Study Evaluating Subjects With Distal Renal Tubular Acidosis

Inclusion Criteria:

1. Female or male subjects ≥ 6 months of age and ≤ 65 years of age at time of consent;
2. Subject presents with a previous diagnosis of primary dRTA of at least 4 months duration for subjects < 12 years of age, and at least one year for those ≥ 12 years of age, based on documented history of non-anion gap, hyperchloremic, hypokalemic metabolic acidosis;
3. Subject requires ≥ 0.9 mEq/kg/day of alkali therapy to maintain serum bicarbonate levels above the LLN for the laboratory providing results;
4. Subject or parent/guardian is willing and able to understand and sign informed consent and willing to comply with protocol instructions; child assent when appropriate; and

5. Heterosexually active female subjects of childbearing potential and non-sterilized males must use at least one of the following acceptable birth control methods from informed consent through 7 days after the last dose of study product:

   1. Double-barrier methods of contraception: condom or occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository)
   2. Established use of oral, injectable, or implanted hormonal methods of contraception
   3. Placement of an intrauterine device or intrauterine system
   4. Abstinence Females of childbearing potential are those who have reached the onset of menarche (or 8 years of age, whichever comes first) and are not postmenopausal (≥ 1 year without menses prior to Visit 1), surgically sterile, or status post hysterectomy (≥ 1 month prior to Visit 1). From informed consent through 7 days after the last dose of study product, female subjects must agree to refrain from egg donation and male subjects must agree to refrain from sperm donation.

Exclusion Criteria:

1. Female subject who is pregnant or lactating or has plans for pregnancy during the study;
2. Subject has evidence of proximal tubule dysfunction (eg, hypophosphatemia, low serum uric acid, glycosuria, or amino aciduria);
3. Subject presents with another diagnosed condition as a potential etiology for her/his dRTA (eg, systemic lupus erythematosus, Sjogren's syndrome), in the opinion of the Investigator;
4. Subject requires therapy with potassium sparing diuretics, angiotensin converting enzyme inhibitors, angiotensin II receptor blockers, trimethoprim, drospirenone and other progestins, nephrotoxic antibiotics, penicillins, tacrolimus, or medications known to delay gastric emptying or otherwise interfere with absorption of study product;
5. Subject has evidence of obstructive uropathy or other findings on renal ultrasound associated with Visit 1 expected to require intervention during the course of the study, in the opinion of the Investigator;

6. Subject has any of the following laboratory abnormalities associated with Visit 1:

   1. AST and/or ALT > 1.5x upper limit of normal (ULN)
   2. Serum potassium > 5.0 mEq/L or <3.0 mEq/L or hypokalemia accompanied by clinical symptoms (eg, muscle cramps) or significant ECG changes (eg T wave depression, U wave elevation)
   3. Estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 (according to the Modified Schwartz formula for children [<12years of age] and Chronic Kidney Disease - Epidemiology Collaboration [CKD-EPI] equation for adolescents and adults [≥12 years of age])
   4. Total bilirubin > ULN, except with known Gilbert's disease or in patients with dRTA and known hemolytic anemia due to a defect in SLC4A1.
7. Subject has been hospitalized or had outpatient surgery (other than minor skin and dRTA disease-related procedures or ear tube placement) in the past 6 months or is planning surgery in the next 6 months;
8. In the opinion of the Investigator, the subject has a major medical or psychiatric condition (eg, significant cardiac disease, schizophrenia) or an unstable condition (eg, uncontrolled hypertension, asthma, diabetes, hypercholesterolemia, or cardiac disease) that would potentially interfere with the subject safely completing the study;
9. In the opinion of the Investigator, the subject has a history of difficulty taking oral medication and/or conditions that may hinder absorption of the study drug (eg, any difficulty of swallowing, malabsorption, delayed gastric emptying, esophageal compression, intestinal obstruction, or other chronic gastrointestinal disease);
10. Self-reported or parent/guardian reported alcohol abuse or drug abuse within the past 12 months;
11. Subject is a solid organ or bone marrow transplant recipient;
12. Subject has a history of malignancy within 5 years prior to Visit 1, except for localized skin or cervical carcinoma; or
13. Subject is known to have allergy or intolerance to any ADV7103 or placebo constituents.