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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DOXY 100 (DOXY 100).
| Breastfeeding | Doxycycline is excreted into human milk at low concentrations (M/P ratio approximately 0.3-0.4). The American Academy of Pediatrics considers tetracyclines compatible with breastfeeding, but theoretical risks of teeth discoloration and bone growth inhibition in nursing infants exist. The amount absorbed by the infant is likely small, but caution is advised. Alternative antibiotics are preferred. |
| 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. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to any tetracycline antibiotic","Pregnancy (risk of fetal harm)","Children under 8 years of age (except for anthrax or other serious conditions where benefit outweighs risk)"]
| 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."] |
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| 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. |