DORYX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DORYX (DORYX).
Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing the addition of amino acids to the growing peptide chain.
| Metabolism | Doxycycline is partially metabolized in the liver via unknown pathways, with minimal involvement of CYP450 enzymes. It undergoes enterohepatic recirculation. |
| Excretion | Renal (40-60% as unchanged drug via glomerular filtration), biliary/fecal (20-30% as active and inactive metabolites), incomplete excretion leads to enterohepatic recirculation. |
| Half-life | Terminal elimination half-life is 18-22 hours in healthy adults; prolonged to 21-36 hours in renal impairment; clinically relevant for once-daily dosing and monitoring for accumulation. |
| Protein binding | 80-90% bound primarily to serum albumin; binding is reversible and saturable at high concentrations. |
| Volume of Distribution | 0.7-1.1 L/kg (approx 50-84 L in 70 kg adult), indicating extensive tissue penetration beyond plasma volume. |
| Bioavailability | Oral immediate-release: 90-100%; oral delayed-release (Doryx): ~100% relative to immediate-release; IV bioavailability is 100%. |
| Onset of Action | Oral immediate-release: 2-4 hours to therapeutic serum concentrations; oral delayed-release (Doryx): 3-5 hours; IV: immediate but not typical. |
| Duration of Action | Approximately 24 hours with once-daily dosing due to half-life; sustained drug levels for 24-48 hours after last dose, supporting QD dosing and extended effects. |
| Molecular Weight | 444.43 |
100 mg orally every 12 hours on day 1, then 100 mg orally every 24 hours. For severe infections: 100 mg orally every 12 hours.
| Dosage form | CAPSULE, DELAYED RELEASE |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. For severe renal impairment (CrCl <30 mL/min): administer 100 mg every 24 hours. |
| Liver impairment | No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B). For severe hepatic impairment (Child-Pugh C): use with caution; no specific dose adjustment guidelines, but consider reduced dose or extended interval. |
| Pediatric use | Children ≥8 years and >45 kg: 100 mg every 12 hours on day 1, then 100 mg every 24 hours. Children ≥8 years and ≤45 kg: 2.2 mg/kg every 12 hours on day 1, then 2.2 mg/kg every 24 hours. Maximum 200 mg/day. |
| Geriatric use | No specific dose adjustment based on age alone. Use with caution in elderly due to potential renal impairment; adjust dose based on renal function. Consider increased risk of esophageal irritation; take with full glass of water. |
| 1st trimester | Doxycycline is generally avoided during the first trimester due to risk of teratogenicity, specifically skeletal development abnormalities and potential for permanent tooth discoloration, though the risk is lower than with tetracycline. |
| 2nd trimester | Contraindicated due to risk of bone and tooth development effects in the fetus, including dental discoloration and enamel hypoplasia; alternative antibiotics preferred. |
| 3rd trimester | Contraindicated due to risk of bone and tooth development effects in the fetus; may also cause fatty liver in pregnant women. |
Clinical note
Comprehensive clinical and safety monograph for DORYX (DORYX).
| Placental transfer | Doxycycline crosses the placenta readily, achieving fetal serum concentrations approximately 20-60% of maternal levels. |
| Breastfeeding | Doxycycline is excreted into breast milk in low concentrations but is considered incompatible with breastfeeding due to potential for serious adverse reactions in the nursing infant, including dental discoloration and bone growth suppression. Use only if benefits outweigh risks; consider alternative antibiotics. |
■ FDA Black Box Warning
No black box warning.
| Serious Effects |
Hypersensitivity to doxycycline or any tetracyclinePregnancy (second and third trimesters)Breastfeeding (unless no alternative)Children under 8 years of age (due to tooth discoloration and bone growth inhibition)Severe hepatic impairment
| Precautions | Photosensitivity: Patients may experience exaggerated sunburn reactions, Esophageal injury: Risk of ulceration; take with adequate fluids, Superinfection: Overgrowth of non-susceptible organisms, including fungi, Intracranial hypertension: Rarely causes pseudotumor cerebri, Use in pregnancy: Category D; may cause fetal harm, Use in children <8 years: May cause permanent tooth discoloration and enamel hypoplasia, Hepatic impairment: Use with caution; may cause hepatotoxicity, Renal impairment: No dosage adjustment typically needed, but monitor for toxicity |
| Food/Dietary | Avoid concurrent administration with dairy products (milk, yogurt, cheese), calcium-fortified foods, and iron-rich foods (e.g., spinach, red meat) as they chelate doxycycline, reducing absorption. Separate by at least 2-3 hours. Alcohol may decrease effectiveness and increase side effects. |
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| Lactation Rating | L4 (Hazardous) |
| Teratogenic Risk | First trimester: Tetracyclines cross placenta; risk of impaired bone and tooth development, but data in humans are limited. Second and third trimesters: Avoid due to risk of permanent tooth discoloration and reversible inhibition of bone growth (category D). |
| Fetal Monitoring | Monitor maternal liver function, renal function, and CBC. Fetal ultrasound for skeletal development if prolonged exposure. Assess infant for gastrointestinal disturbance if breastfeeding. |
| Fertility Effects | Animal studies show no impairment of fertility at therapeutic doses. Human data insufficient; no known effect on human fertility. |
| Clinical Pearls | DORYX (doxycycline hyclate delayed-release tablets) is a tetracycline antibiotic with enhanced gastrointestinal tolerability due to enteric coating. Administer with adequate fluid to reduce esophageal irritation. Avoid use in children under 8 years due to permanent tooth discoloration and bone growth impairment. Monitor for photosensitivity reactions, especially in patients on concurrent retinoids. Not effective against atypical pneumonia caused by Mycoplasma pneumoniae if resistance suspected. |
| Patient Advice | Take with a full glass of water to prevent esophageal irritation. · Avoid lying down for at least 30 minutes after taking to reduce risk of esophagitis. · Do not take with dairy products, antacids, or iron supplements as they reduce absorption. · Use sun protection (sunscreen, protective clothing) as this drug increases sensitivity to sunlight. · Complete the full course even if symptoms improve to prevent resistance. · Report any signs of severe headache or vision changes (possible pseudotumor cerebri). · Notify your doctor if you are pregnant, breastfeeding, or planning pregnancy. · Do not use outdated tetracyclines as they may cause kidney damage. |