Felodipine

 BRAND NAMES 

• Plendil: A widely known brand name for extended-release felodipine. 

• Lexxel: A combination medicine that contains both felodipine and enalapril. 

• Renedil: A brand name used in select countries/regions. 

• Generic felodipine: Often marketed simply as “Felodipine,” usually labeled with ER or XR to indicate extended-release form. 

MECHANISM OF ACTION

 Felodipine is a long-acting 1,4-dihydropyridine calcium channel blocker (CCB) that reduces blood pressure by preventing calcium ions from entering vascular smooth muscle cells. It works by selectively binding to voltage-gated L-type calcium channels and keeping them in an inactive state, which leads to relaxation of arterial smooth muscle, widening of blood vessels (vasodilation), and a decrease in peripheral resistance.

 PHARMACOKINETICS

 Absorption:

 Completely absorbed, though low bioavailability (15–20%) is due to extensive CYP3A4-mediated first-pass metabolism. 

Distribution:

 Large volume of distribution (approx. 10 L/kg), indicating extensive tissue distribution. 

Metabolism:

 Primarily in the liver via CYP3A4 into six inactive metabolites. 

Elimination: 

Primarily through urine (70%) as metabolites, with 10% in feces. PHARMACODYNAMICS

 Felodipine is a dihydropyridine calcium channel blocker (CCB) that lowers blood pressure by selectively inhibiting calcium ion influx through voltage-gated L-type channels in vascular smooth muscle. This action causes vasodilation, reduces peripheral vascular resistance, and leads to dose-dependent reductions in blood pressure, with a minor, temporary reflex increase in heart rate. 

ADMINISTRATION

 Felodipine is an extended-release tablet taken by mouth once a day, typically in the morning. The usual starting dose is 5 mg daily, and the maintenance dose generally ranges from 2.5 mg to 10 mg, adjusted at intervals of about two weeks if needed. The tablet should be swallowed whole do not crush, split, or chew it. It may be taken either on an empty stomach or with a light meal that is low in fat and carbohydrates. 

DOSAGE AND STRENGTH

  Available strengths: Extended-release tablets are typically available in 2.5 mg, 5 mg, and 10 mg. • Usual dosage: o Starting dose: 5 mg once daily o Maintenance dose: 2.5 mg to 10 mg once daily o Dose adjustments are usually made at 2-week intervals based on response. o Administration: Taken once daily (preferably in the morning) and swallowed whole. 

DRUG INTERACTIONS 

Felodipine interacts significantly with substances that affect the CYP3A4 enzyme. CYP3A4 inhibitors, such as grapefruit juice, ketoconazole, and erythromycin, can raise felodipine blood levels, potentially leading to low blood pressure (hypotension) and reflex tachycardia. Conversely, CYP3A4 inducers like St. John’s wort and phenytoin may lower its effectiveness. Taking felodipine together with other antihypertensive medications can result in excessively low blood pressure. 

FOOD INTERACTIONS 

The most important food interaction with Felodipine is with grapefruit and grapefruit juice, which should be avoided because they can markedly raise drug levels, leading to side effects such as dizziness and low blood pressure. Other potential interactions include pomegranate juice, high-fat meals, and alcohol. Felodipine is best taken on an empty stomach or with a light, low-fat meal. 

CONTRAINDICATIONS

 Felodipine is contraindicated in individuals with a known allergy to felodipine or other dihydropyridines, during pregnancy and breastfeeding, and in women of childbearing potential. It should also be avoided in patients experiencing acute myocardial infarction, decompensated heart failure, unstable angina, or significant obstruction of heart valves. 

SIDE EFFECTS

 • Peripheral edema (swelling of ankles or legs)

 • Headache 

• Flushing 

• Dizziness 

• Palpitations 

• Fainting 

• Chest pain 

• Severe allergic reactions 

OVER DOSE 

Excess intake of felodipine can be dangerous and requires urgent medical attention. It may lead to very low blood pressure, severe dizziness, fainting, a fast pulse, and in extreme cases, failure of the heart and circulation. If an overdose is suspected, seek immediate emergency care or contact a poison control center without delay. 

TOXICITY 

Felodipine toxicity, typically resulting from an overdose, can cause dangerously low blood pressure (severe hypotension), reflex tachycardia, and sometimes slow heart rate (bradycardia). As a calcium channel blocker, felodipine has a narrow safety margin in overdose, and excessive amounts can lead to life-threatening circulatory collapse. While common side effects like peripheral edema and headache are usually dose-related, an overdose demands immediate medical attention.