You are here: Urology Textbook > Drugs in Urology > Doxycycline

Doxycycline: Mechanism of Action, Side Effects and Dosage

Tetracyclines are broad-spectrum antibiotics with a similar spectrum of activity. Modern representatives include doxycycline, which is most commonly used in urology, and minocycline.

Mechanism of Action:

Bacteriostatic by inhibiting bacterial protein biosynthesis: Doxycycline binds to the 30S subunit of the ribosomes and prevents translation.

Antibiotic Spectrum of Doxycycline:

Against streptococci, pneumococci, gonococci (increasing resistance), meningococci, Gram-negative enterobacteria, mycoplasma (increasing resistance of M. genitalium), chlamydia, and Treponema pallidum.

Often resistant are staphylococci, enterococci, Pseudomonas, E. coli Proteus, Serratia, Klebsiella, and anaerobes.

Urological Indications for Doxycycline:

Non-gonococcal urethritis, chlamydial infections, epididymitis or prostatitis with suspected sexual transmission, treatment of syphilis (in case of penicillin allergy), lymphogranuloma venereum, granuloma inguinale, doxycycline post-exposure prophylaxis (Doxy-PEP) against STIs.

Pharmacokinetics of Doxycycline:

• With good oral absorption, the bioavailability of doxycycline exceeds 75%. Absorption is impaired by multivalent metal ions (calcium, magnesium, iron, or aluminum), so tetracyclines should not be taken with dairy products, antacids, or dietary supplements (2 hours before and 4 hours after taking the medication).
• Half-life 15 hours. High protein binding. Low hepatic metabolism. 50% renal excretion and the remainder is excreted biliary (via the feces).

Side Effects of Doxycycline

• GI tract: Vomiting, diarrhea, oral thrush, esophageal ulcers (when taken without drinking plenty of fluids or immediately before bedtime), pseudomembranous enterocolitis. 
• Teeth: Enamel discoloration (yellow), enamel defects, and caries when administered to infants.
• Skin: Photosensitivity, nail discoloration.
• Immune system: Allergic reactions; there is cross-allergy between tetracyclines.
• Other: Dizziness. Rare side effects are increased intracranial pressure, kidney damage, or liver damage.

Drug Interactions:

Reduced bioavailability when doxycycline is administered concomitantly with multivalent metal ions (calcium, magnesium, iron, or aluminum). Increased effect of phenprocoumon or warfarin, increased effective levels of digoxin, sulfonylureas, and cyclosporine. Reduced effect of oral contraceptives.

Contraindications:

Children under 8 years of age, pregnancy, breastfeeding. Severe liver dysfunction. Myasthenia gravis (only for intravenous administration of doxycycline).

Dosage of Doxycycline

• 200 mg Doxycycline 1-0-0 on the first day, then 100 mg 1-0-0 p.o. or i.v. For genitourinary infections, the dosage is usually 100 mg 1-0-1.
• Children over 8 years of age receive 4 mg/kgBW on the first day and 2 mg/kgBW from the second day of treatment onwards.
• Doxycycline post-exposure prophylaxis (Doxy-PEP) against STIs: A single dose of 200 mg doxycycline within three days of unprotected sexual intercourse reduces the risk of chlamydia infection (by 70–80%), syphilis (by 70–80%), and gonorrhea (by 50%) in high-risk patients (Luetkemeyer et al., 2023).

References

Luetkemeyer AF, Donnell D, Dombrowski JC, Cohen S, Grabow C, Brown CE, Malinski C, Perkins R, Nasser M, Lopez C, Vittinghoff E, Buchbinder SP, Scott H, Charlebois ED, Havlir DV, Soge OO, Celum C; DoxyPEP Study Team. Postexposure Doxycycline to Prevent Bacterial Sexually Transmitted Infections. N Engl J Med. 2023 Apr 6;388(14):1296-1306. doi: 10.1056/NEJMoa2211934.

Simon und Stille 1997 SIMON, C. ; STILLE, W.: Antibiotika-Therapie in Klinik und Praxis.
9. Auflage.
Stuttgart New York : Schattauer, 1997

  Deutsche Version: Pharmakologie und Nebenwirkungen von Doxycyclin

Urology-Textbook.com – Choose the Ad-Free, Professional Resource

This website is designed for physicians and medical professionals. It presents diseases of the genital organs through detailed text and images. Some content may not be suitable for children or sensitive readers. Many illustrations are available exclusively to Steady members. Are you a physician and interested in supporting this project? Join Steady to unlock full access to all images and enjoy an ad-free experience. Try it free for 7 days—no obligation.

Urology-Textbook.com – Choose the Ad-Free, Professional Resource

This website is designed for physicians and medical professionals. It presents diseases of the genital organs through detailed text and images. Some content may not be suitable for children or sensitive readers. Many illustrations are available exclusively to Steady members. Are you a physician and interested in supporting this project? Join Steady to unlock full access to all images and enjoy an ad-free experience. Try it free for 7 days—no obligation.