DORYX

Clinical safety rating: caution

Comprehensive clinical and safety monograph for DORYX (DORYX).

How it works

Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing the addition of amino acids to the growing peptide chain.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for DORYX (DORYX).

Breastfeeding	Doxycycline is excreted in breast milk in low concentrations; M/P ratio 0.6-1.0. Theoretical risk of dental staining in infants; generally avoided if alternative available, but short-term use may be acceptable with infant monitoring.
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

Warnings & precautions

■ FDA Black Box Warning

No black box warning.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to doxycycline or any tetracycline","Pregnancy (relative; Category D)","Children under 8 years of age (relative; due to tooth discoloration)"]

Clinical Precautions

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"]

Clinical Tips & Counseling

Drug interactions

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DORYX

Clinical safety rating: caution

Comprehensive clinical and safety monograph for DORYX (DORYX).

How it works

Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, preventing the addition of amino acids to the growing peptide chain.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for DORYX (DORYX).

Breastfeeding	Doxycycline is excreted in breast milk in low concentrations; M/P ratio 0.6-1.0. Theoretical risk of dental staining in infants; generally avoided if alternative available, but short-term use may be acceptable with infant monitoring.
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

Warnings & precautions

■ FDA Black Box Warning

No black box warning.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to doxycycline or any tetracycline","Pregnancy (relative; Category D)","Children under 8 years of age (relative; due to tooth discoloration)"]