Use of Tolvaptan, a Vasopressin Antagonist, to Increase Urine Dilution and Reduce Cystine Urolithiasis Among Patients With Homozygous Cystinuria: a Pilot Investigation
Phase: NA
Conditions: Cystinuria
Sponsor: Caleb Nelson

TITLE:  Use of tolvaptan, a vasopressin antagonist, to increase urine dilution and reduce 
cystine urolithiasis among patients with homozygous cystinuria: a pilot investigation 
NCT02538016 
Latest IRB Approval Date: 9/23/2019 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
A. Specific Aims/Objectives  
The goal of this research project is to establish that in short-term use, tolvaptan is a safe and 
potentially effective new therapy for cystinuria, by conducting a short-term pilot study of  the 
safety and tolerability of this drug, and assess impact on urinary stone risk parameters, 
among adolescent and young adult patients with clinical cystinuria. 
Specific Aim 1) To characterize the short-term safety profile of tolvaptan therapy in 
adolescent patients with cystinuria.  
Hypothesis 1a: Tolvaptan will be well tolerated with low adverse effects, minimal disruption of 
serum electrolytes, and no detectable alterations in blood pressure and other cardiovascular 
parameters  
Specific Aim 2) To characterize the short-term effect of tolvaptan on urinary risk factors for 
urolithiasis in adolescent patients with cystinuria.  
Hypothesis 2a: Tolvaptan therapy will result in >25% increased urine output, decrease in 
urinary osmolality of >25%, and increase in urinary cystine capacity of >25% 
B. Background and Significance  
Cystinuria pathophysiology. Cystinuria is a rare disorder of amino acid metabolism that leads to 
high levels of cystine in the urine. (Cystine is a dimeric amino acid formed from two cysteine amino 
acid residues linked by a disulfide bond.) Patients with cystinuria have mutations in one of two 
genes (SLC3A1 and SLC7A9) that encode subunits of the amino acid transporters that are 
responsible for reabsorbing filtered cystine and dibasic amino acids (ornithine, lysine, and 
arginine) from the lumen of the proximal renal tubule into the tubular cells. Although in normal 
individuals virtually 100% of the filtered load of amino acids is reabsorbed from the proximal 
tubule, homozygotes (and some heterozygotes, depending on the mutation) are unable to 
reabsorb these amino acids. These individuals therefore excrete large amounts of these amino 
acids into the urine. As cystine is relatively insoluble in urine, it precipitates into crystals and dense 
stone stones, resulting in clinical urolithiasis. The condition is rare; homozygous cystinuria occurs 
in about 1/15,000 persons in the United States (~20,000 affected individuals nationwide)(1). Age 
at presentation is variable, but significant numbers of patients present during childhood or 
adolescence with clinical stone disease, with over 80% presenting before age 20(2).  
 
Urolithiasis in patients with cystinuria is a difficult problem to manage. Stones tend to be large and 
recurrent, form rapidly, and require repeated surgical treatments. This often has devastating 
effects on renal function over the long-term, such increased probability of nephrectomy, high 
incidence of decreased GFR, and progression (in some rare cases) to end-stage renal disease(2, 
3).  
 
Contemporary cystinuria management. Metabolic strategies for preventing cystine stones focus on 
increasing solubility of cystine in the urine, through dilution, alkalinization, or chelation.  

 
Hydration therapy is the underlying foundation of all therapy for cystinuria. Hydration therapy is 
based on an idea that, given a relatively constant amount of cystine being excreted in the urine 
each day, adequate hydration will result in dilution of the fixed cystine load to a concentration 
below that at which crystallization typically occurs. Target concentrations are usually set at about 
250 mg/L, as stone formation rates increase significantly at concentrations above this. While 
simple in concept, and although there is longstanding evidence that hyperhydration can be 
effective in reducing stone recurrence(4), in practice adequate oral hydration is difficult to achieve 
for many patients. The target cystine concentration requires a urine volume of over 3 L per day, 
which in turn requires fluid intake of greater than 3.5-4 L per day. Many patients find that they 
cannot sustain this level of intake voluntarily.  
 
A complementary strategy for reducing cystine crystallization is to chemically alter the solubility of 
cystine. Below pH of 7.0, the solubility of cystine is relatively constant at about 250 mg/L. 
However, as pH rises above 7.0, solubility increases to about 500 mg/L at 7.5(1). Thus, 
alkalinization has been used to increase urinary pH to a range that permits significantly more 
cystine in solution in the urine, regardless of volume. Potassium citrate is the agent most 
commonly used for this purpose, is well tolerated, and avoids the potential negative effects of 
using the sodium salts, as sodium intake appears to increase cystine excretion(1, 5).  
 
Dietary modification to reduce cystine intake is attractive, in theory. Reduction in dietary animal 
protein intake has been found to reduce the excretion of cystine and other amino acids(6). Such 
reduction is also associated with increase in urine pH. However, exogenous protein is not the only 
source of cystine in the body; the amino acid is produced as part of metabolic processes. Thus, 
the potential impact of reduced intake is blunted  
 
Chelation therapy for cystinuria. For a large proportion of cystinuria patients, oral hydration and 
alkalinization are insufficient to adequately manage urinary cystine levels. For such patients, 
chelation therapy is utilized as an adjunct. The drugs most commonly used for this purpose are d-
penicillamine and the newer agent α --mercaptopropionylglycine (tiopronin, thiola). The 
mechanism for both agents is similar: both molecules contain a thiol group, which reduces the 
disulfide bond in the cystine molecule, splitting it into two cysteine residues. The cysteine residue 
then bonds to the thiol group of the drug, forming a drug-cysteine compound that is 50 times more 
soluble than the cysteine-cysteine dimer (cystine)(7).  
 
Treatment with these agents is limited by the substantial toxicity observed in both drugs. Adverse 
reactions include aplastic anemia, agranulocytosis, leukopenia, thrombocytopenia, Goodpasture’s 
syndrome or myasthenia gravis, severe gastrointestinal distress (nausea, vomiting, diarrhea), 
arthralgia, and lupus-like symptoms(8, 9). Therapy discontinuation rates are between 30-70% due 
to side effects(10). Thus, the value of the currently-available therapeutic agents is lowered by 
these toxic effects, and many patients are unable to achieve adequate urinary cystine control, 
resulting in recurrent stone disease with all its attendant morbidity.  
 
Chelation has also been reported using the ACE inhibitor captopril. Like d-penicillamine and α-
MPG, captopril contains a thiol group and can complex with cysteine to improve solubility. 
However, clinical studies have reported conflicting results(11-14) and there are no randomized 
controlled trials (RCTs) demonstrating efficacy or improved outcomes.  
 
The combination of oral hydration, alkalinization, and chelation represents a multifaceted approach 
to stone prevention in cystinuria. Unfortunately, few patients achieve adequate results with current 
medical therapy. In one study, only 15% of medically-managed patients durably maintained 
adequate urinary cystine concentrations(15).  Clearly, new therapies are urgently needed for this 

devastating illness. However, since the introduction of α-MPG in the 1980’s there have been few 
new options  
 
Measurement of urinary cystine. Cystine levels can be measured simply as the quantity of cystine 
per volume of urine, but as many factors affect cystine solubility, this is a poor predictor of clinical 
stone formation. Therefore, more complex measures have been developed. Cystine 
supersaturation is the ratio of the measured urinary cystine concentration to the empirically-
determined saturation concentration of the patient’s urine. Values above 1 indicated that the urine 
is supersaturated with cystine, and target values are typically less than 0.6(16). However, because 
the thiol-containing drugs commonly used to manage cystinuria (e.g. thiola) can interfere with 
accurate measurement of cystine levels, the cystine capacity test was developed to account for 
such drugs(17). This proprietary test (Litholink Corp., Chicago IL) is reported as a value in mg/L 
above or below zero. Positive values indicated that the urine is undersaturated with cystine, while 
negative values indicate that the urine is supersaturated with cystine. Target values during 
treatment are positive, preferably about 150 mg/L. 
 
Tolvaptan: mechanism and effects. Tolvaptan (Samsca) is a selective arginine vasopressin V2-
receptor antagonist. Activation of arginine vasopressin V2-receptors in the distal nephron 
increases the number of aquaporin channels in the apical membrane of collecting duct cells, 
thereby increasing water absorption from the tubular lumen into the interstitium. Conversely, 
inhibition of V2-receptors reduces the number of aquaporin channels, increasing urinary excretion 
of water, with minimal changes in electrolyte excretion. Tolvaptan has been used clinically for 
treatment of hyponatremia(18), congestive heart failure(19), syndrome of inappropriate antidiuretic 
hormone(20) and autosomal dominant polycystic kidney disease(21). It appears to have a good 
safety profile with few adverse reactions. Although most clinical studies have been in adults, 
examples of use in the pediatric population do exist (19, 22).  
 
Tolvaptan dosing. In published studies dosing of tolvaptan has varied considerably. Most studies 
in adults have used doses of 15-120 mg once daily, in either fixed or increasing dosages, with 
increases usually limited by tolerance. In the SALT trials, dosing was 15-60 mg once daily, 
adjusted for effect on serum sodium levels. This translated to a dose of 0.2-0.8 mg/kg. In the 3-
year RCT by Torres et al., dosing was twice daily, with morning and afternoon doses of 45-90 mg 
and 15-30 mg respectively(21), which translates to doses of 0.6-1.1 mg/kg in the morning, and 0.2-
0.4 mg/kg in the afternoon (total daily doses 0.8-1.5 mg/kg).  In the pediatric heart failure study by 
Regen et al., dosing ranged from 0.1-1.3 mg/kg (median 0.3 mg/kg).  
 
Tolvaptan safety. In short-term studies of tolvaptan effects in healthy Japanese, Korean, and 
Caucasian men, tolvaptan was generally well-tolerated with few apparent adverse reactions(23-
26). The most common side effect was thirst, presumed to be an effect of the pharmacologic 
action of the drug. Similar adverse event profiles were noted in 7-day RCTs among adult patients 
with congestive heart failure (27, 28).  A single-dose study in a series of pediatric patients with 
heart failure also identified no significant adverse effects(19).  
 
Findings have generally been favorable in longer-term trials, as well. The SALT-1and SALT-2 trials 
were RCTs examining 30-day outcomes of tolvaptan among patients with hyponatremia(18). (The 
investigators hypothesized that the aquaresis associated with tolvaptan would increase serum 
sodium levels and thereby improve clinical outcomes.) In this seriously ill population (hyponatremia 
was due to chronic heart failure, liver cirrhosis, or syndrome of inappropriate antidiuretic hormone 
(SIADH) secretion), the rates of adverse events were similar in treatment and placebo groups. The 
most common tolvaptan-associated effect was thirst and dry mouth. In an open label extension of 
the SALT studies, 111 adult patients with hyponatremia continued to take tolvaptan for a mean of 

701 days(29); again, adverse reactions related to aquaresis were observed, but the drug was 
otherwise well tolerated.  
 
The longest-term RCT of tolvaptan was the TEMPO 3:4 trial, comparing tolvaptan to placebo 
during a 3 year period among patients with autosomal dominant polycystic kidney disease 
(ADPKD)(21). As in other studies, the most common adverse effects in the tolvaptan group were 
those related to aquaresis (thirst, polyuria), and these led to drug discontinuation in 8.3% of 
patients. However, in this trial the tolvaptan group also had a significantly higher incidence of 
elevated liver function enzymes; elevated alanine aminotransferase was seen in 4.9% of tolvaptan 
patient vs. 1.2% of placebo patients. Overall, 1.2% of patients in the tolvaptan group discontinued 
the study drug due to abnormal liver tests. Abnormal liver tests returned to normal in all cases, 
either before or after discontinuation of study drug, and there were no persistent sequelae 
reported. 
 
For all female subjects in the study, we will be conducting a pregnancy test prior to drug 
administration. If a positive pregnancy test is found, they would be withdrawn from the study. 
Medical staff will also notify the subject of their positive pregnancy and the CTSU nurses/ clinicians 
will give them standard guidance with their pregnancy status.  
 
C. Preliminary Studies  
We reviewed our cystinuria experience at the Boston Children’s Hospital Pediatric Kidney Stone 
Clinic and, using the data warehouse, the i2b2 search query tool, and nephrology and urology 
department records, we were able to identify approximately 30 patients seen over the past 5 years 
with a diagnosis of cystinuria and cystine stones. We are currently in the process of performing a 
retrospective review of these patients to describe such characteristics as age at presentation, 
number of surgical treatments required, recurrence of stones, etc.  
 
Tolvaptan in cystinuria. We have not yet treated any pediatric cystinuria patients with tolvaptan. 
We believe that, given the uncertainty regarding safety and efficacy of this treatment in this 
population, the treatment should be administered within the framework of a research study with 
careful monitoring. The only reported instance of using tolvaptan for treatment of cystinuria was 
reported by de Boer et al. in two adult patients(30). Each of these patients was treated for 5 days 
with tolvaptan; both exhibited a significant increase in urine output, decrease in urine cystine 
concentration, and a minor increase in plasma osmolality. Both patients experience minor thirst 
symptoms but otherwise tolerated treatment well. The authors concluded that this was a promising 
potential treatment for cystinuria (and in fact any chronic lithogenic condition), and that further 
studies of this agent were warranted.   
D. Design and Methods  
(1) 
Study Design 
We will conduct a single-arm, unblinded, short-term prospective evaluation of tolvaptan in 
patients with cystinuria. The goal will be to obtain safety and short-term effectiveness data 
on Tolvaptan in adolescent to young adult patients, to demonstrate tolerability and favorable 
impact on urinary parameters associated with cystine urolithiasis risk.  
(2) 
Patient Selection and Inclusion/Exclusion Criteria  
Sample population 
For this pilot study 16 patients with cystinuria will be recruited for 8 complete participants. 
Subjects will be recruited from our existing database of cystinuria patients seen in the 

Boston Children’s Hospital Pediatric Kidney Stone Clinic, and from new patients diagnosed 
during the research period who present to Boston Children’s Hospital. We will also consider 
recruitment through advertising in other outlets e.g. International Cystinuria Foundation, 
Rare Kidney Stone Consortium.  
Inclusion criteria:  
Males and females age 12 – 25 years 
Weight ≥ 25kg 
Confirmed cystinuria via:  
Documented cystine stones (stone >75% cystine on chemical 
analysis), 
Cystine crystals in urine (pathognomonic hexagonal crystals), 
Urinary cystine levels greater than 250 mg/L or  
Genetic screening.  
Estimated GFR greater than 80 ml/min/1.73 m2  
Exclusion criteria:  
Concurrent non-renal disease that might increase risk of complications 
due to aquaresis.  
Liver or biliary disease (chronic or acute) 
Malabsorption syndrome or other gastrointestinal condition that may 
interfere with response to therapy 
Non-cutaneous malignancy within last 5 years 
History of adverse reaction or allergy to Tolvaptan or other arginine 
vasopressin V2-receptor antagonists 
Positive pregnancy test 
Currently breastfeeding 
Inability or unwillingness to consent/assent 
(3) 
Description of Study Treatments or Exposures/Predictors  
Starting at between 10AM and 2PM on Day 1, Tolvaptan will be administered orally. See 
dose chart below:  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
T-CUPS:  
 
Tolvaptan use in Cystinuria and Urolithiasis: A Pilot Study  
 
DOSING SCHEDULE by WEIGHT 
 

Weight (kg) 
Day 1-4 
Day 5-8 
12.5 kg -37.49 kg (mean=25kg) 
For illustration: We will not 
recruit anyone weighing less 
that 25kg.  
7.5mg (.6mg/kg -.2mg/kg)  
15mg (1.2mg/kg - .4mg/kg) 
37.5kg-62.49kg (mean =50kg) 
15.0 mg (.4mg/kg - .24 
mg/kg) 
30mg (.8mg/kg - .48mg/kg) 
62.5 kg -87.49kg (mean 75kg) 
22.5 mg (.36mg/kg - 
.26mg/kg) 
45.0mg (.72mg/kg - .52mg/kg) 
87.5 kg – 112.49kg (mean 
100kg) 
30.0 mg (.34mg/kg - 
.27mg/kg) 
60.0mg (.68mg/kg -.54mg/kg) 
112.5kg – 137.5kg (mean 
125kg) 
37.5 mg (.33 mg/kg -
.27mg/kg) 
60.0mg (.66mg/kg - .54mg/kg) 
 
This daily dose will continue for a total of 4 doses, through Day 4. On Day 5, the dose will 
be increased per chart, up to a maximum does of 60 mg. If tolerated, the higher dose will be 
continued for a total of 4 doses through Day 8. No drug will be given on day 9 or 10.   
 
Tolvaptan is produced commercially as 15 mg triangular tablets and 30 mg round tablets. 
 
Patients currently on chelation therapy will NOT discontinue these medications during the 
study period. 
 
(4) 
Definition of Primary and Secondary Outcomes/Endpoints  
The primary outcome will be urinary cystine levels as measured by cystine capacity 
(Litholink Corp; mg/L). Four 24-hour urine samples will be obtained during the study: one at 
baseline 3-6 days prior to the measurement, one on day 3-4 of the dosing period, one on 
day 7-8 of the dosing period, and one 3-6 days after the washout period. Each 24 hour 
urine sample will be sent individually for analysis by Litholink Corp, which performs the 
cystine assays.  
 
Secondary outcomes will include daily urine output and urine osmolality. Additional data 
points to be collected include serum sodium and other electrolyte levels, serum osmolality, 
plasma AVP concentration, and urinary electrolytes and osmolality. Urinary symptoms will 
be measured with the AUA symptom score. 
(5) 
Data Collection Methods, Assessments, Interventions and Schedule (what 
assessments performed, how often)  
All information will be collected and reported onto a paper case report forms (CRFs), 
which will later be entered into REDCap. 24 hour urines and clinical (vital signs, 
weights, fluid intake and output, thirst and dry mouth) and laboratory data (urine 
cultures/analysis, serum electrolytes and liver function tests) will be collected 
throughout the duration of the patient’s participation in the research study. The 
following table indicates the procedures that will be done each day the patient is 
involved with the research study: 
3-6 days before   
Day 0 
Day 1 
Day 2 
Day 3 

Day 0 
 
24 hour urine 
collection. 
CTSU-Outpt. 
Physical exam. 
Blood sample. 
Urine sample. 
CTSU – admitted. 
Tolvaptan given 
orally. 
Urine sample. 
CTSU – 
discharged 
Tolvaptan given 
orally. 
Blood sample. 
Urine Sample 
CTSU – 
outpatient. 
Tolvaptan given 
orally. 
24 hour urine 
collection. 
 
 
Day 4 
Day 5 
Day 6 
Day 7 
Day 8 
CTSU – 
outpatient. 
Tolvaptan given 
orally. 
Blood sample. 
 
CTSU – admitted. 
Tolvaptan given 
orally. 
Urine sample. 
CTSU – 
discharged. 
Tolvaptan given 
orally. 
Blood sample. 
Urine Sample 
CTSU – 
outpatient. 
Tolvaptan given 
orally. 
24 hour urine 
collection. 
 
CTSU – 
outpatient. 
Tolvaptan given 
orally. 
Blood sample. 
 
Day 9 
Day 10 
3-6 days after    
Day 10 
CTSU – 
outpatient. 
No medication 
given. 
.Urine sample 
 
CTSU – 
outpatient. 
No medication 
given. 
Blood sample. 
24 hour urine 
collection. 
  
(6) 
Study Timeline (as applicable) 
The study will be conducted through the Clinical and Translational Study Unit at Boston 
Children’s Hospital. The treatment period will for 8 days. Subjects will be spend two 
24=hour periods under inpatient observation; the remainder of the period will be under 
outpatient observation, with daily visits to the CTSU. The day prior to the treatment period 
(Day 0) will be used to obtain baseline clinical and laboratory data. Study drug will be 
administered starting on Day 1 through Day 8, with a 2 day washout period on days 9 and 
10. Patients will be monitored during the period with 24-hour urine collection for cystine 
stone risk profile, daily weights, vital signs, blood draws, fluid intake and output, and 
assessment of subjective outcomes.  
E. Adverse Event Criteria and Reporting Procedures  
Subjects will be monitored for drug tolerability and safety. Patients will be observed in the inpatient 
CTSU setting for 24 hours after the initial dose (Day 1) and also for 24 hours after the increased 
dose (Day 5). During each of these 24 hour periods, subjects will undergo around the clock 
monitoring of vital signs and daily input and outputs.. On Day 2-4 and Day 6-8 subjects will be 
monitored on an outpatient basis, coming in each day to the CTSU. At each outpatient visit vital 
signs will be checked. Serum Electrolytes will be checked on days 0, 2, 4, 6, 8,and 10. Liver 
function tests will be obtained at baseline, Day 4, and Day 8, and Day 10. Thirst and dry mouth will 
be assessed daily with visual analog scales. (31-33).  
 

Criteria for cessation of treatment will include abnormal serum sodium (>5 mmol/L above or below 
normal range), potassium (>0.2 mmol/L above or below normal range), or CO2 (>2 mmol/L above 
or below normal range). Other criteria will include unstable vital signs (e.g. tachycardia, 
hypotension), intolerable subjective symptoms of thirst or voiding symptoms, or other symptoms 
subjectively attributed to the medication.    
 
Subjects that experience adverse reaction at the higher dose level will be reduced to the lower 
dose level; if adverse effects persist at the lower dose level, the study drug will be discontinued. 
 
For other potential adverse events not listed above, the investigators will decide on a case-by-case 
basis whether treatment should be continued, taking the subject’s short-term and long-term health 
and safety as the primary factor for consideration. 
F. Data Management Methods  
Clinical and laboratory data will be maintained in a secure REDCap database.   
G. Quality Control Method  
Trained research personnel will be collecting data and entering it into REDCap. There also 
will be data checks within the REDCap system. 
H. Data Analysis Plan  
In this pilot study, the primary analysis will be description of the change from baseline during 
treatment of cystine stone risk profile. This will be demonstrated graphically. With respect to the 
primary endpoint, differences in cystine capacity between baseline and low-dose treatment phase, 
and between baseline and the high-dose treatment phases, will be compared with paired t-tests. 
Data regarding thirst and dry mouth will also be recorded and demonstrated graphically. 
I. Statistical Power and Sample Considerations  
As a pilot study with very low numbers of subjects, statistical analysis will not be feasible for 
adverse effects. Adverse effects will be classified with respect to whether they resulted in the 
subject discontinuing study medication or requiring additional monitoring, testing, or 
treatment, or not. For electrolyte and cardiovascular measures, we will analyze these 
outcomes according to proportion of subjects experiencing at least one outlier measurement 
(defined as a clinically abnormal value based on the standard normal range for each test) for 
each parameter (each of the serum chemistry values, and cardiovascular measures). 
J. Study Organization  
Data for this study will be managed via the REDCap web-based data management system at 
Boston Children’s Hospital. This database will store patient-level variables and clinical 
outcome data. PHI on individual study participants will be maintained in a password protected 
database. Data within the PHI database will be linked to the clinical data in the primary 
database via study identification numbers.  
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* If you are an investigator submitting an IND or IDE, this document alone does not constitute and 
complete protocol. You must submit your full IND/IDE application as an attachment for this section.