METOLAZONE TABLETS, USP
2.5 mg, 5 mg and 10 mg

Metolazone Tablets, USP for oral administration contain 2.5 mg, 5 mg or 10 mg of metolazone, USP, a diuretic/saluretic/antihypertensive drug of the quinazoline class.

Metolazone has the molecular formula C₁₆H₁₆ClN₃O₃S, the chemical name 7-chloro-1, 2, 3, 4-tetrahydro-2-methyl-3-(2-methylphenyl)-4-oxo-6-quinazolinesulfonamide, and a molecular weight of 365.83. The structural formula is:

Metolazone is only sparingly soluble in water, but more soluble in plasma, blood, alkali, and organic solvents. Inactive Ingredients: colloidal silicon dioxide, FD&C Yellow #6 Lake HT, magnesium stearate and microcrystalline cellulose. In addition, the 10 mg strength contains D&C Yellow #10 Lake HT and FD&C Blue #2 Lake HT.

Metolazone is a quinazoline diuretic, with properties generally similar to the thiazide diuretics. The actions of metolazone result from interference with the renal tubular mechanism of electrolyte reabsorption. Metolazone acts primarily to inhibit sodium reabsorption at the cortical diluting site and to a lesser extent in the proximal convoluted tubule. Sodium and chloride ions are excreted in approximately equivalent amounts. The increased delivery of sodium to the distal tubular exchange site results in increased potassium excretion. Metolazone does not inhibit carbonic anhydrase. A proximal action of metolazone has been shown in humans by increased excretion of phosphate and magnesium ions and by a markedly increased fractional excretion of sodium in patients with severely compromised glomerular filtration. This action has been demonstrated in animals by micropuncture studies.

When metolazone tablets are given, diuresis and saluresis usually begin within one hour and may persist for 24 hours or more. For most patients, the duration of effect can be varied by adjusting the daily dose. High doses may prolong the effect. A single daily dose is recommended. When a desired therapeutic effect has been obtained, it may be possible to reduce dosage to a lower maintenance level.

The diuretic potency of metolazone at maximum therapeutic dosage is approximately equal to thiazide diuretics. However, unlike thiazides, metolazone may produce diuresis in patients with glomerular filtration rates below 20 mL/min.

Metolazone and furosemide administered concurrently have produced marked diuresis in some patients where edema or ascites was refractory to treatment with maximum recommended doses of these or other diuretics administered alone. The mechanism of this interaction is unknown (see WARNINGS and PRECAUTIONS: Drug Interactions).

Maximum blood levels of metolazone are found approximately eight hours after dosing. A small fraction of metolazone is metabolized. Most of the drug is excreted in the unconverted form in the urine.

Metolazone tablets are indicated for the treatment of salt and water retention including:

• edema accompanying congestive heart failure;
• edema accompanying renal diseases, including the nephrotic syndrome and states of diminished renal function.

Metolazone tablets are also indicated for the treatment of hypertension, alone or in combination with other antihypertensive drugs of a different class. Mykrox^® tablets, a more rapidly available form of metolazone, are intended for the treatment of new patients with mild to moderate hypertension. A dose titration is necessary if Mykrox^® tablets are to be substituted for Zaroxolyn^® tablets and other formulations of metolazone that share its slow and incomplete bioavailability, in the treatment of hypertension.

The routine use of diuretics in an otherwise healthy woman is inappropriate and exposes mother and fetus to unnecessary hazard. Diuretics do not prevent development of toxemia of pregnancy, and there is no evidence that they are useful in the treatment of developed toxemia.

Edema during pregnancy may arise from pathologic causes or from the physiologic and mechanical consequences of pregnancy. Metolazone tablets are indicated in pregnancy when edema is due to pathologic causes, just as it is in the absence of pregnancy (see PRECAUTIONS). Dependent edema in pregnancy resulting from restriction of venous return by the expanded uterus is properly treated through elevation of the lower extremities and use of support hose; use of diuretics to lower intravascular volume in this case is illogical and unnecessary. There is hypervolemia during normal pregnancy which is harmful to neither the fetus nor the mother (in the absence of cardiovascular disease), but which is associated with edema, including generalized edema, in the majority of pregnant women. If this edema produces discomfort, increased recumbency will often provide relief. In rare instances, this edema may cause extreme discomfort which is not relieved by rest. In these cases, a short course of diuretics may be appropriate.

Anuria, hepatic coma or precoma, known allergy or hypersensitivity to metolazone.

Rarely, the rapid onset of severe hyponatremia and/or hypokalemia has been reported following initial doses of thiazide and non-thiazide diuretics. When symptoms consistent with severe electrolyte imbalance appear rapidly, drug should be discontinued and supportive measures should be initiated immediately. Parenteral electrolytes may be required. Appropriateness of therapy with this class of drugs should be carefully reevaluated.

Hypokalemia may occur with consequent weakness, cramps, and cardiac dysrhythmias. Serum potassium should be determined at regular and appropriate intervals, and dose reduction, potassium supplementation or addition of a potassium-sparing diuretic instituted whenever indicated. Hypokalemia is a particular hazard in patients who are digitalized or who have or have had a ventricular arrhythmia; dangerous or fatal arrhythmias may be precipitated. Hypokalemia is dose related.

DO NOT INTERCHANGE: DO NOT INTERCHANGE ZAROXOLYN^® TABLETS AND OTHER FORMULATIONS OF METOLAZONE THAT SHARE ITS SLOW AND INCOMPLETE BIOAVAILABILITY AND ARE NOT THERAPEUTICALLY EQUIVALENT AT THE SAME DOSES TO MYKROX^® TABLETS, A MORE RAPIDLY AVAILABLE AND COMPLETELY BIOAVAILABLE METOLAZONE PRODUCT. FORMULATIONS BIOEQUIVALENT TO ZAROXOLYN^® AND FORMULATIONS BIOEQUIVALENT TO MYKROX^® SHOULD NOT BE INTERCHANGED FOR ONE ANOTHER.

Patients should be informed of possible adverse effects, advised to take the medication as directed, and promptly report any possible adverse reactions to the treating physician.

None reported.

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.

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.

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.

Safety and effectiveness in pediatric patients have not been established in controlled clinical trials. There is limited experience with the use of metolazone in pediatric patients with congestive heart failure, hypertension, bronchopulmonary dysplasia, nephrotic syndrome and nephrogenic diabetes insipidus. Doses used generally ranged from 0.05 to 0.1 mg/kg administered once daily and usually resulted in a 1 to 2.8 kg weight loss and 150 to 300 cc increase in urine output. Not all patients responded and some gained weight. Those patients who did respond did so in the first few days of treatment. Prolonged use (beyond a few days) was generally associated with no further beneficial effect or a return to baseline status and is not recommended.

There is limited experience with the combination of metolazone and furosemide in pediatric patients with furosemide-resistant edema. Some benefited while others did not or had an exaggerated response with hypovolemia, tachycardia, and orthostatic hypotension requiring fluid replacement. Severe hypokalemia was reported and there was a tendency for diuresis to persist for up to 24 hours after metolazone was discontinued. Hyperbilirubinemia has been reported in 1 neonate. Close clinical and laboratory monitoring of all children treated with diuretics is indicated. See CONTRAINDICATIONS, WARNINGS and PRECAUTIONS.

Clinical studies of metolazone 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.

Metolazone is usually well tolerated, and most reported adverse reactions have been mild and transient. Many metolazone related adverse reactions represent extensions of its expected pharmacologic activity and can be attributed to either its antihypertensive action or its renal/metabolic actions. The following adverse reactions have been reported. Several are single or comparably rare occurrences. Adverse reactions are uled in decreasing order of severity within body systems.

Cardiovascular: Chest pain/discomfort, orthostatic hypotension, excessive volume depletion, hemoconcentration, venous thrombosis, palpitations.

Central and Peripheral Nervous System: Syncope, neuropathy, vertigo, paresthesias, psychotic depression, impotence, dizziness/lightheadedness, drowsiness, fatigue, weakness, restlessness (sometimes resulting in insomnia), headache.

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

Gastrointestinal: Hepatitis, intrahepatic cholestatic jaundice, pancreatitis, vomiting, nausea, epigastric distress, diarrhea, constipation, anorexia, abdominal bloating, abdominal pain.

Hematologic: Aplastic/hypoplastic anemia, agranulocytosis, leukopenia, thrombocytopenia.

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

Musculoskeletal: Joint pain, acute gouty attacks, muscle cramps or spasm.

Other: Transient blurred vision, chills, dry mouth.

In addition, adverse reactions reported with similar antihypertensive-diuretics, but which have not been reported to date for metolazone include: bitter taste, sialadenitis, xanthopsia, respiratory distress (including pneumonitis), and anaphylactic reactions. These reactions should be considered as possible occurrences with clinical usage of metolazone.

Whenever adverse reactions are moderate or severe, metolazone dosage should be reduced or therapy withdrawn.

Intentional overdosage has been reported rarely with metolazone and similar diuretic drugs.

Orthostatic hypotension, dizziness, drowsiness, syncope, electrolyte abnormalities, hemoconcentration and hemodynamic changes due to plasma volume depletion may occur. In some instances depressed respiration may be observed. At high doses, lethargy of varying degree may progress to coma within a few hours. The mechanism of CNS depression with thiazide overdosage is unknown. Also, GI irritation and hypermotility may occur. Temporary elevation of BUN has been reported, especially in patients with impairment of renal function. Serum electrolyte changes and cardiovascular and renal function should be closely monitored.

There is no specific antidote available but immediate evacuation of stomach spans is advised. Dialysis is not likely to be effective. Care should be taken when evacuating the gastric spans to prevent aspiration, especially in the stuporous or comatose patient. Supportive measures should be initiated as required to maintain hydration, electrolyte balance, respiration, and cardiovascular and renal function.

Effective dosage of metolazone tablets should be individualized according to indication and patient response. A single daily dose is recommended. Therapy with metolazone tablets should be titrated to gain an initial therapeutic response and to determine the minimal dose possible to maintain the desired therapeutic response.

Suitable initial dosages will usually fall in the ranges given.

Edema of cardiac failure:

•  Metolazone tablets 5 to 20 mg once daily.

Edema of renal disease:

•  Metolazone tablets 5 to 20 mg once daily.

Mild to moderate essential hypertension:

•  Metolazone tablets 2.5 to 5 mg once daily.
  New patients- If considered desirable to switch patients currently on Zaroxolyn^® tablets and other formulations of metolazone that share its slow and incomplete bioavailability to Mykrox^®, the dose should be determined by titration starting at one tablet (0.5 mg) once daily and increasing to two tablets (1 mg) once daily if needed.

The time interval required for the initial dosage to produce an effect may vary. Diuresis and saluresis usually begin within one hour and persist for 24 hours or longer. When a desired therapeutic effect has been obtained, it may be advisable to reduce the dose if possible. The daily dose depends on the severity of the patient's condition, sodium intake, and responsiveness. A decision to change the daily dose should be based on the results of thorough clinical and laboratory evaluations. If antihypertensive drugs or diuretics are given concurrently with metolazone tablets, more careful dosage adjustment may be necessary. For patients who tend to experience paroxysmal nocturnal dyspnea, it may be advisable to employ a larger dose to ensure prolongation of diuresis and saluresis for a full 24-hour period.

The time interval required for the initial dosage regimen to show effect may vary from three or four days to three to six weeks in the treatment of elevated blood pressure. Doses should be adjusted at appropriate intervals to achieve maximum therapeutic effect.

Metolazone Tablets, USP are available containing 2.5 mg, 5 mg and 10 mg of metolazone.

The 2.5 mg tablets are peach, round, biconvex, unscored tablets debossed with M on one side of the tablet and 172 on the other side.They are available as follows:

NDC 0378-6172-01
bottles of 100 tablets

NDC 0378-6172-10
bottles of 1000 tablets

The 5 mg tablets are orange, round, biconvex, unscored tablets debossed with M on one side of the tablet and 173 on the other side.They are available as follows:

NDC 0378-6173-01
bottles of 100 tablets

NDC 0378-6173-10
bottles of 1000 tablets

The 10 mg tablets are light green, round, biconvex, unscored tablets debossed with M on one side of the tablet and 174 on the other side.They are available as follows:

NDC 0378-6174-01
bottles of 100 tablets

NDC 0378-6174-10
bottles of 1000 tablets

Store at 20° to 25°C (68° to 77°F). [See USP for Controlled Room Temperature.]

Protect from light.

Dispense in a tight, light-resistant container as defined in the USP using a child-resistant closure.