In short
Doxycycline is an antibiotic belonging to the tetracycline class, authorised as a medicine and used to treat various bacterial infections. In the clinical trials listed here, doxycycline is being studied in two different settings: as part of a screen-and-treat strategy to prevent preterm birth in high-risk pregnant women, and to measure how well it penetrates bone in patients undergoing hip replacement surgery.
Key points
- Doxycycline is a tetracycline antibiotic authorised for treating bacterial infections.
- One Phase 3 trial with 1,794 participants is testing a screen-and-treat strategy for vaginal flora abnormalities to reduce preterm birth in high-risk pregnancies.
- One Phase 2 trial with 30 participants is measuring doxycycline penetration into bone in patients having total hip arthroplasty.
- Both trials are currently in Authorised status in the EU Clinical Trials Information System.
- The preterm birth trial compares an innovative molecular screening strategy against usual care with no screening before 18 weeks of gestation.
- Doxycycline is given orally as 100 mg film-coated or scored tablets in both trials.
What is doxycycline?
Doxycycline (anhydrous) is an antibiotic belonging to the tetracycline class of medicines. It is an authorised medicine, listed in the Sandwell and West Birmingham NHS Trust formulary as a formulary option within the tetracyclines section. Doxycycline is available in the United Kingdom as 100 mg capsules, licensed for oral use and authorised by the Medicines and Healthcare products Regulatory Agency (MHRA). In the trial records, the substance appears under several product names including Granudoxy 100 mg, Doxycycline Biogaran 100 mg, Doxycycline Arrow 100 mg, Doxycycline Teva 100 mg and Doxycycline Sandoz 100 mg.
How does doxycycline work?
Doxycycline is a tetracycline antibiotic. Tetracyclines work by interfering with the ability of bacteria to produce proteins essential for their growth and survival. The NHS formulary classifies doxycycline within the tetracyclines section (05.01.03), alongside other tetracycline antibiotics such as demeclocycline, lymecycline, minocycline, oxytetracycline and tetracycline. The formulary also notes that dispersible doxycycline tablets are allowed as a mouthwash for painful oral inflammation, recurrent aphthous ulcers and herpetiform lesions.
Which conditions is doxycycline used or studied for?
- Bacterial infections — as an authorised tetracycline antibiotic, doxycycline is used for various infections where tetracyclines are appropriate.
- Vaginal flora abnormalities and bacterial vaginosis in pregnancy — a Phase 3 trial is evaluating doxycycline as part of a screen-and-treat strategy to reduce preterm birth in pregnant women at high risk.
- Bone penetration in hip surgery — a Phase 2 trial is measuring how well doxycycline penetrates cancellous bone in patients undergoing total hip arthroplasty for coxofemoral osteoarthritis.
- Painful oral inflammation — dispersible doxycycline tablets are used as a mouthwash for painful oral inflammation, recurrent aphthous ulcers and herpetiform lesions.
How is doxycycline given?
Doxycycline is given orally. In the United Kingdom, it is available as 100 mg capsules in pack sizes of 8, 14 and 50 capsules, licensed for oral use. In the clinical trials, doxycycline is administered as 100 mg film-coated or scored tablets, given orally at a dose of 200 mg. The NHS formulary also lists dispersible tablets that can be used as a mouthwash for oral inflammatory conditions.
What do the clinical trials show?
Two clinical trials involving doxycycline are registered, with a combined enrolment of 1,824 participants. One is a large Phase 3 trial with 1,794 participants, and the other is a small Phase 2 trial with 30 participants. Both trials are currently in Authorised status in the EU Clinical Trials Information System.
The Phase 3 trial, AUTOP 2, is a multicentre randomised study evaluating a screen-and-treat strategy for vaginal flora abnormalities by molecular biology using point-of-care multiplex technology before 18 weeks of gestation. It compares this innovative strategy against usual care with no screening. The trial aims to reduce the rate of preterm birth in pregnant women at high risk, defined as those with a previous history of preterm birth or late fetal loss. Doxycycline (Granudoxy 100 mg) is one of several antibiotics used in the treatment strategy alongside azithromycin, metronidazole and ceftriaxone.
The Phase 2 trial is focused on doxycycline alone, measuring how well the drug penetrates cancellous bone in patients undergoing total hip arthroplasty for coxofemoral osteoarthritis. The study compares several doxycycline products — Biogaran, Arrow, Teva, Sandoz and Granudoxy — all given as 100 mg tablets at a 200 mg oral dose.
| Trial identifier | Phase | Condition | Status | Participants |
|---|---|---|---|---|
| NCT06349122 | Phase 3 | Vaginal flora abnormalities, high risk preterm birth, bacterial vaginosis | Authorised | 1794 |
| 2025-524744-36-00 | Phase 2 | Coxofemoral osteoarthritis requiring total hip arthroplasty | Authorised | 30 |
Who can take part in these trials?
The Phase 3 AUTOP 2 trial enrols pregnant women at high risk of preterm birth, specifically those with a previous history of preterm birth or late fetal loss. The Phase 2 bone penetration trial enrols patients requiring total hip arthroplasty for coxofemoral osteoarthritis. Further eligibility criteria are available in the individual registry records.
What are the trials measuring?
The Phase 3 trial measures the rate of preterm birth before 37 weeks of gestation, comparing the innovative screen-and-treat group against the usual care group. The Phase 2 trial measures doxycycline penetration in cancellous bone using the ratio of cancellous bone concentration to plasmatic concentration. This provides data on how much of the drug reaches the bone relative to how much remains in the blood.
Ongoing research and future directions
Doxycycline is the subject of ongoing research in two distinct areas. The large Phase 3 AUTOP 2 trial is investigating whether early molecular screening for vaginal flora abnormalities, followed by targeted antibiotic treatment including doxycycline, can reduce preterm birth rates in high-risk pregnancies. The Phase 2 trial is generating data on doxycycline penetration into bone, which may inform its use in bone and joint infections. Both trials are authorised but not yet reporting results.