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Mykrox Side Effects

Generic name: metolazone

Medically reviewed by Last updated on Jul 12, 2022.

Note: This document contains side effect information about metolazone. Some dosage forms listed on this page may not apply to the brand name Mykrox.

Applies to metolazone: oral tablet.

Serious side effects of Mykrox

Along with its needed effects, metolazone (the active ingredient contained in Mykrox) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking metolazone:

Incidence not known

  • Black, tarry stools
  • bleeding gums
  • blistering, peeling, or loosening of skin
  • bloating
  • blood in urine or stools
  • blurred vision
  • bone pain
  • chest pain
  • chills
  • clay-colored stools
  • cold sweats
  • coma
  • confusion
  • constipation
  • convulsions
  • cough
  • dark urine
  • decreased urine
  • diarrhea
  • dizziness, faintness, or lightheadedness when getting up from lying or sitting position
  • drowsiness
  • dry mouth
  • fast, irregular, pounding, or racing heartbeat or pulse
  • fever
  • flushed, dry skin
  • fruit-like breath odor
  • general tiredness and weakness
  • headache
  • incoherent speech
  • increased hunger
  • increased thirst
  • increased urination
  • indigestion
  • irritability
  • itching
  • joint or muscle pain
  • light-colored stools
  • loss of appetite
  • lower back or side pain
  • metallic taste
  • mood changes
  • muscle pain or cramps
  • nausea and vomiting
  • numbness or tingling in hands, feet, or lips
  • pain in lower legs
  • painful or difficult urination
  • pinpoint red spots on skin
  • rash
  • red irritated eyes
  • red skin lesions, often with a purple center
  • redness or swelling of lower leg
  • shortness of breath
  • sore throat
  • sores, ulcers, or white spots in mouth or on lips
  • sugar in the urine
  • sweating
  • swelling of face, ankles, or hands
  • swollen or painful glands
  • tightness in chest
  • trembling
  • troubled breathing
  • unexplained weight loss
  • unpleasant breath odor
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • upper right abdominal pain
  • vomiting of blood
  • weak pulse
  • wheezing
  • yellow eyes and skin

Get emergency help immediately if any of the following symptoms of overdose occur while taking metolazone:

Symptoms of overdose

  • Fainting
  • irregular, fast or slow, or shallow breathing
  • pale or blue lips, fingernails, or skin
  • unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness
  • weakness and heaviness of legs

Other side effects of Mykrox

Some side effects of metolazone may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

  • Blue-green to black skin discoloration
  • burning, tingling, numbness, or pain in the hands, arms, feet, or legs
  • cracked, dry, or scaly skin
  • decreased interest in sexual intercourse
  • feeling of constant movement of self or surroundings
  • hives or welts
  • inability to have or keep an erection
  • loss in sexual ability, desire, drive, or performance
  • pain, redness, or sloughing of skin at place of injection
  • restlessness
  • sensation of pins and needles
  • sensation of spinning
  • stabbing pain

For Healthcare Professionals

Applies to metolazone: oral tablet.


Metabolic side effects are the most common and profound. The rapid onset of hyponatremia or hypokalemia is often sudden and may be profound, particularly if metolazone (the active ingredient contained in Mykrox) is given with a loop diuretic. Hypokalemia may be important in patients with underlying cardiac arrhythmias. Metolazone may increase serum calcium and uric acid levels and lower serum magnesium and phosphate levels. Glucose intolerance is reported in rare cases.[Ref]

A rare case of hyperosmolar nonketotic hyperglycemia is associated with metolazone.[Ref]


Cardiovascular side effects are uncommon. Postural hypotension is reported in less than 5% of patients. Rare cases of venous thrombosis are reported, thought to be due to metolazone-induced hypovolemia and increased serum concentrations of clotting factors. Rare cardiovascular side effects also include palpitations, hypovolemia, and chest pain.[Ref]


Renal insufficiency, manifest as a rise in serum creatinine and BUN, may occur, although, in most cases, creatinine clearance increases as a result of metolazone (the active ingredient contained in Mykrox) therapy.[Ref]

Nervous system

It is not clear whether the patients who developed syncope and seizure activity were hypotensive or hypovolemic at the time of the seizures or that metolazone (the active ingredient contained in Mykrox) can definitively be implicated. In one case the patient was also taking theophylline and had hypomagnesemia, which may be a complication of metolazone therapy.[Ref]

Nervous system side effects include headache, dizziness, and fatigue. Two cases of syncope and seizures are reported. Metolazone-induced hypovolemia and electrolyte changes may induce hepatic encephalopathy in some patients.[Ref]


A case of cutaneous hypersensitivity angiitis has been reported in a patient who had previously tolerated thiazide diuretics, indicating that, despite the chemical similarity between thiazides and metolazone (the active ingredient contained in Mykrox) there is not necessarily cross-reactivity.[Ref]

Hypersensitivity reactions include rare case reports of necrotizing vasculitis, angiitis, and pruritic rashes.[Ref]


Hematologic abnormalities are rare. Cases of reversible hypoplastic anemia, aplastic anemia, agranulocytosis, and mild leukopenia are reported.[Ref]


Gastrointestinal side effects are rare, and include a case of acute pancreatitis. Nausea, vomiting, anorexia, and abdominal bloating are also rare.[Ref]


Hepatic side effects include a rare case of cholestatic jaundice.[Ref]


Musculoskeletal cramps are associated with metolazone (the active ingredient contained in Mykrox) therapy, as with other diuretics, and may be associated with electrolyte disorders and rapid intravascular volume shifts.[Ref]

More about Mykrox (metolazone)

Patient resources

Other brands


Professional resources

Related treatment guides


1. Anderson PE, Ellis GG, Austin SM "Case report: metolazone-associated hypercalcemia and acute pancreatitis." Am J Med Sci 302 (1991): 235-7

2. Bennett WM, Porter GA "Efficacy and safety of metolazone in renal failure and the nephrotic syndrome." J Clin Pharmacol 13 (1973): 357-64

3. Craswell PW, Ezzat E, Kopstein J, Varghese Z, Moorhead JF "Use of metolazone, a new diuretic, in patients with renal disease." Nephron 12 (1974): 63-73

4. "Product Information. Zaroxolyn (metolazone)." Rhone Poulenc Rorer (2001):

5. Fitzgerald M, Brennan N "Muscle cramps, collapse, and seizures in two patients taking metolazone." Br Med J 1 (1976): 1381-2

6. Stern A "Metolazone, a diuretic agent." Am Heart J 91 (1976): 262-3

7. Black W, Shiner P, Roman J "Severe electrolyte disturbances associated with metolazone and furosemide." South Med J 71 (1978): 381

8. Rowe P, Mather H "Hyperosmolar non-ketotic diabetes mellitus associated with metolazone." Br Med J 291 (1985): 25-6

9. Pickkers P, Schachter M, Hughes AD, Feher MD, Sever PS "Thiazide-induced hyperglycaemia: a role for calcium-activated potassium channels?" Diabetologia 39 (1996): 861-4

10. Nichols T "Initial experience with metolazone." Minn Med 60 (1977): 549-53

11. Weinrauch L, Belok S, Gauvin G, D'Elia J "Palpable acute necrotizing arteritis secondary to metolazone." Cutis 30 (1982): 83-4

12. Cox N, Hodkin P "Vasculitis due to metolazone." Postgrad Med J 67 (1991): 860

13. Suh K "Hypoplastic anemia associated with metolazone." JAMA 242 (1979): 139-40

14. Donovan K "Neutropenia and metolazone." Br Med J 299 (1989): 981

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.