Non-Statin Lipid-Lowering Drugs
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Direct answer
Non-statin lipid-lowering drugs reduce LDL or triglycerides by mechanisms other than HMG-CoA reductase inhibition. Ezetimibe blocks intestinal cholesterol absorption, PCSK9 inhibitors stop LDL receptor breakdown, and fibrates mainly lower triglycerides through PPAR-alpha activation. They are added to a statin when LDL stays above target or when a statin cannot be tolerated.
What you must remember
- Ezetimibe: blocks the NPC1L1 transporter at the intestinal brush border, lowering LDL by around 20 per cent and combining well with a statin.
- PCSK9 inhibitors: monoclonal antibodies such as evolocumab and alirocumab prevent PCSK9 from degrading LDL receptors, giving large LDL falls by subcutaneous injection.
- Bempedoic acid: inhibits ATP citrate lyase upstream of HMG-CoA reductase, is activated mainly in the liver, and so causes fewer muscle symptoms.
- Fibrates: PPAR-alpha agonists that lower triglycerides the most and raise HDL, with a myositis risk that is higher with gemfibrozil.
- Niacin: lowers LDL, triglycerides and lipoprotein(a), but causes prostaglandin-mediated flushing, hyperglycaemia and hyperuricaemia.
- Bile acid resins: cholestyramine and colesevelam bind bile acids and raise LDL receptor numbers, but they raise triglycerides and cause constipation.
- Adverse effect to remember: bempedoic acid raises uric acid, so gout and tendon rupture are the points to recall.
Mechanism at a glance
Each class works at a different step of cholesterol handling, and the mechanism explains most of its adverse effects. The table summarises the main classes.
| Class | Main mechanism | Key adverse effect |
|---|---|---|
| Ezetimibe | Blocks intestinal cholesterol uptake | Rare diarrhoea, raised transaminases |
| PCSK9 inhibitors | Preserve LDL receptors | Injection-site reactions |
| Bempedoic acid | ATP citrate lyase inhibition in liver | Hyperuricaemia, gout |
| Fibrates | PPAR-alpha activation | Myositis, gallstones |
| Niacin | Reduces hepatic VLDL output | Flushing, hyperglycaemia |
| Bile acid resins | Bile acid sequestration | Constipation, raised triglycerides |
The class chosen depends on the lipid pattern: LDL-dominant disease favours ezetimibe or PCSK9 inhibitors, while high triglycerides favour fibrates. Linking each adverse effect to its mechanism is the fastest way to answer recall questions.
Resins are less useful when triglycerides are already high, because they can push them up further. In practice an LDL that stays high on a statin usually prompts ezetimibe first, with a PCSK9 inhibitor reserved for patients who remain above target or cannot take the other agents.
Where the exam tries to catch you
Lipid drug questions usually test a mechanism and the adverse effect that follows from it, so the traps below pair them.
- Trap: fibrate and statin are combined without thought. Correct: gemfibrozil raises statin levels and myositis risk, so fenofibrate is the usual choice when a fibrate is used with a statin.
- Trap: resins are given to a patient with hypertriglyceridaemia. Correct: resins can raise triglycerides, so they are avoided in that setting.
- Trap: niacin flushing is treated with an antihistamine. Correct: flushing is prostaglandin-mediated, so aspirin taken beforehand reduces it.
Frequently asked questions
Which lipid-lowering drug is usually added first to a statin?
Ezetimibe is the usual first add-on to a statin when LDL remains above target or the statin dose cannot be raised further. Its LDL lowering is modest, but its safety with statins is well established.
Which drug blocks intestinal cholesterol absorption?
Ezetimibe blocks the NPC1L1 transporter at the intestinal brush border, reducing the cholesterol that reaches the liver. This lowers LDL cholesterol, and ezetimibe is commonly combined with a statin for additional effect.
What is the main adverse effect of niacin and how is it reduced?
Flushing is the main adverse effect of niacin, caused by prostaglandin release, and aspirin taken beforehand reduces it. Hyperglycaemia and hyperuricaemia also limit niacin use in patients with diabetes or gout.
Why are PCSK9 inhibitors given by injection?
PCSK9 inhibitors such as evolocumab and alirocumab are monoclonal antibodies that are not absorbed by mouth. They are therefore given by subcutaneous injection every few weeks, and injection-site reactions are the commonest adverse effect.
Why is bempedoic acid less likely to cause muscle symptoms?
Bempedoic acid is activated in the liver rather than in skeletal muscle, which is why muscle symptoms are less common than with statins. It can raise uric acid, so gout and tendon rupture are the adverse effects to remember for bempedoic acid.