Glimepiride

Glimepiride is a shorter-acting sulphonylurea (SU) used in type 2 diabetes mellitus (T2DM) to lower glucose by stimulating endogenous insulin release. In modern UK practice, SUs are typically used when metformin is contraindicated/not tolerated, when rapid HbA1c reduction is needed, or as a cost-effective add-on - but consider SGLT2 inhibitors and/or GLP-1 RAs first-line where there is CVD/CKD/HF benefit per NICE.

🧠 Mode of action

• Primary: Binds the SUR1 subunit of pancreatic β-cell K_ATP channels (Kir6.2) → channel closure → membrane depolarisation → voltage-gated Ca²⁺ influx → insulin exocytosis.
• Secondary effects: ↓ hepatic glucose output and ↑ peripheral uptake occur secondary to higher insulin - not a direct hepatic action.
• Requires some residual β-cell function (ineffective in absolute insulin deficiency).

📋 Indications

• T2DM: monotherapy when metformin unsuitable, or as add-on to metformin/other agents when HbA1c remains above target.

💉 Dose (adult)

• Start: 1 mg once daily with breakfast (or first main meal).
• Titrate: increase by 1–2 mg increments at ≥1–2-weekly intervals according to capillary glucose/HbA1c.
• Usual range: 1–4 mg OD; max 6 mg/day.
• Renal/hepatic impairment, frailty, or high hypoglycaemia risk: stay at the lowest effective dose and uptitrate cautiously; consider an alternative SU (e.g., gliclazide in CKD) or another class.
• Peri-operative/fasting: omit on the morning of surgery or if NPO; consider VRIII if prolonged fasting or intercurrent illness.

🤝 Interactions (clinically relevant)

• CYP2C9 substrate: inhibitors ↑ exposure (e.g., fluconazole, miconazole oral gel – significant), inducers ↓ effect (e.g., rifampicin, carbamazepine).
• Protein-binding displacement / potentiation: warfarin, fibrates, sulphonamides, co-trimoxazole, chloramphenicol → ↑ hypoglycaemia risk.
• β-blockers: may mask adrenergic warning signs of hypoglycaemia (tremor, palpitations).
• Alcohol: can potentiate hypoglycaemia and cause disulfiram-like reactions (rare).
• Always verify specifics in the BNF.

⚠️ Cautions

• Renal impairment: higher hypoglycaemia risk; dose cautiously and consider alternatives in advanced CKD.
• Hepatic impairment: avoid or use extreme caution (impaired gluconeogenic recovery from hypos).
• Elderly/frail, irregular meals, weight loss, alcohol excess: heightened hypoglycaemia risk - keep doses low and review regularly.
• Driving / DVLA: counsel on hypo risk; carry glucose; check DVLA guidance if recurrent severe hypos.
• Pregnancy & breastfeeding: generally avoid; insulin preferred in pregnancy.

⛔ Contraindications

• Hypersensitivity to sulphonylureas/sulphonamides.
• Type 1 diabetes, DKA, or marked hepatic failure.

🧪 Monitoring

• Glycaemia: HbA1c every 3 months until stable; SMBG during titration or if hypos suspected.
• Renal (U&Es/eGFR) and LFTs: baseline and periodically; adjust/avoid if declining function.
• FBC: rare blood dyscrasias - check if infection/bruising/unexpected anaemia.
• Weight & BMI: anticipate gain; reinforce lifestyle input.

🥴 Side effects

• Hypoglycaemia (most important) - sweating, tremor, hunger, confusion; nocturnal hypos possible.
• Weight gain (insulin-mediated anabolism).
• GI upset (nausea, dyspepsia), headache, dizziness.
• Rare: cholestatic hepatitis/jaundice, SIADH/hyponatraemia, photosensitivity, pruritus, rash, blood dyscrasias.

👟 Practical use & counselling (UK ward/clinic)

• Take with breakfast; eat regular meals and carry fast-acting carbs (e.g., glucose tabs).
• Educate on “15-15 rule” for hypos: 15 g fast carbs → recheck in 15 min → repeat if needed; follow with starchy snack.
• Sick-day: if not eating or vomiting, withhold glimepiride to avoid hypos; check glucose more often; seek advice early.
• Discuss weight management and consider pairing with metformin or adding an SGLT2 inhibitor / GLP-1 RA where indicated by NICE (CVD/CKD/HF).

🧮 Dose “maths” you’ll use

• Titrate every 1–2 weeks to fasting/pre-meal targets (e.g., 5–7 mmol/L individualised).
• If recurrent hypos or wide variability → step down the dose or de-escalate to a non-hypoglycaemic agent.

📚 References

• BNF: Glimepiride
• NICE NG28: Type 2 diabetes in adults - management (current UK guidance).
• DVLA: Assessing fitness to drive - diabetes (Group 1/2) guidance.