MONODOX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MONODOX (MONODOX).
Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, blocking the attachment of aminoacyl-tRNA to the mRNA-ribosome complex.
| Metabolism | Metabolized primarily in the liver via glucuronidation; does not undergo significant CYP450-mediated metabolism. |
| Excretion | Renal: ~40% (glomerular filtration, tubular secretion); biliary: ~20-60% (enterohepatic circulation); fecal: ~30% (unabsorbed or excreted in bile). |
| Half-life | Terminal elimination half-life: 14-22 hours (mean ~18 hours) in adults; prolonged up to 24-48 hours in renal impairment; no dose adjustment in mild-moderate renal impairment but caution in severe (CrCl <30 mL/min). |
| Protein binding | 88-96% bound to plasma proteins (primarily albumin, also lipoproteins). |
| Volume of Distribution | 1.3-1.8 L/kg (extensive tissue penetration; distributes into bone, teeth, liver, spleen, pleural fluid, synovial fluid, and CSF (inflamed meninges)). |
| Bioavailability | Oral (fasting): 95-100% (food reduces absorption by ~10-20%); IV: 100%. |
| Onset of Action | Oral: 1-2 hours (time to peak serum concentration ~2-4 hours); IV: immediate upon completion of infusion. |
| Duration of Action | 12-24 hours (bacteriostatic effect persists, trough levels maintained with twice-daily dosing; longer for renal elimination). |
| Action Class | Tetracyclines |
| Brand Substitutes | Doxid 100mg Tablet, Rapidoxyn 100mg Tablet, Doxygee 100mg Tablet, Doxytop 100mg Tablet, Detab Tablet, G Dox Capsule, Duradox Capsule, Doxycyline Capsule |
100 mg orally or IV every 12 hours on day 1, then 100 mg orally or IV every 24 hours; for severe infections, 100 mg every 12 hours.
| Dosage form | CAPSULE |
| Renal impairment | No dose adjustment required in mild to moderate renal impairment; avoid use in severe renal impairment (CrCl <10 mL/min) due to anti-anabolic effects; if necessary, reduce dose or extend dosing interval. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% or extend interval; Child-Pugh C: contraindicated or use with extreme caution at reduced dose. |
| Pediatric use | For children ≥8 years: 4.4 mg/kg orally or IV on day 1 (divided every 12 hours), then 2.2 mg/kg once daily; maximum 100 mg/day. Not recommended for children <8 years due to permanent tooth discoloration. |
| Geriatric use | Use lowest effective dose due to increased risk of photosensitivity, gastrointestinal effects, and potential for drug accumulation; monitor renal function; no specific dose adjustment recommended for elderly with normal renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MONODOX (MONODOX).
| Breastfeeding | Not recommended during breastfeeding. Doxycycline is excreted into breast milk in low concentrations (M/P ratio unknown); theoretical risk of permanent tooth discoloration and bone growth inhibition in nursing infants. American Academy of Pediatrics considers doxycycline compatible with breastfeeding for short-term use, but alternative agents preferred. |
| Teratogenic Risk | FDA Pregnancy Category D. Tetracyclines cross placenta. First trimester: No increased risk major malformations from limited human data; animal studies show skeletal anomalies. Second and third trimesters: Avoid due to risk of permanent tooth discoloration (yellow-gray-brown) and enamel hypoplasia; also inhibit fetal bone growth. Increased risk of maternal hepatotoxicity and pancreatitis. |
■ FDA Black Box Warning
No FDA black box warning identified.
| Serious Effects |
["Hypersensitivity to doxycycline or any tetracycline class antibiotic","Use in children under 8 years of age (except for anthrax or tick-borne diseases)","Pregnancy (relative contraindication; use only if benefit outweighs risk)"]
| Precautions | ["Risk of tooth discoloration and enamel hypoplasia in children under 8 years old","Risk of photosensitivity (exaggerated sunburn reaction)","Risk of esophageal ulceration (take with adequate fluids)","Hepatotoxicity (rare)","Pseudomembranous colitis (Clostridioides difficile-associated diarrhea)","Intracranial hypertension (pseudotumor cerebri)","Use during pregnancy may cause fetal harm","Inhibition of bone growth in premature infants"] |
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| Fetal Monitoring | Monitor maternal hepatic function (LFTs) and renal function. Fetal ultrasound for skeletal development if exposure in 2nd/3rd trimester. Assess infant for jaundice, tooth discoloration after birth. |
| Fertility Effects | No known adverse effects on human fertility. Animal studies do not indicate impaired fertility. Tetracyclines may decrease spermatogenesis at high doses in animals, but clinical significance unclear. |