Furosemide and probably other loop diuretics given concomitantly with metolazone can cause unusually large or prolonged losses of fluid and electrolytes (see WARNINGS).
When metolazone tablets are used with other antihypertensive drugs, care must be taken, especially during initial therapy. Dosage adjustments of other antihypertensives may be necessary.
Alcohol, Barbiturates, and Narcotics
The hypotensive effects of these drugs may be potentiated by the volume contraction that may be associated with metolazone therapy.
Diuretic-induced hypokalemia can increase the sensitivity of the myocardium to digitalis. Serious arrhythmias can result.
Corticosteroids or ACTH
May increase the risk of hypokalemia and increase salt and water retention.
Serum lithium levels may increase (see WARNINGS).
Diuretic-induced hypokalemia may enhance neuromuscular blocking effects of curariform drugs (such as tubocurarine) - the most serious effect would be respiratory depression which could proceed to apnea. Accordingly, it may be advisable to discontinue metolazone three days before elective surgery.
Salicylates and Other Non-Steroidal Anti-Inflammatory Drugs
May decrease the antihypertensive effects of metolazone tablets.
Metolazone may decrease arterial responsiveness to norepinephrine, but this diminution is not sufficient to preclude effectiveness of the pressor agent for therapeutic use.
Insulin and Oral Antidiabetic Agents
See PRECAUTIONS: General: Glucose Tolerance.
Efficacy may be decreased due to urinary alkalizing effect of metolazone.
Metolazone, as well as other thiazide-like diuretics, may affect the hypoprothrombinemic response to anticoagulants; dosage adjustments may be necessary.