Table 2: Comparative values of TTKG, Na and K balance before and after ondansetron show no effect on renal K wasting.

Before ondansetronAfter ondansetron

PK (mmol/L)103.9 ± 0.33.9 ± 0.20.774
UK (mmol/L)1050.7 ± 22.724.7 ± 22.80.019
POsm (mmol/kg)10287.2 ± 4.2283.8 ± 18.00.573
UOsm (mmol/kg)10761.4 ± 183.3356.7 ± 123.40.001
PAld (pmol/L)10323.4 ± 484.8153.9 ± 268.50.353
TTKG5*5.1 ± 1.94.7 ± 2.80.463
eGFR (ml/min/1.73 m2)10148.9 ± 17.9166.8 ± 46.80.207
PNa (mmol/L)10138.6 ± 1.8133.9 ± 18.00.426
FENa (%)100.8 ± 0.63.1 ± 2.540.025

Balance studies

Na intake (mmol)102840.0 ± 2034.18032.8 ± 7257.50.080
Na output (mmol)1050.7 ± 22.7113.8 ± 41.60.002
K intake (mmol)101459.7 ± 1306.12274.0 ± 1693.00.347
K output (mmol)1050.7 ± 22.724.8 ± 22.80.019
Net Na balance (mmol/kg/hr observation)100.15 ± 0.390.06 ± 0.110.520
Net K balance (mmol/kg/hr observation)100.11 ± 0.070.39 ± 0.820.305

Values are presented as mean ± standard deviation.
Student’s -test, paired, two-tailed, significance < 0.05.
Net balance = (intake − output)/weight (kg)/time (hr) of observation period.
PK: plasma potassium, mmol/L; UK: urine K, mmol/L; Posm: plasma osmolality, mmol/kg; Pald: plasma aldosterone, pmol/L (lower limit of detection 69 pmol/L); TTKG: transtubular potassium gradient; eGFR: estimated glomerular filtration rate (Schwartz [15]); Pna: plasma sodium, mmol/L; FENa: fractional excretion of sodium (%).
*5 subjects were not included in this analysis as they developed hypotonic urine relative to blood, invalidating the TTKG assumptions.