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Pharmacotherapeutic group: Calcium channel blockers, selective calcium channel blockers with mainly vascular effects, dihydropyridine derivatives. ATC code: C08CA02.
Pharmacology: Pharmacodynamics: Mechanism of Action: Felodipine is a vascular selective calcium antagonist, which lowers arterial blood pressure by decreasing systemic vascular resistance. Due to the high degree of selectivity for smooth muscle in the arterioles, felodipine in therapeutic doses has no direct effect on cardiac contractility or conduction. Because there is no effect on venous smooth muscle or adrenergic vasomotor control, felodipine is not associated with orthostatic hypotension.
Felodipine possesses a mild natriuretic/diuretic effect and fluid retention does not occur.
Pharmacodynamic effects: Felodipine is effective in all grades of hypertension. It can be used as monotherapy or in combination with other hypertensive medicinal products, e.g., β-adrenoceptor blockers, diuretics or ACE-inhibitors, in order to achieve an increased antihypertensive effect. Felodipine reduces both systolic and diastolic blood pressure and can be used in isolated systolic hypertension.
Felodipine has anti-anginal and anti-ischemic effects due to improved myocardial oxygen supply/demand balance. Coronary vascular resistance is decreased and coronary blood flow and myocardial oxygen supply are increased by felodipine due to dilatation of both epicardial arteries and arterioles. The reduction in systemic blood pressure caused by felodipine leads to decreased left ventricular afterload and myocardial oxygen demand.
Felodipine improves exercise tolerance and reduces anginal attacks in patients with stable effort-induced angina pectoris. Felodipine can be used as monotherapy or in combination with β-adrenoceptor blockers in patients with stable angina pectoris.
Haemodynamic effects: The primary haemodynamic effect of felodipine is a reduction of total peripheral vascular resistance, which leads to a decrease in blood pressure. These effects are dose-dependent. Generally, a reduction in blood pressure is evident two hours after the first oral dose and lasts for at least 24 hours and the trough/peak ration is usually well above 50%.
Plasma concentrations of felodipine are positively correlated to the decrease in total peripheral resistance and blood pressure.
Cardiac effects: Felodipine in therapeutic doses has no effect on cardiac contractility or atrioventricular conduction or refractoriness. Antihypertensive treatment with felodipine is associated with significant regression of pre-existing left ventricular hypertrophy.
Renal effects: Felodipine has a natriuretic and diuretic effect due to reduced tubular reabsorption of filtered sodium. Felodipine does not affect daily potassium excretion. The renal vascular resistance is decreased by felodipine. Felodipine does not influence urinary albumin excretion.
In cyclosporin-treated renal transplant recipients, felodipine reduces blood pressure and improves both the renal blood flow and the glomerular filtration rate. Felodipine may also improve early renal graft function.
Clinical efficacy: In the HOT (Hypertension Optimal Treatment) study, the effect on major cardiovascular events (i.e., acute myocardial infarction, stroke and cardiovascular death) was studied in relation to diastolic blood pressure targets <90 mmHg, <85 mmHg and <80 mmHg and achieved blood pressure, with felodipine as baseline therapy.
A total of 18,790 hypertensive patients (DBP 100-115 mmHg), aged 50-80 years were followed for a mean period of 3.8 years (range 3.3-4.9). Felodipine was given as monotherapy or in combination with a betablocker, and/or an ACE-inhibitor and/or a diuretic. The study showed benefits of lowering SBP and DBP down to 139 and 83 mmHg, respectively.
According to the STOP-2 (Swedish Trial in Old Patients with Hypertension-2 Study), performed in 6,614 patients, aged 70-84 years, dihydropyridine calcium antagonists (felodipine and isradipine) have shown the same preventive effect on cardiovascular mortality and morbidity as other commonly used classes of antihypertensive medicinal products-ACE inhibitors, beta-blockers and diuretics.
Paediatric population: There is limited clinical trial experience of the use of felodipine in hypertensive paediatric patients. In a randomized, double-blind, 3-week, parallel group study in children aged 6-16 years with primary hypertension, the antihypertensive effects of once daily felodipine 2.5 mg (n=33), 5 mg (n=33) and 10 mg (n=31) were compared with placebo (n=35). The study failed to demonstrate the efficacy of felodipine in lowering blood pressure in children aged 6-16 years (see Dosage & Administration).
The long-term effects of felodipine on growth, puberty and general development have not been studied. The long-term efficacy of antihypertensive therapy as therapy in childhood to reduce cardiovascular morbidity and mortality in adulthood has also not been established.
Pharmacokinetics: Absorption: Felodipine is administered as extended-release tablets, from which it is completely absorbed in the gastrointestinal tract. The systemic availability of felodipine is approximately 15% and is independent of dose in the therapeutic dose range. The extended-release tablets produce a prolonged absorption phase of felodipine. This results in even felodipine plasma concentrations within the therapeutic range for 24 hours. Maximum blood plasma levels (tmax) are achieved with the prolonged-release form after 3 to 5 hours. The rate but not the extent of absorption of felodipine is increased when taken simultaneously with food with a high fat content.
Distribution: The plasma protein binding of felodipine is approximately 99%. It is bound predominantly to the albumin fraction. Volume of distribution at steady state is 10 L/kg.
Biotransformation: Felodipine is extensively metabolized in the liver by cytochrome P450 3A4 (CYP3A4) and all identified metabolites are inactive. Felodipine is a high clearance medicinal product with an average blood clearance of 1,200 mL/min. There is no significant accumulation during long-term treatment.
Elderly patients and patients with reduced liver function have on average higher plasma concentrations of felodipine than younger patients. The pharmacokinetics of felodipine is not changed in patients with renal impairment, including those treated with haemodialysis.
Elimination: The half-life of 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. About 70% of a given dose is excreted as metabolites in the urine; the remaining fraction is excreted in the faeces. Less than 0.5% of a dose is recovered unchanged in urine.
Linearity/non-linearity: Plasma concentrations are directly proportional to dose within the therapeutic dose range 2.5-10 mg.
Paediatric population: In a single dose (felodipine prolonged-release 5 mg) pharmacokinetic study with a limited number of children aged between 6 and 16 years (n=12) there was no apparent relationship between the age and AUC, Cmax or half-life of felodipine.
Toxicology: Preclinical safety data: Reproduction toxicity: In a study on fertility and general reproductive performance in rats treated with felodipine, a prolongation of parturition resulting in difficult labour/increased foetal deaths and early post-natal deaths was observed in the medium and high dose groups. These effects were attributed to the inhibitory effect of felodipine in high doses on uterine contractility. No disturbances of fertility were observed when doses within the therapeutic range were given to rats.
Reproduction 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. The anomalies in the foetus were induced when felodipine was administered during early foetal development (before day 15 of pregnancy). In a reproduction study in monkeys, an abnormal position of the distal phalange(s) was noticed.
There were no other preclinical findings considered to be of concern and the reproductive findings are considered to be related to the pharmacological action of felodipine, when given to normotensive animals. The relevance of these findings for patients receiving felodipine is unknown. However, there have been no reported clinical incidences of phalangeal changes in foetus/neonate exposed to felodipine in-utero, from the information maintained within the internal patient safety databases.
