Doxycycline is a highly active broad-spectrum antibiotic of tetracycline group. It is effective against a wide range of Gram-positive and Gram-negative bacteria, spirochete, mycoplasma, rickettsia and mycobacteria. Doxycycline is used as an alternate to penicillin in the treatment of gonorrhoea and syphilis. Doxycycline has its main mechanism of action on protein synthesis. Inside the bacterial cell, it inhibits protein synthesis.

Pharmacology

Doxycycline Hydrochloride is a semisynthetic tetracycline antibiotic with broad spectrum activity. It is primarily a bacteriostatic antibiotic. It has a similar spectrum of activity to other tetracyclines but in particular is more active against Staphylococcus aureus and Nocardia. The drug is often active against penicillin-resistant strains of Staphylococcus aureus and against strains of those organisms that are resistant to other Tetracyclines. Certain Gram-negative strains of E. coli, Proteus mirabilis and Klebsiella, which are often resistant to Tetracycline, may be sensitive to Doxycycline. In addition, 70-90% of the various anaerobes are sensitive to Doxycycline and Bacteroides fragilis is more likely to be sensitive to Doxycycline than to other tetracyclines.

Doxycycline is active against most strains of Haemophilus influenzaeand is particularly useful for infections with H. ducreyi, Actinomyces, Brucella and Vibrio cholerae. It is also active against Nocardia, Chlamydia, Mycoplasma and a wide range of Rickettsiae. Doxycycline is active against spirochetes such as Borellia recurrentis, Treponema pallidum and Treponema pertenue. It is also active against Plasmodium falciparum.

Doxycycline Hydrochloride is indicated in the following infections caused by susceptible microorganisms:

• Respiratory tract infections: Pneumonia, influenza, sinusitis, bronchitis, tonsillitis, tracheitis.
• Gastrointestinal tract infections: Cholera, traveler's diarrhea, shigella dysentery, acute intestinal amebiasis.
• Chlamydial infections: Lympho-granuloma venereum, psittacosis, trachoma.
• Sexually transmitted diseases: Non gonococcal urethritis, acute pelvic inflammatory disease, uncomplicated urethral and endocervical or rectal infections, gonorrhoea, syphilis, pyelonephritis, cystitis.
• Other infections: Impetigo, furunculosis, inclusion conjunctivitis, brucellosis, tularemia, cellulitis, acne and Q-fever.

Usual dose: 200 mg on first day, then 100 mg daily for 7-10 days.

Severe infections (including refractory urinary tract infections): 200 mg daily for 10 days.

Acne: 100 mg daily.

Uncomplicated genital chlamydia, non-gonococcal urethritis: 100 mg twice daily for 7-21 days (14-21 days in pelvic inflammatory disease).

Administration

Capsules should be swallowed whole with plenty of fluid during meals while sitting or standing.

Doxycycline is contraindicated to the patients who have shown hypersensitivity to any of the tetracyclines. Doxycycline is contraindicated to the children under 8 years of age. It is also contraindicated to pregnant women and to the lactating mothers.

Nausea, vomiting, diarrhoea, skin rashes, hemolytic anaemia, eosinophilia may be reported.

The use of drugs of the tetracycline class during tooth development (last half of pregnancy, infancy and childhood to the age of 8 years) may cause permanent discoloration of teeth. Tetracyclines drugs, therefore should not be used in this age group.

Pregnancy & Lactation

Doxycycline should be avoided in pregnant women, because of the risk of both staining and effect on bone growth in the foetus. Doxycyclines enter breast milk, and mothers taking these drugs should not breastfeed their child.