Handbook of Drug Interactions

266 Auer
Ototoxicity: Loop diuretics may lead to dose-related hearing loss (is usually reversible).
Ototoxicity is more common with decreased renal function and with concurrent
administration of other ototoxic drugs such as aminoglycosides.
Hyperuricemia may cause gout. Loop diuretics may cause increased uric acid reabsorption
in the proximal tubule, secondary to hypovolemic states.
Hypomagnesemia: Loop diuretics may cause a reduction in sodium chloride reabsorption,
decrease normal lumen-positive potential (secondary to potassium recycling),
generate positive lumen potential that drives divalent cationic reabsorption (calcium
magnesium), and finally, loop diuretics increase magnesium and calcium excretion
(hypomagnesemia may occur in some patients that can be reversed by oral magnesium
administration)
Allergic reactions with furosemide: skin rash, eosinophilia, interstitial nephritis
(less often).
Other adverse events: Dehydration (may be severe); hyponatremia (less common
than with thiazides thought may occur in patients who increased water intake in response
to a hypovolemic thirst); hypercalcemia may occur in severe dehydration and if a hypercalcemia
condition (e.g., oat cell long carcinoma) is also present.
6.4.5. Contraindications/Concerns and Cautions
Obviously it is best not to use this medication in a dehydrated patient if water is
being restricted. Weakness or lethargy could be an indicator that blood potassium has
dropped too low.
Because of the increased calcium excretion brought on by furosemide (i.e., an
increase in urinary calcium levels), there could be a problem using this medication in
patients with a history of calcium oxalate bladder stone formation.
It is extremely difficult to overdose with this medication. Toxic doses reported
are over 100 times a typical oral dose of medication. It is important to realize that in
the treatment of heart failure (this drug’s primary use), a crisis can arise at any time.
Taking ginseng may reduce action of loop diuretics resulting in problems with
high blood pressure or water retention.
6.4.6. Drug Interactions
One of the most common drug interactions to be aware of is the interaction between
furosemide and vasodilating heart medications (especially the ACE inhibitors such as
enalapril and captopril). Furosemide may decrease circulating blood volume as it causes
a depletion in body water. Thus, water and electrolyte balance must be stable before a
vasodilator is added in.
The bronchodilator theophylline may be able to reach higher blood levels when
used in conjunction with furosemide. This means that the theophylline dose may need
to be reduced.
Loop diuretics can increase the risk of digitalis-induced cardiac toxicity.
Furosemide may lead to displacement of plasma protein binding of warfarin and
clofibrate (with elevated plasma levels of these drugs).
Loop diuretics reduce lithium renal clearance and can increase lithium serum concentrations.
Furosemide may increase renal toxicity of cephalosporin antibiotics.