Felodipine is a medication of the calcium channel blocker type which is used to treat high blood pressure. It was patented in 1978 and approved for medical use in 1988. Medical uses Felodipine is used to treat high blood pressure and stable angina. It should not be used for people who are pregnant, have acute heart failure, are having a heart attack, have an obstructed heart valve, or have obstructions that block bloodflow out of the heart. For people with liver failure the dose needs to be lowered, because felodipine is cleared by the liver. Adverse effects The only very common side effect, occurring in more than 1/10 people, is pain and swelling in the arms and legs. Common side effects, occurring in between 1% and 10% of people, include flushing, headache, heart palpitations, dizziness and fatigue. Felodipine can exacerbate gingivitis. Interactions Felodipine is metabolized by cytochrome P450 3A4, so substances that inhibit or activate CYP3A4 can strongly effect how much felodipine is present. CYP3A4 inhibitors, which increase the amount of felodipine available per dose, include cimetidine, erythromycin, itraconazole, ketoconazole, HIV protease inhibitors, and grapefruit juice. CYP3A4 activators, which decrease the amount of felodipine available per dose, include phenytoin, carbamazepine, rifampicin, barbiturates, efavirenz, nevirapine, and Saint John's wort. Mechanism of action Felodipine is a calcium channel blocker. Felodipine has additionally been found to act as an antagonist of the mineralocorticoid receptor, or as an antimineralocorticoid. Different calcium channels are present in vascular tissue and cardiac tissue; an in vitro study on human vascular and cardiac tissues comparing how selective various calcium channel blockers are for vascular compared to cardiac tissue found the following vascular/cardiac tissue ratios: mibefradil 41, felodipine 12; nifedipine 7, amlodipine 5, and verapamil 0.2. Chemistry Felodipine is a member of the 1,4-dihydropyridine class of calcium channel blockers. It is a racemic mixture, and is insoluble in water but is soluble in dichloromethane and ethanol. History The Swedish company Hässle, a division of Astra AB, discovered felodipine; it filed a patent application in 1979 claiming felodipine as an antihypertensive drug. Astra partnered this drug and others with Merck & Co. in the US under a 1982 agreement between the companies. The drug was approved by the FDA in 1991 after a three and a half year review; the drug entered a very crowded market the included the other calcium channel blockers nifedipine, verapamil, nicardipine, and isradipine. The FDA