If you’ve ever had a skin infection or respiratory tract infection, you may have been prescribed antibiotics.
One of the most common antibiotics? Doxycycline.
This particular medication is a common broad-spectrum antibiotic often prescribed to treat a variety of infections.
There are many factors that influence the dosage you may be prescribed by your doctor or health care provider, how your body absorbs doxycycline, and how long the antibiotic will stay in your system.
It is commonly used for treatment of:
- Acne and rosacea
- Skin infections
- Eyelid infections
- Chlamydia infection and pelvic inflammatory disease caused by chlamydia
- Bacterial respiratory infections including sinusitis and pneumonia
- Bacterial gastroenteritis
- Oral infections (such as periodontitis)
- Malaria prophylaxis
- Lyme disease prophylaxis and treatment
- Anthrax exposure
How Long Doxycycline Stays in Your System
Doxycycline has a half-life of 14-24 hours, depending on factors such as age, weight, and dosage.
A half-life is the time it takes for the substance in your body to be reduced to half of the strength of the original dosage.
If your dose of doxycycline is 150 mg, for example, then it will take approximately 18-19 hours before it is reduced in the body by half (or 75 mg) and about 28-42 hours for the medication to be completely out of your system.
The half-life of your medication matters when it comes to other drugs or supplements you take that may interact with it, or when you want to consume substances that may alter how your body responds.
Factors to Consider
How quickly your body clears a medication depends on many factors.
As people get older, their body composition typically changes.
The muscle to fat ratio tends to favor fat, and this can increase the half-life of medications.
This may mean that it takes an older person’s body more time to clear medication than it does someone who is younger.
Older people may also not have absorption as effective as people who are younger, so this may affect dosage, which can also influence the half-life.
Whether your health changes in response to normal aging processes or you have chronic conditions like type 2 diabetes, cardiovascular disease, high blood pressure, or autoimmune disease, these may all affect how your body absorbs and metabolizes drugs, including antibiotics.
People who have metabolic disorders like diabetes may experience changes to the way that medicine absorbs, metabolizes, and is cleared from the body.
However, this does not universally apply the same for all medications.
Activity level, fitness, genetics, and other health conditions can all significantly affect how your body processes and gets rid of drugs.
While the half-life of doxycycline is an average of 18 hours, if your kidneys filter more slowly, you have liver disease, or you have genetic variants that change the way your cytochrome P450 cycle metabolizes drugs, it may stay in your system for a longer time.
A person’s body mass can influence the way that certain drugs are absorbed and distributed in the body’s tissues.
This does not universally apply to all drugs, but for some, the clearance of medication and half-life can take longer.
Drugs that do not absorb as well because of body mass or require a higher dosage to compensate for body mass may have a shorter half-life because of absorption or dosage changes.
The dosage of a drug that you are prescribed can influence how quickly it clears the body.
The higher the dose, the longer it will take to be cleared.
Certain factors, like age and activity level, can also increase or decrease the half-life of a drug.
Not all drugs are metabolized and excreted in the same way.
Doxycycline is primarily excreted through feces and urine, but first, it has to be metabolized by the liver and kidneys.
The rate at which your liver processes the medication can affect how quickly it leaves the body.
The metabolic function of your body is not necessarily determined by your body weight or activity level.
Your genes play a big role in how your body responds to medication and how it is metabolized in the body.
Most medications must be metabolized by enzymes in the cytochrome P450 system.
If you consume other drugs or foods that are processed by this system, you may experience an interaction. Interactions may increase or decrease the effects of a prescription, sometimes with serious results.
Doxycycline Side Effects
Doxycycline has some common side effects.
More rarely, doxycycline can cause more serious problems or allergic reactions. These could include:
- Headache, blurred vision, or vision loss (known as intracranial hypertension)
- Hives, rash, or other allergic reactions
- Skin redness, blistering, or peeling
- Swollen glands
- Difficulty breathing or swallowing or other allergic reactions
- Swelling of the eyes, lips, throat, tongue, or face
- Unusual bleeding or bruising
- Joint pain
- Chest pain
- Discoloration of permanent teeth in young children
If you notice any of these symptoms, you should be evaluated by a doctor or health care provider right away.
If you are experiencing oral swelling, difficulty breathing, or any severe symptoms, please call 911 or be seen in an ER.
Doxycycline Interactions and Warnings
What to avoid while taking doxycycline
Doxycycline can have interactions with other prescriptions, OTC medications, and dietary supplements.
Your prescription label insert will tell you what not to take with doxycycline.
Your pharmacist and doctor should also give you more details.
Some things to avoid while taking doxycycline include:
- Dairy products (within two hours of taking each dose)
- Sun exposure
- Tanning beds
Doxycycline may interact with the following, so be sure that your doctor and pharmacist know what you are taking:
- Anticoagulants (blood thinners)
- Iron supplements (and multivitamins that contain iron)
- Magnesium supplements (and multivitamins that contain magnesium)
- Oral contraceptives, since doxycycline can render them less effective
Doxycycline should not be taken by children under age 8 except in rare cases recommended by their pediatrician.
It is not safe during pregnancy or breastfeeding unless a physician determines the benefits of its use outweigh the risks.
It should be used with caution and close guidance from a physician by those who have liver disease, kidney disease, or myasthenia gravis.
In rare cases, doxycycline can cause toxicity in the liver.
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K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
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Effect of diabetes mellitus on pharmacokinetic and pharmacodynamic properties of drugs. (2012).
Human cytochromes p450 in health and disease. (2013).
Effect of obesity on the pharmacokinetics of drugs in humans. (2010).
Pharmacokinetics and pharmacodynamics of the tetracyclines including glycylcyclines. (2006).
Doxycycline hyclate. (2021).