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Mykrox (Metolazone) - Side Effects and Adverse Reactions



Adverse experience information is available from more than 14 years of accumulated marketing experience with other formulations of metolazone for which reliable quantitative information is lacking and from controlled clinical trials with MYKROX from which incidences can be calculated.

In controlled clinical trials with MYKROX, adverse experiences resulted in discontinuation of therapy in 6.7-6.8% of patients given ½ to 1 mg of MYKROX.

Adverse experiences occurring in controlled clinical trials with MYKROX with an incidence of >2%, whether or not considered drug-related, are summarized in the following table.

Incidence of Adverse Experiences Volunteered or Elicited (by Patient in Percent)*
* Percent of patients reporting an adverse experience one or more times.
† All doses combined (½, 1, and 2 mg).

n = 226†
Dizziness (lightheadedness) 10.2
Headaches 9.3
Muscle Cramps 5.8
Fatigue (malaise, lethargy, lassitude) 4.4
Joint Pain, swelling 3.1
Chest Pain (precordial discomfort) 2.7

Some of the adverse effects reported in association with MYKROX also occur frequently in untreated hypertensive patients, such as headache and dizziness, which occurred in 14.8 and 7.4% of patients in a smaller parallel placebo group.

The following adverse effects were reported in less than 2% of the MYKROX treated patients.


Cold extremities, edema, orthostatic hypotension, palpitations.

Central and Peripheral Nervous System

Anxiety, depression, dry mouth, impotence, nervousness, neuropathy, weakness, “weird” feeling.


Pruritus, rash, skin dryness.

Eyes, Ears, Nose, Throat

Cough, epistaxis, eye itching, sinus congestion, sore throat, tinnitus.


Abdominal discomfort (pain, bloating), bitter taste, constipation, diarrhea, nausea, vomiting.




Back pain.

Other Adverse Experiences

Adverse experiences reported with other marketed metolazone formulations and most thiazide diuretics, for which quantitative data are not available, are listed in decreasing order of severity within body systems. Several are single or rare occurrences.


excessive volume depletion, hemoconcentration, venous thrombosis.

Central and Peripheral Nervous System

syncope, paresthesias, drowsiness, restlessness (sometimes resulting in insomnia).


toxic epidermal necrolysis (TEN), Stevens-Johnson Syndrome, necrotizing angiitis (cutaneous vasculitis), skin necrosis, purpura, petechiae, dermatitis, photosensitivity, urticaria, pruritus, skin rashes.


hepatitis, intrahepatic cholestatic jaundice, pancreatitis, anorexia, nausea, diarrhea, abdominal pain.


aplastic (hypoplastic) anemia, agranulocytosis, leukopenia, thrombocytopenia.


hypokalemia (see WARNINGS, Hypokalemia), hyponatremia, hyperuricemia, hypochloremia, hypochloremic alkalosis, hyperglycemia, glycosuria, increase in serum urea nitrogen (BUN) or creatinine, hypophosphatemia, hypomagnesemia, hypercalcemia.


acute gouty attacks.


transient blurred vision, chills.

In addition, rare adverse experiences reported in association with similar antihypertensive-diuretics but not reported to date for metolazone include: sialadenitis, xanthopsia, respiratory distress (including pneumonitis), and anaphylactic reactions. These experiences could occur with clinical use of metolazone.

Drug label data at the top of this Page last updated: 2006-01-12

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