In addition to the general indications for all members of the tetracycline antibiotics group, doxycycline is frequently used to treat Lyme disease, chronic prostatitis, sinusitis, pelvic inflammatory disease [1,2], acne, rosacea [3,4], and rickettsial infections [5].

Doxycycline is used in prophylaxis against malaria in combination with other agents such as quinine [6]. The antimalarial effect of doxycycline is delayed because of its mechanism of action, which is to specifically impair the progeny of the apicoplast genes, resulting in their abnormal cell division [7].

Branhamella catarrhalis, Brucella melitensis, Chlamydia pneumoniae, and Mycoplasma pneumoniae are generally susceptible to doxycycline, while some Haemophilus spp., Mycoplasma hominis, and Pseudomonas aeruginosa have developed resistance to varying degrees.

It is used in the treatment and prophylaxis of anthrax (caused by Bacillus anthracis). It is also effective against Yersinia pestis (the infectious agent of bubonic plague), and is prescribed for the treatment of Lyme disease [8-11], ehrlichiosis[12,13] and Rocky Mountain spotted fever. Because doxycycline is one of the few medications shown to be effective in treating Rocky Mountain spotted fever, doxycycline is indicated for use in children for this illness.

When bacteriologic testing indicates appropriate susceptibility to the drug, doxycycline may be used to treat and prevent:
Escherichia coli infections
Chlamydia trachomatis infections
Enterobacter aerogenes (formerly Aerobacter aerogenes) infections
Lyme disease (Lyme borreliosis complex) (caused by B. burgdorferi)
Rocky mountain spotted fever
Folliculitis
Acne and other inflammatory skin diseases, such as hidradenitis suppurativa
Shigella spp. infections
Acinetobacter spp.  infections
Respiratory tract infections caused by Haemophilus influenzae
Respiratory tract and urinary tract infections
Upper respiratory infections caused by Streptococcus pneumoniae
Methicillin-resistant Staphylococcus aureus (MRSA) infections

Doxycycline kills the symbiotic Wolbachia bacteria in the reproductive tracts of parasitic filarial nematodes, making the nematodes sterile, and thus reducing transmission of diseases such as onchocerciasis and elephantiasis [14]. Field trials in 2005 showed an eight-week course of doxycycline almost completely eliminates the release of microfilariae [15].

Dosage and Administration

Adults: The usual dose of oral Doxycycline is 200 mg on the first day of treatment (administered 100 mg every 12 hours or 50 mg every 6 hours) followed by a maintenance dose of 100 mg/day. The maintenance dose may be administered as a single dose or as 50 mg every 12 hours. In the management of more severe infections (particularly chronic infections of the urinary tract), 100 mg every 12 hours is recommended.

Uncomplicated gonococcal infections in adults (except anorectal infections in men): 100 mg, by mouth, twice a day for 7 days. As an alternate single visit dose, administer 300 mg stat followed in one hour by a second 300 mg dose.

Acute epididymo-orchitis caused by N. gonorrhoeae: 100 mg, by mouth, twice a day for at least 10 days.

Primary and secondary syphilis: 300 mg a day in divided doses for at least 10 days.

Uncomplicated urethral, endocervical, or rectal infection in adults caused by Chlamydia trachomatis: 100 mg, by mouth, twice a day for at least 7 days.

Nongonococcal urethritis caused by C. trachomatis and U. urealyticum: 100 mg, by mouth, twice a day for at least 7 days.

Acute epididymo-orchitis caused by C. trachomatis: 100 mg, by mouth, twice a day for at least 10 days.

Inhalational anthrax (post-exposure):

ADULTS: 100 mg of Doxycycline, by mouth, twice a day for 60 days.

CHILDREN: weighing less than 45 kgs: 2.2 mg/kg of body weight, by mouth, twice a day for 60 days. Children weighing 45kg or more should receive the adult dose.