Many medications can cause subtle changes in renal function without
necessarily raising the BUN and serum creatinine. These changes in
renal function may present as electrolyte imbalances or as acid-base
abnormalities (Table 2). Some of the medications have already been
discussed. For instance, hypomagnesemia or hypokalemia can be seen
with both aminoglycoside and cisplatin therapy. Diuretics, both of the
thiazide and loop types, can also present with hypomagnesemia, hypokalemia,
and metabolic alkalosis. Volume depletion with secondary hyperaldosteronism
stimulates distal potassium and hydrogen secretionz5
resulting in hypokalemia and metabolic alkalosis. Hyponatremia is commonly
associated with thiazide-type diuretics. Distal natriuresis causes
volume depletion with subsequent release of aldosterone and ADH.
Because the medullary concentration gradient is maintained, more water
is reabsorbed distally in the face of increased ADH in comparison to
salt. Loop diuretics, however, can cause a washout of the medullary
concentration gradient; therefore, despite increased ADH release resulting
from volume depletion, increased water reabsorption does not
occur, and hyponatremia is not seen. Vigorous diuresis, however, can
cause significant sodium chloride loss with hyponatremia resulting from
volume depletion from any diuretic when patients are on severe salt
restriction but continue to maintain free water intake. Cyclophosphamide
and vincristine have a direct antidiuretic effect in the distal tubule,
causing impaired free water e~cretion,'5~8 ,t hus leading to hyponatremia.
NSAID use may also cause hyponatremia by potentiating ADH effect
because normally prostaglandins inhibit ADH action. Other drugs that
may cause hyponatremia are listed in Table 2.