Daily oral Kamuvudine-9 (K9) for diabetic macular edema

Inclusion Criteria:

* Aged 18 years or older.
* Diagnosis of diabetes mellitus, type 1 or 2 with non-proliferative or non-high risk proliferative diabetic retinopathy. Any one of the following will be considered sufficient evidence that diabetes is present:
* Current regular use of insulin for the treatment of diabetes
* Current regular use of oral hypoglycemic agents for the treatment of diabetes
* DME based on investigator's clinical evaluation and evident on fundus photographs, fluorescein angiograms, or spectral domain-optical coherence tomography (SD-OCT)
* HbA1c of ≤12% at screening.
* BCVA of ≥ 24 and ≤ 68 letters (20/50 or worse but at least 20/320) by an ETDRS chart. BCVA of the non-study eye must be no worse than 20/400 Snellen equivalent).
* Mean central subfield thickness (CST) of at least 325 µm by SD-OCT.
* Intraocular pressure of ≤ 21 mm Hg on 2 or fewer IOP lowering medications.
* Capable of providing informed consent.
* Capable and willing to follow study protocol.
* Females of childbearing potential must agree to abstain from sex or use adequate method of contraception for the duration of the study period and for 28 days after the last dose of study drug.
* Males must agree to abstain from sex or use adequate method of contraception for the duration of the study period and for 28 days after the last dose of study drug.

Exclusion Criteria:

* Body weight \< 55 kg.
* Macular edema considered to be due to causes other than diabetes.
* Proliferative diabetic retinopathy or iris neovascularization (including the anterior chamber angle) in the study eye.
* Inability to follow the study protocol, based on the investigator's assessment.
* Females who are pregnant or breastfeeding.
* Panretinal or scatter laser photocoagulation within 12 months of screening.
* Topical steroid or topical NSAID in the study eye or oral NSAID treatment within 30 days of screening.
* Active ocular inflammation of any history of intraocular inflammation within 1 year.
* Prior intraocular or periocular treatment for DME including any of the following:

Intravitreous injection of anti-VEGF therapies including but not limited to bevacizumab, ranibizumab, aflibercept, faricimab, and/or brolucizumab within 6 weeks of screening Intravitreous or sub-Tenon delivery of steroid therapy (e.g. triamcinolone, dexamethasone) within 12 months or fluocinolone acetonide implant within 3 years of screening.

* Macular laser for the treatment of DME within 6 months of screening
* Aphakia or total absence of the posterior capsule in the study eye.
* Yttrium aluminium garnet (YAG) laser capsulotomy in the study eye within 2 months of screening.
* Any change in systemic steroid therapy within 3 months of screening.
* Any ocular surgery in the study eye within 12 weeks of screening.
* Presence of severe foveal ischemia in the study eye, defined as foveal avascular zone (FAZ) of \>1.5 mm2 on OCT-Angiography (OCT-A) or fluorescein angiography (FA).
* Retinal or choroidal neovascularization due to ocular conditions other than diabetic retinopathy (e.g. presumed ocular histoplasmosis, high myopia (spherical equivalent greater than 8 diopters), age-related macular degeneration) in the study eye.
* History or presence of viral disease of the cornea or conjunctiva including epithelial herpes simplex keratitis (dendritic keratitis), vaccinia, varicella, any mycobacterial infections of the eye, or any fungal disease of any ocular structure or history of infectious retinitis in the study eye.
* History or presence of any disease or condition that in the investigator's opinion would preclude study treatment or follow-up or that, in the opinion of the investigator, would render them as unlikely to benefit from study treatment.
* History or presence of any other condition except for DME in the study eye that could affect interpretation of study assessments (e.g., but not limited to, geographic atrophy, macular hole, macular pucker, foveomacular traction, retinal vein occlusion, retinal degenerations), in the opinion of the investigator.
* Any lens or corneal opacity in the study eye which impairs visualization of the posterior pole of the retina, in the opinion of the investigator.
* History or current evidence of hypersensitivity to any components of the study medication, as assessed by the investigator.
* Taking any medications containing nucleotide reverse transcriptase inhibitors (NRTIs), including but not limited to Abacavir, Emtricitabine, Lamivudine, or Zidovudine; trade names Atripla, Biktarvy, Cimduo, Combivir, Complera, Delstrigo, Descovy, Dovato, Emtriva, Epivir, Epzicom, Genvoya, Odefsey, Retrovir, Stribild, Symfi, Symtuza, Triumeq, Trizivir, Truvada, Ziagen.
* History of taking medications with known retinal toxicity (e.g., hydroxychloroquine, chloroquine, pentosan polysulfate sodium, and amiodarone).
* Clinically significant unstable medical condition (other than diabetes) that would pose a risk to the participant, according to investigator's judgment (e.g., cardiovascular instability, systemic infection), or clinically significant laboratory abnormality.
* Clinically significant abnormal liver or kidney function at screening. The following values \[alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \> 3 times the upper limit of normal (ULN) or estimated Glomerular Filtration Rate (eGFR) \< 30 mL/min/1.73m2\] are exclusionary regardless of clinical symptoms.
* Active cancer or history of cancer, except for the following: basal cell carcinoma or successfully treated squamous cell carcinoma of the skin, cervical carcinoma in situ, prostatic carcinoma in situ, or other malignancies curatively treated and with no evidence of disease recurrence for at least 3 years.
* Treatment with other investigational drug within 6 weeks or 5 half-lives of drug prior to screening, whichever is longer.
* Participation in another clinical trial within 12 weeks before the screening visit or during the study (participation in clinical trials solely involving observation, over-the-counter vitamins, supplements, or diets are not exclusionary).
* Plans to move away from study site within the next 2 months.