Doxycycline

 

1. Generic & Brand Names

• Generic: Doxycycline

• Brands: Vibramycin®, Oracea® (low-dose acne), Doryx® (delayed-release), Monodox®

• Formulations:

  • Tablets/capsules (20mg, 50mg, 100mg)

  • Delayed-release tablets (75mg, 100mg, 150mg)

  • Oral suspension (25mg/5mL)

  • IV injection (100mg/vial)

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2. Drug Class & Mechanism

• Class: Tetracycline antibiotic

• Mechanism:

  • Inhibits 30S ribosomal subunit → bacteriostatic

  • Anti-inflammatory effects (key for acne)

• Spectrum:

  • Respiratory: Mycoplasma, Chlamydia, Legionella

  • Skin: P. acnes, S. aureus (MSSA)

  • Other: Rickettsia, Lyme disease, Malaria prophylaxis

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3. FDA-Approved Uses

Condition	Key Applications
Acne Vulgaris	Inflammatory acne (≥8 years)
Respiratory Infections	Community-acquired pneumonia (CAP), sinusitis, bronchitis
Other Uses	Lyme disease, malaria prophylaxis, STIs (chlamydia)

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4. Dosing Regimens

Indication	Adult Dose	Pediatric Dose (≥8 yrs)*
Inflammatory Acne	50-100 mg daily (Oracea®: 40 mg AM)	0.5-1 mg/kg/day
CAP/Sinusitis	100 mg q12h × 72h → 100 mg daily	2.2 mg/kg q12h (max 100 mg/dose)
Lyme Disease	100 mg q12h × 14-21 days	1-2 mg/kg q12h (max 100 mg/dose)

🚫 Avoid under age 8 (tooth discoloration)
Notes:

• Take with full glass of water (minimize esophageal irritation)

• Avoid dairy/antacids 2h before/after (chelates Ca²⁺/Mg²⁺)

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5. Side Effects

Common (≥10%)	Serious (<1%)
Nausea/vomiting	Photosensitivity (severe sunburns)
Esophageal irritation	Intracranial hypertension (headache, vision loss)
Diarrhea	Hepatotoxicity (jaundice)
Vaginal candidiasis	Stevens-Johnson Syndrome
Tooth discoloration (children/fetus)	Esophageal ulceration

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6. Black Box Warnings & Contraindications

• 🚫 Absolute Contraindications:

  • Pregnancy (Category D: fetal tooth/bone toxicity)

  • Children <8 years (permanent tooth discoloration)

  • Severe hepatic impairment

• Critical Warnings:

  • Photosensitivity: Risk persists 72h post-dose → strict sun avoidance

  • Avoid with: Isotretinoin (↑ intracranial pressure risk)

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7. Drug Interactions

Medication	Risk	Management
Antacids/Ca²⁺/Fe²⁺	↓ Absorption by 90%	Separate by 2-3 hours
Warfarin	↑ INR → bleeding	Monitor INR weekly
Penicillins	Antagonistic effect	Avoid concurrent use
Alcohol	↓ Efficacy + ↑ hepatotoxicity risk	Avoid

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8. Acne-Specific Protocols

1. Initial Therapy:

   • 100 mg daily × 4-12 weeks

2. Maintenance:

   • Reduce to 50 mg daily or Oracea® (40 mg delayed-release)

3. Adjunct Therapy:

   • Combine with topical retinoids/benzoyl peroxide

4. Monitor:

   • Liver enzymes q6mo for chronic use

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9. Respiratory Infection Notes

• First-line for:

  • Atypical pneumonia (Mycoplasma, Chlamydia)

  • COPD exacerbations with purulent sputum

• Not for:

  • Streptococcal pharyngitis

  • Viral bronchitis

• Resistance Concerns:

  • S. pneumoniae resistance ~15% (use only if atypical suspected)

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10. Storage & Administration

• Tablets: Store at 20-25°C; protect from light/moisture

• Suspension: Refrigerate; discard after 14 days

• IV: Administer over 1-4 hours; avoid sunlight exposure during infusion

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Clinical Practice Tips

⚠️ Sun Exposure Warning:

• Patients should use SPF 50+, wear hats, avoid UV lights

• Photosensitivity rash may resemble sunburn → differentiate from allergy

⚠️ Esophageal Safety:

• Never take at bedtime/lying down → risk of ulceration

• If nausea: take with non-dairy food (e.g., apple sauce)

✅ Acne Advantages:

• Anti-inflammatory effect reduces papules/pustules faster than antibiotics alone

• Oracea® (40 mg) minimizes resistance risk

❌ Avoid in Pregnancy:

• Permanent yellow-gray tooth discoloration in fetus

• Alternative acne agents: Azelaic acid, Erythromycin topicals

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Doxycycline vs. Other Acne Antibiotics

Parameter	Doxycycline	Minocycline	Erythromycin
Acne Efficacy	+++	++++	++
Photosensitivity	Severe	Moderate	Minimal
CNS Effects	Rare	Vertigo (15-30%)	Rare
Cost	$	$$$	$$

💡 Pro Tip: For acne, use sub-antimicrobial doses (e.g., Oracea® 40 mg) to reduce resistance while maintaining anti-inflammatory benefits.

Prescribing Status: Widely available; monitor for resistance development with long-term use.