The two doses of sodium bicarbonate being tested are 0.5 and 0.8 mEq/kg-lean body weight (LBW) per day. Sodium bicarbonate, also known as baking soda, may help prevent kidney failure in people with chronic kidney disease. However, the dose to prescribe in order to test this possibility in a clinical trial is uncertain. The BASE pilot clinical trial will help determine the best dose of sodium bicarbonate to prescribe in a future study that will test the long-term safety and efficacy of sodium bicarbonate as a treatment to preserve kidney function in individuals with chronic kidney disease.

Inclusion Criteria:

1. Serum bicarbonate 20-28 mEq/L at screening (the average of the two most recent values in Baseline must be 20-28 mEq/L prior to randomization)

2. Moderate to severe chronic kidney disease (CKD) at the time of screening, defined as one of the following:

   • eGFR 20-44 ml/min/1.73m2 or
   • eGFR 45-59 ml/min/1.73m2 plus random urinary albumin:creatinine (ACR) ≥100 mg/gm

3. Blood pressure <160/100 mm Hg at screening (must be <150/100 mm Hg prior to randomization)

4. Lean body weight 38.0-96.0 kg at the time of screening

5. Age allowing legal consent without parental involvement (18-21 years, depending on individual state regulations)

6. Able to provide consent

7. Able to travel to study visits

8. Able to read English

9. In the opinion of the site investigator, willing and able to follow the study treatment regimen and comply with the site investigator's recommendations

10. In the opinion of the site investigator, medically stable

Exclusion Criteria:

1. Use of chronic daily oral alkali (such as sodium bicarbonate, sodium citrate, potassium citrate, etc) with one exception: calcium carbonate ≤1500 mg/day is allowed, as some will take this for the indication of bone health
2. On five or more antihypertensive and/or diuretic agents, regardless of the indication
3. Serum potassium <3.3 or ≥5.5 mEq/L at screening (must be 3.5-5.5 mEq/L prior to randomization)
4. Self-reported vegetarian
5. New York Heart Association Class 3 or 4 heart failure symptoms, known left ventricular ejection fraction ≤30%, or hospital admission for heart failure within the past 3 months
6. Frequent urinary tract infections (≥2 in the past year)
7. Presence of indwelling urinary catheter or urinary conduit (such as neobladder or urostomy)
8. Factors judged to limit adherence to interventions (e.g., alcoholism, history of missing clinic visits, chronic gastrointestinal disorder that makes compliance with the intervention unreliable)
9. Organ transplant recipients (excluding cornea)
10. Active glomerular disease requiring or potentially requiring immunosuppressive treatment
11. Chronic immunosuppressive therapy (for ≥3 months) for any indication. This does not include oral steroids <10 mg per day, inhaled steroids, or topical steroids
12. Anticipated initiation of dialysis or kidney transplantation within 12 months as assessed by the site investigator
13. Current participation in another interventional research study
14. Malignancy requiring therapy within 2 years (basal or squamous cell skin carcinoma and localized prostate cancer are exempted)
15. Pregnancy or planning to become pregnant or currently breast-feeding. Women of childbearing potential (pre-menopausal and not surgically sterilized) will have urine pregnancy test before enrollment.
16. Life expectancy <12 months as determined by the site investigator
17. Institutionalized individuals, including prisoners and nursing home residents
18. Plans to leave the immediate area within the next 12 months
19. Routinely leaves town for multiple weeks each year such that protocol visits would be missed
20. Chronic use of supplemental oxygen
21. Use of both angiotensin-converting-enzyme inhibitor (ACEI) and Angiotensin II Receptor Blockers (ARBs)