# Antidiabetic Drugs > Antidiabetic drugs for FMGE Pharmacology: metformin, sulfonylureas, SGLT2 inhibitors, GLP-1 agonists, insulin types, hypoglycaemia and DKA in exam notes. - Canonical URL: https://prepelephant.com/topics/fmge/pharmacology/antidiabetic-drugs-fmge - Exam / course: FMGE · Subject: Pharmacology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Antidiabetic Drugs", PrepElephant, https://prepelephant.com/topics/fmge/pharmacology/antidiabetic-drugs-fmge ## Direct answer Metformin has held first-line status for type 2 diabetes for decades because it lowers glucose without weight gain or hypoglycaemia, acting through AMPK activation and reduced hepatic glucose output; its only feared complication, lactic acidosis, is avoided by withholding it when the estimated GFR falls below 30 mL/min, perioperatively, and in decompensated cardiorespiratory illness. Sulfonylureas close the pancreatic ATP-sensitive potassium channel and risk hypoglycaemia and weight gain; SGLT2 inhibitors spill glucose into urine delivering heart and kidney protection with a unique euglycaemic ketoacidosis risk; GLP-1 receptor agonists add weight loss at the cost of nausea. Insulin remains the only option in type 1 diabetes, with onset times that examiners expect verbatim: rapid analogues around 15 minutes, soluble regular at 30, NPH peaking at 6 to 8 hours, and glargine lasting about 24 without a peak. ## What you must remember - Diagnostic numbers: HbA1c 6.5 per cent or more, fasting plasma glucose 126 mg/dL or more, two-hour OGTT or random plasma glucose 200 mg/dL or more with symptoms. - Metformin: holds in eGFR below 30, suspend 48 hours after iodinated contrast in renal impairment; causes vitamin B12 deficiency with long-term use; the extended-release form improves gastrointestinal tolerance; safe in pregnancy guidelines today. - Sulfonylureas: glibenclamide causes the worst hypoglycaemia in the elderly; chlorpropamide adds SIADH and a disulfiram-like reaction; all cause weight gain. - SGLT2 inhibitors (dapagliflozin, empagliflozin): genital mycotic infection and urinary infection, volume depletion, euglycaemic diabetic ketoacidosis (hold three days before surgery), rare Fournier gangrene, and cardiovascular-renal benefit independent of glucose. - GLP-1 receptor agonists (semaglutide, liraglutide): weight loss and nausea; gallbladder disease and pancreatitis warnings; contraindicated in personal or family medullary thyroid carcinoma or MEN2. - DPP-4 inhibitors (sitagliptin): weight-neutral, nasopharyngitis and arthralgia; dose-adjusted in renal impairment; no hypoglycaemia as monotherapy. - Insulin storage, an Indian practical favourite: unopened pens or vials refrigerated at 2–8 °C; the in-use pen kept at room temperature for up to 28 days; rotate injection sites to avoid lipohypertrophy. - Hypoglycaemia (below 70 mg/dL): the rule of 15 — 15 g fast-acting carbohydrate, recheck in 15 minutes; unconscious patient gets intravenous dextrose or intramuscular glucagon 1 mg, never oral feeding. - Pioglitazone is contraindicated in heart failure (fluid retention) and carries fracture and bladder-caution signals. ## A typical exam case: diabetic ketoacidosis A 20-year-old presents drowsy with glucose 480 mg/dL, pH 7.10, ketones strongly positive, potassium 3.0 mmol/L. The examiner's ordered sequence: begin isotonic saline — the fluid deficit of several litres is the immediate killer — and correct the potassium before or with the insulin infusion, because insulin drives potassium into cells and a starting level of 3.0 means insulin without potassium can precipitate fatal arrhythmia. Only then starts the regular insulin infusion at 0.1 units/kg/hour. When glucose falls below about 200 mg/dL, add dextrose to the fluids and continue the insulin until ketoacidosis clears — stopping insulin because the glucose normalised is the classic error, since ketogenesis outlives glycaemia. Bicarbonate is reserved for pH below 6.9. Hunt the precipitant: in this teenager, omitted insulin during an exam-season illness is the usual story; in an older patient, infection or infarction. Contrast the ward round question: the same sugar levels in a type 2 patient on glibenclamide with confusion at 3 a.m. is sulfonylurea hypoglycaemia — a long-acting drug in an elderly kidney is an admission in itself, treated with dextrose and observation for recurrent dips, not a sandwich and discharge. ## Where students slip Blaming metformin for hypoglycaemia in a patient also on glibenclamide is the most frequent attribution error; metformin monotherapy does not cause it. The second is missing SGLT2-associated ketoacidosis because the glucose reads "only 180 mg/dL" — the euglycaemia is precisely the trap, and ketones must be checked. Third, the insulin-storage and mixing questions: glargine cannot be mixed with other insulins in the same syringe, and mixing short with NPH alters their kinetics. Finally, writing "diet, exercise and tablets" for a thin, ketotic young patient delays lifesaving insulin — phenotypic type 1 in a lean Indian adolescent is common enough that the default must be insulin until the picture clarifies. ## Frequently asked questions ### What is the first-line oral drug for type 2 diabetes and its main contraindications? Metformin, withheld when eGFR is below 30 mL/min, in decompensated heart or respiratory failure, and perioperatively to avoid lactic acidosis. ### Why must potassium be checked before the insulin infusion in DKA? Insulin shifts potassium intracellularly; a level below about 3.3 mmol/L must be replaced first, or fatal arrhythmia follows. ### Which oral agents cause hypoglycaemia and weight gain? Sulfonylureas, worst with glibenclamide in the elderly and in renal impairment; metformin, DPP-4 inhibitors and SGLT2 inhibitors do not cause hypoglycaemia as monotherapy. ### What is the unique ketoacidosis risk of SGLT2 inhibitors? Euglycaemic diabetic ketoacidosis — glucosuria lowers insulin and raises glucagon despite near-normal glucose, so ketones rise while the meter looks reassuring. ### How is unopened insulin stored in the Indian household? Refrigerated between 2 and 8 °C, never frozen; the pen in use stays at cool room temperature for up to 28 days, away from sunlight and stove heat. ### Which antidiabetic drug class needs avoidance in medullary thyroid carcinoma history? GLP-1 receptor agonists such as semaglutide and liraglutide, owing to rodent C-cell tumour signals and MEN2/MTC contraindications.