Both the calcium antagonist felodipine and the ACE inhibitor ramipril reduce blood pressure by dilation of the peripheral blood vessels. Calcium antagonists dilate the arterial beds while ACE inhibitors dilate both arterial and venous beds. Vasodilatation and thereby reduction of blood pressure may lead to activation of the sympathetic nervous system and the renin-angiotensin system. Inhibition of ACE results in decreased plasma angiotensin II.
The onset of the antihypertensive effect of a single dose of felodipine/ramipril is 1 to 2 hours. The maximum antihypertensive effect is achieved within 2 to 4 weeks and is maintained during long-term therapy. The blood pressure reduction is maintained throughout the 24‑hour dosage interval. Morbidity and mortality data are not available.
Felodipine is a vascular selective calcium antagonist, which lowers arterial blood pressure by decreasing peripheral vascular resistance via a direct relaxant action on vascular smooth muscles. Due to its selectivity for smooth muscle in the arterioles, felodipine, in therapeutic doses, has no direct effect on cardiac contractility or conduction. The renal vascular resistance is decreased by felodipine. The normal glomerular filtration rate is not influenced. In patients with impaired renal function, the glomerular filtration rate may increase. Felodipine possesses a mild natriuretic/diuretic effect and fluid retention does not occur.
Ramipril is a prodrug which hydrolyses to the active metabolite ramiprilat, a potent and long-acting ACE (angiotensin converting enzyme) inhibitor. In plasma and tissue, ACE catalyses the conversion of angiotensin I to the vasoconstrictor angiotensin II and also the breakdown of the vasodilator bradykinin. The vasodilatation induced by the ACE inhibitor reduces blood pressure pre-load and after-load. Since angiotensin II also stimulates the release of aldosterone, ramiprilat reduces secretion of aldosterone. Ramipril reduced peripheral arterial resistance without major changes in renal plasma flow or glomerular filtration rate. In hypertensive patients, ramipril leads to a reduction in supine and standing blood pressure without a compensatory rise in heart rate.
The bioavailability is approximately 15% and is not influenced by concomitant intake of food. The peak plasma concentration is reached after 3 to 5 hours. Binding to plasma proteins is more than 99%. The distribution volume at steady state is 10 l/kg. The half-life for felodipine in the elimination phase is approximately 25 hours and steady state is reached after 5 days. There is no risk of accumulation during long-term treatment. Mean clearance is 1200 ml/min. Decreased clearance in older people leads to higher plasma concentrations of felodipine. Age only partly explains the interindividual variation in plasma concentration, however. Felodipine is metabolised in the liver and all identified metabolites are devoid of vasodilating properties. Approximately 70% of a given dose is excreted as metabolites in the urine and about 10% with the faeces. Less than 0.5% of the dose is excreted unchanged in the urine. Impaired renal function does not influence the plasma concentration of felodipine.
The pharmacokinetic parameters of ramiprilat are calculated after intravenous administration of ramipril. Ramipril is metabolised in the liver, and aside from the active metabolite ramiprilat, pharmacologically inactive metabolites have been identified. The formation of active ramiprilat may be decreased in patients with impaired liver function. The metabolites are excreted mainly via the kidneys. The bioavailability of ramiprilat is approximately 28% after oral administration of ramipril. After intravenous administration of 2.5 mg ramipril, approximately 53% of the dose is converted to ramiprilat. A maximum serum concentration of ramiprilat is achieved after 2 to 4 hours. Absorption and bioavailability are not influenced by concomitant intake of food. The protein binding of ramiprilat is approximately 55%. The distribution volume is approximately 500 litres. The effective half-life, after repeated daily dosage of 5 to 10 mg, is 13 to 17 hours. Steady-state is achieved after approximately 4 days. Renal clearance is 70 to 100 ml/min and total clearance is approximately 380 ml/min. Impaired renal function delays the elimination of ramiprilat and excretion in the urine is reduced.
In felodipine/ramipril fixed dose combination the pharmacokinetics of ramipril, ramiprilat and felodipine are essentially unaltered compared to the mono products, felodipine ER tablets and ramipril tablets. Felodipine does not influence the ACE inhibition caused by ramiprilat. The fixed combination tablets are thus regarded as bioequivalent to the free combination.
Repeated-dose toxicity studies performed with the combination in rats and monkeys did not demonstrate any synergistic effects.
Non-clinical data for felodipine and ramipril reveal no special hazard for humans based on conventional studies of genotoxicity and carcinogenic potential.
In investigations on fertility and general reproductive performance in rats, a prolongation of parturition resulting in difficult labour/increased foetal deaths and early postnatal deaths was observed. Reproduction toxicity studies in rabbits have shown a dose-related reversible enlargement of the mammary glands of the parent animals and dose-related digital anomalies in the foetuses.
Studies in rats, rabbits and monkeys did not disclose any teratogenic properties. Daily doses during pregnancy and lactation in rats produced irreversible renal pelvis dilatation in the offspring.
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