Action And Clinical Pharmacology
Mechanism of Action
Eplerenone binds to the mineralocorticoid receptor and blocks the binding of aldosterone, a component of the renin-angiotensin-aldosterone-system (RAAS). Aldosterone synthesis, which occurs primarily in the adrenal gland, is modulated by multiple factors, including angiotensin II and non-RAAS mediators, such as adrenocorticotropic hormone (ACTH) and potassium. Aldosterone binds to mineralocorticoid receptors in both epithelial (e.g., kidney) and nonepithelial (e.g., heart, blood vessels, and brain) tissues, and increases blood pressure through induction of sodium reabsorption and possibly other mechanisms through both genomic and non-genomic effects.
Eplerenone has been shown to produce sustained increases in plasma renin and serum aldosterone, consistent with inhibition of the negative regulatory feedback of aldosterone on renin secretion. The resulting increased plasma renin activity and aldosterone circulating levels do not overcome the effects of eplerenone.
Eplerenone selectively binds to recombinant human mineralocorticoid receptors relative to its binding to recombinant human glucocorticoid, progesterone and androgen receptors.
In dose-ranging studies of chronic heart failure (NYHA classification II-IV), the addition of eplerenone to standard therapy resulted in expected dose-dependent increases in aldosterone. Similarly, in a cardiorenal substudy of EPHESUS, therapy with eplerenone led to a significant increase in aldosterone. These results are consistent with blockade of the mineralocorticoid receptor in these populations.
No consistent effects of eplerenone on heart rate, QRS duration, or PR or QT interval were observed in 147 normal subjects evaluated for electrocardiographic changes during pharmacokinetic studies.
General: Eplerenone is cleared predominantly by cytochrome P450 (CYP) 3A4 metabolism, with an elimination half-life of 4 to 6 hours. Steady state is reached within 2 days. Absorption is not affected by food. Inhibitors of CYP3A4 increase blood levels of eplerenone.
Absorption and Distribution: Mean peak plasma concentrations of eplerenone are reached approximately 1.5 to 2 hours following oral administration. The absolute bioavailability of eplerenone is 69% following administration of a 100 mg oral tablet. Both peak plasma levels (Cmax) and area under the curve (AUC) are dose proportional for doses of 25 to 100 mg and less than proportional at doses above 100 mg.
The plasma protein binding of eplerenone is about 50% and it is primarily bound to alpha 1-acid glycoproteins. The apparent volume of distribution at steady state ranged from 42 to 90 L. Eplerenone does not preferentially bind to red blood cells.
Metabolism and Excretion: Eplerenone metabolism is primarily mediated via CYP3A4. No active metabolites of eplerenone have been identified in human plasma.
Less than 5% of an eplerenone dose is recovered as unchanged drug in the urine and feces. Following a single oral dose of radiolabeled drug, approximately 32% of the dose was excreted in the feces and approximately 67% was excreted in the urine. The elimination half-life of eplerenone is approximately 3 to 6 hours. The apparent plasma clearance is approximately 10 L/hr.
Special Populations and Conditions
Age, Gender, and Race:The pharmacokinetics of eplerenone at a dose of 100 mg once daily has been investigated in the elderly (≥ 65 years), in males and females, and in blacks. The pharmacokinetics of eplerenone did not differ significantly between males and females. At steady state, elderly subjects had increases in Cmax (22%) and AUC (45%) compared with younger subjects (18 to 45 years). At steady state, Cmax was 19% lower and AUC was 26% lower in blacks (see WARNINGS AND PRECAUTIONS, Geriatric Use and DOSAGE AND ADMINISTRATION).
Renal Insufficiency: The pharmacokinetics of eplerenone was evaluated in patients with varying degrees of renal insufficiency and in patients undergoing hemodialysis. Compared with control subjects, steady-state AUC and Cmax were increased by 38% and 24%, respectively, in patients with severe renal impairment and were decreased by 26% and 3%, respectively, in patients undergoing hemodialysis. No correlation was observed between plasma clearance of eplerenone and creatinine clearance. Eplerenone is not removed by hemodialysis (see WARNINGS AND PRECAUTIONS, Hyperkalemia).
Hepatic Insufficiency: The pharmacokinetics of eplerenone 400 mg has been investigated in patients with moderate (Child-Pugh Class B) hepatic impairment and compared with normal subjects. Steady-state Cmax and AUC of eplerenone were increased by 3.6% and 42%, respectively (see DOSAGE AND ADMINISTRATION).
Heart Failure: The pharmacokinetics of eplerenone 50 mg was evaluated in 8 patients with heart failure (NYHA classification II-IV) and 8 matched (gender, age, weight) healthy controls. Compared with the controls, steady state AUC and Cmax in patients with stable heart failure were 38% and 30% higher, respectively.
(see DRUG INTERACTIONS)
Drug-drug interaction studies were conducted with a 100 mg dose of eplerenone.
Eplerenone is metabolized primarily by CYP3A4. A potent inhibitor of CYP3A4 (ketoconazole) caused increased exposure of 5.4 fold; while less potent CYP3A4 inhibitors (erythromycin, saquinavir, verapamil, and fluconazole) resulted in increases ranging from 2.0-2.9 fold. Grapefruit juice caused only a small increase (about 25%) in exposure (see DRUG INTERACTIONS).
Eplerenone is not an inhibitor of CYP1A2, CYP3A4, CYP2C19, CYP2C9, or CYP2D6. Eplerenone did not inhibit the metabolism of amiodarone, amlodipine, astemizole, chlorzoxazone, cisapride, dexamethasone, dextromethorphan, diclofenac, 17α-ethinyl estradiol, fluoxetine, losartan, lovastatin, mephobarbital, methylphenidate, methylprednisolone, metoprolol, midazolam, nifedipine, phenacetin, phenytoin, simvastatin, tolbutamide, triazolam, verapamil, and warfarin in vitro. Eplerenone is not a substrate or an inhibitor of P-Glycoprotein at clinically relevant doses.
No clinically significant drug-drug pharmacokinetic interactions were observed when eplerenone was administered with cisapride, cyclosporine, digoxin, glyburide, midazolam, oral contraceptives (norethindrone/ethinyl estradiol), simvastatin, or warfarin. St. Johns Wort (a CYP3A4 inducer) caused a small (about 30%) decrease in eplerenone AUC.
No significant changes in eplerenone pharmacokinetics were observed when eplerenone was administered with aluminum and magnesium-containing antacids.