Pharmacology · Short notes

Endocrine Pharmacology: Short Notes & Cheat Sheet

Insulin and oral antidiabetics, thyroid drugs, corticosteroids, sex hormones, bone drugs and pituitary hormones.

Short notes

Read these before you attempt the topic's MCQs.

How long each insulin works

A schematic, not to scale. Rapid-acting insulin covers meals, glargine provides a flat basal level, and NPH peaks in between.

Insulin

Rapid-acting (lispro, aspart, glulisine) is given at mealtimes. Regular (short-acting) insulin is the only kind given IV, for example in DKA.
NPH (isophane) is intermediate-acting. Glargine, detemir and degludec are long-acting basal insulins with no peak.
Adverse effects: hypoglycaemia, weight gain, lipodystrophy at injection sites, and hypokalaemia, because insulin drives K+ into cells.
DKA treatment: IV fluids, IV regular insulin, and potassium replacement.

Oral and non-insulin antidiabetics

Metformin reduces glucose production in the liver (via AMPK) and is first-line for type 2 diabetes. Used alone it causes no hypoglycaemia or weight gain. Risks: GI upset, lactic acidosis (avoid when eGFR is below 30) and B12 deficiency.
Sulfonylureas (glibenclamide, gliclazide, glimepiride) close K-ATP channels in β-cells. They cause hypoglycaemia (worst with glibenclamide in the elderly) and weight gain. Meglitinides (repaglinide) are short-acting and taken with meals.
Pioglitazone (PPAR-γ agonist) improves insulin sensitivity but causes fluid retention, so it is contraindicated in heart failure. It also raises fracture risk.
DPP-4 inhibitors (the '-gliptins') are weight-neutral. Linagliptin needs no renal dose adjustment.
GLP-1 agonists (liraglutide, semaglutide) cause weight loss and nausea. Avoid them with a history of medullary thyroid cancer or MEN2.
SGLT2 inhibitors (the '-gliflozins') cause glucose loss in urine, genital fungal infections and euglycaemic DKA, and protect the heart and kidneys.
Acarbose causes flatulence. Hypoglycaemia while taking it must be treated with glucose, not sucrose.

Thyroid

Levothyroxine (T4) is taken on an empty stomach and has a half-life of about 7 days, so TSH is checked after about 6 weeks. Iron and calcium reduce its absorption.
Propylthiouracil (PTU) also blocks conversion of T4 to T3 in the tissues. It is preferred in the first trimester and in thyroid storm, but is hepatotoxic.
Carbimazole or methimazole is preferred at other times. It is teratogenic in the first trimester.
All thionamides can cause agranulocytosis, so warn patients to report a sore throat or fever.
Iodide (Lugol's solution) quickly inhibits hormone release (Wolff–Chaikoff effect) and is used before surgery. Radioactive iodine is contraindicated in pregnancy. Propranolol controls symptoms.

Corticosteroids

They act on intracellular receptors to change gene transcription. They reduce prostaglandins and leukotrienes by inhibiting phospholipase A2 (via annexin-1).
Glucocorticoid potency relative to hydrocortisone (1): prednisolone 4, methylprednisolone 5, dexamethasone and betamethasone about 25–30 (with no mineralocorticoid action). Fludrocortisone is mainly a mineralocorticoid and is used in Addison's disease.
Adverse effects: Cushingoid features, hyperglycaemia, osteoporosis, cataract, glaucoma, infection, myopathy, psychosis, growth suppression and HPA axis suppression.
Taper the dose after more than about 3 weeks of use. Give the dose in the morning.
Dexamethasone treats cerebral oedema. Betamethasone or dexamethasone given to the mother speeds fetal lung maturity.

Sex hormones, bone and pituitary

Combined oral contraceptives suppress FSH and LH, which stops ovulation. Contraindications: previous VTE, migraine with aura, breast cancer, liver disease, and smokers over 35. Enzyme inducers such as rifampicin and carbamazepine make them fail.
Emergency contraception: levonorgestrel 1.5 mg within 72 hours, or ulipristal within 120 hours.
Tamoxifen blocks oestrogen in the breast but stimulates the uterus (endometrial cancer, VTE). Raloxifene treats osteoporosis without stimulating the endometrium. Clomiphene induces ovulation. Anastrozole and letrozole are aromatase inhibitors.
Finasteride inhibits 5α-reductase and treats BPH. Pregnant women should not handle crushed tablets.
Bisphosphonates (alendronate) must be taken upright with water, 30 minutes before food. Risks: oesophagitis and osteonecrosis of the jaw. Teriparatide (a PTH analogue) builds bone; denosumab targets RANKL.
Pituitary drugs: desmopressin (V2 agonist) for central diabetes insipidus and bed-wetting; octreotide for acromegaly and variceal bleeding; cabergoline and bromocriptine for high prolactin; oxytocin for labour induction and postpartum haemorrhage (PPH); tolvaptan for SIADH.

Cheat sheet

High-yield facts in one place. Cover the right-hand column and test yourself.

Antidiabetics: mechanism and key risk

Class	Mechanism · risk
Metformin	↓ hepatic gluconeogenesis · lactic acidosis, B12
Sulfonylureas	Close K-ATP → insulin release · hypoglycaemia
Pioglitazone	PPAR-γ · oedema, heart failure
DPP-4 inhibitors	↑ incretins · weight neutral
GLP-1 agonists	Incretin mimetic · nausea, weight loss
SGLT2 inhibitors	Glucosuria · genital infection, euglycaemic DKA
Acarbose	α-glucosidase · flatulence, treat hypo with glucose

Steroid potency (glucocorticoid : mineralocorticoid)

Steroid	Relative potency
Hydrocortisone	1 : 1
Prednisolone	4 : 0.8
Methylprednisolone	5 : 0.5
Dexamethasone	25–30 : 0
Fludrocortisone	10 : 125

Drugs of choice

Condition	Drug
Type 2 diabetes (first line)	Metformin
DKA	IV regular insulin + fluids + K+
Hyperthyroid, 1st trimester / storm	Propylthiouracil
Hypothyroidism	Levothyroxine
Myxoedema coma	IV liothyronine / levothyroxine + hydrocortisone
Central diabetes insipidus	Desmopressin
Nephrogenic diabetes insipidus	Thiazide
Addison's disease	Hydrocortisone + fludrocortisone
Hyperprolactinaemia	Cabergoline

Memory aids

PTU for the 1st trimester and the Thyroid storm: Propylthiouracil is chosen in early pregnancy and thyroid storm; carbimazole/methimazole otherwise.
Gliflozins make you 'flow' glucose: SGLT2 inhibitors cause glucosuria, with genital infections and UTIs.

Exam traps

Regular insulin, not a rapid-acting analogue, is the classic insulin for IV infusion in DKA.
Metformin does not cause hypoglycaemia when used alone.
Dexamethasone has no mineralocorticoid activity, so it is useless for Addisonian salt loss.
Tamoxifen increases endometrial cancer risk; raloxifene does not.
Thiazides, paradoxically, treat nephrogenic diabetes insipidus.

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