Demeclocycline !

A tetracycline better known for a side effect: it makes the kidney resist ADH, which is why it is sometimes used in SIADH.

Updated 2026-11-01

Class: Tetracyclines
Target: Bacterial ribosome, 30S subunit (16S rRNA, A site)
ATC code: J01AA01

Bacterial ribosome, 30S subunit (16S rRNA, A site)Demeclocycline

The figure shows tetracycline, the parent drug that occupies the same ribosomal site, bound to the Escherichia coli 70S ribosome.

Target in 3D: Bacterial ribosome, 30S subunit (16S rRNA, A site). PDB structure 5J5B (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

As an antibiotic, demeclocycline binds the 30S subunit and blocks aminoacyl-tRNA from the A site. In the kidney it reduces the response of the collecting duct to antidiuretic hormone, causing a dose-dependent, reversible nephrogenic diabetes insipidus.

Absorbed by mouth
Binds the bacterial 30S subunit and blocks tRNA entry
In the kidney, blunts the action of ADH
More water is excreted (useful in SIADH)

Pharmacokinetics

Absorption: Absorbed by mouth; minerals and dairy products reduce it.
Half-life: About 10–16 hours.

Indications

Infections caused by susceptible bacteria (now seldom used for this)
Off-label: chronic hyponatraemia due to SIADH, using its effect on the kidney Syndrome of inappropriate antidiuretic hormone secretion (SIADH) →

Adverse effects

Common

Thirst and frequent urination
Nausea, vomiting and diarrhoea
Photosensitivity

Contraindications

Allergy to any tetracycline
Second half of pregnancy and children up to 8 years

Key interactions

Antacids, calcium, iron, magnesium: Reduce absorption.
Warfarin: Anticoagulant effect may increase.

What is monitored

Serum sodium and fluid balance when used in SIADH
Kidney function
Skin after sun exposure

Administration and safety

Taken with water, apart from dairy products, antacids and iron
Strong sun exposure is avoided

Nursing care

Record intake and output
Teach sun protection
Teach to report excessive thirst or urination, or severe headache

Pregnancy and breastfeeding

Like other tetracyclines it can cause fetal harm and is avoided in pregnancy.

Test yourself

Think of the answer, then tap the question to see it.

Which kidney effect does demeclocycline have?

A reversible, dose-dependent nephrogenic diabetes insipidus.

Why is it sometimes used in SIADH?

It makes the kidney less responsive to ADH, so more free water is excreted.

Which skin reaction is common with demeclocycline?

Photosensitivity (exaggerated sunburn).

Add to my cards (3)

Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

← Back to the class: Tetracyclines

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - DEMECLOCYCLINE HYDROCHLORIDE- demeclocycline tablet (DailyMed (U.S. National Library of Medicine), 2026); Demeclocycline: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.