DOXY-LEMMON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DOXY-LEMMON (DOXY-LEMMON).
Doxycycline is a tetracycline antibiotic that inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing aminoacyl-tRNA from binding to the mRNA-ribosome complex.
| Metabolism | Doxycycline is primarily metabolized in the liver via glucuronidation; also undergoes enterohepatic recirculation. It is not significantly metabolized by CYP450 enzymes. |
| Excretion | Renal (approx. 40% as unchanged drug via glomerular filtration), biliary/fecal (approx. 60% as active and inactive metabolites, with significant enterohepatic recycling). Dose adjustment not required in mild renal impairment, but caution in severe hepatic dysfunction. |
| Half-life | Terminal elimination half-life: 18-22 hours (mean ~20 hours) in adults with normal renal function. Clinically, this supports twice-daily dosing; prolonged in severe renal impairment (up to 40-60 hours) or hepatic impairment. |
| Protein binding | 80-90% bound to plasma proteins, primarily albumin. Protein binding decreases in uremia or severe hypoalbuminemia, potentially increasing free fraction. |
| Volume of Distribution | Approximately 0.75-1.0 L/kg (range 0.5-1.5), indicating extensive tissue penetration. High Vd reflects accumulation in bone, teeth, liver, spleen, and inflammatory fluids; clinically relevant for deep-seated infections. |
| Bioavailability | Oral: 88-100% (range 77-100%); absorption is rapid but slightly reduced by food (especially dairy, calcium, iron). Bioavailability after IM is approximately 70-80% due to erratic absorption. Intravenous: 100%. |
| Onset of Action | Oral: 1-2 hours after a single dose for therapeutic concentrations; peak effect on bacterial inhibition occurs within 2-4 hours. Intravenous: immediate onset with peak levels at end of infusion (30-60 min). |
| Duration of Action | Therapeutic levels persist for 12-24 hours after a single dose, supporting 12-hourly dosing. Bacteriostatic activity may last 24-48 hours after discontinuation due to slow release from tissues. |
| Molecular Weight | 444.4 |
100 mg orally or intravenously every 12 hours on day 1, then 100 mg orally or intravenously once daily.
| Dosage form | CAPSULE |
| Renal impairment | For CrCl <30 mL/min: 100 mg every 24 hours. No adjustment for CrCl ≥30 mL/min. Not removed by hemodialysis. |
| Liver impairment | Child-Pugh Class A: no adjustment. Child-Pugh Class B or C: reduce dose by 50% or avoid use due to hepatotoxicity risk. |
| Pediatric use | Children >8 years: 4.4 mg/kg divided into two doses on day 1, then 2.2 mg/kg once daily. Maximum 200 mg/day. Not recommended in children <8 years. |
| Geriatric use | No specific dose adjustment, but monitor renal function; consider starting at lower dose (e.g., 100 mg once daily) due to age-related renal impairment. |
| 1st trimester | Doxycycline is contraindicated in first trimester due to risk of fetal harm (skeletal development, teeth discoloration). Category D. |
| 2nd trimester | Contraindicated in second trimester due to potential for teeth discoloration and bone growth retardation in fetus. |
| 3rd trimester | Contraindicated in third trimester due to risk of permanent teeth discoloration and enamel hypoplasia in the developing fetus. |
Clinical note
Comprehensive clinical and safety monograph for DOXY-LEMMON (DOXY-LEMMON).
| Placental transfer | Doxycycline crosses the placenta extensively. Fetal serum concentrations reach approximately 60-100% of maternal levels. |
| Breastfeeding | Doxycycline is excreted in breast milk in low concentrations. Theoretical risk of teeth discoloration and bone growth suppression in nursing infants; however, absorption by infant is minimal due to calcium chelation in milk. Caution advised; alternative antibiotics preferred during breastfeeding. |
■ FDA Black Box Warning
None (doxycycline does not have a black box warning; however, tetracyclines during tooth development may cause permanent tooth discoloration and enamel hypoplasia).
| Serious Effects |
Hypersensitivity to doxycycline or any tetracyclinePregnancy (all trimesters)Breastfeeding (relative contraindication; caution advised)Children under 8 years of age (risk of permanent teeth discoloration)Severe hepatic impairment
| Precautions | Photosensitivity: avoid excessive sunlight or UV light, Esophageal ulceration: take with adequate fluids, avoid lying down after dose, Use in pregnancy: category D; avoid in pregnant women (risk of fetal harm, particularly skeletal development), Use in children under 8 years: may cause permanent tooth discoloration and bone growth retardation, Hepatotoxicity: rare, but monitor liver function in prolonged therapy, Intracranial hypertension: report headaches, visual disturbances, Overgrowth of nonsusceptible organisms including fungi, Potential for Clostridioides difficile-associated diarrhea |
| Food/Dietary | Dairy products (milk, cheese, yogurt) can chelate doxycycline, reducing absorption. Avoid taking with dairy or calcium-rich foods within 2 hours of the dose. High-iron foods and supplements also impair absorption. Alcohol may reduce effectiveness and increase hepatotoxicity risk. Avoid concurrent intake of antacids, bismuth subsalicylate, and zinc. |
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| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Doxycycline is a tetracycline antibiotic that crosses the placenta. First trimester: Avoid due to potential teratogenic effects (limb abnormalities, neural tube defects) based on animal data, though human data are limited. Second and third trimesters: Contraindicated due to risk of permanent tooth discoloration (yellow-gray-brown) and enamel hypoplasia in the fetus, and inhibition of skeletal growth (reversible if short course). Category D. |
| Fetal Monitoring | Monitor maternal liver function and renal function during therapy. For fetal: ultrasound if first-trimester exposure to assess anatomy. No specific monitoring required for second/third trimester short courses. |
| Fertility Effects | No known adverse effects on fertility in humans. Animal studies show no impairment. |
| Clinical Pearls | DOXY-LEMMON (doxycycline hyclate) is a tetracycline antibiotic with activity against atypical pathogens. Avoid in children <8 years due to tooth discoloration and bone growth impairment. Use with caution in hepatic impairment. Photosensitivity is common; advise sun avoidance. Administer with a full glass of water to prevent esophageal irritation. Can be taken with food if GI upset occurs, but avoid dairy, antacids, iron, and calcium within 2 hours of dosing. Monitor for superinfection, including C. difficile diarrhea. |
| Patient Advice | Take exactly as prescribed; do not skip doses or stop early even if you feel better. · Take with a full glass of water and remain upright for at least 30 minutes after dosing to reduce risk of esophageal irritation. · Avoid sun exposure and use sunscreen; this medication can cause severe sunburn. · Do not take with dairy products (milk, cheese, yogurt), antacids, iron supplements, or calcium supplements within 2 hours before or after your dose. · If you are using oral contraceptives, consider additional non-hormonal contraception as effectiveness may be reduced. · Report any severe headache, vision changes, or skin rash to your healthcare provider immediately. · This medication may cause permanent tooth discoloration if used during tooth development (last half of pregnancy, infancy, childhood up to age 8 years). · Store at room temperature, away from light and moisture. Keep out of reach of children. |