Felodipine is an agent in the dihydropyridine class of calcium channel blockers. Felodipine is FDA approved and indicated in the treatment of essential hypertension. Reduction in blood pressure lowers the risk of cardiovascular morbidity and mortality. The most significant benefit of the antihypertensive effect of felodipine is a decrease in the incidence of stroke. In patients presenting with mild to moderate hypertension, felodipine ER monotherapy is equivalent in efficacy to cardio-selective beta-blockers, thiazide diuretics, ACE inhibitors, and other calcium channel antagonists. In patients with severe hypertension uncontrolled by beta-blockers and diuretics, felodipine ER can be an add-on therapy.
Non-FDA approved uses of felodipine:
The first step in vascular smooth muscle contraction is the influx of calcium into the smooth muscle cell via voltage-dependent L-type calcium channels. The binding of cytosolic calcium to calmodulin follows this action resulting in the activation of myosin light-chain kinase (MLCK). The activated MLCK phosphorylates myosin light-chain resulting in the attachment of myosin head with actin, ultimately causing smooth-muscle contraction and vasoconstriction. The vascular smooth muscle contraction causes an increase in peripheral vascular resistance and an increase in blood pressure.
Felodipine, like the other dihydropyridine calcium-channel blockers, blocks the voltage-dependent L-type calcium channels and prevents the entry of calcium into the smooth muscle cell. Reduced cytosolic calcium results in a decrease in peripheral vascular resistance, vasodilation, and ultimately decrease in blood pressure. Felodipine selectively dilates arterioles and has no impact on venous vessels. In the in-vitro studies, research shows that felodipine has a higher selectivity than other commonly used dihydropyridine calcium channel blockers like amlodipine and nifedipine for vascular tissue in comparison to cardiac tissue. Also, the clinical trials of felodipine have not shown any negative inotropic effect.
Felodipine results in a dose-dependent decrease in systolic and diastolic blood pressure. Additionally, felodipine causes a reflex increase in heart rate (reflex tachycardia).
Felodipine is an orally administered drug. It is available in the strengths of 2.5 mg, 5 mg, and 10 mg. Felodipine dosing is often as an extended-release (ER) tablet formulation. The ER formulation offers several benefits, including once-daily dosing, minimal drug interactions, and lesser adverse effects. It is recommended to start the patient on a 5 mg dose of felodipine ER once daily. The recommended dosage range of felodipine is 2.5 to 10 mg once daily. The tablet should be swallowed whole and not crushed or chewed.
Felodipine is almost completely absorbed after oral administration. However, the bioavailability is only about 20% because of extensive first-pass metabolism of felodipine. The plasma concentration of felodipine increases when administered along with high fat or high carbohydrate diet. Felodipine is highly protein-bound and has a high volume of distribution.
The utility of felodipine in special population groups:
Pediatric population: Felodipine should not be used in pediatric patients since there has been no assessment of its safety and efficacy.
Pregnancy: Felodipine should is contraindicated in pregnant patients.
Elderly patients: In patients above 65 years of age, it is recommended to start them on a low dose of felodipine (2.5 mg). While changing the dose of the medication, their blood pressure should undergo strict monitoring.
Hepatic impairment: Patients with liver impairment have higher plasma concentration of felodipine since it undergoes hepatic metabolism. It is not recommended to use felodipine in patients with hepatic impairment.
Renal impairment: Felodipine is safe for use in patients with renal failure.
Cytochrome P450 3A4 metabolizes felodipine. The plasma level of felodipine increases when used in conjunction with CYP 3A4 inhibitors such as azole antifungals (itraconazole and ketoconazole), macrolide antibiotics (clarithromycin and azithromycin), HIV protease inhibitors, immunosuppressants (cyclosporine), cimetidine or grapefruit juice.
The plasma level and efficacy of felodipine decrease when it is co-administered with CYP3A4 inducers such as anticonvulsants (phenytoin and carbamazepine), saint john’s wort, or rifampicin.
When metoprolol is subsequently administered with conventional felodipine formulation in the treatment of essential hypertension, the plasma level concentration of metoprolol increases while that of felodipine remains unchanged. If felodipine is co-administered with theophylline, it results in a decrease in the plasma concentration of theophylline.
The adverse effects of felodipine classify as either dose-dependent or dose-independent:
The absolute contraindication of felodipine use includes hypersensitivity to felodipine or its ingredients.
The relative contraindications for the use of felodipine include:
It is essential for healthcare personnel and patients to monitor blood pressure and heart rate regularly. Routine laboratory monitoring is not necessary for patients who are taking felodipine. Patients should undergo regular assessment for adverse effects such as peripheral edema, flushing, headache or dizziness, and the provider should titrate the dose accordingly.
Mild to moderate overdose of felodipine can result in hypotension secondary to peripheral vasodilation and reflex tachycardia. However, a severe overdose of felodipine can cause life-threatening profound hypotension and bradycardia. The risk of overdose increases in elderly individuals, patients with liver impairment, and concomitant administration of felodipine with beta-blockers. Symptoms of overdose can include lightheadedness, syncope, altered mental status, and shock secondary to profound hypotension. The release of insulin from the pancreas depends on the influx of calcium through the L-type channels. Felodipine blocks these calcium channels and results in hyperglycemia because of decreased insulin release.
The first step in the management of felodipine overdose is to maintain a patent airway. In patients who have consumed an excess of felodipine ER tablets but have not yet developed any symptoms, they should be started on gastrointestinal decontamination with whole bowel irrigation if they present within 6 to 8 hours of drug ingestion. Patients with hypotension should undergo resuscitation with intravenous fluids. However, caution is necessary for individuals with congestive heart failure and pulmonary edema. Vasopressor therapy with dopamine or norepinephrine is an as-need option for hypotension. Intravenous calcium gluconate or calcium chloride (given via central line) are also options in the treatment of felodipine overdose. In patients with severe overdose, atropine should be administered intravenously for bradycardia. The vital signs, serum electrolytes, especially potassium, blood glucose, urine output, and ECG, should be monitored regularly. Hyperinsulinemia-euglycemia (HIE) therapy is also an established modality of treatment for calcium channel blocker overdose. This therapy helps to mobilize glucose from the peripheral tissue to serve as an alternative source of energy for the myocardium.
Felodipine ER with once-daily administration is convenient to use anti-hypertensive medication. Healthcare personnel should be aware of the indications and adverse effects of felodipine. The physicians need to obtain an appropriate medication history to look for drug interactions since felodipine is metabolized by CYP 3A4. The healthcare personnel, including pharmacists, should educate the patients regarding medication adherence and regular monitoring of blood pressure. If patients develop symptomatic hypotension, the medication should be discontinued immediately, and the patient should present to the emergency department.
Clinicians (MDs, DOs, NPs, PAs) will make the decision to dose felodipine when appropriate. The pharmacist should verify all dosing is suitable for the clinical scenario, and report back any discrepancies. The pharmacy should also perform medication reconciliation since as discussed, felodipine can have significant drug-drug interactions. Nursing will be in charge of administration for inpatients, and will see the patient on subsequent outpatient visits, and can monitor for adverse reactions as well as medication compliance and therapy effectiveness, reporting back to the healthcare team any adverse findings.
Felodipine therapy requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, and pharmacists, all collaborating across disciplines to achieve optimal patient results. [Level V]
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