Doxycycline

VIBRAMYCIN

What it isTetracycline inhibiting the 30S ribosomal subunit; atypical, tick-borne and skin infections.

Why this oneUsable in renal failure unlike other tetracyclines, and first-line for Rickettsia at any age.

What limits itPhotosensitivity and pill esophagitis — take upright with water. Cations bind it; avoid in pregnancy.

FDA-approved for

FDA dosing	Population	Start	Target	Max
Bacterial infection	Adults	200 mg day 1 (100 mg q12h)	100 mg/day	100 mg q12h (severe/chronic)
Bacterial infection	Peds >8 y & <45 kg	4.4 mg/kg/day divided BID day 1	2.2 mg/kg/day	2.2 mg/kg q12h (severe/life-threatening)
Uncomplicated gonorrhea	Adults	100 mg BID × 7 days	100 mg BID	300 mg stat then 300 mg in 1 h (single-visit alt.)

Renal No excessive accumulation at usual doses in renal impairment (no adjustment)

Hepatic Undefined

Take with adequate fluid to reduce risk of esophageal irritation/ulceration.
If gastric irritation occurs, may give with food or milk (absorption not markedly affected).
Streptococcal infections: continue therapy ≥10 days.
Children ≥45 kg receive the adult dose.

Photosensitivity
Permanent tooth discoloration/enamel hypoplasia and reversible bone growth inhibition with use in later pregnancy/childhood
Superinfection / C. difficile
Intracranial hypertension

Pregnancy Tetracyclines may cause fetal harm (tooth discoloration, inhibition of bone growth) with use in 2nd/3rd trimester

Lactation Undefined

NO BOXED WARNINGS

Principal riskEsophagitis if taken without adequate fluid

Cost, est. cash$300–$2,500/month

Generic entryLong generic

Therapeutic safety burden1 / 4

Overdose danger1 / 4

Weight-gain liability0 / 4

Sedation liability0 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk2 / 4

Legacy pregnancy categoryD

Defining liabilityAllergy, gastrointestinal effects and agent-specific renal, hepatic, hematologic or interaction risks.

Box: minimal PK interactions