Quinapril

Quinapril is rapidly de-esterified to quinaprilat (quinapril diacid, the principal metabolite) which is a potent ACE inhibitor.

ACE is a peptidyl dipeptidase that catalyses the conversion of angiotensin I to the vasoconstrictor angiotensin II which is involved in vascular control and function through many different mechanisms, including stimulation of aldosterone secretion by the adrenal cortex. The mode of action of quinapril in humans and animals is to inhibit circulating and tissue ACE activity, thereby decreasing vasopressor activity and aldosterone secretion.

In animal studies, the antihypertensive effect of quinapril outlasts its inhibitory effect on circulating ACE, whereas, tissue ACE inhibition more closely correlates with the duration of antihypertensive effects. Administration of 10 mg to 40 mg of quinapril to patients with mild to severe hypertension results in a reduction of both sitting and standing blood pressure with minimal effect on heart rate. Antihypertensive activity commences within 1 hour with peak effects usually achieved by 2 to 4 hours after dosing. Achievement of maximum blood pressure lowering effects may require 2 weeks of therapy in some patients. At the recommended doses, antihypertensive effects are maintained in most patients throughout the 24 hour dosing interval and continued during long term therapy.

In a randomised clinical trial using target doses of 2.5 mg, 5 mg, 10 mg and 20 mg of quinapril, in 112 children and adolescents with hypertension or high normal blood pressure over 8 weeks (2 weeks double blind and 6 weeks extension) failed to reach its primary objective of reduction of diastolic blood pressure after 2 weeks. For systolic blood pressure (secondary objective of efficacy) at Week 2 only there was a statistically significant linear dose response across treatments with a significant difference between the quinapril 20 mg QD and placebo treatment groups.

Long term effects of quinapril on growth, puberty and general development have not been studied.

Peak plasma quinapril concentrations are observed within 1 hour of oral administration. The extent of absorption is approximately 60%, and is not influenced by food. Following absorption, Quinapril is de-esterified to its major active metabolite, quinaprilat, and to minor inactive metabolites. Quinapril has an apparent half-life of approximately 1 hour. Peak plasma quinaprilat concentrations are observed approximately 2 hours following an oral dose of quinapril. Quinaprilat is eliminated primarily by renal excretion and has an effective accumulation half-life of 3 hours. In patients with renal insufficiency and creatinine clearance of ≤40 mL/min, peak and trough quinaprilat concentrations increase, time to peak concentration increases, apparent half-life increases, and time to steady state may be delayed. The elimination of quinaprilat is also reduced in elderly patients (>65 years) and correlates well with the impaired renal function which frequently occurs in the elderly. Quinaprilat concentrations are reduced in patients with alcoholic cirrhosis due to impaired de-esterification of quinapril. Studies in rats indicate that quinapril and its metabolites do not cross the blood-brain barrier.

Lactation

After a single oral dose of 20 mg of quinapril in six breast-feeding women, the M/P (milk to plasma ratio) for quinapril was 0.12. Quinapril was not detected in milk after 4 hours after the dose. Quinalaprilat milk levels were undetectable (<5 µg/L) at all time points. It is estimated that a breastfed infant would receive about 1.6% of the maternal weight-adjusted dosage of quinapril.

The pharmacokinetics of quinapril has been studied in a single dose study (0.2 mg/kg) in 24 children aged 2.5 months to 6.8 years and a multiple dose study (0.016-0.468 mg/kg) in 38 children aged 5-16 years old, weighing 66-98 kg on average.

As in adults, quinapril was rapidly converted to quinaprilat. Quinaprilat concentrations generally peaked 1 to 2 hours post dose and declined with a mean half-life of 2.3 hours. In infants and young children the exposure following a single 0.2 mg/kg dose is comparable to that observed in adults after a single 10 mg dose. In a multiple dose study in school age and adolescents, the AUC and C_max values of quinaprilat were observed to increase linearly with increasing dose of quinapril on a mg/kg basis.

The results of the preclinical tests do not add anything of further significance.