Apo-Doxy , Doryx, Doxy, Doxycin , Monodox, Novodoxylin , Vibramycin, Vibra-Tabs
Classifications: antibiotic; tetracycline;
Therapeutic: antibiotic

Prototype: Tetracycline
Pregnancy Category: D


50 mg, 75 mg, 100 mg capsules, tablets; 200 mg injection


Semisynthetic broad-spectrum long-acting tetracycline antibiotic derived from oxytetracycline. Doxycycline is more lipophilic than the other tetracyclines, which allows it to pass easily through the lipid layer of bacteria where reversible binding to the 30 S ribosomal subunits of bacteria occurs. This blocks the binding of transfer RNA (tRNA) to the messenger RNA (mRNA) of the bacteria, resulting in inhibition of bacterial protein synthesis.

Therapeutic Effect

Primarily bacteriostatic against both gram-positive and gram-negative bacteria. Similar in use to tetracycline.


Similar to those of tetracycline (e.g., chlamydial and mycoplasmal infections); gonorrhea, syphilis in penicillin-allergic patients; rickettsial diseases; acute exacerbations of chronic bronchitis.

Unlabeled Uses

Treatment of acute PID, leptospirosis, prophylaxis for rape victims, suppression and chemoprophylaxis of chloroquine-resistant Plasmodium falciparum malaria, short-term prophylaxis and treatment of travelers' diarrhea caused by enterotoxigenic strains of Escherichia coli. Intrapleural administration for malignant pleural effusions, post-exposure anthrax treatment and prophylaxis.


Sensitivity to any of the tetracyclines; use during period of tooth development including last half of pregnancy; pregnancy (category D), lactation, infants, and children <8 y (causes permanent yellow discoloration of teeth, enamel hypoplasia, and retardation of bone growth).

Cautious Use

Alcoholism; hepatic disease; GI disease; sulfite hypersensitivity; sunlight (UV) exposure.

Route & Dosage

Adult: PO/IV 100 mg q12h on day 1, then 100 mg/d as single dose (max: 100 mg q12h)
Child (>8 y): PO/IV 4.4 mg/kg in 1–2 doses on day 1, then 2.2–4.4 mg/kg/d in 1–2 divided doses

Adult: PO 200 mg immediately, followed by 100 mg h.s., then 100 mg b.i.d. for 3 d

Primary and Secondary Syphilis
Adult: PO 300 mg/d in divided doses for at least 10 d

Travelers' Diarrhea
Adult: PO 100 mg/d during risk period (up to 2 wk) beginning day 1 of travel

Acute Pelvic Inflammatory Disease
Adult: IV 100 mg q12h until improved, then 100 mg PO bid to complete 14 d

Adult: PO 100 mg q12h on day 1, then 100 mg q.d.
Child: PO >8 y, >45 kg, 100 mg q12h on day 1, then 100 mg q.d.; >8 y, <45 kg, 2.2 mg/kg q12h day 1, then 2.2 mg/kg/q.d.

Anthrax Post-Exposure
Adult/Adolescent/Child (>8 y, >45 kg): IV 100 mg q12h, then switch to PO for a total of 60
Child (≤45 kg or 8 y): IV 2.2 mg/kg q12h, then switch to PO for a total of 60


  • Check expiration date. Degradation products of tetracycline are toxic to the kidneys.
  • Give with food or a full glass of milk to minimize nausea without significantly affecting bioavailability of drug (UNLIKE MOST TETRACYCLINES).
  • Consult physician about ordering the oral suspension for patients who are bedridden or have difficulty swallowing.

PREPARE: Intermittent: Reconstitute by adding 10 mL sterile water for injection, or D5W, NS, LR, D5/LR, or other diluent recommended by manufacturer, to each 100 mg of drug. ??Further dilute with 100–1000 mL (per 100 mg of drug) of compatible infusion solution to produce concentrations ranging from 0.1 to 1 mg/mL. 

ADMINISTER: Intermittent: IV infusion rate will usually be prescribed by physician. Duration of infusion varies with dose but is usually 1–4 h. Recommended minimum infusion time for 100 mg of 0.5 mg/mL solution is 1 h. Infusion should be completed within 12 h of dilution.When diluted with LR or D5/LR, infusion must be completed within 6 h to ensure adequate stability. Protect all solutions from direct sunlight during infusion.  

INCOMPATIBILITIES Solution/additive: Potassium phosphate. Y-site: Allopurinol, heparin, meropenem, piperacillin/tazobactam, TPN.

  • Store oral and parenteral forms (prior to reconstitution) in tightly covered, light-resistant containers at 15°–30° C (59°–86° F) unless otherwise directed.
  • Refrigerate reconstituted solutions for up to 72 h. After this time, infusion must be completed within 12 h.

Adverse Effects (≥1%)

Special Senses: Interference with color vision. GI: Anorexia, nausea, vomiting, diarrhea, enterocolitis; esophageal irritation (oral capsule and tablet). Skin: Rashes, photosensitivity reaction. Other: Thrombophlebitis (IV use), superinfections.

Diagnostic Test Interference

Like other tetracyclines, doxycycline may cause false increases in urinary catecholamines (fluorometric methods); false decreases in urinary urobilinogen; false-negative urine glucose with glucose oxidase methods (e.g., Clinistix, TesTape); parenteral doxycycline (containing ascorbic acid) may cause false-positive determinations using Benedict's reagent or Clinitest.


Drug: antacids, iron preparation, calcium, magnesium, zinc, kaolin-pectin, sodium bicarbonate can significantly decrease absorption; effects of both doxycycline and desmopressin antagonized; increases digoxin absorption, thus increasing risk of digoxin toxicity; methoxyflurane increases risk of renal failure.


Absorption: Completely absorbed from GI tract. Peak: 1.5–4 h. Distribution: Penetrates eye, prostate, and CSF; crosses placenta; distributed into breast milk. Metabolism: In GI tract. Elimination: 20–30% in urine and 20–40% in feces in 48 h. Half-Life: 14–24 h.

Nursing Implications

Assessment & Drug Effects

  • Report sudden onset of painful or difficult swallowing promptly to physician. Doxycycline (capsule and tablet forms) is associated with a comparatively high incidence of esophagitis, especially in patients >40 y.
  • Report evidence of superinfections (see Appendix F).

Patient & Family Education

  • Take capsule or tablet forms with a full glass (240 mL) of water to ensure passage into stomach and prevent esophageal ulceration. Avoid taking capsule or tablet within 1 h of lying down or retiring.
  • Avoid exposure to direct sunlight and ultraviolet light during and for 4 or 5 d after therapy is terminated to reduce risk of phototoxic reaction. Phototoxic reaction appears like an exaggerated sunburn. Sunscreens provide little protection.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2023 Last Updated On: 01/27/2023 (0)
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