Doxycycline

# Doxycycline ## Overview - **Classification**: Tetracycline antibiotic - **Mechanism**: Inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing addition of amino acids to growing peptide chains. ## Primary Indications 1. **Bacterial Infections** - Wide range including respiratory, urinary, skin, ophthalmic, and sexually transmitted infections. 2. **Acne Vulgaris** - Moderate to severe inflammatory acne (anti-inflammatory properties at sub-antimicrobial doses). 3. **Malaria Prophylaxis** - Prevention of malaria in endemic areas. ## Adult Dosing ### Standard Dosing **General Bacterial Infections (e.g., Atypical Pneumonia, UTI, Skin/Soft Tissue)** - **Dose**: **100 mg** - **Frequency**: Every 12 hours - **Route**: Oral or IV - **Duration**: 7-14 days, or as clinically indicated **Acne Vulgaris (Anti-inflammatory Dose)** - **Dose**: **20 mg** - **Frequency**: Every 12 hours - **Route**: Oral - **Duration**: Long-term (months) **Malaria Prophylaxis** - **Dose**: **100 mg** - **Frequency**: Once daily - **Route**: Oral - **Duration**: Start 1-2 days before travel, continue daily during travel, and for 4 weeks after leaving endemic area. **Lyme Disease (Early Localized)** - **Dose**: **100 mg** - **Frequency**: Every 12 hours - **Route**: Oral - **Duration**: 10-21 days ### Dose Adjustments - **Renal Impairment**: No dose adjustment typically needed. Doxycycline is eliminated non-renally. - **Hepatic Impairment**: Use with caution. Monitor for increased adverse effects. Consider lower doses if severe impairment. - **Elderly Patients**: No specific dose adjustment; monitor for adverse effects due to potential polypharmacy or comorbidities. ## Pediatric Dosing **General Warning: Avoid in children <8 years of age due to risk of permanent tooth discoloration and enamel hypoplasia. Use in this age group only when other agents are contraindicated or ineffective, or for severe/life-threatening infections (e.g., Rocky Mountain Spotted Fever, Anthrax) where benefits outweigh risks.** ### Neonates (0-28 days) - **Dose**: Not recommended. - **Special Notes**: High risk of permanent tooth discoloration. ### Infants (1-12 months) - **Dose**: Not recommended. - **Special Notes**: High risk of permanent tooth discoloration. ### Children (1-12 years) - **For Severe/Life-Threatening Infections (e.g., RMSF, Anthrax)** - **Dose**: **2.2 mg/kg** - **Frequency**: Every 12 hours - **Route**: Oral or IV - **Maximum**: **100 mg/dose** - **Special Notes**: Weigh benefits vs. risks. For children >45 kg, use adult dose. ### Adolescents (13-18 years) - **Dose**: Refer to Adult Dosing section. - **Maximum**: Adult dose. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to doxycycline or other tetracyclines. - **Absolute**: Pregnancy (causes tooth discoloration, bone growth inhibition in fetus). - **Absolute**: Children <8 years of age (except for severe, life-threatening infections where benefits outweigh risks). ### Common Adverse Effects - **Very Common (>10%)**: Photosensitivity (sunburn-like reaction), Nausea, Vomiting, Diarrhea. - **Common (1-10%)**: Esophagitis, Dysphagia, Rash, Vaginitis. - **Serious but Rare**: Pseudomembranous colitis (C. difficile), Intracranial hypertension (pseudotumor cerebri), Severe skin reactions (SJS/TEN), Hepatotoxicity. ### Key Drug Interactions - **Antacids (containing Al, Ca, Mg), Iron, Zinc, Bismuth Subsalicylate**: Decreased doxycycline absorption. - **Effect and clinical significance**: Reduced efficacy of doxycycline. - **Monitoring requirement**: Separate administration by at least **2-3 hours**. - **Warfarin**: May potentiate anticoagulant effect. - **Effect and clinical significance**: Increased bleeding risk. - **Monitoring requirement**: Monitor INR closely. - **Oral Contraceptives**: May reduce efficacy of oral contraceptives. - **Effect and clinical significance**: Risk of unintended pregnancy. - **Monitoring requirement**: Advise use of backup contraception. - **Retinoids (e.g., Isotretinoin)**: Increased risk of intracranial hypertension. - **Effect and clinical significance**: Additive risk. - **Monitoring requirement**: Avoid concomitant use. ## Monitoring & Follow-up - **Before Treatment**: Obtain baseline liver function tests if pre-existing hepatic impairment. - **During Treatment**: Monitor for signs of esophageal irritation, photosensitivity, or GI upset. - **Clinical Signs**: Watch for persistent headache (intracranial hypertension), severe diarrhea (C. diff), or worsening rash. ## Clinical Pearls - 💡 **Tip 1**: Take with a full glass of water and remain upright for at least **30 minutes (preferably 1 hour)** after dose to prevent esophagitis. - 💡 **Tip 2**: Avoid direct sun exposure and use sun protection (clothing, sunscreen) due to high photosensitivity risk. - 💡 **Tip 3**: May be taken with food/milk to reduce GI upset, but be aware this may slightly decrease absorption. Avoid taking with dairy if possible. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.