Quinapril

Introduction Overview

Generic Name

quinapril

Brand Name

Accupril

Dosage Form

oral tablet (5 mg, 10 mg, 20 mg, 40 mg)

Drug Class

Angiotensin Converting Enzyme Inhibitors (ACE inhibitors)

Pharmacokinetics

Absorption:
Quinapril is an orally administered prodrug that is rapidly absorbed from the gastrointestinal tract. After oral administration, it undergoes extensive first-pass hepatic metabolism to its active metabolite, quinaprilat. Peak plasma concentrations of quinapril occur approximately 1 hour post-dose, with peak plasma concentrations of quinaprilat observed within 2 to 4 hours. The presence of food can reduce the rate but not the extent of quinapril absorption, which generally does not significantly affect clinical efficacy.

Distribution:
Quinapril and quinaprilat demonstrate moderate plasma protein binding. The volume of distribution varies, but quinaprilat, the active moiety, distributes extensively into tissues, including the cardiovascular system and kidneys, which are primary sites of action. Tissue binding contributes to the duration of action beyond plasma half-life. Quinapril crosses the placenta and is excreted in small amounts into breast milk; however, clinical data on tissue distribution are limited.

Metabolism:
Quinapril is extensively hydrolyzed by hepatic esterases to quinaprilat, the pharmacologically active diacid form. This biotransformation is a rapid process and essential for its antihypertensive activity. Quinapril itself possesses minimal ACE inhibitory activity, with most effects attributed to quinaprilat. Minimal metabolism occurs beyond this step, and no active metabolites beyond quinaprilat have been identified.

Elimination:
Quinaprilat is primarily eliminated via renal excretion. Approximately 60% to 70% of the dose is excreted in urine as quinaprilat and its conjugates, with the remaining via feces. The elimination half-life of quinaprilat is approximately 2 hours; however, the antihypertensive effect persists for 24 hours due to tissue binding and slow dissociation from ACE. Renal impairment can significantly reduce clearance, necessitating dose adjustments. Hemodialysis does not effectively remove quinaprilat.

Dosage Forms

Available Dosage Forms:
Quinapril is commercially available as oral tablets in the following strengths: 5 mg, 10 mg, 20 mg, and 40 mg.

Dosages for Adults and Adolescents:
- For hypertension: Initial dosage typically starts at 10 or 20 mg once daily in patients not using diuretics. Maintenance doses range from 20 mg up to 80 mg daily, administered as a single dose or divided into two doses.
- For congestive heart failure: Initial dose is 5 mg twice daily with maintenance doses of 20 to 40 mg daily divided into two doses. Dose titration is generally weekly.

Specific Patient Populations:
- Geriatric patients often begin with a 10 mg once daily dose for both hypertension and heart failure, with titration similar to younger adults.
- Patients with renal impairment require dose adjustment consistent with degree of renal function decline.
- No specific formulations for pediatric use are currently available; use in pediatric populations is off-label and should be carefully considered.

Clinical guidelines emphasize individual titration based on therapeutic response and tolerability, with careful monitoring of kidney function and electrolytes during dose adjustments.

Mechanism Of Action

Quinapril is an angiotensin-converting enzyme (ACE) inhibitor that exerts its primary effect by competitively inhibiting ACE, the enzyme responsible for converting angiotensin I to the potent vasoconstrictor angiotensin II. By blocking ACE, quinapril decreases the production of angiotensin II, which leads to vasodilation, decreased aldosterone secretion, and reduced sodium and water retention. This cascade results in lowered systemic vascular resistance and blood pressure.

At the cellular level, inhibition of ACE also reduces the breakdown of bradykinin, a vasodilatory peptide, thus enhancing vasodilation through increased levels of nitric oxide and prostacyclin. The net effect is improved endothelial function and decreased blood vessel constriction, contributing to antihypertensive and cardioprotective effects.

Clinically, this mechanism helps reduce cardiac preload and afterload, beneficial in the management of hypertension and heart failure. Quinapril's effects help prevent remodeling of the heart and vasculature, thus slowing progression of hypertensive and heart failure-related organ damage.

Compared to other ACE inhibitors, quinapril has favorable pharmacokinetic profiles, with rapid conversion to quinaprilat and sustained tissue binding affording once or twice daily dosing. Clinical trials have demonstrated its efficacy in blood pressure control, morbidity reduction in heart failure, and protective effects in patients with left ventricular dysfunction. Ongoing research evaluates its potential benefits in chronic kidney disease and post-myocardial infarction management.

Pharmacological Actions

Inhibition of angiotensin-converting enzyme, reducing angiotensin II levels
Vasodilation resulting from decreased angiotensin II-mediated vasoconstriction
Increased bradykinin levels leading to enhanced nitric oxide and prostacyclin-mediated vasodilation
Reduction in aldosterone secretion, decreasing sodium and water retention
Lowering peripheral vascular resistance and blood pressure
Reduction of cardiac preload and afterload, improving cardiac output in heart failure
Prevention of pathological cardiac and vascular remodeling in hypertension and heart failure
Renal protective effects via reduction in intraglomerular pressure and proteinuria
Improvement in endothelial function and arterial compliance
Modulation of sympathetic nervous system activity through reduced angiotensin II signaling

Therapeutic Or Clinical Uses

Treatment of hypertension (high blood pressure) as monotherapy or in combination
Management of congestive heart failure as adjunct therapy with diuretics and/or digitalis
Reduction of risk of stroke and myocardial infarction related to hypertension
Improvement of symptoms and exercise tolerance in heart failure
Off-label uses may include prevention of diabetic nephropathy progression
Protection against left ventricular dysfunction following myocardial infarction
Potential use in chronic kidney diseases with proteinuria
Adjunct therapy to reduce cardiovascular morbidity and mortality in at-risk populations

Side Or Adverse Effects

Cough, typically persistent and dry, common with ACE inhibitors
Headache
Dizziness and lightheadedness due to hypotension, especially after initial dosing
Nausea, vomiting, and abdominal pain
Fatigue or tiredness
Hyperkalemia (elevated blood potassium levels), which may cause muscle weakness and cardiac arrhythmias
Angioedema characterized by swelling of the face, lips, tongue, or throat, potentially life-threatening
Renal impairment or worsening renal function, particularly in patients with renal artery stenosis
Hypotension, especially in volume-depleted patients
Elevated liver enzymes and rare cases of liver dysfunction or cholestatic jaundice
Rare blood dyscrasias including neutropenia, agranulocytosis, or thrombocytopenia
Skin rash and pruritus
Alterations in taste
Increased serum creatinine and blood urea nitrogen in susceptible individuals

Precautions

Use with caution in patients with a history of angioedema related to previous ACE inhibitor therapy
Monitor renal function and potassium levels regularly during therapy, especially in those with renal impairment
Avoid use or careful monitoring in patients with bilateral renal artery stenosis or severe renal impairment
Cautious use in volume- or salt-depleted patients to prevent symptomatic hypotension
Inform patients about the risk of persistent cough and need to report angioedema symptoms immediately
Avoid concomitant use with aliskiren in patients with diabetes or renal impairment
Pregnancy avoidance during the second and third trimesters due to potential fetal toxicity
Reduce dose in elderly patients or those with renal dysfunction
Educate patients to avoid potassium supplements or potassium-containing salt substitutes unless directed
Exercise caution when co-administered with NSAIDs due to potential for renal impairment
Monitor blood pressure frequently during dose titration to avoid hypotension
Patients should avoid sudden position changes to minimize dizziness and orthostatic hypotension
Permanent discontinuation recommended in patients developing severe hyperkalemia or angioedema
Use cautiously in patients with liver dysfunction as metabolism may be affected

Warnings

Do not use quinapril during pregnancy due to risk of fetal injury or death; discontinue immediately if pregnancy is detected
History of angioedema contraindicates quinapril use due to potential for life-threatening swelling
Concomitant use with sacubitril-containing products (e.g., Entresto) is contraindicated within 36 hours
Risk of hyperkalemia, especially in patients with renal impairment, diabetes, or those using potassium-sparing diuretics
Potential for acute renal failure in predisposed patients; monitor renal function especially after initiation or dose changes
Risk of symptomatic hypotension particularly in volume-depleted or heart failure patients on concomitant diuretics
Serious allergic reactions including anaphylaxis may occur though rare
May cause neutropenia or agranulocytosis; patients with autoimmune disorders require monitoring
Avoid use with aliskiren in patients with diabetes or kidney disease due to increased risk of adverse events
Patients should be warned about signs of infection or bleeding and seek prompt medical attention if noted

Contraindication

Known hypersensitivity to quinapril or any other ACE inhibitors
History of angioedema related to previous ACE inhibitor therapy
Concurrent use or within 36 hours of sacubitril-containing medications (e.g., Entresto)
Pregnancy, especially during the second and third trimesters
Use with aliskiren in patients with diabetes or renal impairment
Bilateral renal artery stenosis
Patients with hypersensitivity to any component of the formulation
Severe hypotension or hemodynamic instability
Patients with hereditary or idiopathic angioedema

Drug Interactions

Potassium-sparing diuretics, potassium supplements, or salt substitutes can increase risk of hyperkalemia
NSAIDs (e.g., ibuprofen, naproxen) may reduce antihypertensive efficacy and increase risk of renal impairment
Diuretics may potentiate hypotensive effects; consider dose adjustment
Lithium clearance may be decreased leading to potential lithium toxicity
Gold injections used for arthritis may increase risk of nitritoid reactions when combined with ACE inhibitors
Immunosuppressants such as temsirolimus, sirolimus, or everolimus may increase risk of adverse renal effects
Other antihypertensives may have additive hypotensive effects
Concomitant use with sacubitril-containing drugs is contraindicated
Aliskiren coadministration in diabetic or renal impaired patients increases risk of adverse effects and is contraindicated
Avoid combination with other medications known to raise potassium levels, such as trimethoprim
Nonsteroidal anti-inflammatory drugs may also blunt renal function and elevate serum creatinine when used with quinapril
Careful monitoring required if combining with medications affecting the renin-angiotensin-aldosterone system

Preparations Of The Drug

Oral tablets available in 5 mg, 10 mg, 20 mg, and 40 mg strengths
Formulated for once or twice daily dosing depending on indication and patient response
Packaged to maintain stability at room temperature, protected from moisture and heat
No injectable or alternative formulations widely available for clinical use
Available as branded product Accupril as well as generic formulations
Tablets should be swallowed whole, may be taken with or without food
Dosing flexibility allows for titration in increments suitable for individualized therapy
Supplied in blister packs or bottles depending on manufacturer and market
No extended-release formulations currently available