Anti-infective
Tetracyclines
Doxycycline, lymecycline and similar — Broad-spectrum antibiotics used for chest infections, acne, and some tick-borne and atypical infections.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
Quick answer
What is Tetracyclines?
Tetracyclines are broad-spectrum antibiotics effective against many bacteria and some atypical organisms. They are widely used for acne and rosacea, chest infections, and certain tick-borne, travel and sexually transmitted infections.
- How it works: They stop bacteria making the proteins they need to grow and multiply, halting the infection so the immune system can clear it.
- In practice: In practice tetracyclines such as doxycycline are versatile antibiotics used for chest infections, acne and rosacea, some sexually transmitted and atypical infections, and the prevention or treatment of certain tick-borne and travel infections.
What it is
Tetracyclines are broad-spectrum antibiotics effective against many bacteria and some atypical organisms. They are widely used for acne and rosacea, chest infections, and certain tick-borne, travel and sexually transmitted infections.
How it works
They stop bacteria making the proteins they need to grow and multiply, halting the infection so the immune system can clear it. The same binding chemistry that makes them stick to bacterial targets also makes them bind dietary calcium and metals — which is why milk, antacids and iron block their absorption.
In practice
In practice tetracyclines such as doxycycline are versatile antibiotics used for chest infections, acne and rosacea, some sexually transmitted and atypical infections, and the prevention or treatment of certain tick-borne and travel infections. A handful of very practical points dominate their use. They bind to calcium, iron and magnesium, so they must be separated from milk, antacids, and iron or calcium supplements, which otherwise block absorption. They can cause photosensitivity, so people are warned to protect against strong sun. They are generally avoided in pregnancy, breastfeeding and young children because they can stain developing teeth and affect bone. To reduce the risk of throat irritation and ulceration, doxycycline is swallowed with plenty of water, sitting or standing upright, and not right before lying down. They can slightly reduce the reliability of some treatments and interact with anticoagulation. As ever, the course is completed and they do nothing for viral illness.
Examples
Practical use
How to take it & use it well
- Take it with a full glass of water and stay sitting or standing upright for a while afterwards, as these tablets can irritate or get stuck in the gullet if you lie down too soon.
- Keep it well separated from milk, dairy, indigestion remedies, and supplements containing iron, calcium, magnesium or zinc, as these bind to the antibiotic and stop it being absorbed properly.
- Protect your skin from strong sun and use sun cream, as these antibiotics can make you burn more easily than usual.
- For acne, be patient, as it often takes a couple of months of regular use before you see a clear improvement. Keep taking it as prescribed even before then.
- If you miss a dose, take it when you remember unless it is nearly time for the next one, then skip it. Do not take a double dose to catch up.
- These antibiotics are not used in pregnancy, while breastfeeding, or in young children, as they can affect developing bones and teeth, so tell your prescriber if any of these apply.
Common uses
- Acne and rosacea
- Chest and atypical respiratory infections
- Some tick-borne, travel and sexually transmitted infections
Monitoring
- Treatment response (e.g. acne over weeks)
- Photosensitivity and gastrointestinal tolerance
- Anticoagulation where co-prescribed; signs of raised intracranial pressure (rare)
Weighing it up
Advantages & disadvantages
Advantages
- They are effective for acne and for several infections, including some chest, skin and tick-borne infections.
- For acne they can produce a marked improvement over a couple of months when taken regularly.
- Most are taken once or a couple of times a day by mouth, which is convenient.
- One of them is also widely used to prevent malaria in travellers.
- They cover bacteria that some other antibiotics miss, which makes them useful in particular situations.
Disadvantages
- They make the skin more sensitive to sunlight, so sunburn is more likely without precautions.
- Their absorption is easily blocked by milk, antacids and iron, so timing around food and supplements matters.
- They can irritate the gullet and cause heartburn if not taken upright with plenty of water.
- They cannot be used in pregnancy, while breastfeeding, or in young children because they affect developing bones and teeth.
- Like all antibiotics, they can upset the stomach, cause thrush and contribute to resistance if overused.
Key safety principles
What to watch for
- Separate from milk, antacids and iron/calcium supplements, which block absorption.
- Can cause photosensitivity — protect against strong sunlight; swallow doxycycline upright with plenty of water to avoid throat ulceration.
- Avoid in pregnancy, breastfeeding and young children (tooth staining/bone effects).
Key interactions
What to avoid or check alongside
- Milk, dairy products and supplements or remedies containing calcium, iron, magnesium or zinc bind the antibiotic and greatly reduce how much is absorbed.
- Indigestion remedies and antacids should be separated by a good gap for the same reason.
- Taken with the blood thinner warfarin, they can increase its effect and the risk of bleeding, so monitoring may be needed.
- They should not be taken at the same time as certain acne treatments taken by mouth that affect vitamin A, as this combination can raise pressure in the brain.
- Tell your prescriber about all supplements and medicines, as several can affect how well the antibiotic works.
Patient & carer advice
- Take with plenty of water, sitting or standing up, and not just before bed
- Keep it well apart from milk, indigestion remedies and iron or calcium tablets
- Use sun protection, and tell us if you are or could be pregnant
Answers
Tetracyclines: frequently asked questions
Why can't I take this antibiotic with milk?
The calcium in milk and dairy binds to the antibiotic in your gut and stops much of it being absorbed, so it works far less well. Keep dairy, indigestion remedies and iron or calcium supplements well separated from your dose.
Can I take a tetracycline in pregnancy?
No, these antibiotics are avoided in pregnancy and breastfeeding, and in young children, because they can affect developing bones and discolour forming teeth. Tell your prescriber if you are or could be pregnant so they can choose a safer alternative.
Why do I burn so easily on doxycycline?
These antibiotics make your skin more sensitive to sunlight, so you can burn more quickly than usual. Cover up, avoid strong midday sun and use a good sun cream while you are taking it.
How long until my acne improves?
Acne usually takes a couple of months of regular treatment before you notice a clear improvement, so it is important to keep going even if nothing seems to change at first. Your prescriber will review how it is working.
What should I do if the tablet feels stuck in my throat?
Always take it with a full glass of water and stay upright for a while afterwards, as these tablets can irritate the gullet. If you get burning chest pain or feel a tablet has lodged, drink more water and tell your pharmacist or GP.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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