Conditions: Diabetic Macular Edema
Keywords: Diabetic Macular Edema Microglia Dextromethorphan
Allocation: NA | Intervention model: SINGLE_GROUP
Enrollment: 7
Healthy volunteers: no

Brief summary:
Background: Many people with diabetes have macular edema (swelling) at the back of the eye. Macular edema can cause loss of vision. Studies suggest that inflammation may be involved in the swelling. A drug called dextromethorphan may help prevent the inflammation and the swelling. Dextromethorphan is approved for use as a cough medicine, but it has not been studied to see if it can help in diabetic macular edema.

Objectives: To see if dextromethorphan can help treat diabetic macular edema.

Eligibility: Individuals at least 18 years of age who have diabetic macular edema in at least one eye.

Design:

* This study lasts 2 years, and will require at least 14 visits to the National Eye Institute outpatient clinic. Study visits will be every month for the first 2 months and then every other month. Each visit will take about 2 to 4 hours.
* Participants will be screened with a physical exam, medical history, eye exam, and blood tests. One eye with macular edema will be chosen as the study eye for testing.
* Participants will take dextromethorphan twice a day, about 12 hours apart, for 2 years. A study diary will help keep track of the date, time, and number of pills taken.
* Participants will have study visits once a month for the first 2 months and then every other month for the rest of the study. Each study visit will involve eye exams and blood and urine tests.
* Four months after starting the study medication, participants may have laser surgery or other treatments for the macular edema, if it is needed.

Detailed description:
Objective:

Diabetic retinopathy (DR) is one of the leading causes of blindness in the United States. A frequent manifestation of DR is diabetic macular edema (DME) for which the only proven treatment is laser photocoagulation. In the retina, microglia are capable of migrating through the retina to sites of inflammation to associate closely with neurons and the vasculature, and are key cellular players in the mediation of processes of chronic inflammation implicated in DME. For these reasons, microglia represent a promising cellular target for forms of therapy that limit the deleterious inflammatory changes found in DR. The objective of this study is to investigate the safety and efficacy of dextromethorphan as a microglia inhibitor in participants with DME.

Study Population:

Eligibility criteria include presence of diabetic retinopathy with retinal thickening due to diabetic macular edema within 3000 μm of the center of the macula as measured by optical coherence tomography (OCT), and visual acuity better than 20/200 in the study eye.

Design:

Five participants will be initially enrolled in this unmasked pilot study. However, up to an additional three participants may be enrolled to account for participants who withdraw from the study prior to receipt of six months of study treatment. Participants will take an oral dose of 60 mg of dextromethorphan twice daily for 24 months. During each visit, participants will have their visual acuity measured and will undergo OCT testing to measure retinal thickness. Beginning at the Month 4 visit, participants will be assessed for worsening disease defined as loss of ≥ 15 Early Treatment Diabetic Retinopathy Study (ETDRS) letters of vision compared to baseline or a ≥ 50% increase in total central retinal thickness as measured by OCT. Individual participants deemed to have worsening disease may stay on the study and continue to receive study medication, but will be allowed to receive focal laser therapy for any amenable leaking microaneurysms and/or anti-vascular endothelial growth factor (VEGF) intravitreal injections (such as bevacizumab or ranibizumab) at the discretion of the treating physician. Additionally, beginning at the Month 6 visit, participants will be eligible for treatment, with either focal laser or anti-VEGF injections if they have center-involving macular edema.

Outcome Measures:

The primary outcome is the change in retinal thickness measured by OCT at 6 months compared to baseline. Secondary outcomes include the change in retinal thickness as measured by OCT at 12, 18 and 24 months compared to baseline, change in best-corrected visual acuity (BCVA) at 6, 12, 18 and 24 months compared to baseline, change in mean macular sensitivity as measured by microperimetry at 6, 12, 18 and 24 months compared to baseline, as well as changes in fluid leakage in the macula as demonstrated by fluorescein angiography at 6, 12, 18 and 24 months compared to baseline. Safety outcomes include the number and severity of systemic and ocular toxicities, and adverse events.

Arms:
arm 1: None

Interventions: intervention 1: Dextromethorphan hydrobromide
Intervention descriptions: intervention 1: Participants instructed to take 60 mg dextromethorphan capsules orally two times a day for 24 months.

Protocol document: