DO NOT INTERCHANGE
MYKROX TABLETS ARE A RAPIDLY AVAILABLE FORMULATION OF
METOLAZONE FOR ORAL ADMINISTRATION. MYKROX TABLETS AND OTHER FORMULATIONS OF
METOLAZONE THAT SHARE ITS MORE RAPID AND COMPLETE BIOAVAILABILITY ARE NOT
THERAPEUTICALLY EQUIVALENT TO ZAROXOLYN TABLETS AND OTHER FORMULATIONS OF
METOLAZONE THAT SHARE ITS SLOW AND INCOMPLETE BIOAVAILABILITY. FORMULATIONS
BIOEQUIVALENT TO MYKROX AND FORMULATIONS BIOEQUIVALENT TO ZAROXOLYN SHOULD NOT
BE INTERCHANGED FOR ONE ANOTHER.
General
Fluid and Electrolytes
All patients receiving therapy with MYKROX Tablets should
have serum electrolyte measurements done at appropriate intervals and be
observed for clinical signs of fluid and/or electrolyte imbalance: namely,
hyponatremia, hypochloremic alkalosis, and hypokalemia. In patients with severe
edema accompanying cardiac failure or renal disease, a low-salt syndrome may be
produced, especially with hot weather and a low-salt diet. Serum and urine
electrolyte determinations are particularly important when the patient has
protracted vomiting, severe diarrhea, or is receiving parenteral fluids.
Warning signs of imbalance are: dryness of mouth, thirst, weakness, lethargy,
drowsiness, restlessness, muscle pains or cramps, muscle fatigue, hypotension,
oliguria, tachycardia, and gastrointestinal disturbances such as nausea and
vomiting. Hyponatremia may occur at any time during long term therapy and, on
rare occasions, may be life threatening.
The risk of hypokalemia is increased when larger doses are
used, when diuresis is rapid, when severe liver disease is present, when corticosteroids
are given concomitantly, when oral intake is inadequate or when excess
potassium is being lost extrarenally, such as with vomiting or diarrhea.
Thiazide-like diuretics have been shown to increase the
urinary excretion of magnesium; this may result in hypomagnesemia.
Glucose Tolerance
Metolazone may raise blood glucose concentrations possibly
causing hyperglycemia and glycosuria in patients with diabetes or latent diabetes.
Hyperuricemia
MYKROX regularly causes an increase in serum uric acid and
can occasionally precipitate gouty attacks even in patients without a prior
history of them.
Azotemia
Azotemia, presumably prerenal azotemia, may be precipitated
during the administration of MYKROX Tablets. If azotemia and oliguria worsen
during treatment of patients with severe renal disease, MYKROX Tablets should
be discontinued.
Renal Impairment
Use caution when administering MYKROX Tablets to patients
with severely impaired renal function. As most of the drug is excreted by the
renal route, accumulation may occur.
Orthostatic Hypotension
Orthostatic hypotension may occur; this may be potentiated
by alcohol, barbiturates, narcotics, or concurrent therapy with other antihypertensive
drugs. In controlled clinical trials, 1.4% of patients treated with MYKROX
Tablets (½ mg) had orthostatic hypotension; this effect was not reported in the
placebo group.
Hypercalcemia
Hypercalcemia may infrequently occur with metolazone,
especially in patients taking high doses of vitamin D or with high bone turnover
states, and may signify hidden hyperparathyroidism. Metolazone should be
discontinued before tests for parathyroid function are performed.
Systemic Lupus Erythematosus
Thiazide diuretics have exacerbated or activated systemic
lupus erythematosus and this possibility should be considered with MYKROX
Tablets.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Mice and rats administered metolazone 5 days/week for up to
18 and 24 months, respectively, at daily doses of 2, 10, and 50 mg/kg, exhibited
no evidence of a tumorigenic effect of the drug. The small number of animals
examined histologically and poor survival in the mice limit the conclusions
that can be reached from these studies.
Metolazone was not mutagenic in vitro in the Ames Test using
Salmonella typhimurium strains TA-97, TA-98, TA-100, TA-102, and TA-1535.
Reproductive performance has been evaluated in mice and
rats. There is no evidence that metolazone possesses the potential for altering
reproductive capacity in mice. In a rat study, in which males were treated
orally with metolazone at doses of 2, 10, and 50 mg/kg for 127 days prior to
mating with untreated females, an increased number of resorption sites was
observed in dams mated with males from the 50 mg/kg group. In addition, the
birth weight of offspring was decreased and the pregnancy rate was reduced in
dams mated with males from the 10 and 50 mg/kg groups.
Pregnancy
Teratogenic Effects: Pregnancy Category B
Reproduction studies performed in mice, rabbits, and rats
treated during the appropriate period of gestation at doses up to 50 mg/kg/ day
have revealed no evidence of harm to the fetus due to metolazone. There are,
however, no adequate and well-controlled studies in pregnant women. Because
animal reproduction studies are not always predictive of human response, MYKROX
Tablets should be used during pregnancy only if clearly needed. Metolazone
crosses the placental barrier and appears in cord blood.
Non-Teratogenic Effects
The use of MYKROX Tablets in pregnant women requires that
the anticipated benefit be weighed against possible hazards to the fetus. These
hazards include fetal or neonatal jaundice, thrombocytopenia, and possibly
other adverse reactions which have occurred in the adult. It is not known what
effect the use of the drug during pregnancy has on the later growth,
development, and functional maturation of the child. No such effects have been
reported with metolazone.
Labor and Delivery
Based on clinical studies in which women received metolazone
in late pregnancy until the time of delivery, there is no evidence that the
drug has any adverse effects on the normal course of labor or delivery.
Nursing Mothers
Metolazone appears in breast milk. Because of the potential
for serious adverse reactions in nursing infants from metolazone, a decision
should be made whether to discontinue nursing or to discontinue the drug, taking
into account the importance of the drug to the mother.
Pediatric Use
Safety and effectiveness of MYKROX Tablets in pediatric
patients have not been established, and such use is not recommended.
Geriatric Use
Clinical studies of MYKROX did not include sufficient
numbers of subjects aged 65 and over to determine whether they respond differently
from younger subjects. Other reported clinical experience has not identified
differences in responses between the elderly and younger patients. In general,
dose selection for an elderly patient should be cautious, usually starting at
the low end of the dosing range, reflecting the greater frequency of decreased
hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.
This drug is known to be substantially excreted by the
kidney, and the risk of toxic reactions to this drug may be greater in patients
with impaired renal function. Because elderly patients are more likely to have
decreased renal function, care should be taken in dose selection, and it may be
useful to monitor renal function.
Last updated on RxList: 5/4/2009