Statins.
Statins are among the most prescribed drugs in the world and among the most misunderstood by patients. The mechanism is simple; what makes them worth studying carefully is that their main safety issue is concentration-dependent, which turns a metabolic interaction into a clinical one.
The mechanism in one sentence
Statins inhibit HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis in the liver.
The liver makes most of the body’s cholesterol, and HMG-CoA reductase is the rate-limiting step in that pathway. Inhibiting it lowers intracellular cholesterol, and the hepatocyte responds by expressing more LDL receptors on its surface to pull cholesterol in from the blood. That upregulation, rather than the reduced synthesis itself, is what produces most of the fall in circulating LDL. Because synthesis runs highest overnight, shorter-acting agents are taken in the evening; longer-acting ones such as atorvastatin and rosuvastatin work whenever they are taken.
Members of the class
| Drug | What sets it apart |
|---|---|
| Atorvastatin | High intensity, long half-life, CYP3A4 substrate. |
| Rosuvastatin | High intensity, minimally metabolised by CYP3A4. |
| Simvastatin | CYP3A4 substrate with the tightest interaction restrictions of the group. |
| Pravastatin | Hydrophilic and largely not CYP-metabolised, so fewer interactions. |
What the class is used for
- Secondary prevention after myocardial infarction, stroke or established vascular disease
- Primary prevention where estimated cardiovascular risk crosses the local threshold
- Familial hypercholesterolaemia
- Diabetes with additional cardiovascular risk factors
Side effects, derived from the mechanism
Each entry below follows from the mechanism above rather than being a separate fact. Read the middle column as the answer to the question, why would that happen.
| Effect | Why it follows |
|---|---|
| Myalgia and myopathy | Statins reduce products of the same mevalonate pathway that muscle cells rely on, and the risk rises with plasma concentration. That concentration dependence is why interactions matter so much in this class. |
| Rhabdomyolysis | The severe end of the same process, rare but capable of causing acute kidney injury through myoglobin release. Unexplained muscle pain is therefore always worth reporting. |
| Transaminase rise | Usually mild and asymptomatic. Significant hepatotoxicity is rare, and routine monitoring practice varies between guidelines. |
| New-onset diabetes | A small but real increase in incidence, consistently seen in trials and outweighed by cardiovascular benefit in patients who meet treatment thresholds. |
Contraindications and cautions
- Pregnancy and breastfeeding
- Active liver disease or persistently raised transaminases
- Caution with strong CYP3A4 inhibitors, particularly alongside simvastatin
The part you cannot derive
The grapefruit interaction is real but narrower than its reputation. It inhibits intestinal CYP3A4, so it matters for simvastatin and atorvastatin and barely at all for rosuvastatin or pravastatin, which are not meaningfully CYP3A4 substrates. Advice that tells every statin patient to avoid grapefruit is over-broad.
Exam traps
Not every statin has the CYP3A4 problem
Pravastatin and rosuvastatin largely bypass it. Questions test whether you know the class is not uniform.
Timing depends on half-life
Simvastatin is an evening dose because cholesterol synthesis peaks overnight and its half-life is short. Atorvastatin and rosuvastatin last long enough that timing does not matter.
Muscle symptoms are not automatically statin myopathy
Most muscle complaints in statin users are not caused by the drug, which is why creatine kinase and a structured rechallenge exist rather than immediate permanent discontinuation.
Members of this class that get confused
Within a class, the members differ on one property at a time, and that property is what exam questions are usually built on. These pairs split cleanly.
- Simvastatin vs Atorvastatin — Atorvastatin is higher intensity and has a long half-life, so it can be taken at any time of day.
Test yourself on this
Reading a mechanism and being able to retrieve it under time are different skills, and only the second one is examined. These are free and need no account.
- Cardiovascular pharmacology practice questions — 10 questions with explanations
- Statins, grapefruit and CYP3A4
- Counselling on statin muscle pain
- CYP450 inducers and inhibitors
- Creatinine clearance calculator (Cockcroft-Gault) — free calculator with a worked example
Common questions
Why do statins cause muscle pain?
Statins block the mevalonate pathway, which supplies products that skeletal muscle depends on, and the risk rises with the concentration of drug in the blood. That is why anything raising statin levels, such as a CYP3A4 inhibitor, raises the risk of myopathy with it.
Do all statins interact with grapefruit?
No. Grapefruit inhibits intestinal CYP3A4, so it affects simvastatin and atorvastatin. Rosuvastatin and pravastatin are not meaningfully metabolised by CYP3A4 and are largely unaffected.
Should statins be taken at night?
Only the short-acting ones. Cholesterol synthesis peaks overnight, so simvastatin is given in the evening. Atorvastatin and rosuvastatin have long enough half-lives that the time of day makes no practical difference.
Other drug classes
Beta blockers · ACE inhibitors · Anticoagulants · Diuretics · Opioids · Benzodiazepines · All drug classes
Study aid only. This page is written for learning and examination practice. It is not medical advice, not clinical decision support, and must never be used to make a decision about a real patient. Always verify against your local formulary, the product literature and a qualified pharmacist. See our medical disclaimer.
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