A Phase 4 interventional study of Doxycycline 40 MG ( 20mg twice daily) and Doxycycline 200 MG ( 100 mg twice daily) in Ocular Rosacea and Antimicrobial Resistance, sponsored by University of California, San Francisco. Completed at 1 site in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-27.
Sponsored by University of California, San Francisco · Phase 4, Interventional, and Supportive care
Ocular rosacea is an inflammatory disease of the eyelids and ocular surface. Like the facial disease, the ocular condition is chronic and recurrent. Sequelae of ocular rosacea vary from mild to severe. Ocular rosacea may cause chronic eye redness, blepharitis, recurrent chalazia, dry eye, corneal erosion, corneal vascularization, and corneal ulceration. Rosacea affecting the cornea can result in vision loss.
Prescription eye drops and ointments can be used topically to control mild ocular rosacea. However, severe disease, or rosacea that is not well controlled with local treatments is treated systemically. The most commonly used systemic treatment for rosacea is the bacteriostatic antibiotic doxycycline. Rosacea treatment doses of doxycycline vary widely. Treatment-dose doxycycline for systemic infections is 100mg twice a day. However, as rosacea is considered an inflammatory disease, doxycycline is often dosed at what is termed, sub-microbial dose doxycycline (SDD). Initially introduced in the oral medicine literature, SDD are doses 40mg and lower because systemic administration at this dose does not appear to alter the oral mucosa flora or increase resistance rates when given long-term for periodontal disease. Whereas 100mg doxycycline, even when given short term, may increase the percentage of culturable nasopharyngeal flora that is resistant to doxycycline. The FDA does not categorize SDD an antibiotic, stating this dosing is expected to exhibit only anti-inflammatory activity.
Even though SDD is widely used for the treatment of rosacea, very little confirmatory data exists, to indicate if this dose alters any other systemic mucosa flora or increases antibiotic resistance rates. The classification of 40mg as "sub-microbial" has never been evaluated in patients diagnosed with ocular rosacea. Additionally, confirmation of a "sub-microbial" dose has not been investigated with more sophisticated genomics and resistance tools such as metagenomic deep sequencing (MDS). The goal of this proposal is to use MDS to determine whether SDD given to patients with ocular rosacea can be truly considered sub-microbial, or if a 40mg dose of doxycycline can in fact alter the microbiome of the conjunctiva and gut and increase resistance rates when prescribed for 8 weeks. The investigators plan to evaluate the effect of SDD on resistance and microbiome alteration through a randomized controlled masked trial.
This is a randomized, controlled, masked trial comparing sub-microbial dose doxycycline, treatment dose Doxycycline, and placebo in the treatment of ocular rosacea.
Participants will be recruited from the F.I. Proctor Foundation and the Ophthalmology clinics at the UCSF Wayne and Gladys Valley Center for Vision and consented for participation in an IRB-approved study protocol. Participants with a diagnosis of ocular rosacea (n=50) will be prospectively enrolled and randomized to one of three arms in a 2:2:1 fashion:
Arm A will receive submicrobial dose doxycycline (40mg) administered as 20mg twice day for 8 weeks Arm B will receive a placebo twice a day for 8 weeks Arm C will receive 200mg of oral doxycycline administered as 100mg twice a day for 8 weeks
233 studies on the registry are indexed under Rosacea; 23 are open to participants now.
This study's enrollment of 46 is below the median of 61 across 200 interventional studies indexed under Rosacea.
Browse Rosacea studies →University of California, San Francisco is the lead sponsor of 2,169 studies on the registry; 372 are open to participants now.
Of its 267 completed or terminated interventional studies of FDA-regulated products, 202 (76%) have results posted.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Arm A will receive submicrobial dose doxycycline (40mg) administered as 20mg twice a day for 8 weeks
Drug: Doxycycline 40 MG ( 20mg twice daily)
Arm C will receive 200mg of oral doxycycline administered as 100mg twice a day for 8 weeks
Drug: Doxycycline 200 MG ( 100 mg twice daily)
Arm B will receive a placebo twice a day for 8 weeks
Drug: Placebo
Submicrobial dose doxycycline (40mg) to be administered as 20mg twice daily
200 mg dose doxycycline to be administered as 100mg twice daily
Placebo to be administered in tablet form twice daily
Frequency of Antimicrobial Resistance (AMR) genetic determinants
The frequency of AMR genetic determinants in rectal swab samples between arms will be compared, correcting for baseline
Time frame: 8 weeks
Differences in Simpson's diversity of the microbiome of the conjunctiva and gut
Simpson's diversity is the probability that any two randomly chosen reads will be for different organisms (at the genus level). This will be expressed in terms of effective number.
Time frame: 4 weeks , 8 weeks, 3 - 6 months
Ocular Surface Disease Index (OSDI) will be compared
Scores range from 0 to 100, with higher scores indicating greater symptom severity. Standard 12-question created by the Outcomes Research Group at Allergan Inc will be used.
Time frame: 4 weeks , 8 weeks, 3 - 6 months
Tear Breakup Time (TBUT) scores will be compared
Numbers representing how many seconds after a full blink a discontinuity in the tear film appears. Obtained with the Oculus keratography topographer This is a scale typically measured from 1-10, and the seconds correspond to the amount of time it takes for a tear film discontinuity to be observed. The lower the number the faster the tear break up and the worse the objective dry eye.
Time frame: 4 weeks , 8 weeks, 3 - 6 months
Plan to share: No
Ran from Jun 2023 to primary completion in Jul 2025, 24 months.
Of 12 phase 4 interventional studies under Rosacea, half reached primary completion within 13 months of starting (the median), counting those still running; a quarter within 6 and three quarters within 21. This study's 24 months is above that.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is completed, as verified in Oct 2026. You cannot join it, but the record below documents what was studied.
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Studies of the drug tested here: Doxycycline
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