Tetracyclines: Doxycycline, Minocycline & Tetracycline for Respiratory, Urinary & Atypical Infection

Tetracyclines like Doxycycline and Minocycline treat respiratory, urinary, and atypical infections. Learn the mechanism, spectrum, uses, side effects, and interactions.

Introduction

Tetracyclines are broad-spectrum, bacteriostatic antibiotics that inhibit bacterial protein synthesis.

They are often used for:

• Respiratory infections

• Urinary tract infections

• Acne

• Atypical pathogens

The prototype drug is Tetracycline, with derivatives like Doxycycline and Minocycline.

Medications in the Class

• Tetracycline (prototype)

• Doxycycline

• Minocycline

• Tigecycline (glycylcycline, a derivative with broader spectrum)

• Oxytetracycline

Mechanism of Action

Tetracyclines attach to the 30S ribosomal subunit. This stops aminoacyl-tRNA from joining the mRNA-ribosome complex. As a result, the body inhibits protein synthesis. They are bacteriostatic.

Spectrum of Activity

• Gram-positive bacteria: Staphylococcus aureus (including some MRSA), Streptococcus spp.

• Gram-negative bacteria: Haemophilus influenzae, E. coli, Klebsiella

• Atypical pathogens: Mycoplasma pneumoniae, Chlamydia spp., Rickettsia spp., Legionella spp.

• Anaerobes: Some activity

• Not effective against: Pseudomonas aeruginosa

Indications (When Used)

• Respiratory tract infections: community-acquired pneumonia, bronchitis

• Urinary tract infections

• Skin infections: acne vulgaris, MRSA skin infections

• Tick-borne infections: Rickettsia, Lyme disease

• Sexually transmitted infections: Chlamydia

• Prophylaxis for malaria (Doxycycline)

Contraindications (When Not to Use)

• Children <8 years old (risk of tooth discoloration)

• Pregnancy (can affect fetal bone and teeth development)

• Severe hepatic impairment

• Known hypersensitivity to tetracyclines

Side Effects

• Gastrointestinal upset: nausea, vomiting, diarrhea

• Photosensitivity (sunburn risk)

• Tooth and bone discoloration in children

• Rare: hepatotoxicity, intracranial hypertension

• Esophageal irritation (especially with Doxycycline)

Drug Interactions

• Calcium, magnesium, iron, aluminum, zinc: bind tetracyclines → reduced absorption

• Warfarin: may enhance anticoagulant effect

• Penicillin: may antagonize bactericidal effect

• Oral contraceptives: reduced efficacy (controversial, monitor)

Antidote

No specific antidote exists. Supportive care is given in overdose. Activated charcoal may reduce absorption if given early.

Monitoring of Potential Complications

• Liver function tests during prolonged therapy

• Monitor for allergic reactions

• Renal function in patients with pre-existing kidney disease

• Advise patients on sun protection due to photosensitivity

Tetracyclines are flexible antibiotics. They treat respiratory, urinary, skin, and atypical infections. They offer broad coverage. To avoid tooth stains, liver damage, and drug interactions, use the product with caution and monitor its effects closely.