|Systematic (IUPAC) name|
|(4S,4aR,5S,5aR,6R,12aS)-4-(dimethylamino)- 3,5,10,12,12a-pentahydroxy- 6-methyl- 1,11-dioxo- 1,4,4a,5,5a,6,11,12a-octahydrotetracene- 2-carboxamide|
|Licence data||US FDA:|
|Pregnancy cat.||D (US)|
|Legal status||POM (UK) ℞-only (US)|
|Routes||oral, buccal, intravenous therapy, intramuscular injection|
|ATC code||J01 A01|
|Mol. mass||444.43 g/mol|
| (what is this?)
Doxycycline is a member of the tetracycline antibiotics group, and is commonly used to treat a variety of infections. Doxycycline is a semisynthetic tetracycline invented and clinically developed in the early 1960s by Pfizer Inc. and marketed under the brand name Vibramycin. Vibramycin received US Food and Drug Administration approval in 1967,. Other brand names include Monodox, Microdox, Periostat, Vibra-Tabs, Oracea, Doryx, Vibrox, Adoxa, Doxyhexal, Doxylin, Doxoral, Doxy-1 and Atridox (topical doxycycline hyclate for periodontitis).
Medical uses 
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, acne, rosacea, and rickettsial infections.
It is used in prophylaxis against malaria. It should not be used alone for initial treatment of malaria, even when the parasite is doxycycline-sensitive, because the antimalarial effect of doxycycline is delayed. This delay is related to its mechanism of action, which is to specifically impair the progeny of the apicoplast genes, resulting in their abnormal cell division.
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) and Leptospirosis. It is also effective against Yersinia pestis (the infectious agent of bubonic plague), and is prescribed for the treatment of Lyme disease, ehrlichiosis and Rocky Mountain spotted fever. In fact, because doxycycline is one of the few medications shown to be effective in treating Rocky Mountain spotted fever (with the next-best alternative being chloramphenicol), doxycycline is indicated even for use in children for this illness. Otherwise, it is not indicated for use in children under the age of eight years.
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
- Acne and other inflammatory skin diseases, such as hidradenitis suppurativa
- Shigella species infections
- Acinetobacter species (formerly Mima species and Herellea species) infections
- Respiratory tract infections caused by Haemophilus influenzae
- Respiratory tract and urinary tract infections
- Upper respiratory infections caused by Streptococcus pneumoniae (formerly Diplococcus pneumoniae)
- Methicillin-resistant Staphylococcus aureus (MRSA) infections
- As combined therapy when treating a patient for Chlamydia trachomatis, because up to 50% of patients will be infected with the beta lactam-resistant strain of this bacterium.
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. Field trials in 2005 showed an eight-week course of doxycycline almost completely eliminates the release of microfilariae.
Adverse effects 
Cautions and side effects are similar to those of other members of the tetracycline antibiotic group.
An erythematous rash in sun-exposed parts of the body has been reported to occur in 7.3–21.2% of persons taking doxycycline for malaria prophylaxis. One study examined the tolerability of various malaria prophylactic regimens and found doxycycline did not cause a significantly higher percentage of all skin events (photosensitivity not specified) when compared with other antimalarials. The rash resolves upon discontinuation of the drug.
Unlike some other members of the tetracycline group, it may be used in those with renal impairment.
The combination of doxycycline with dairy, antacids, calcium supplements, iron products, and laxatives containing magnesium is not inherently dangerous, but any of these foods and supplements may decrease doxycycline's effectiveness.[verification needed]
Previously, doxycycline was believed to impair the effectiveness of many types of hormonal contraception due to CYP450 induction. Recent research has shown no significant loss of effectiveness in oral contraceptives while using most tetracycline antibiotics (including doxycycline), although many physicians still recommend the use of barrier contraception for people taking the drug to prevent unwanted pregnancy.
Doxycycline–metal ion complexes are unstable at acid pH, therefore more doxycycline enters the duodenum for absorption compared with the earlier compounds. In addition, food has less effect on absorption than on absorption of earlier drugs with doxycycline serum concentrations being reduced by ∼20% by test meals compared with 50% for tetracycline.
Physical and chemical properties 
Expired tetracyclines or tetracyclines allowed to stand at a pH less than 2 are reported to be nephrotoxic due to the formation of a degradation product, anhydro-4-epitetracycline causing Fanconi syndrome. In the case of doxycycline, the absence of a hydroxyl group in C-6 prevents the formation of the nephrotoxic compound. Nevertheless, tetracyclines and doxycycline itself have to be taken with precaution in patients with kidney injury, as they can worsen azotemia due to catabolic effects.
Experimental applications 
At subantimicrobial doses, doxycycline is an inhibitor of matrix metalloproteases, and has been used in various experimental systems for this purpose, such as for recalcitrant recurrent corneal erosions. Doxycycline has been demonstrated to reduce the in vitro growth of human breast and prostate cancer cells, possibly through G1 phase cell cycle arrest. Doxycycline and other tetracyclines are also highly osteotropic, and in animal models of breast cancer bone metastases, doxycycline treatments have reduced the growth of breast cancer tumours in the bone. Doxycycline has been used successfully in the treatment of one patient with lymphangioleiomyomatosis, an otherwise progressive and fatal disease. It has also been shown to attenuate cardiac hypertrophy (in mice), a deadly consequence of prolonged hypertension. In chronic obstructive pulmonary disease, doxycycline has been shown to improve lung functions in patients with stable symptoms. Doxycycline is also used in "Tet-on" and "Tet-off" tetracycline-controlled transcriptional activation to regulate transgene expression in organisms and cell cultures.
Other experimental applications include treating:
- Vancomycin-resistant enterococcus
- Infected animal bite wounds (Pasteurella multocida, Pasteurella pneumotropica)
- Rheumatoid arthritis instead of minocycline (both of which have demonstrated modest efficacy for this disease)
- Chronic inflammatory lung diseases (panbronchiolitis, asthma, cystic fibrosis, bronchitis) Both doxycycline and minocycline have shown effectiveness in asthma due to immune suppressing effects.
- Pancreatic cancer
- Prevention of aortic aneurysm in people with Marfan syndrome and vascular Ehlers-Danlos syndrome
- Multiple sclerosis
- Meibomian gland dysfunction
- Treatment of filariasis and onchocerciasis due to filariae and onchocercae (in general, harbouring endosymbiotic Wolbachia bacteria, doxycycline kills the bacteria, and (by removal of the endosymbiotes) the nematodes)
- New daily persistent headache
- Idiopathic pulmonary fibrosis
- Abdominal Aortic Aneurysm
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- The Anti-Wolbachia Consortium uses drugs like doxycycline to treat parasitic diseases