Doxycycline

Doxycycline is a broad-spectrum antibiotic belonging to the tetracycline class. It is used to treat a variety of infections, including respiratory infections, urinary tract infections, skin infections, and sexually transmitted diseases such as chlamydia and gonorrhea. Doxycycline is also used to prevent and treat malaria, and to prevent infections from tick bites.

Doxycycline works by inhibiting protein synthesis in microbial cells, which prevents them from growing and reproducing. This antibiotic is taken orally and is known for its effectiveness and ability to act on a wide range of bacterial organisms.

However, like any antibiotic, doxycycline should be taken strictly as prescribed by your doctor to avoid the development of antibiotic resistance in bacteria and to minimize the risk of side effects.

Indications Doxycycline

1. Respiratory Infections: Treatment of bronchitis, pneumonia and other respiratory tract infections.
2. Urinary Tract Infections: Treatment of cystitis, urethritis and other urinary tract infections.
3. Skin and Soft Tissue Infections: Treatment of acne, rosacea, impetigo and other skin infections.
4. Sexually Transmitted Infections: Treatment for Chlamydia, Gonorrhea, and Syphilis.
5. Gastrointestinal infections: Treating some forms of diarrhea, including those caused by bacteria.
6. Malaria: Prevention and treatment of malaria in combination with other drugs.
7. Infection Prevention: Preventing infections from animal or tick bites.
8. Lyme Disease: Treatment for Early Stages of Lyme Disease.
9. Tropical infections: Treatment of tropical infections such as typhoid, brucellosis and others.

Release form

1. Capsules: One of the most common forms, usually containing 100 mg of the active ingredient. Capsules are swallowed whole with water.
2. Tablets: Also a commonly used form, which may be preferred by those who have difficulty taking capsules.
3. Soluble tablets: These tablets are dissolved in water before use, which may be convenient for patients with difficulty swallowing solid dosage forms.
4. Injectable solution: Doxycycline is also available as an injectable solution, which can be used in clinical settings, especially for severe infections.
5. Oral suspension: This form is suitable for children and adults who have difficulty taking tablets or capsules.

Pharmacodynamics

1. Inhibition of bacterial protein synthesis: Doxycycline binds to bacterial ribosomes and inhibits the functioning of the ribosomal system, which leads to disruption of protein synthesis and inhibition of bacterial growth and reproduction.
2. Bacteriostatic action: This means that doxycycline stops the growth and reproduction of bacteria, but does not destroy them completely. The body has time to fight the infection.
3. Effect on intracellular parasites: Doxycycline is effective against intracellular bacteria such as Chlamydia and Mycoplasma due to its ability to penetrate and accumulate in cells.
4. Anti-inflammatory action: In addition to its antibacterial action, doxycycline has some anti-inflammatory effect, which may be useful in the treatment of infections accompanied by inflammation.
5. Long half-life: Doxycycline has a long half-life, allowing effective drug concentrations to be achieved in the body even with a single dose per day.

Doxycycline has activity against a broad spectrum of bacteria, including many gram-positive and gram-negative organisms:

• Staphylococci: Including Staphylococcus aureus, including methicillin-resistant strains (MRSA).
• Streptococci: Including Streptococcus pneumoniae and Streptococcus pyogenes (group A beta-hemolytic streptococci).
• Enterococcus faecalis: However, some strains of Enterococcus faecalis may be resistant to doxycycline.
• Neisseria gonorrhoeae: However, in recent years, resistance has emerged in some strains.
• Haemophilus influenzae: Including beta-lactamase-positive strains.
• Moraxella catarrhalis: Doxycycline may be effective against some strains.
• Mycoplasmas and Chlamydia: These intracellular bacteria are usually sensitive to doxycycline.
• Rickettsia, Borrelia, and others: Doxycycline is also used to treat rickettsial diseases, borreliosis (including Lyme disease), and other infections caused by anaerobic organisms.

Pharmacokinetics

1. Absorption: Doxycycline is usually administered orally as tablets or capsules. After administration, the drug is rapidly and almost completely absorbed from the gastrointestinal tract, although its absorption may be reduced by concomitant ingestion of food, especially food rich in calcium.
2. Distribution: Doxycycline is widely distributed in tissues and organs of the body, including the skin, lungs, liver, kidneys, spleen, bones, and others. It also crosses the placental barrier and is excreted in breast milk.
3. Metabolism: Doxycycline is metabolized to a small extent in the liver. It is mainly excreted unchanged from the body through the kidneys and to a lesser extent through the intestines.
4. Elimination: The plasma half-life of doxycycline is approximately 12-25 hours, allowing it to be administered as a single or once daily dose for many infectious diseases.
5. Protein binding: Doxycycline binds to plasma proteins to a small extent, approximately 80-90%.

Dosing and administration

General recommendations:

1. Adults and children over 12 years old:

   • For common infections, the usual starting dose is 200 mg on the first day of treatment (divided into two doses of 100 mg every 12 hours), followed by 100 mg daily for the duration of treatment. In some cases, the dose may remain 200 mg daily, depending on the doctor's advice.
   • For more severe infections, the dose may need to be increased to 200 mg daily throughout the course of treatment.

2. Children under 12 years:

   • Doxycycline is generally not recommended for use in children under 12 years of age due to the potential for adverse effects on developing teeth and bones.

Specific conditions:

• Malaria prophylaxis: Doxycycline is used at a dose of 100 mg per day, starting 1-2 days before entering a malarious region, throughout the stay and continuing for 4 weeks after departure.
• Acne Treatment: The usual dose is 100 mg per day, the course of treatment may vary in duration depending on the doctor's recommendations.
• Atypical infections such as chlamydia or mycoplasma: Longer treatment with doxycycline 100 mg twice daily may be required.

Tips for taking:

• Doxycycline should be taken with plenty of water to avoid irritation of the esophagus.
• It is best to take the medication with or immediately after food to reduce stomach irritation, but avoid taking it with dairy products as calcium may interact with doxycycline, reducing its effectiveness.
• Do not take doxycycline immediately before bed.

Use Doxycycline during pregnancy

Use of doxycycline during pregnancy has traditionally been discouraged due to potential developmental risks associated with other tetracyclines, such as impaired bone formation and tooth staining. However, recent studies are beginning to reconsider this position:

1. A 2016 review article highlighted that doxycycline has significant bioavailability and a broad therapeutic spectrum, and its benefits may outweigh potential risks, particularly in the treatment of diseases such as typhus and murine typhus, which can seriously affect pregnancy outcomes in Southeast Asia. This study did not find a direct association between doxycycline use and teratogenic effects or tooth staining in children, which distinguishes it from other tetracyclines (Cross et al., 2016).
2. Another study conducted in 2022 used the FDA adverse event database to describe cases of doxycycline use during pregnancy. The results show limited data on the safety of doxycycline for rickettsial infections during pregnancy, but support the need for more research to more accurately assess its safety (Kaundinnyayana & Kamath, 2022).

Thus, although doxycycline has traditionally been considered contraindicated during pregnancy due to potential risks to the fetus, new data suggest that its use may be justified in certain clinical situations where the benefits outweigh the potential risks. Always consult your physician before starting doxycycline treatment during pregnancy.

Contraindications

1. Allergy to doxycycline or other tetracyclines. Reactions may include skin rash, itching, angioedema, and, in rare cases, anaphylactic shock.
2. Pregnancy, especially during the second and third trimesters. Doxycycline may affect the development of fetal bones and teeth, which may result in permanent yellow-gray or brown discoloration of the teeth and slow bone growth.
3. Breastfeeding period. Doxycycline can pass into breast milk and have a negative effect on the growth and development of teeth and bones in infants.
4. Children under 8 years of age. As with pregnancy, use of doxycycline in children may cause permanent staining of teeth and problems with bone development.

Also, doxycycline should be used with extreme caution in the presence of conditions such as:

• Liver failure. Liver dysfunction may affect the metabolism of doxycycline, requiring dosage adjustment.
• Mycoses (fungal infections). Doxycycline can aggravate these conditions by suppressing normal microflora.

Side effects Doxycycline

1. Gastrointestinal disorders: Nausea, vomiting, diarrhea, and heartburn are common side effects. These symptoms may be reduced by taking the medication with food.
2. Photosensitivity: Doxycycline may increase the skin's sensitivity to sunlight, resulting in mild sunburn with even brief exposure to the sun.
3. Fungal infections: Like other antibiotics, doxycycline can disrupt the body's normal microflora, promoting the development of candidiasis (thrush), especially in women.
4. Changes in tooth color: Long-term use of doxycycline may cause tooth staining, especially in children.
5. Allergic reactions: Skin rashes, itching, Quincke's edema (swelling of the deep layers of the skin, sometimes accompanied by difficulty breathing) and other serious allergic reactions are possible.
6. Increased intracranial pressure: This is a less common but serious side effect that can cause headache, visual disturbances, and even optic nerve impingement.
7. Liver Effects: In rare cases, doxycycline may cause liver enzymes to increase, indicating liver stress or damage.

Overdose

1. Gastrointestinal disorders: Higher doses of doxycycline may increase gastrointestinal side effects such as nausea, vomiting, diarrhea, and abdominal discomfort.
2. Hepatotoxicity: Liver failure may develop, especially in the presence of pre-existing liver problems.
3. Photosensitivity: Increased sensitivity to sunlight may result in severe sunburn with prolonged skin exposure.
4. Effects on the kidneys: Overdose may have negative effects on kidney function, especially in people with existing kidney problems.
5. Hypertoxic effects: Serious side effects such as intracerebral hypertensive crises or cardiac arrhythmias may develop.
6. Dysbacteriosis: Overdose can disrupt the intestinal microflora, causing dysbacteriosis and increasing the risk of developing intestinal infections.

Interactions with other drugs

1. Antacids, calcium, magnesium, iron, or aluminum-containing medications: These medications may reduce the absorption of doxycycline from the gastrointestinal tract. Therefore, they should be taken at least 2 hours before or after taking doxycycline.
2. Medicines containing vitamins, minerals or other trace elements: Similar to antacids, medicines containing these elements may interfere with the absorption of doxycycline.
3. Medicines that affect blood formation (anticoagulants): Doxycycline may enhance the effect of anticoagulants, which may lead to an increased risk of bleeding. In such cases, the dose of the anticoagulant may need to be adjusted.
4. Photosensitizing drugs: Doxycycline may increase the photosensitivity of the skin when used with drugs such as retinoids, tetracyclines, etc. This may lead to an increased risk of sunburn and skin reactions.
5. Drugs that affect the liver: Doxycycline may increase the hepatotoxicity of some drugs that affect the liver. Therefore, caution should be exercised when co-administered with such drugs.
6. CNS (central nervous system) drugs: Doxycycline may enhance the sedative effects of other CNS drugs such as benzodiazepines, sleeping pills, or alcohol.