Tetracycline and Other Drugs that Interact with Magnesium: Administration of tetracycline with quinapril reduced the absorption of tetracycline by approximately 28% to 37% in subjects. Decreased absorption is due to the presence of magnesium carbonate as an excipient in the quinapril formulation. This interaction should be considered if co-prescribing quinapril and tetracycline.
Lithium: Increased serum lithium levels and symptoms of lithium toxicity have been reported in patients receiving concomitant lithium and ACE inhibitor therapy due to the sodium-losing effect of these agents. Quinapril and lithium should be co-administered with caution, and frequent monitoring of serum lithium levels is recommended. If a diuretic is also used, it may increase the risk of lithium toxicity.
Non-Steroidal Anti-inflammatory Agents Including Selective Cyclooxygenase-2 Inhibitors: In patients who are elderly, volume-depleted (including those on diuretic therapy), or with compromised renal function, co-administration of non-steroidal anti-inflammatory drugs (NSAIDs), including selective cyclooxygenase-2 (COX-2) inhibitors, with ACE inhibitors, including quinapril, may result in deterioration of renal function, including possible acute renal failure. These effects are usually reversible. Monitor renal function periodically in patients receiving quinapril and NSAID therapy.
The antihypertensive effect of ACE inhibitors, including quinapril, may be attenuated by NSAIDs.
Agents that Inhibit Mammalian Target of Rapamycin (mTOR) or Dipeptidyl Peptidase-4 (DPP-IV): Patients taking a concomitant mTOR inhibitor (e.g. temsirolimus) or a concomitant DPP-IV inhibitor (e.g. vildagliptin) therapy may be at increased risk for angioedema. Caution should be used when starting an mTOR inhibitor or a DPP-IV inhibitor in a patient already taking an ACE inhibitor.
Other Agents: No clinically important pharmacokinetic interactions occurred when quinapril was used concomitantly with propranolol, hydrochlorothiazide, digoxin or cimetidine.
The anticoagulant effect of a single dose of warfarin (measured by prothrombin time) was not significantly changed by quinapril co-administration twice daily.
Co-administration of multiple 10 mg doses of atorvastatin with 80 mg quinapril resulted in no significant change in the steady-state pharmacokinetic parameters of atorvastatin.
Concomitant Diuretic Therapy: Patients on diuretics, especially those on recently instituted diuretic therapy, may occasionally experience an excessive reduction of blood pressure after initiation of therapy with quinapril. Hypotensive effects after the first dose of quinapril may be minimized by discontinuing the diuretic a few days prior to initiation of therapy. If it is not possible to discontinue the diuretic, the starting dose of quinapril should be reduced. In patients in whom a diuretic is continued, medical supervision should be provided for up to 2 hours after the initial dosage of quinapril (see Dosage & Administration and Precautions).
Agents Increasing Serum Potassium: Quinapril is an ACE inhibitor capable of lowering aldosterone levels, which in turn can result in potassium retention. Therefore, concomitant therapy of quinapril with potassium-sparing diuretics (e.g. spironolactone, triamterene, or amiloride), potassium supplements, potassium-containing salt substitutes or other drugs known to raise serum potassium levels should be used with caution and with appropriate monitoring of serum potassium (see Precautions). In patients who are elderly or have compromised renal function, co-administration of an ACE inhibitor with sulfamethoxazole/trimethoprim has been associated with severe hyperkalemia, which is thought to be due to trimethoprim. Quinapril and trimethoprim-containing products should therefore, be co-administered with caution, and with appropriate monitoring of serum potassium.
Dual Blockage of the Renin-Angiotensin System: Dual blockage of the RAS with angiotensin receptors blockers, ACE inhibitors, or aliskiren is associated with increased risks of hypotension, hyperkalemia, and changes in renal function (including acute renal failure) compared to monotherapy. Closely monitor blood pressure, renal function and electrolytes in patients on quinapril and other agents that affect the RAS.
Do not administer quinapril in combination with aliskiren in patients with diabetes, in patients with moderate to severe kidney insufficiency (GFR <60 mL/min/1.73 m2), in patients with hyperkalemia (>5 mmol/L) or in congestive heart failure patients who are hypotensive (see Contraindications).
Do not administer quinapril in combination with angiotensin receptor blockers or other ACE inhibitors in diabetic patients with end organ damage, in patients with moderate to severe kidney insufficiency (GFR <60 mL/min/1.73 m2), in patients with hyperkalemia (>5 mmol/L), or in congestive heart failure patients who are hypotensive (see Contraindications).