DOXY 100
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DOXY 100 (DOXY 100).
Doxycycline inhibits bacterial protein synthesis by reversibly binding to the 30S ribosomal subunit, preventing the addition of amino acids to the growing peptide chain. It also exhibits anti-inflammatory effects by inhibiting matrix metalloproteinases and reducing cytokine production.
| Metabolism | Doxycycline is partially metabolized in the liver via glucuronidation, but the majority is excreted unchanged in the urine and feces. It does not undergo significant cytochrome P450 metabolism. |
| Excretion | Renal (approximately 40% as unchanged drug) and fecal/biliary (approximately 50-60% as inactive metabolites and unchanged drug). |
| Half-life | Terminal elimination half-life is 18-22 hours in adults; prolonged to 20-30 hours in renal impairment. |
| Protein binding | 80-90% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 1.5-2.0 L/kg; indicates extensive tissue penetration, including into bone and teeth. |
| Bioavailability | Oral: approximately 90-100%; IV: 100%. |
| Onset of Action | Oral: 1-2 hours; IV: immediate (within minutes). |
| Duration of Action | Approximately 24 hours; once-daily dosing maintains therapeutic levels. |
| Molecular Weight | 444.43 |
100 mg orally or intravenously every 12 hours on day 1, then 100 mg daily.
| Dosage form | INJECTABLE |
| Renal impairment | CrCl 10-50 mL/min: no adjustment; CrCl <10 mL/min: reduce dose to 100 mg every 24 hours. |
| Liver impairment | Child-Pugh Class A and B: no adjustment; Class C: reduce dose by 50% or extend interval. |
| Pediatric use | For children >8 years and weight <45 kg: 4.4 mg/kg divided every 12 hours on day 1, then 2.2 mg/kg daily; for ≥45 kg: same as adult dose. |
| Geriatric use | No specific dose adjustment required, but monitor renal function and consider lower starting dose due to potential age-related decline in renal function. |
| 1st trimester | Avoid due to risk of teratogenicity (inhibition of bone growth and tooth discoloration). |
| 2nd trimester | Avoid; associated with permanent tooth discoloration and reversible bone growth inhibition in the fetus. |
| 3rd trimester | Avoid; risks include tooth discoloration and inhibition of bone growth. |
Clinical note
Comprehensive clinical and safety monograph for DOXY 100 (DOXY 100).
| Placental transfer | Crosses placenta readily; detectable in fetal serum and tissues. |
| Breastfeeding | Doxycycline is excreted in breast milk in low concentrations. Theoretical risk of tooth discoloration and bone growth inhibition in the nursing infant, but clinical significance is minimal with short-term use. Consider alternatives if prolonged therapy is required. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to doxycycline or any tetracyclinePatients with porphyriaPregnancy (relative, but generally avoided)Children under 8 years of age
| Precautions | Use during tooth development (last half of pregnancy, infancy, childhood to age 8) may cause permanent tooth discoloration and enamel hypoplasia., Photosensitivity reactions: avoid excessive sunlight or UV light., May cause intracranial hypertension (pseudotumor cerebri) especially in women of childbearing age; discontinue if symptoms occur., Use in pregnancy may cause fetal harm; avoid use during pregnancy unless no alternative., May cause hepatotoxicity, especially with high doses or in patients with pre-existing liver disease., May exacerbate systemic lupus erythematosus., May cause esophageal injury; take with adequate fluids., Consider alternative in patients with renal impairment as anti-anabolic effect can increase BUN., May cause overgrowth of nonsusceptible organisms including C. difficile. |
| Food/Dietary | Avoid dairy products (milk, cheese, yogurt), calcium-fortified foods, and antacids or supplements containing aluminum, calcium, magnesium, iron, or zinc within 2 hours of doxycycline as they reduce absorption. However, doxycycline may be taken with food to reduce GI upset, except heavy dairy. |
Loading safety data…
| Lactation Rating |
| L2 (Safely Preferable in limited data, but caution advised) |
| Teratogenic Risk | Doxycycline (DOXY 100) is a tetracycline antibiotic. Tetracyclines can cause fetal harm when administered to a pregnant woman. Use during the second and third trimesters (weeks 13 to 40) may cause permanent discoloration of deciduous teeth (yellow-gray-brown) and reversible inhibition of bone growth. Use during the first trimester is associated with a small increased risk of neural tube defects and other malformations in some studies, but data are limited. Doxycycline binds calcium less avidly than older tetracyclines, but the same risks apply. Avoid use during pregnancy unless no alternative therapy is available. |
| Fetal Monitoring | Monitor maternal liver function tests, renal function, and complete blood count during prolonged therapy. In neonates exposed in utero after week 25, monitor for signs of bone growth suppression and dental discoloration. No specific fetal monitoring is required, but due to potential risks, fetal ultrasound may be considered if exposure occurred during critical periods of organogenesis. |
| Fertility Effects | Doxycycline has no known direct effect on fertility. It may reduce the efficacy of hormonal contraceptives by altering gut flora, potentially reducing enterohepatic circulation of estrogen. Advise use of additional non-hormonal contraception during treatment and for 7 days after discontinuation. |
| Clinical Pearls | Administer with a full glass of water to reduce esophageal irritation. Avoid giving with milk, antacids, or calcium supplements as they chelate tetracyclines. Doxycycline is highly lipophilic, so it penetrates tissues well. It is the preferred tetracycline in renal impairment due to minimal renal clearance. Use photosensitivity precautions; avoid sun exposure. Can cause benign intracranial hypertension (pseudotumor cerebri); discontinue if headache or visual disturbances occur. In pediatric use (<8 years), avoid due to permanent tooth discoloration and bone growth inhibition. |
| Patient Advice | Take exactly as prescribed; do not stop even if you feel better. · Take with a full glass of water; avoid lying down for at least 30 minutes after taking. · Avoid milk, yogurt, antacids, iron supplements, and calcium supplements within 2 hours of dosing. · Wear sunscreen and protective clothing; doxycycline increases sensitivity to sunlight. · Complete the full course to prevent resistance. · If you miss a dose, take it as soon as you remember unless it is near the time for the next dose; do not double the dose. |