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Doxycycline is an antibiotic in the tetracycline family. It is fairly effective for acne, and it comes in several dose strengths. All forms of doxycycline are best taken with meals, and none are safe for pregnant, conceiving, or breastfeeding women. Doxycycline treats only the red, pus-filled pimples of acne; it won't improve acne cysts (nodules) deep under the skin. Doxycycline won’t treat clogged pores: blackheads or whiteheads.

Side Effects
Potential side effects fall into two categories: those associated with swallowing the drug (nausea, irritation of the esophagus, heartburn, and even potentially vomiting) and those associated with the drug circulating throughout the body (loose stools, yeast infection in women, and easy sunburning). Taking doxycycline with meals helps to prevent those in the first category, while taking sub-antimicrobial doses (see below) helps minimize the chance of experiencing those in the second category.

Sub-antimicrobial Dosing

At high doses, doxycycline inhibits the growth of the acne-associated bacterium
Propionibacterium acnes. However, at low doses (≤ 40 mg daily dose) called sub-antimicrobial doses, doxycycline also helps acne by reducing inflammation in the skin. Generally, I prefer to use sub-antimicrobial dosing whenever possible.

Oracea is a 40 mg capsule of doxycycline combining 30 mg immediate-release doxycycline with 10 mg delayed release doxycycline. While it is FDA-approved to treat rosacea, it is also effective in the treatment of acne, in my experience. Because 40 mg of Oracea daily is sub-antimicrobial (meaning that the doxycycline isn’t strong enough to kill bacteria at this low dose), there are far fewer side effects. Loose stools and yeast infection in women are rarely seen with Oracea. Also, nausea, heartburn, stomach upset, and easy sunburning are less common with Oracea 40 mg daily than with higher doses of doxycycline in my experience. If Oracea is not available, I would recommend doxycycline 20 mg tablets twice a day as a generic alternative for sub-antimicrobial dose doxycycline.

Additionally, antibiotic resistance can occur in the community if many patients take anti-microbial dose (full dose) doxycycline. However, antibiotic resistance does not occur at sub-antimicrobial doses of doxycycline.

Risk of Inflammatory Bowel Disease
There is evidence that long-term usage of anti-microbial dose (full dose) tetracycline-type antibiotics or multiple short courses of these antibiotics increase the risk of developing inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease, as demonstrated in this 2012
article published in the medical journal Pediatrics. However, sub-antimicrobial dosing of doxycycline probably does not increase the risk of developing inflammatory bowel diseases, as the mechanism of action by which this increased risk occurs seems to be related to anti-bacterial activity against intestinal flora. Sub-antimicrobial doxycycline dosing does not alter the intestinal or vaginal bacterial flora, as shown in this study.

High Dose Extended Release Doxycycline
If higher-dose doxycycline is needed, then an extended-release form of the drug called doxycycline hyclate ER (brand name
Doryx) is preferred in my opinion over plain doxycycline due to fewer side effects. The extended release formula helps prevent the side effects of nausea, heartburn, and stomach upset. However, loose stools, yeast infection in women, and easy sunburning can all be seen with doxycycline hyclate ER (Doryx) at doses above 50 mg daily.

Other Considerations
Absorption of doxycycline is impaired if taken with high amounts of calcium or magnesium, as might be found in milk, certain anti-acid medications (calcium carbonate), calcium supplements, or multi-vitamins/multi-minerals.

Doxycycline is safe for patient with low kidney function (chronic kidney disease) because it is mostly excreted in the stool. Only a small fraction of the daily dose of doxycyline is excreted in the urine. Treatment with doxycycline does not lead to deterioration of kidney function or drug accumulation, even in advanced kidney failure. However, patients with significant liver disease may benefit from an alternate choice of acne treatment.

Children under 8 years old should not take doxycycline or any member of the tetracycline family for the treatment of acne, as this could impair healthy formation of the teeth.