How can drugs change our salt concentration?

Otis Kingsman spoke to Georgetown University's professor of medicine, Joseph G Verbalis to find the answer...

Joe - Now hyponatraemia refers not to low sodium in the body. It refers to low sodium concentration in the blood, and that can be caused by two different mechanisms. The first is in fact a excess loss of body sodium, but the more common ideology is an excess of body water due to the inability of the kidney to maximally excrete all the water consumed

Otis - Hyponatraemia is generally caused by a low salt diet, rather than medication. On the off chance, however, it's due for drugs causing the kidneys to not dilute for urine, leaving the concentration of salt in the blood to be much higher.

Joe - If you drink a lot of fluid, I don't care what kind of fluid it is, your body reacts by suppressing the secretion of the hormone from the pituitary called arginine vasopressin (AVP), that controls kidney water excretion. When you suppress the level of AVP, the kidney can excrete up to 20 litres a day, which protects us against becoming hyponatraemic

Otis - Excess water that would dilute for salt in our blood too much is put into urine to be excreted through the kidneys.

Joe - But many drugs cause an inability of the pituitary to completely suppress antidiuretic hormone (AVP). And in that case, the kidney cannot maximally excrete the free water. And if that occurs, then if more water than that is consumed, then that will accumulate in the body. That will then dilute the sodium concentration down to a lower level, which we call hyponatraemia.

Otis - Most medication doesn't affect our ability to absorb salt. It affects our inability to excrete the maximum amount of water from the body.

Joe - So, Kandi, most medications do not cause the body to fail to absorb or use sodium. They caused the body to retain excess water. And the treatment for that is not to take more sodium in, it is to limit the amount of water that is ingested. Again, not necessarily only water, but any fluids that are ingested, because most fluids are largely water.

Otis - Thank you to professor Joe Verbalis for helping us find the answer. Next week, we'll be splashing about in this science question from listener Ed:

Ed - Is it recommended to drink Cola after swimming in a river, and does it really reduce the risk of getting an upset stomach?