Doxycycline vs. Azithromycin

• Doxycycline and azithromycin are antibiotics used to treat many different types of bacterial infections.
• Brand names for doxycycline include Vibramycin, Oracea, Adoxa, Atridox, Acticlate, Acticlate Cap, Doryx, Doxteric, Doxy, and Monodox.
• Brand names for azithromycin include Zithromax, Zithromax Tri-Pak, Zithromax Z-Pak, and Zmax.
• Doxycycline and azithromycin are different types of antibiotics. Doxycycline is a tetracycline antibiotic and azithromycin is a macrolide antibiotic.
• Side effects of doxycycline and azithromycin that are similar include diarrhea or loose stools, nausea, abdominal pain, and vomiting.
• Side effects of doxycycline that are different from azithromycin include tooth discoloration if used in persons below 8 years of age and exaggerated sunburn.
• Side effects of azithromycin that are different from doxycycline include rash, nervousness, vaginitis, tongue discoloration, ringing in the ears, and indigestion.

Doxycycline is a tetracycline antibiotic used to treat many different types of infections, including respiratory tract infections due to Hemophilus influenzae, Streptococcus pneumoniae, or Mycoplasma pneumoniae. It is used also in the treatment of syphilis, acne, periodontal disease, non-gonococcal urethritis (due to Ureaplasma), Rocky Mountain spotted fever, typhus, chancroid, cholera, brucellosis, and anthrax.

Azithromycin is a macrolide antibiotic related to erythromycin and clarithromycin (Biaxin) used to treat bacterial infections such as otitis media (infection of the middle ear), tonsillitis, laryngitis, bronchitis, pneumonia, sinusitis, uncomplicated skin and skin structure infections, Mycobacterium avium complex, acute bacterial flare ups of chronic obstructive pulmonary disease (COPD), acute pelvic inflammatory disease, and several sexually transmitted infectious diseases (STDs) such as non-gonococcal urethritis and cervicitis.

Doxycycline

Doxycycline is generally well-tolerated. The most common side effects are

• diarrhea or loose stools,
• nausea,
• abdominal pain, and
• vomiting.

Tetracyclines, such as doxycycline, may cause tooth discoloration if used in persons below 8 years of age. Exaggerated sunburn can occur with tetracyclines; therefore, sunlight should be minimized during treatment.

Azithromycin

The most common side effects of azithromycin are:

• Diarrhea or loose stools
• Nausea
• Abdominal pain
• Vomiting

Other possible side effects of azithromycin include:

• Rash
• Nervousness
• Vaginitis
• Tongue discoloration
• Ringing in the ears
• Indigestion

Possible serious side effects of azithromycin include:

• Angioedema
• Abnormal liver tests
• Cholestatic jaundice
• Steven-Johnson Syndrome
• Serious allergic reactions
• Abnormal heart beats

Antibiotics can alter the normal bacteria in the colon and encourage overgrowth of some bacteria such as Clostridium difficile, which causes inflammation of the colon (pseudomembranous colitis). Patients who develop signs of pseudomembranous colitis after starting azithromycin (diarrhea, fever, abdominal pain, and possibly shock) should contact their physician immediately.

• The absorption of doxycycline is not markedly affected by food, and therefore, it can be taken with meals.
• For most infections, doxycycline is taken once or twice daily for 7 to 14 days.
• For adult infections, the usual dose of oral doxycycline is 200 mg on the first day of treatment (100 mg every 12 hours) followed by a dose of 100 to 200 mg/day as a single dose or divided and administered twice daily.

• Azithromycin (except Zmax) can be taken with or without food, but food reduces stomach upset.
• Zmax should be taken on an empty stomach 1 hour before or 2 hours after a meal since food reduces its absorption.
• The adult azithromycin dose is 500-2000 mg in multiple or single doses.
• For most infections, azithromycin is taken once daily for a relatively short course of treatment (usually five days).
• The first dose is often a "double dose," twice as much as the remainder of the doses given.
• For acute bacterial sinusitis, azithromycin way be taken once daily for three days.
• Zmax usually is given as a single 2 gm dose.

Doxycycline

• It is recommended that doxycycline not be taken at the same time as aluminum, magnesium, or calcium based antacids, such as Mylanta, Maalox, Tums, or Rolaids because, like food, these medications bind doxycycline in the intestine and prevent its absorption. Similarly, doxycycline should not be taken with minerals (such as calcium or iron) or with bismuth subsalicylate (Pepto Bismol).
• Doxycycline may enhance the activity of warfarin (Jantoven, Coumadin) and cause excessive "thinning" of the blood leading to exaggerated bleeding, necessitating a reduction in the dose of warfarin. Phenytoin (Dilantin), carbamazepine (Tegretol), and barbiturates (such as phenobarbital) may enhance the metabolism (destruction) of doxycycline thus making it less effective.
• Doxycycline may interfere with the action of penicillins and should not be combined with penicillins. It may also reduce the effect of oral contraceptives. Combining tetracycline and methoxyflurane (Penthrane) may reduce kidney function.

Azithromycin

• Azithromycin (except Zmax) should not be taken at the same time as aluminum- or magnesium-based antacids, such as Mylanta or Maalox, because antacids will bind the azithromycin and prevent it from being absorbed from the intestine.

Doxycycline

• Tetracycline antibiotics, such as doxycycline, can have toxic effects on development of bone in the fetus. Therefore, tetracyclines are not recommended during pregnancy unless there is no other appropriate antibiotic.
• Doxycycline is secreted into breast milk but the extent of absorption by the breastfed infant is not known. Since tetracyclines can cause toxic effects on bone, the use of tetracyclines in nursing mothers is of concern. The physician must decide whether to recommend that a nursing mother discontinue nursing during treatment with tetracyclines or change to a different antibiotic.

Azithromycin

• There are no adequate studies of azithromycin in pregnant women. Azithromycin should only be used during pregnancy if it is clearly necessary.
• It is not known if azithromycin is secreted in breast milk.