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[Pharmacology](https://durgical.com/en/pharmacology/) · [Tetracyclines](https://durgical.com/en/pharmacology/classes/tetracyclines/)

# 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](https://durgical.com/en/pharmacology/classes/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](https://www.rcsb.org/structure/5J5B) · Drag to rotate · pinch to zoom

## 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) →](https://durgical.com/en/conditions/syndrome-of-inappropriate-antidiuretic-hormone-secretion/)

## Adverse effects

### Common

- Thirst and frequent urination
- Nausea, vomiting and diarrhoea
- Photosensitivity

### Serious (rare, important)

- Nephrogenic diabetes insipidus (polyuria, polydipsia, weakness) with long-term use
- Tooth discoloration and slowed bone growth in children and late pregnancy
- Intracranial hypertension

## 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.

## Memory aid

«Demeclo dries the collecting duct»: ADH knocks, the kidney does not answer.

## 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).

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## Related drugs

- [Tetracycline](https://durgical.com/en/pharmacology/tetracycline/)
- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)

## Related conditions

- [Syndrome of inappropriate antidiuretic hormone secretion (SIADH)](https://durgical.com/en/conditions/syndrome-of-inappropriate-antidiuretic-hormone-secretion/)

[← Back to the class: Tetracyclines](https://durgical.com/en/pharmacology/classes/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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=539add06-e0a0-401a-b4f6-20776084aa9c) (DailyMed (U.S. National Library of Medicine), 2026); [Demeclocycline: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682103.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J01AA01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/demeclocycline/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/demeclocycline/