doxycycline
Periostat, Vibramycin

doxycycline calcium
Vibramycin

doxycycline hyclate
Bio-Tab, Doryx, Doxy 100, Doxy 200, Doxy Caps, Doxychel Hyclate, Periostat, Vibramycin, Vibra-Tabs

doxycycline monohydrate
Monodox, Vibramycin

Available forms
Available by prescription only
doxycycline calcium
Syrup: 50 mg/5 ml
doxycycline hyclate
Capsules: 20 mg, 50 mg
Capsules (delayed-release): 100 mg
Powder for injection: 100 mg, 200 mg
Tablets: 20 mg
Tablets (film-coated): 20 mg, 50 mg, 100 mg
doxycycline monohydrate
Capsules: 50 mg, 100 mg
Oral suspension: 25 mg/5 ml

Indications and dosages
 Infections caused by sensitive organisms. Adults and children who weigh 45 kg (99 lb) or more: 100 mg P.O. q 12 hours on day 1; then 100 mg P.O. daily. Or, 200 mg I.V. on day 1 in one or two infusions; then 100 to 200 mg I.V. daily.
Children older than age 8 who weigh less than 45 kg: 4.4 mg/kg P.O. or I.V. daily, divided q 12 hours day 1; then 2.2 to 4.4 mg/kg daily.
 Gonorrhea in patients allergic to penicillin. Adults: 100 mg P.O. b.i.d. for 7 days; or 300 mg P.O. initially and repeat dose in 1 hour.
 Syphilis in patients allergic to penicillin. Adults: 100 mg P.O. b.i.d. for 2 weeks (early detection) or 4 weeks (if longer than 1 year’s duration).
 Chlamydia trachomatis nongonococcal urethritis, and uncomplicated urethral, endocervical, or rectal infections. Adults: 100 mg P.O. b.i.d. for at least 7 days.
 Acute pelvic inflammatory disease (PID) ◇. Adults: 250 mg I.M. ceftriaxone, followed by 100 mg doxycycline P.O. b.i.d. for 14 days. Hospitalized adults and adolescents can receive 100 mg I.V. or P.O. q 12 hours with 2 g cefoxitin I.V. q 6 hours or 2 g cefotetan I.V. q 12 hours. Continue until at least 24 hours after significant clinical improvement. Then switch to doxycycline 100 mg P.O. b.i.d. to complete 14 days of treatment.
 Acute epididymoorchitis caused by C. trachomatis or Neisseria gonorrhoeae. Adults: 100 mg P.O. b.i.d for at least 10 days.
 Prevention of traveler’s diarrhea commonly caused by enterotoxigenic Escheria coli. Adults: 100 mg P.O. daily for up to 3 days.
 Prophylaxis for rape victims ◇. Adults and adolescents: 100 mg P.O. b.i.d. for 7 days after a single 2-g oral dose of metronidazole is given in conjunction with a single 125-mg I.M. dose of ceftriaxone.
 Chemoprophylaxis for malaria in travelers to areas where chloroquine-resistant Plasmodium falciparum is endemic and mefloquine is contraindicated ◇. Adults: 100 mg P.O. once daily. Begin prophylaxis 1 to 2 days before travel to malarious areas; continue daily while in affected area, and continue for 4 weeks after return from malarious area.
Children older than age 8: Give 2 mg/kg P.O. daily as a single dose; don’t exceed 100 mg daily. Use the same dosage schedule as for adults.
 Lyme disease ◇. Adults and children age 9 and older: 100 mg P.O. b.i.d. or t.i.d. for 10 to 30 days.
 Pleural effusions related to cancer ◇. Adults: 500 mg doxycycline diluted in 250 ml normal saline and instilled into pleural space via chest tube.
 Trachoma. Adults: 2.5 to 4 mg/kg P.O. once daily for 36 to 40 days.
 Adjunct to other antibiotics for inhalation, GI, and oropharyngeal anthrax. Adults: Initially, 100 mg every 12 hours I.V. until susceptibility test results are known. Switch to 100 mg P.O. b.i.d. when clinically appropriate. Treat for 60 days total.
Children older than age 8 who weigh more than 45 kg (99 lb): 100 mg every 12 hours I.V.; then switch to 100 mg P.O. b.i.d. when clinically appropriate. Treat for 60 days total.
Children older than age 8 who weigh 45 kg or less: 2.2 mg/kg every 12 hours I.V.; then switch to 2.2 mg/kg P.O. b.i.d. when clinically appropriate. Treat for 60 days total.
Children age 8 and younger: 2.2 mg/kg every 12 hours I.V.; then switch to 2.2 mg/kg P.O. b.i.d. when clinically appropriate. Treat for 60 days total.
 Cutaneous anthrax. Adults: 100 mg P.O. q 12 hours for 60 days.
Children older than age 8 who weigh more than 45 kg: 100 mg P.O. q 12 hours for 60 days.
Children older than age 8 who weigh 45 kg or less: 2.2 mg/kg P.O. q 12 hours for 60 days.
Children age 8 and younger: 2.2 mg/kg P.O. q 12 hours for 60 days.
 Adjunct to scaling and root planing to promote attachment level gain and to reduce pocket depth in patients with adult periodontitis (Periostat). Adults: 20 mg P.O. b.i.d. more than 1 hr before or 2 hours after the morning and evening meals and after scaling and root planing. Treatment is effective for 9 months.

Pharmacodynamics
Antibacterial action: Doxycycline is bacteriostatic; it binds reversibly to ribosomal units, thereby inhibiting bacterial protein synthesis.
 Spectrum of activity of the drug includes many gram-negative and gram-positive organisms, Mycoplasma, Rickettsia, Chlamydia species, and spirochetes.

Pharmacokinetics
Absorption: About 90% to 100% is absorbed after oral administration. Doxycycline has the least affinity for calcium of all tetracyclines; its absorption is insignificantly altered by milk or other dairy products.
Distribution: Distributed widely into body tissues and fluids, including synovial, pleural, prostatic, and seminal fluids; bronchial secretions; saliva; and aqueous humor. CSF penetration is poor. Doxycycline readily crosses the placental barrier, and is 25% to 93% protein-bound.
Metabolism: Insignificantly metabolized; some hepatic degradation occurs.
Excretion: Excreted primarily unchanged in urine by glomerular filtration; some may be excreted in breast milk. Plasma half-life is 22 to 24 hours after multiple dosing in adults with normal renal function; 20 to 30 hours in patients with severe renal impairment. Some drug is excreted in feces.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug or other tetracyclines. Use cautiously in patients with impaired renal or hepatic function. Use during last half of pregnancy and in children younger than age 8 may cause permanent discoloration of teeth, enamel defects, and bone growth retardation.

Interactions
Drug-drug. Antacids containing aluminum, calcium, or magnesium; cimetidine; laxatives containing magnesium; oral iron products; sodium bicarbonate; zinc: Decreases absorption of oral doxycycline. Give antibiotic 1 hour before or 2 hours after these drugs.
Carbamazepine, hydantoins, phenobarbital: Decreases antibiotic effect. Avoid use together.
Digoxin: Increases bioavailability. Monitor serum digoxin levels. Lowered dosages of digoxin may be needed.
Insulin: Tetracyclines may reduce insulin requirements. Monitor serum glucose level.
Methoxyflurane: Causes nephrotoxicity when used with tetracyclines. Monitor serum levels carefully.
Oral anticoagulants: Increases anticoagulant effect. Monitor PT and INR and adjust dosage as needed.
Oral contraceptives: Decreases contraceptive effectiveness and increases risk of breakthrough bleeding. Advise a nonhormonal form of birth control.
Penicillin: May antagonize bactericidal effects. Administer penicillin 2 to 3 hours before tetracycline.
Drug-lifestyle. Alcohol use: May decrease antibiotic effect. Discourage alcohol use.
Sun exposure: May cause photosensitivity reactions. Advise patient to take precautions.

Adverse reactions
CNS: intracranial hypertension (pseudotumor cerebri).
CV: pericarditis, thrombophlebitis.
EENT: glossitis, dysphagia.
GI: anorexia, epigastric distress, nausea, vomiting, diarrhea, dysphagia, esophageal ulcers, oral candidiasis, enterocolitis, anogenital inflammation.
Hematologic: neutropenia, eosinophilia, thrombocytopenia, hemolytic anemia.
Hepatic: hepatotoxicity.
Skin: maculopapular and erythematous rashes, photosensitivity, increased pigmentation, urticaria.
Other: hypersensitivity reactions (anaphylaxis), permanent discoloration of teeth, enamel defects, bone growth retardation if used in children younger than age 8, superinfection.

Effects on lab test results
• May increase BUN and liver enzyme levels.
• May increase eosinophil count. May decrease hemoglobin and hematocrit and platelet, neutrophil, and WBC counts.

Overdose and treatment
Signs and symptoms of overdose are usually limited to the GI tract.
 Give antacids or empty stomach by gastric lavage if ingestion occurred within the preceding 4 hours.

Special considerations
• Doxycycline causes false-negative results in urine tests using glucose oxidase reagent (Diastix, Chemstrip uG, or glucose enzymatic test strip); parenteral dosage form may cause false-negative Clinitest results.
• Doxycycline also causes false elevations in fluorometric tests for urinary catecholamines.
 ALERT Don’t confuse doxycycline with doxylamine or dicyclomine.
 ALERT Check expiration date. Outdated or deteriorated tetracyclines have been linked to reversible nephrotoxicity (Fanconi’s syndrome).
• Reconstitute powder for injection with sterile water for injection. Use 10 ml in a 100-mg vial and 20 ml in a 200-mg vial. Dilute solution to 100 to 1,000 ml for I.V. infusion. Don’t infuse solutions more concentrated than 1 mg/ml.
• Reconstituted solution is stable for 72 hours if refrigerated and protected from light.
• Give I.V. infusion slowly (minimum 1 hour). Infusion must be completed within 12 hours (within 6 hours in lactated Ringer’s solution or D₅W in lactated Ringer’s solution).
• Don’t give drug S.C. or I.M.
• Drug may be used in patients with impaired renal function; it doesn’t accumulate or cause a significant rise in BUN levels.
• Cutaneous anthrax, with signs of systemic involvement, extensive edema, or lesions on the head or neck, requires I.V. therapy and a multidrug approach.
• Additional antimicrobials for anthrax multidrug regimens include rifampin, vancomycin, penicillin, ampicillin, chloramphenicol, imipenem, clindamycin, and clarithromycin.
• Corticosteroids may be considered as adjunctive therapy for patients with anthrax who have severe edema and for meningitis, based on experience with bacterial meningitis of other etiologies.
• Ciprofloxacin or doxycycline are first-line therapy for anthrax. Amoxicillin 500 mg P.O. t.i.d. for adults and 80 mg/kg/day divided q 8 hours for children is an option for completion of therapy after clinical improvement.
• Follow current CDC recommendations for anthrax.
• Immunocompromised patients should receive the usual doses and regimens for anthrax.
• With larger doses or prolonged therapy, watch for superinfection, especially in high-risk patients.
Pregnant patients
• Adverse effects on developing teeth and bones are dose-limited; doxycycline might be used in pregnant women for a short time (7 to 14 days) before 6 months of gestation.
• Pregnant women should receive the usual doses and regimens for anthrax.
Breast-feeding patients
• Avoid use in breast-feeding women.
Pediatric patients
• Avoid use in children younger than age 8 unless other drugs prove ineffective or are contraindicated. Tetracyclines may cause permanent tooth discoloration and enamel hypoplasia.

Patient education
• Instruct patient to take entire amount as prescribed, even if he feels better.
• Tell patient to take oral form with food or milk if GI upset occurs.
• Tell patient to check tongue for fungal infection. Stress good oral hygiene.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use