Ethacrynic acid is a potent loop diuretic whose side effects fall into two broad categories: problems caused by the drug doing its job too well (dehydration, electrolyte losses, metabolic shifts) and problems caused by the drug acting on tissues it was never meant to reach, most notably the inner ear. It remains the only loop diuretic without a sulfonamide chemical structure, which keeps it in clinical use despite a side-effect profile that many clinicians consider less forgiving than its better-known relatives, furosemide and bumetanide.
How It Works and Why That Matters for Side Effects
Ethacrynic acid blocks a transporter in the kidney called the Na⁺-K⁺-2Cl⁻ symporter, located in the thick ascending limb of the loop of Henle. By shutting down this transporter, the drug prevents the kidney from reabsorbing sodium, potassium, and chloride, which pulls water along with them into the urine.1PubMed. The clinical pharmacology of ethacrynic acid That mechanism is the same one all loop diuretics exploit, but understanding it explains why most of ethacrynic acid’s routine side effects revolve around losing too much fluid and too many electrolytes too quickly.
Electrolyte and Fluid-Related Side Effects
The most common problems patients experience with ethacrynic acid are direct consequences of aggressive diuresis. Sodium, potassium, chloride, calcium, and magnesium all leave the body faster than usual. Potassium loss is the most clinically monitored because low potassium can trigger dangerous heart rhythm disturbances, muscle weakness, and cramping. The drug can also push the blood toward metabolic alkalosis, a state where the blood becomes too basic, largely because chloride and hydrogen ions are swept out alongside sodium and potassium.2PubMed. The clinical pharmacology of ethacrynic acid This alkalosis is usually preventable with potassium chloride supplements, which replace both the lost potassium and the lost chloride at once.
Volume depletion itself carries a chain of consequences: dizziness on standing, low blood pressure, increased thirst, and in severe cases kidney function that worsens because there simply is not enough circulating blood to perfuse the kidneys adequately. Older adults and people who are already dehydrated from illness or poor oral intake are at higher risk. Clinicians often start at a low dose and increase slowly, monitoring blood chemistry closely in the first days and weeks.
Effects on Blood Sugar
Ethacrynic acid can interfere with carbohydrate metabolism, an effect that matters most for people with diabetes. An early study published in JAMA found that a high maintenance dose of 200 mg daily altered carbohydrate metabolism in diabetic patients compared with placebo, though the effect was not significantly different from the patients’ own control periods before the trial.3JAMA. Ethacrynic Acid and Diabetes In practical terms, this means blood sugar may drift upward during treatment, and people with diabetes or prediabetes should expect their glucose to need closer monitoring. The mechanism is thought to involve potassium depletion impairing insulin release, the same pathway that explains why thiazide diuretics also nudge blood sugar higher.
Hearing Loss and Inner-Ear Toxicity
Ototoxicity is the side effect that distinguishes ethacrynic acid from most other cardiovascular drugs and is the one that worries clinicians the most. The same Na-K-2Cl transporter that the drug blocks in the kidney also exists in the stria vascularis, a structure inside the cochlea that maintains the chemical environment the inner ear needs to convert sound into nerve signals. When ethacrynic acid disrupts this transporter, the fluid balance inside the cochlea shifts, the electrical potential that drives hearing drops, and the result can be sudden hearing loss or tinnitus.4PubMed Central. Ototoxic effects and mechanisms of loop diuretics
Most of the time, this hearing loss is temporary and resolves once the drug is stopped or the dose is reduced. Permanent deafness is rare when ethacrynic acid is used alone in patients with normal or near-normal kidney function. The risk climbs sharply, however, in people with severe acute or chronic kidney failure, because the drug accumulates to higher blood levels when the kidneys cannot clear it efficiently.5PubMed Central. Ototoxic effects and mechanisms of loop diuretics Intravenous administration, which delivers a bolus of drug directly into the bloodstream and produces a rapid spike in concentration, also raises the ototoxic risk compared with oral dosing.
Research into exactly how the damage happens has turned up an interesting finding: ethacrynic acid does not appear to harm the stria vascularis when applied directly to cochlear tissue in a laboratory dish. Instead, one of the earliest changes seen in live animals is the loss of blood flow to the vessels supplying the cochlea’s lateral wall, suggesting that the drug may cause ischemia (a cut-off of blood supply) in the inner ear, and the strial damage follows secondarily.6PubMed Central. Ototoxic effects and mechanisms of loop diuretics This distinction is more than academic: it means the ear damage may involve vascular injury rather than simple chemical toxicity, which has implications for who is most vulnerable and whether any protective strategies might eventually be developed.
Dangerous Pairings With Other Drugs
The ototoxic risk of ethacrynic acid does not exist in a vacuum. When the drug is combined with aminoglycoside antibiotics, the two can interact synergistically to produce permanent hearing loss far worse than either drug alone. A classic animal study showed that guinea pigs given a loading dose of kanamycin (an aminoglycoside) followed two hours later by intravenous ethacrynic acid lost cochlear function permanently, confirming clinical reports of the same outcome in humans.7JAMA Otolaryngology–Head & Neck Surgery. Interaction of Kanamycin and Ethacrynic Acid: Severe Cochlear Damage in Guinea Pigs More recent research with gentamicin, another widely used aminoglycoside, showed that co-administration of ethacrynic acid worsened cochlear hair cell loss, auditory nerve fiber degeneration, and spiral ganglion neuron damage, with the drug apparently increasing gentamicin’s access to the inner ear through the blood-labyrinth barrier.8PubMed. Ethacrynic acid regulates gentamicin ototoxicity via the blood-labyrinth barrier
Beyond the aminoglycoside interaction, ethacrynic acid shares the broader drug-interaction profile common to loop diuretics. The potassium loss it causes can make digoxin toxicity more likely, amplify the blood-pressure-lowering effect of ACE inhibitors, and interfere with blood sugar control in people taking antidiabetic medications. NSAIDs can blunt the diuretic effect by promoting sodium retention in the kidney, and lithium levels can rise because the kidney reabsorbs more lithium when sodium is being aggressively excreted.9PubMed. A Comprehensive Review of the Pharmacologic Perspective on Loop Diuretic Drug Interactions with Therapeutically Used Drugs For patients on multiple medications, these interactions often require dose adjustments or more frequent lab monitoring.
Gastrointestinal Symptoms
Nausea, vomiting, diarrhea, and abdominal discomfort are among the more common non-electrolyte side effects. They tend to be dose-related and are sometimes severe enough to limit treatment. Intravenous ethacrynic acid has historically been linked to gastrointestinal bleeding, particularly in critically ill patients, which was one of the reasons the IV formulation fell out of favor in many hospitals. Oral dosing is generally better tolerated in the GI tract, though patients occasionally report appetite loss or a sensation of stomach upset that improves if the drug is taken with food. Pancreatitis has been reported on rare occasions, a side effect shared with other loop diuretics.10PubMed. Probable loop diuretic-induced pancreatitis in a sulfonamide-allergic patient
Skin Reactions
Because ethacrynic acid is typically prescribed to patients who have already had an allergic reaction to sulfonamide-based diuretics, there is an understandable hope that it will be well tolerated from a hypersensitivity standpoint. It usually is, but it can still cause skin problems of its own. Serious skin reactions have been documented, and the drug can predispose patients to metabolic alkalosis alongside these dermatologic effects.11Side Effects of Drugs Annual. Diuretics The rashes are uncommon enough that they rarely dominate prescribing decisions, but they are worth knowing about, especially because the patient population receiving ethacrynic acid has already demonstrated a tendency toward drug allergies.
Rare but Severe Hematologic Effects
Agranulocytosis, a precipitous drop in white blood cells that leaves the body unable to fight infections, has been reported in association with ethacrynic acid. At least one published case was fatal.12Annals of Internal Medicine. Fatal agranulocytosis complicating treatment with ethacrynic acid This is exceedingly rare, and its rarity means it is not routinely screened for, but an unexplained fever or signs of infection during treatment should prompt a blood count. Other blood-related effects, including mild changes in platelet counts and anemia, have been noted in scattered reports but are not well characterized.
Pediatric and Critically Ill Patients
Ethacrynic acid sees occasional use in pediatric intensive care settings, typically as a continuous intravenous infusion for children who need aggressive fluid removal after cardiac surgery or during organ failure. A study of critically ill children receiving the drug by continuous infusion found that more than half developed metabolic alkalosis, although potassium and magnesium levels did not change significantly during treatment.13PubMed Central. Ethacrynic Acid continuous infusions in critically ill pediatric patients The alkalosis finding reinforces the importance of monitoring acid-base status in younger patients, who may be less able to compensate for rapid shifts in blood chemistry. Dosing in children requires careful weight-based calculation and close observation, since the therapeutic window can be narrow.
Patients with liver cirrhosis are another group where ethacrynic acid carries extra risk. Cirrhosis already disrupts electrolyte balance and kidney function, and the addition of a powerful loop diuretic can tip the patient into hepatic encephalopathy if ammonia levels rise alongside the alkalosis. These patients need cautious, low-dose therapy and very frequent lab work.
Pregnancy
Data on ethacrynic acid in pregnancy is thin. One older study specifically examined the drug in pregnant women with excessive fluid retention and found no instances of birth defects, concluding that ethacrynic acid was safe and effective for use during pregnancy.14American Journal of Obstetrics and Gynecology. Ethacrynic acid (a new diuretic), pregnancy, and excessive fluid retention That said, the study dates to 1968 and reflects the standards of its era. Modern prescribing guidelines generally advise caution with all diuretics in pregnancy because aggressive fluid removal can reduce blood flow to the placenta. Ethacrynic acid is not typically a first-choice drug during pregnancy, but the absence of teratogenic signals is somewhat reassuring for cases where the clinical need is compelling and alternatives are not tolerated.
Why It Is Still Prescribed Despite the Side-Effect Profile
Given the list of potential problems, a reasonable question is why anyone would choose ethacrynic acid over furosemide or bumetanide. The answer almost always comes back to sulfonamide allergy. Furosemide, bumetanide, and torsemide all contain a sulfonamide group in their chemical structure. For patients with a true allergy to sulfonamide-containing medications, ethacrynic acid is the only loop diuretic option available.15American Journal of Therapeutics. The Pleiotropic Effects of Ethacrynic Acid In practice, this niche is small but not negligible. Some patients use ethacrynic acid as a temporary bridge while they undergo desensitization protocols for furosemide, while others remain on it long term because desensitization is not feasible or not successful.
The drug has also found a specialized role in diagnostic imaging. Diuretic renal scintigraphy, a nuclear medicine scan used to evaluate whether the urinary tract is obstructed, normally uses furosemide to “wash out” the radiotracer. In patients who cannot receive furosemide due to sulfonamide allergy, ethacrynic acid has been used as a substitute and provided useful diagnostic information without adverse clinical effects in the small series studied.16PubMed. Diuretic Renal Scintigraphy in Patients with Sulfonamide Allergies: Possible Alternative Use of Ethacrynic Acid These are low-dose, single-use applications where the risk of side effects is minimal.
Practical Monitoring if You Are Taking Ethacrynic Acid
If your doctor prescribes ethacrynic acid, expect more frequent blood work than you would see with some other diuretics, at least initially. The basics include a metabolic panel that covers sodium, potassium, chloride, bicarbonate, and kidney function markers like creatinine. Magnesium and calcium deserve attention too, especially if you are on the drug long term. Blood glucose checks are warranted if you have diabetes or are at risk for it.
You should report any change in hearing, ringing in the ears, or a sense of fullness in the ears immediately. These symptoms can be the first sign of ototoxicity and may be reversible if the drug is stopped promptly. The risk goes up if you are also taking an aminoglycoside antibiotic, cisplatin, or another drug known to affect hearing, so make sure every prescriber involved in your care knows the full medication list.
Staying well hydrated and maintaining adequate dietary potassium (from foods like bananas, potatoes, and leafy greens, or from supplements your doctor prescribes) can help offset some of the electrolyte losses. Standing up slowly from a sitting or lying position reduces the chance of a blood-pressure drop catching you off guard. And if you notice unusual bleeding, severe diarrhea, or skin changes, those warrant a call to your provider rather than a wait-and-see approach.