CLINICAL PHARMACOLOGY SECTION

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Perindopril Erbumine is a pro-drug for perindoprilat, which inhibits ACE in human subjects and animals. The mechanism through which perindoprilat lowers blood pressure is believed to be primarily inhibition of ACE activity. ACE is a peptidyl dipeptidase that catalyzes conversion of the inactive decapeptide, angiotensin I, to the vasoconstrictor, angiotensin II.

Angiotensin II is a potent peripheral vasoconstrictor, which stimulates aldosterone secretion by the adrenal cortex, and provides negative feedback on renin secretion. Inhibition of ACE results in decreased plasma angiotensin II, leading to decreased vasoconstriction, increased plasma renin activity and decreased aldosterone secretion. The latter results in diuresis and natriuresis and may be associated with a small increase of serum potassium.

ACE is identical to kininase II, an enzyme that degrades bradykinin. Whether increased levels of bradykinin, a potent vasodepressor peptide, play a role in the therapeutic effects of Perindopril Erbumine remains to be elucidated.

While the principal mechanism of perindopril in blood pressure reduction is believed to be through the renin-angiotensin-aldosterone system, ACE inhibitors have some effect even in apparent low-renin hypertension. Perindopril has been studied in relatively few black patients, usually a low- renin population, and the average response of diastolic blood pressure to perindopril was about half the response seen in nonblack patients, a finding consistent with previous experience of other ACE inhibitors.

​​12.2 Pharmacodynamics

After administration of perindopril, ACE is inhibited in a dose and blood concentration-related fashion, with the maximal inhibition of 80 to 90% attained by 8 mg persisting for 10 to 12 hours. Twenty-four hour ACE inhibition is about 60% after these doses. The degree of ACE inhibition achieved by a given dose appears to diminish over time (the ID50 increases). The pressor response to an angiotensin I infusion is reduced by perindopril, but this effect is not as persistent as the effect on ACE; there is about 35% inhibition at 24 hours after a 12 mg dose.

12.3 Pharmacokinetics

Absorption: Oral administration of Perindopril Erbumine results in peak plasma concentrations that occur at approximately 1 hour. The absolute oral bioavailability of perindopril is about 75%. Following absorption, approximately 30 to 50% of systemically available perindopril is hydrolyzed to its active metabolite, perindoprilat, which has a mean bioavailability of about 25%. Peak plasma concentrations of perindoprilat are attained 3 to 7 hours after perindopril administration. Oral administration of Perindopril Erbumine with food does not significantly lower the rate or extent of perindopril absorption relative to the fasted state. However, the extent of biotransformation of perindopril to the active metabolite, perindoprilat, is reduced approximately 43%, resulting in a reduction in the plasma ACE inhibition curve of approximately 20%, probably clinically insignificant. In clinical trials, perindopril was generally administered in a non-fasting state.

With 4 mg, 8 mg and 16 mg doses of Perindopril Erbumine, Cmax and AUC of perindopril and perindoprilat increase in a dose-proportional manner following both single oral dosing and at steady state during a once-a-day multiple dosing regimen.

Distribution: Approximately 60% of circulating perindopril is bound to plasma proteins, and only 10 to 20% of perindoprilat is bound. Therefore, drug interactions mediated through effects on protein binding are not anticipated.

Metabolism and Elimination: Following oral administration perindopril exhibits multicompartment pharmacokinetics including a deep tissue compartment (ACE binding sites). The mean half-life of perindopril associated with most of its elimination is approximately 0.8 to 1 hours.

Perindopril is extensively metabolized following oral administration, with only 4 to 12% of the dose recovered unchanged in the urine. Six metabolites resulting from hydrolysis, glucuronidation and cyclization via dehydration have been identified. These include the active ACE inhibitor, perindoprilat (hydrolyzed perindopril), perindopril and perindoprilat glucuronides, dehydrated perindopril and the diastereoisomers of dehydrated perindoprilat. In humans, hepatic esterase appears to be responsible for the hydrolysis of perindopril.

The active metabolite, perindoprilat, also exhibits multicompartment pharmacokinetics following the oral administration of Perindopril Erbumine. Formation of perindoprilat is gradual with peak plasma concentrations occurring between 3 and 7 hours. The subsequent decline in plasma concentration shows an apparent mean half-life of 3 to 10 hours for the majority of the elimination, with a prolonged terminal elimination half-life of 30 to 120 hours resulting from slow dissociation of perindoprilat from plasma/tissue ACE binding sites. During repeated oral once daily dosing with perindopril, perindoprilat accumulates about 1.5 to 2 fold and attains steady state plasma levels in 3 to 6 days. The clearance of perindoprilat and its metabolites is almost exclusively renal.

Elderly: Plasma concentrations of both perindopril and perindoprilat in elderly patients (greater than 70 years) are approximately twice those observed in younger patients, reflecting both increased conversion of perindopril to perindoprilat and decreased renal excretion of perindoprilat [see Dosage and Administration (2.1) and Use In Specific Populations (8.5)].

Heart Failure: Perindoprilat clearance is reduced in congestive heart failure patients, resulting in a 40% higher dose interval AUC.

Renal Impairment: With perindopril doses of 2 mg to 4 mg, perindoprilat AUC increases with decreasing renal function. At creatinine clearances of 30 to 80 mL/min, AUC is about double that at 100 mL/min. When creatinine clearance drops below 30 mL/min, AUC increases more markedly.

In a limited number of patients studied, perindopril clearance by dialysis ranged from about 40 to 80 mL/min. Perindoprilat clearance by dialysis ranged from about 40 to 90 mL/min [see Dosage and Administration (2.3)].

Hepatic Impairment: The bioavailability of perindoprilat is increased in patients with impaired hepatic function. Plasma concentrations of perindoprilat in patients with impaired liver function were about 50% higher than those observed in healthy subjects or hypertensive patients with normal liver function.

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BOXED WARNING SECTION

WARNING: FETAL TOXICITY

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