Zetia vs Amlodipine: Combining the Two (Rationale + Risk)

What does each drug actually do?

Ezetimibe blocks the sterol transporter Niemann-Pick C1-Like 1 (NPC1L1) at the brush border of the small intestine, reducing absorption of cholesterol and plant sterols; hepatic cholesterol stores fall, LDL receptors increase, and LDL is cleared from the blood [1]. In a 2-week trial in 18 patients it inhibited cholesterol absorption by 54% compared with placebo [1]. In two 12-week placebo-controlled trials that enrolled 1,719 adults, ezetimibe 10 mg lowered LDL-C by 18% versus a 1% rise on placebo, with maximal response reached within about 2 weeks [1].

Amlodipine is a dihydropyridine calcium channel blocker. It relaxes arterial smooth muscle, lowers peripheral resistance and brings blood pressure down; it is prescribed for high blood pressure and for angina, and it is taken once daily. Tablets come in 2.5 mg, 5 mg and 10 mg strengths [3]. It is not a lipid-lowering drug.

The two sets of uses do not overlap. Every Zetia indication is about lowering LDL-C or plant sterol levels [1].

Is there an interaction between ezetimibe and amlodipine?

The Zetia label's interaction table lists three clinically important interactions. Cyclosporine increases both ezetimibe and cyclosporine concentrations. Fenofibrate plus ezetimibe may increase cholesterol excretion into bile and cause gallstones, and fibrates other than fenofibrate are not recommended with ezetimibe. Bile acid sequestrants such as cholestyramine lower ezetimibe exposure [1]. Amlodipine is not among them.

That is a statement about the Zetia label's interaction table, not a drug-interaction study of the pair. What is documented is how ezetimibe is handled: it is rapidly conjugated to ezetimibe-glucuronide, with minimal CYP oxidation [1].

Where statins come in

Ezetimibe is used with a statin, or alone when additional LDL-C lowering therapy is not possible [1]. The Zetia label defers to the statin's own label for the risks of that combination [1]. Amlodipine matters for one statin in particular. Multiple doses of amlodipine 10 mg raised simvastatin 80 mg exposure by 77%, and the Norvasc label says to limit simvastatin to 20 mg daily in patients taking amlodipine; the combination is not contraindicated. The Norvasc label says amlodipine does not affect atorvastatin exposure. A fixed-dose amlodipine-atorvastatin tablet, Caduet, has been approved since 2004 [4].

This page covers single-ingredient ezetimibe. Ezetimibe/simvastatin (Vytorin), rosuvastatin/ezetimibe and bempedoic acid/ezetimibe are separate products with their own labels, warnings and dosing [1].

What the outcome trials show for each drug

IMPROVE-IT randomized 18,144 patients hospitalized for acute coronary syndrome within the previous 10 days to simvastatin 40 mg plus ezetimibe 10 mg or simvastatin 40 mg plus placebo, with a median follow-up of 6 years. The primary composite occurred in 32.7% versus 34.7% at 7 years (hazard ratio 0.936, 95% CI 0.89 to 0.99) [2]. That trial tested ezetimibe added to simvastatin. The Zetia label itself carries no cardiovascular risk-reduction indication and does not mention the trial [1].

CAMELOT randomized 1,991 patients with angiographically documented coronary artery disease and diastolic blood pressure below 100 mm Hg to amlodipine 10 mg, enalapril 20 mg or placebo for 24 months. Cardiovascular events occurred in 16.6% on amlodipine versus 23.1% on placebo (hazard ratio 0.69, 95% CI 0.54 to 0.88); the enalapril difference versus placebo was not significant [5].

ASCOT-BPLA randomized 19,257 hypertensive patients with at least three other cardiovascular risk factors to an amlodipine-based regimen (5 to 10 mg, adding perindopril as required) or an atenolol-based regimen, and stopped prematurely after a median 5.5 years [6]. Fatal and nonfatal stroke occurred in 327 versus 422 patients (hazard ratio 0.77, 95% CI 0.66 to 0.89, p=0.0003) and all-cause mortality in 738 versus 820 (hazard ratio 0.89, 0.81 to 0.99, p=0.025), while the primary endpoint of nonfatal myocardial infarction plus fatal coronary heart disease was not significantly different (429 versus 474; hazard ratio 0.90, 0.79 to 1.02, p=0.105) [6]. In the CAFE substudy of 2,199 patients, brachial systolic pressures were nearly identical between arms (difference 0.7 mm Hg) while central aortic systolic pressure was 4.3 mm Hg lower on the amlodipine regimen [7].

Side effects reported with each drug

For ezetimibe alone, pooled across 10 placebo-controlled trials (2,396 on ezetimibe versus 1,159 on placebo, median 12 weeks): upper respiratory infection 4.3% versus 2.5%, diarrhea 4.1% versus 3.7%, arthralgia 3.0% versus 2.2%, sinusitis 2.8% versus 2.2%, fatigue 2.4% versus 1.5% [1]. There is no boxed warning [1].

Consecutive transaminase rises of 3 times the upper limit of normal or more occurred in 1.3% of patients taking ezetimibe with a statin versus 0.4% taking a statin alone, and the label says to test liver enzymes as clinically indicated and to consider stopping if rises persist [1]. Myopathy and rhabdomyolysis are possible; in postmarketing reports most patients who developed rhabdomyolysis were also taking a statin or a fibrate [1].

For amlodipine, the Norvasc label reports dose-related edema in placebo-controlled trials: 1.8% at 2.5 mg, 3.0% at 5 mg and 10.8% at 10 mg, versus 0.6% on placebo. Amlodipine has no boxed warning.

Doses when both are prescribed

The Zetia label gives the dose as 10 mg once daily, with or without food. It says a missed dose should be taken as soon as possible without doubling the next one, and that LDL-C can be assessed as early as 4 weeks after starting [1]. The label recommends taking ezetimibe at least 2 hours before or 4 hours after a bile acid sequestrant [1]. The label says ezetimibe is not recommended in moderate or severe hepatic impairment, where total ezetimibe exposure rises about 3- to 4-fold; mild impairment raises it about 1.7-fold [1].

Amlodipine is available as 2.5 mg, 5 mg and 10 mg oral tablets, taken once daily [3].

Are they interchangeable?

No. Ezetimibe's labeled uses are lowering LDL-C in primary hyperlipidemia and familial hypercholesterolemia, and lowering plant sterols in sitosterolemia, alone or with a statin, fenofibrate or other LDL-C lowering therapy [1]. Amlodipine is labeled for high blood pressure and angina. A person with both high LDL-C and high blood pressure is taking two drugs for two separate jobs, not two versions of the same job.