22H24N2O8.


  • Capsules of 50 mg and 100 mg.
  • 5 ml ampoule containing 100 mg of Doxycycline (Hyclate).


Doxycycline is widely used for different infections, such as:

  • Respiratory diseases include bronchitis, acute and chronic pneumonia, pulmonary abscesses, and pleural empyema.
  • Urinary tract infections such as urethritis and pyelonephritis.
  • The ear, nose, and throat infections include otitis, sinusitis, and angina.
  • Intestinal disorders such as salmonellosis, typhoid feverdysentery, and cholera.
  • The diseases of the pelvic organs in men and women as salpingitis, prostatitis, endometritis, and epididymitis.
  • Inflammatory gastrointestinal disorders such as proctitis and peritonitis.
  • Soft-tissue infections and skin infections such as boils, carbuncles, and acne.
  • Sexually transmitted diseases include gonorrhea, chlamydia, primary and secondary Syphilis, and ureaplasmosis.
  • And many infectious diseases such as typhus, leptospirosis, brucellosis, whooping cough, and Q fever, among others.
  • Eye diseases such as trachoma and ulcerative keratitis.
  • La osteomyelitis.
  • Doxycycline is also used to prevent malaria.

Mechanism of action

This bacteriostatic antibiotic belongs to the group of tetracyclines and acts by interfering with bacterial protein synthesis.

It has a broad antibacterial spectrum, including Gram-positive and Gram-negative, aerobic and anaerobic species, spirochetes, mycoplasmas, chlamydia, rickettsiae, and even giant viruses.



The dose and frequency in the administration of Doxycycline are different from other tetracyclines.

There may be an increase in side effects if the recommended doses are exceeded.

The usual dose of administration of Doxycycline is 100-200 mg/day intravenously.


In adults, the usual dose of Doxycycline is 200 mg as the first dose on the first day of treatment, administered in 100 mg every 12 hours or 50 mg every 6 hours, and then continued with a maintenance dose of 100 mg per day.

The recommended maintenance dose is given as a daily dose or as 50 mg every 12 hours.

In the case of more severe infections such as chronic urinary tract infections, 100 mg is recommended every 12 hours.

It should be administered in children over eight years; the recommended dosage scheme for children weighing less than 45.3 kg is 4.41 mg per kg of body weight, administered in two doses on the first day of treatment.

Subsequently, administer 2.2 mg per kg of body weight in the following days as a single daily dose or divided into two doses per day.

Up to 4.41 mg per kg of body weight can be administered in more severe infections.

For children weighing more than 43.5 kg, the recommended dose for adults must be used.

As for the duration of treatment, therapy is usually recommended for 7 to 10 days.

In the case of Syphilis for more than one-year duration, treatment is recommended for four weeks.

During the treatment of malaria:

The recommended doses for adults are 100 mg daily, and a quantity of 2 mg per kg is recommended for children over eight years of age, administered once a day until the adult dose is reached.

It is recommended the administration of the capsules with abundant amounts of fluids. To administer Doxycycline, it is recommended to ingest it with food or milk to reduce the risk of esophageal irritation and ulceration in the stomach.

In case of gastric irritation, Doxycycline can be administered with food.

Side effects

Doxycycline is completely absorbed, so adverse effects in the small intestine, especially diarrhea, are rare.

The following side reactions have been observed in patients receiving tetracyclines:

  • Gastrointestinal reactions: Nausea, anorexia, enterocolitis, vomiting, glossitis, diarrhea, dysphagia, and some inflammatory lesions such as excessive growth of moniliasis in the anogenital region.
  • Skin reactions: The maculopapular and erythematous eruptions. Exfoliative dermatitis has also been reported, but it is of minimal occurrence.
  • Renal toxicity reactions: These have been reported to increase blood urea nitrogen levels, apparently linked to the dose administered.
  • Hypersensitivity reactions: Anaphylactoid purpura, angioneurotic edema, urticaria, anaphylaxis, serum sickness, pericarditis, and exacerbation of systemic lupus erythematosus.
  • Blood reactions: Cases of eosinophilia, hemolytic anemiathrombocytopenia, and neutropenia have been reported using tetracyclines.
  • Other reactions: Inflammation of fontanelles in infants and elevation of intracranial tension in adults.

Hepatotoxicity has rarely been reported. Adverse reactions are caused in cases of oral administration and the parenteral administration of tetracyclines.

Sporadic esophagitis and esophageal ulcerations have been reported in patients receiving treatment in capsules and drug tablets of compounds belonging to the group of tetracyclines. In most cases, this reaction occurs when medications are taken immediately before sleep.

There is no information that they are causing abnormalities in thyroid function.

However, when the medication is administered for a long time, microscopic black or brown colorations are observed in the thyroid gland.

Warnings and contraindications

This drug is contraindicated in people who have known hypersensitivity to tetracyclines.

They should not be administered together with antacids containing aluminum, calcium or magnesium, sodium bicarbonate, and any iron preparation in patients following tetracycline treatment by mouth.

The studies reported that the administration in the recommended doses of Doxycycline does not cause the excessive accumulation of the antibiotic for patients suffering from renal failure.

The use of tetracyclines may increase the incidence of vaginal candidiasis.

Doxycycline is used with great caution in patients with a predisposition to oral candidiasis.

In treating periodontitis in patients with coexisting oral candidiasis, the safety and efficacy of the medication have not been determined.

In case superinfection occurs, appropriate measures should be taken for its treatment.

The category of risk in pregnancy is classified as D, so Doxycycline should not be administered in pregnant women or with the possibility of becoming pregnant, nor should it be administered in children under eight years of age.

This drug can cause fetal toxicity when administered to pregnant women.

However, suppose the potential benefits of its use outweigh the risk that could arise for the fetus and be acceptable under certain conditions. In that case, it must be administered under strict medical supervision.

The use of tetracyclines during the last five months of pregnancy can affect the development of the teeth and cause permanent discoloration in them.

Due to the potential risk that Doxycycline has in infants, a decision must be made about whether treatment or breastfeeding should be discontinued, considering the importance of the drug for the mother.

Doxycycline can cause damage to the nursing baby, such as discoloration and delayed growth of teeth and bones.

An increase in photosensitivity to sunlight and an increase in the chance of getting some infections caused by fungi in the mouth and vagina.

In children under the age of eight, it can affect the development of the teeth and cause permanent discoloration in them.

The use of tetracyclines in children up to 8 years of age can cause tooth damage, a decrease in the average linear skeletal growth, and enamel hypoplasia.

In children under 12 years of age, your pediatrician’s use of this medication should be evaluated and controlled.

The prolonged use of this medicine can cause the appearance of infections caused by microorganisms that are not sensitive to tetracyclines, so it should be administered according to the doctor’s instructions.

It must be used during the time indicated by the doctor, ensuring that the medication is administered at the times and doses recommended.

You should avoid drinking alcohol or drinks with caffeine frequently. At the same time, you are being treated with this medicine because its concomitant intake increases the risks of the adverse effects of Doxycycline.

When driving vehicles, it must be borne in mind that this medication can cause symptoms in some people, such as dizziness, headache, or a decrease in mental abilities to react to any unexpected event.

So it is not recommended to drive a vehicle, operate dangerous machinery or perform any other activity that requires a state of alert.

However, these adverse reactions are infrequent in this type of medication.

If the patient is taking oral contraceptives containing estrogen, you must use other contraception measures to avoid getting pregnant.

Since concomitant use with Doxycycline reduces the effectiveness of contraceptives and increases the risk of pregnancy.

Avoid exposure to the sun or ultraviolet rays since Doxycycline makes the skin more sensitive to sunlight and causes skin rash, itching, redness, and even discoloration of the skin; it should be used to protect factors solar greater than 15.

In case of adverse effects, if, after a few days, these symptoms do not improve or get worse, you should consult the doctor.

Doxycycline should not be administered just before going to sleep. The medication usually can not dissolve correctly due to the patient’s position when lying down and may cause mild irritation in the digestive tract or throat.

If the patient is receiving treatment for any sexually transmitted disease, all sexual contact should be avoided until the treatment has been completed.

It is possible that the couple also needs treatment, so therapy should be performed for both.

It should not be administered in patients with moderate or severe renal insufficiency.


Several investigations have shown that tetracyclines reduce prothrombin activity in plasma, so patients taking anticoagulants may require a reduction in the dose.

It is advisable not to administer the tetracyclines together with penicillin since these can hinder the bactericidal action of penicillin.

The absorption of tetracyclines will decrease with the effect of antacids containing calcium, aluminum, or magnesium and preparations containing iron.

The effect of bismuth subsalicylate also decreases the absorption of tetracyclines.

Drugs such as carbamazepine, barbiturates, and phenytoin shorten the half-life of Doxycycline.

It has also been reported that fatal renal toxicity is caused by the concomitant use of tetracycline and methoxyflurane.

Photosensitivity reactions manifested by an exaggerated sunburn reaction have been observed in some patients undergoing treatment with tetracyclines.

In case of a reaction associated with tetracyclines, the treatment should be suspended immediately after the first evidence of cutaneous erythema.

Some brand names of drug formulations contain sodium metabisulfite, a type of sulfite that can cause allergic-type reactions.

Including the presence of anaphylactic symptoms that endanger the patient’s life or the appearance of less severe asthmatic episodes in certain patients susceptible to this compound.

The overall prevalence of sulfite sensitivity in patients in general, in whom this drug has been administered, and probably low, is unknown.

Sulfite sensitivity is seen more frequently in those who have asthmatic conditions.

In the case of venereal diseases, when the coexistence of infections such as Syphilis or gonorrhea is suspected, it is necessary to perform a previous laboratory examination (in the dark field) before starting treatment.

These tests must be repeated, and the blood serology every month for at least four months.

In long-term therapies, periodic laboratory evaluations are carried out to monitor the organ systems, including hematopoietic, renal, and hepatic.