When metolazone is used with other antihypertensive drugs, take particular care, especially during initial therapy. Dosage of other antihypertensive agents, especially the ganglionic blockers and guanethidine, should be reduced. Hydralazine in therapeutic doses may interfere with the natriuretic action of metolazone. Metolazone may be given with a potassium-sparing diuretic when indicated. In this circumstance, diuresis may be enhanced and dosages should be reduced.
Potassium supplementation is contraindicated when a potassium-sparing diuretic is given.
While not reported for metolazone, use of diuretics have on rare occasion been associated with pathologic changes in the parathyroid gland and with hypercalcemia and hypophosphatemia. Sulfonamide derivatives have been reported to exacerbate or activate systemic lupus erythematosus. These possibilities should be kept in mind with the use of metolazone. Administer metolazone cautiously to patients with severely impaired renal function, since the drug is excreted primarily by the renal route. Observe caution when administering metolazone to hyperuricemic or gouty patients.