Doxycycline – Uses, Mechanism, Dose, Side Effects & Counseling (Drug of the Day)

💊 Doxycycline – Uses, Mechanism, Dose, Side Effects & Counseling (Drug of the Day)

Generic Name: Doxycycline

Drug Class: Tetracycline Antibiotic

Category: Broad-spectrum bacteriostatic antibiotic

📌 Introduction

Doxycycline is a widely prescribed tetracycline antibiotic used to treat respiratory infections, acne, STDs, and zoonotic infections.

It works against both Gram-positive and Gram-negative bacteria and is also effective against atypical organisms.

👉 In exams, doxycycline is frequently asked because of its unique mechanism and contraindication in children & pregnancy.

⚙️ Mechanism of Action

Doxycycline inhibits bacterial protein synthesis.

Binds to 30S ribosomal subunit

Blocks attachment of aminoacyl-tRNA

Prevents addition of amino acids to peptide chain

Stops bacterial growth (bacteriostatic)

📚 Key Point:

Tetracyclines inhibit protein synthesis but do not kill bacteria directly.

🦠 Spectrum of Activity

Effective Against:

Chlamydia

Mycoplasma

Rickettsia

Borrelia (Lyme disease)

Vibrio cholerae

Acne-causing bacteria (Cutibacterium acnes)

Some Gram + and Gram – bacteria

🩺 Indications / Uses

Common Uses

Acne vulgaris

Respiratory tract infections

Urinary tract infections

Sexually transmitted infections (Chlamydia)

Special Uses (Very Important for Exams)

Malaria prophylaxis

Cholera

Lyme disease

Typhus

Brucellosis (with rifampicin)

💊 Adult Dose

Typical dose:

100 mg twice daily on Day 1 → then 100 mg once daily

(Depends on infection severity)

⚠️ Adverse Effects

Nausea, vomiting

Photosensitivity (sunburn risk ☀️)

Esophagitis (take with water)

Tooth discoloration (children)

Hepatotoxicity (rare)

🚫 Contraindications

❌ Pregnancy

❌ Breastfeeding

❌ Children under 8 years

Reason: Deposition in bones & teeth → permanent discoloration

💡 Important Drug Interactions

Avoid taking with:

Milk & dairy products 🥛

Antacids

Iron supplements

Calcium tablets

👉 These reduce absorption due to chelation

👨‍⚕️ Patient Counseling Points (Very Important for Viva)

Take with full glass of water

Do not lie down for 30 minutes

Avoid sunlight exposure

Do not take with milk

Complete full antibiotic course

📚 Exam Pearls

Tetracyclines = 30S inhibitors

Causes teeth discoloration in children

Drug of choice: Chlamydia & Rickettsial infections

Used for malaria prophylaxis

✍️ Conclusion

Doxycycline is a versatile broad-spectrum antibiotic with applications in bacterial, parasitic, and atypical infections. However, its use requires careful counseling due to photosensitivity and effects on bones and teeth.

For pharmacy students, it is a high-yield exam drug and clinically important in everyday practice.