Doxycycline: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on Jan 3, 2024.

1. How it works

• Doxycycline is an antibiotic that may be used to treat a wide range of infections caused by susceptible gram-negative, gram-positive, anaerobic, and other bacteria.
• Doxycycline is derived from oxytetracycline which was first manufactured in the 1950s and works by inhibiting bacterial protein synthesis by binding to a ribosomal subunit, preventing amino acids from being linked together. Without proteins, bacteria are unable to function. Doxycycline is bacteriostatic which means it stops bacteria from reproducing but doesn't necessarily kill them.
• Doxycycline belongs to the group of medicines known as tetracycline antibiotics.

2. Upsides

• Active against a wide range of bacteria including some gram-negative and positive bacteria, anaerobes, and some parasites (such as Balantidium coli and Entamoeba species).
• May be used in the treatment of various infections such as those occurring in the respiratory tract, genitourinary area, sinuses, and on the skin; some examples include:

• Tick-borne infections caused by the Rickettsiae group of bacteria, such as Rocky Mountain Spotted fever and typhus fever
• Respiratory tract infections such as those caused by Haemophilus influenzae, Streptococcus pneumoniae, or Mycoplasma pneumoniae
• Eye or genitourinary infections caused by certain Chlamydia species
• Chancroid, plague, cholera, campylobacter, and brucellosis
• Syphilis and uncomplicated gonorrhea.

• May be used in addition to other treatments for acne.
• Sometimes used as an alternative drug to penicillin when penicillin is contraindicated.
• Generic doxycycline is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

• A headache, nausea, dyspepsia, joint or back pain, nasal and sinus congestion, or a rash.
• Tetracyclines, including doxycycline, form a stable calcium complex in bone-forming tissue. This can affect the growth rate of the fibula in young children and skeletal development in the fetus.
• Can cause permanent tooth discoloration (typically yellow-gray-brown staining) or enamel hypoplasia (underdeveloped tooth enamel) if used during critical periods of tooth development, such as the last half of pregnancy or in children aged less than eight years. The risk is greater with long-term use but has been noted after short-term use.
• Clostridium difficile-associated diarrhea (severe, persistent diarrhea) has been associated with most antibiotics, including doxycycline. Seek medical advice if persistent diarrhea occurs within two months of doxycycline use.
• The use of antibiotics, such as doxycycline, has also been associated with an increased risk of vaginal candidiasis (thrush).
• Cross-resistance is common. This means that if bacteria are resistant to other tetracyclines, they are likely to be resistant to doxycycline.
• May not be suitable for some people including pregnant or lactating women, and children aged less than eight years.
• May interact with some drugs including anticoagulants, penicillins, antacids or iron-containing preparations, antiepileptics, and oral contraceptives.
• Doxycycline may make your skin more sensitive to the sun increasing your risk of sunburn.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

• Doxycycline is an effective antibiotic that treats a wide range of infections. However, it is not usually recommended for children aged less than eight or pregnant women in the last half of their pregnancy.

5. Tips

• Take doxycycline as directed. Some branded and generic versions of doxycycline need to be taken one hour before or two hours after meals. Ensure you know when to take your branded or generic version of doxycycline. Unlike some other tetracyclines, the absorption of doxycycline is not markedly influenced by food or milk.
• Ensure you maintain hydration while taking doxycycline. This may help reduce the incidence of gastrointestinal side effects.
• Take doxycycline exactly as directed and for the duration intended. Do not use it to treat any other infection unless instructed to by your doctor. Doxycycline will not treat infections caused by viruses, such as a cold.
• Avoid excessive sun exposure or artificial ultraviolet light while receiving doxycycline. Seek medical advice if skin redness or skin eruptions develop. Wear sun-protective clothing and use an SPF50+ sunscreen when outside if exposure to sunlight is unavoidable.
• Talk to your doctor immediately if you develop watery or bloody stools, which may be associated with stomach cramps or fever, within a few days to months of discontinuing doxycycline.
• A course of doxycycline may increase the risk of vaginal candidiasis in women. Talk to your doctor or pharmacist about treatments if you develop symptoms of vaginal candidiasis.

6. Response and effectiveness

• Doxycycline is almost completely absorbed after oral administration. Peak concentrations are reached within two to three hours after dosing; however, it may take up to 48 hours before infection-related symptoms start to abate.
• Doxycycline is concentrated by the liver in the bile and excreted in an active form via the urine and feces.

7. Interactions

Medicines that interact with doxycycline may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with doxycycline. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with doxycycline include:

• antacids such as aluminum hydroxide, calcium carbonate, magnesium hydroxide, or sodium bicarbonate, which may affect the absorption of doxycycline
• anticonvulsants, such as phenytoin, phenobarbital, or primidone
• bismuth subsalicylate
• calcium supplements
• iron supplements
• multivitamins
• oral contraceptives (doxycycline may reduce the effectiveness of estrogen-containing oral contraceptives)
• penicillin
• warfarin.

In general, the absorption of tetracyclines is reduced when taken with foods, especially those that contain calcium; however, the absorption of doxycycline does not appear to be affected by food or milk to the same extent as other tetracyclines.

Note that this list is not all-inclusive and includes only common medications that may interact with doxycycline. You should refer to the prescribing information for doxycycline for a complete list of interactions.

References

• Doxycycline. Revised 12/2023. Lupin Pharmaceuticals, Inc. https://www.drugs.com/pro/doxycycline.html

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use doxycycline only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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