Tetracyclines

When it comes to antibiotics with a broad scope, high oral bioavailability, and a versatile range of indications — tetracyclines remain a reliable, if selective, choice in community and hospital pharmacy.

From acne to atypical pneumonia, chlamydia to malaria prevention — doxycycline often leads the charge. But it's not alone. Let's break down tetracyclines in a way that makes sense for pharmacy interns, especially those practicing in Australia.

General Principles of Link:

Anti-Infectives

Medicine Link

1. Doxycycline 

2. Minocycline 

3. Tetracycline 

   
   

How Tetracyclines Work

Tetracyclines are bacteriostatic antibiotics. They:

• Inhibit protein synthesis by reversibly binding to the 30S ribosomal subunit

• Block bacterial growth — rather than directly killing — making host immunity an essential ally

• Also show anti-inflammatory effects, useful in acne and rosacea

Depiction of tetracycline attachment to the 30S ribosomal subunit, emphasizing its role in inhibiting bacteria.

Common Tetracyclines in Practice

Drug	Use	Frequency	Notes
Doxycycline	Acne, chlamydia, Q fever, malaria	Once or twice daily	Best tolerated, most used
Minocycline	Acne, leprosy	Once or twice daily	Pigmentation + dizziness risk
Tetracycline	H. pylori (quadruple therapy)	Four times daily	Less used in Australia
Demeclocycline	SIADH (non-infectious use)	Individualised	Not an antibiotic use

Key Indications

• Dermatological: Acne, rosacea

• Respiratory: Mycoplasma pneumonia, sinusitis, chronic bronchitis

• Sexual Health: Chlamydia, PID, NGU, epididymo-orchitis

• Vector-borne: Q fever, rickettsial diseases (scrub typhus)

• Malaria: Prophylaxis and treatment (with quinine)

• Gastrointestinal: H. pylori (with other agents)

• SIADH: Demeclocycline only (not antibacterial)

  
  

⚠️ Safety First — Key Precautions

Risk Area	Advice
Children <8 years	Avoid unless necessary (teeth staining risk)
Pregnancy	Safe until 18 weeks, avoid after (bone/teeth effects)
Oral Retinoids	Avoid combo — ↑ risk of intracranial hypertension
Renal Impairment	Avoid tetracycline; caution with minocycline
Liver Impairment	Avoid high doses, especially with minocycline
Photosensitivity	Use sun protection, avoid peak UV exposure

Drug-by-Drug Breakdown

1. Doxycycline – The Go-To Agent

✅ First-line for: acne, chlamydia, Q fever, malaria prophylaxis

Dose:

• Acne/Rosacea: 50–100 mg daily

• Chlamydia: 100 mg BD for 1–3 weeks

• Malaria: 100 mg daily (start 2 days before travel, continue 4 weeks post-return)

Practice Tips:

• Excellent GI tolerability

• Once-daily dosing possible for many uses

• Broad spectrum, low resistance

• Fewer CNS or pigmentation issues than minocycline

🗣️ Counselling:

• Take in the morning with food + water

• Stay upright for 30–60 min after dosing

• Avoid antacids/iron/calcium around dose

• Use sun protection

  
  

2. Minocycline – Potent but Problematic

Minocycline

✅ Used for acne when doxycycline unsuitable

Dose:

• Acne: 50–100 mg once or twice daily

• Leprosy: 100 mg daily (part of combo)

Unique Risks:

• Dizziness, vertigo (vestibular effects)

• Autoimmune reactions (e.g., lupus-like syndrome)

• Skin, teeth, and nail pigmentation

🗣️ Counselling:

• Warn about dizziness and pigmentation

• Limit use to <6 months where possible

• Report symptoms of autoimmune reactions

  
  

3. Tetracycline – Rarely Used, Still Relevant

✅ Mostly used in H. pylori eradication protocols

Dose:

• 500 mg QID for 7–14 days (with bismuth, metronidazole, PPI)

Considerations:

• Not currently marketed in Australia (SAS access only)

• Avoid in renal impairment

• Higher risk of GI upset and poor compliance

🗣️ Counselling:

• Take on an empty stomach for best absorption

• Stay upright after dose

• Avoid dairy, iron, zinc supplements near dose

  
  

⚠️ Class-Wide Adverse Effects

Common	Infrequent	Rare
Nausea, diarrhoea, sun sensitivity, oesophageal irritation	Rash, fungal overgrowth, vestibular effects	Lupus flare, hepatitis, intracranial hypertension, pigmentation, C. difficile, anaphylaxis

Practice Pearls for Intern Pharmacists

• Doxycycline is the most pharmacist-recommended tetracycline due to tolerability and broad use

• Check pregnancy stage, child age, and concurrent oral retinoids

• Always discuss sun protection and fluid intake

• Minocycline is not first-line — reserve for refractory acne

• Tetracycline is uncommon in Australian pharmacy shelves

PBS Availability (Australia)

Drug	Forms	PBS Use
Doxycycline	50 mg, 100 mg tabs/caps	Acne, PID, chlamydia, bronchitis
Minocycline	50 mg tablets	Severe acne unresponsive to doxycycline
Tetracycline	Not currently marketed	SAS access only
Demeclocycline	Not available in Australia	SIADH (off-label use globally)