Simvastatin: A moderate-intensity statin, very sensitive to CYP3A4

What it is

Simvastatin is a lipophilic statin given as a prodrug and activated in the liver. Depending on the dose, it lowers LDL cholesterol by 25 to 40%. It is effective and cheap, but it is a very sensitive CYP3A4 substrate: anything that inhibits that enzyme sends its levels and the risk of myopathy soaring.

It is still used in primary and secondary prevention, although atorvastatin and rosuvastatin have displaced it when more potency is needed. Because of its short half-life, it is taken at night.

Mechanism of action

It inhibits:

Its active form inhibits liver HMG-CoA reductase
It lowers LDL by 25–40% depending on the dose
It raises HDL moderately

At the counter

When to recommend it

Hypercholesterolaemia with moderate cardiovascular risk
Secondary prevention (after a heart attack or stroke), if tolerated and reaching the target
Moderate dyslipidaemia
Patients already doing well on it and reaching their LDL target

When not to

Allergy to statins
Active liver disease
Strong CYP3A4 inhibitors (itraconazole, ketoconazole, clarithromycin, erythromycin, protease inhibitors), gemfibrozil or ciclosporin
Pregnancy and breastfeeding

What to say at the counter. Two things when supplying it: 'at night' (it is eliminated quickly) and 'no grapefruit juice'. And always review the medicines: with amlodipine, amiodarone or diltiazem there are maximum simvastatin doses.

Warnings

Important Myopathy: a higher risk than with atorvastatin, especially at high doses + CYP3A4 inhibitors.
Important CYP3A4 interactions: many drugs send it soaring (azoles, macrolides, protease inhibitors, grapefruit juice). With amlodipine or amiodarone, do not exceed 20 mg of simvastatin.
Caution Muscle aches: common and generally mild. They need to be told apart from myopathy.
Caution Raised liver enzymes: monitor ALT/AST.

Pharmacokinetics

Absorption: Rapid oral absorption. Bioavailability of about 5% (intense first-pass metabolism).
Distribution: The active metabolite accumulates in the liver. Protein binding above 95%.
Metabolism: Extensive hepatic metabolism via CYP3A4: it is a very sensitive substrate, so inhibitors of that enzyme greatly increase its concentration.
Elimination: Biliary elimination. Half-life of 2–3 hours, although the active metabolites last longer.

Simvastatin vs atorvastatin

Aspect	Simvastatin	Atorvastatin
LDL-lowering potency	Moderate (25–40%)	High (35–55%)
CYP3A4 interactions	Many (very sensitive substrate)	Moderate
Myopathy risk	Higher (especially with inhibitors)	Lower
Cost	Lower (cheap generic)	Higher
First line today	No (second line)	Yes

Simvastatin if cost is decisive or the patient already tolerates it. Atorvastatin if more potency is needed or there are several medicines.

Self-assessment

Three questions. When you check your answers you will see the explanation for each one.

What is simvastatin's main disadvantage compared with atorvastatin? It frequently causes allergy A higher risk of CYP3A4 interactions and myopathy, especially with inhibitors It does not lower cholesterol
A patient on simvastatin is prescribed clarithromycin (an antibiotic). What should you do? Double the simvastatin dose CYP3A4 interaction: clarithromycin blocks its metabolism. It needs a medical decision or a different antibiotic No problem, they can take both
When is simvastatin best taken? At night, because of its short half-life In the morning on an empty stomach It does not matter, like atorvastatin

Training content. It does not replace the summary of product characteristics or clinical judgement.

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