A tetracycline antibiotic
Demeclocycline
A tetracycline antibiotic, also used to help control low sodium caused by excess antidiuretic hormone.
What is Demeclocycline?
Demeclocycline is a tetracycline antibiotic. As well as treating some infections, it is used to help correct low blood sodium caused by too much antidiuretic hormone, because it reduces the kidneys' response to that hormone. It is not used in pregnancy, breastfeeding or in young children, causes marked sun sensitivity, and must be swallowed upright with water, away from dairy, antacids and iron.
Education and reference only. This is a plain-language guide to Demeclocycline — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Demeclocycline is an antibiotic of the tetracycline group. Besides its antibiotic role, it has a particular use in helping to manage low blood sodium (hyponatraemia) caused by the syndrome of inappropriate antidiuretic hormone (SIADH), because it dampens the kidneys' response to that hormone. It is taken by mouth.
How it works
As an antibiotic, demeclocycline stops bacteria making the proteins they need to grow, which halts the infection. In low-sodium states caused by excess antidiuretic hormone, it works differently: it reduces how well the kidneys respond to that hormone, so the kidneys hold on to less water. Losing this extra water helps raise the blood sodium back towards normal — in effect causing a controlled, deliberate reduction in the kidneys' water retention (similar to a condition called nephrogenic diabetes insipidus), which is monitored closely.
Company & origin
Originated / developed by: Available as a generic medicine from specialist manufacturers..
A tetracycline-class antibiotic in use since the 1950s.
Practical use
How to take Demeclocycline
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Swallow it with a full glass of water while sitting or standing upright.
- Do not take it just before lying down or going to bed, to protect the gullet.
- Avoid taking it at the same time as milk or dairy, antacids, or iron supplements.
- Cover up and use sun protection, as it makes the skin much more sensitive to sunlight.
- Complete the course as prescribed when used as an antibiotic.
- If a dose is missed, take it when you remember unless the next is near, then skip it; do not double up.
Weighing it up
Advantages & disadvantages of Demeclocycline
Advantages
- A useful option for managing low blood sodium caused by excess antidiuretic hormone.
- Also acts as a tetracycline antibiotic against a range of bacteria.
- Taken by mouth.
Disadvantages
- Causes marked sun sensitivity, so skin protection is essential.
- Cannot be used in pregnancy, breastfeeding or in children under twelve.
- Absorption is blocked by dairy, antacids and iron, and it can irritate the gullet if not taken upright with water.
Practical use
Good to know
Demeclocycline must be swallowed sitting or standing upright with a full glass of water and not just before lying down, to avoid irritating the gullet. Avoid taking it at the same time as dairy products, antacids or iron, which stop it being absorbed. It causes marked sensitivity to sunlight, so cover up and use sun protection. It is not used in pregnancy, breastfeeding or in children under twelve, as it can affect developing teeth and bones.
Who should not take it / use with caution
- Women who are pregnant or breastfeeding.
- Children under twelve, because it can stain teeth and affect developing bones.
- People with significant kidney problems (and with caution in liver disease).
Monitoring
- Blood sodium and kidney function when used for low sodium.
- Kidney and liver function with longer use.
- Watch for severe sunburn and gullet irritation.
Side effects
- Marked sensitivity to sunlight, with easy sunburn.
- Nausea, stomach upset or diarrhoea, and irritation of the gullet if not taken upright.
- When used for low sodium, increased thirst and passing more urine (a diabetes-insipidus-like effect).
- Thrush after a course.
Key interactions
- Dairy products, antacids and iron or calcium supplements — block absorption, so separate them in time.
- Blood thinners such as warfarin — effect may be increased.
- Retinoids (such as isotretinoin) — added risk of raised pressure around the brain, so avoided together.
- The combined contraceptive pill — use extra precautions if sickness or diarrhoea occurs.
Available as: tablets and capsules
Answers
Demeclocycline: frequently asked questions
Why is demeclocycline used for low sodium?
It reduces how well the kidneys respond to antidiuretic hormone, so they hold on to less water. Losing the extra water helps raise blood sodium when it is too low because of excess of that hormone.
Why must I take it sitting or standing up?
Tetracyclines can irritate the gullet, so taking it upright with a full glass of water, and not just before lying down, helps it pass into the stomach safely.
Can I take it with milk or antacids?
No, not at the same time. Dairy, antacids and iron all stop it being absorbed, so leave a gap between them.
Can I take it in pregnancy or give it to my child?
No. It is avoided in pregnancy, breastfeeding and in children under twelve, because it can affect developing teeth and bones.
Why does it make me burn in the sun?
It increases the skin's sensitivity to sunlight, so you can burn more easily. Cover up and use sun protection while taking it.
The wider class
About Tetracyclines
Demeclocycline belongs to the tetracyclines class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.