Tetracycline·Infectious Diseases - Tetracyclines

Doxycycline

Atypical CAP, Rickettsia, Q fever, mild MRSA cellulitis, Chlamydia, acne

PBSTETRACYCLINEDoxy, Vibramycin, Doxylin50 mg tabletS4+1

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At a glance

Max Dose

200 mg/day

Half-life

18-22 h

Caution: Esophagitis

HIGH RISK

Caution: Photosensitivity

RISK

Cautions

Avoid / Cautions

Children < 8 years old (permanent tooth staining). Pregnancy Category D (impairs fetal bone growth and stains teeth).

Where it stands

Rapid Summary

Overview

Highly lipophilic, broad-spectrum bacteriostatic tetracycline. Essential for atypical pneumonias, tick-borne diseases, and MRSA skin infections.

Clinical Focus

The capsule will ulcerate the esophagus if it gets stuck. Must take with a full glass of water and remain upright for 30 minutes.

Bottom Line

Doxycycline is a versatile tetracycline for atypical infections, acne, and malaria prophylaxis, but causes severe photosensitivity, oesophageal ulceration (take upright with water), and is contraindicated in pregnancy.

Formulation & Access

Brand Names

Doxy, Vibramycin, Doxylin

Oral Routes

Capsules/Tablets (50 mg, 100 mg).

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Atypical CAP, Rickettsia, Q fever, mild MRSA cellulitis, Chlamydia, acne.

Clinical Place

Unmatched efficacy against tick-borne and atypical intracellular organisms.

Quick reference

Class & Role

Tetracycline — Highly lipophilic, broad-spectrum bacteriostatic tetracycline.

Route / Formulation

Capsules/Tablets (50 mg, 100 mg). (Doxy, Vibramycin, Doxylin)

Usual Dose & Max

PO 100 mg BD. Max 200 mg/day.

Key Indication Doses

CAP / Atypicals / Cellulitis: PO 100 mg BD. Malaria Prophylaxis: PO 100 mg OD (Start 2 days before travel, continue 4 weeks after). Syphilis / Chlamydia: PO 100 mg BD for 7-14 days.

Best Uses

Key Risks

Gastrointestinal: Pill esophagitis, severe esophageal ulceration. HIGH — Nausea, vomiting (very common). Dermatological: Photosensitivity (severe, rapid sunburns). Dental/Bone: Tooth discoloration and enamel hypoplasia if given during tooth development.

Key Interactions

Chelates heavily with multivalent cations. Iron, Calcium, Magnesium (Antacids), and Dairy products will irreversibly bind Doxycycline in the gut, dropping absorption to zero. Separate by 2-4 hours. Phenytoin and Carbamazepine induce Doxy metabolism, slashing its half-life to 7 hours.

Monitoring

Counsel strictly: Take with a full glass of water, do not lie down for 30 mins, avoid direct sunlight, do not take with milk/iron. No specific routine laboratory tests required.

Clinical Pearl

Historically, tetracyclines must be taken on an empty stomach. Doxycycline is the exception. Because it causes intense nausea, it *should* be taken with a meal (just not dairy) to improve tolerance without affecting absorption.

Access

Doxy, Vibramycin, Doxylin50 mg tablet

Brand: Doxy, Vibramycin, Doxylin
Formulation: Capsules/Tablets (50 mg, 100 mg).

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