Inj doxy according to weight
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Doxycycline IV dosing in adults is generally 100 mg q12h on day 1, then 100-200 mg/day. For pediatric patients (>8 years, <45 kg), the standard weight-based dose is 2.2 mg/kg q12h on day 1, then 2.2-4.4 mg/kg/day. Let me pull the exact figures from the textbooks.
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Inj. Doxycycline - Weight-Based Dosing
Adults (>45 kg / >100 lb)
| Indication | Dose | Frequency | Route |
|---|---|---|---|
| General infections | 100 mg | Every 12 hours (Day 1 loading), then 100 mg OD or 50 mg BD | IV / PO |
| Severe infections | 200 mg/day | 100 mg every 12 hours | IV |
| RMSF / Rickettsia | 100 mg | Twice daily | IV or PO |
Pediatric (>8 years, weight <45 kg / <100 lb)
| Indication | Dose | Frequency | Max per dose |
|---|---|---|---|
| General | 2.2 mg/kg/dose | Every 12 hours (Day 1), then 2.2 mg/kg OD | 100 mg |
| Severe / RMSF | 2.2 mg/kg/dose | Twice daily throughout | 100 mg |
| Tick-borne rickettsial infections | 4.4 mg/kg/day | In 2 divided doses | 100 mg/dose |
When weight reaches ≥45 kg: use the full adult dose of 100 mg twice daily.
Key Points
- Maximum single dose: 100 mg (do not exceed even in larger pediatric patients)
- Doxycycline is the drug of choice at any age for RMSF and most rickettsial infections - the concern about teeth staining with short courses (5-7 days) is considered outweighed by the benefit
- Contraindicated in children <8 years (except for RMSF where benefit outweighs risk), and in pregnancy
- IV administration: infuse slowly over 1-4 hours; avoid rapid infusion (phlebitis, cardiotoxicity risk)
- For ≥45 kg children, give the adult dosage directly
Sources:
- Red Book 2021 (AAP) - Rocky Mountain Spotted Fever chapter, p. 999: "The doxycycline dose for RMSF is 2.2 mg/kg of body weight per dose, twice daily, orally or intravenously (maximum 100 mg per dose); the adult dose is 100 mg twice daily."
- Goldman-Cecil Medicine: "Doxycycline 100 mg twice daily for adults or 4.4 mg/kg body weight per day in two divided doses for children under 45.4 kg."
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