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Common side effects

Groups of side effects

  • Anticholinergic: dilated pupils, blurred vision, dry mouth, flushed skin, urinary retention, constipation
    • Tricyclic antidepressants, antihistamines, hyoscine, atropine, antipsychotics, incontinence medications
  • Antihistaminergic: weight gain, sedation
    • Tricyclic antidepressants, antipsychotics, antihistamines
  • Anti-α-adrenergic: postural hypotension, sexual dysfunction, nasal congestion, headache
    • Tricyclic antidepressants, antipsychotics, α-blockers
  • Antidopaminergic: extrapyramidal side effects (e.g. tardive dyskinesias, parkinsonism), hyperprolactinaemia (→ galactorrhoea, oligomenorrhea, subfertility), neuroleptic malignant syndrome, oculogyric crisis
    • Metoclopramide, antipsychotics

Side effects to memorise 

  • TB drugs
    • Rifampicin: orange-red tears/urine + hepatitis
    • Isoniazid: neuropathy + hepatitis
    • Pyrazinamide: + hepatitis
    • Ethambutol: optic neuritis
  • Antiepileptics
    • Phenytoin: toxicity (→ cerebellar syndrome), acne, coarse face, gum hypertrophy, hirsutism + inhibit COCP
    • Carbamazepine: rash, dizziness, hyponatraemia, hair thinning  + inhibit COCP
    • Sodium valproate: tremor, weight gain, hair thinning + teratogenic (avoid if child-bearing age)
    • Lamotrigine: rash (Stevens-Johnson syndrome)
  • Antidepressants
    • SSRI (e.g. fluoxetine, citalopram, sertraline): nausea, low libido, withdrawal, insomnia, hyponatraemia
    • Tricyclic antidepressant (e.g. amitriptyline): [anticholinergic effects], [antihistaminergic effects], [anti-α-adrenergic effects], hyponatraemia (SIADH), arrhythmias
    • Monoamine oxidase A inhibitors (e.g. selegiline): 3Hs – Hypertension, Hepatocellular jaundice, Hyperthermia
  • Antihypertensives
    • ACE inhibitors: dry cough, postural hypotension, acute kindey injury in renal artery stenosis (check U&Es before and 2 weeks after starting), angioedema of the tongue, hyperkalaemia, profound hypotension when started
    • Ca2+ blocker: pedal oedema, headache/flushing/dizziness
    • β-blocker: diabetes risk, impotence, bradycardia, fatigue, cold hands and feet, sleep disturbance
    • α-blocker: [anti-α-adrenergic effects]
  • Diuretics
    • ALL: dehydration, hypotension, hyperuricaemia, hypokalaemia (except K+ sparing), hyponatraemia, hypomagnesaemia
    • Loop: hypocalcaemia (used in treatment of hypercalcaemia)
    • Thiazide (e.g. indapamide): hypercalcaemia
    • K+ sparing: hyperkalaemia, gynaecomastia
  • DMARDs
    • Sulfasalazine: myelosuppression, oligospermia, hepatitis, rashes (Stevens-Johnson syndrome, erythema nodosum), renal problems, discoloured urine
    • Chloroquine: retinopathy, tinnitus, myopathy
    • Methotrexate: hepatic toxicity, pulmonary toxicity, myelosuppression, mucositis
    • TNF antagonists: infusion reactions (including anaphylaxis), infections (including TB reactivation), autoimmune reactions, blood disorders
    • Cyclophosphamide: haemorrhagic cystitis, myelosuppression, alopecia
  • Hypoglycaemics 
    • Insulin: hypoglycaemia, fat-hypertrophy at injection site, hypokalaemia (used in treatment of hyperkalaemia), weight gain
    • Metformin: weight loss, lactic acidosis, metallic taste, GI disturbance, B12 deficiency
    • Sulphonylureas (e.g. gliclazide): hypoglycaemia, weight gain
    • Thiazolidinediones (glitazones, e.g. pioglitazone): fluid retention (→ heart failure, oedema), hepatotoxicity, fractures
    • DPP4-inhibitors (gliptins, e.g. sitagliptin): pancreatitis
    • SGLT2-inhibitors (flozins, e.g. empagliflozin): UTIs/thrush, risk of DKA, weight loss, may increase risk of amputations
  • Contraception
  • Antipsychotics
    • ALL: [antidopaminergic effects], [anticholinergic effects], [antihistaminergic effects], [anti-α-adrenergic effects]
    • Clozapine: agranulocytosis
    • Chlorpromazine: cholestatic jaundice
    • Haloperidol: prolonged QT interval, interference with temperature regulation
  • Lithium: toxicity (tremor/ataxia/dysarthria → coma, convulsions, hypotension), diarrhoea, hypothyroidism, diabetes insipidus
  • Steroids: diabetes risk, cushingoid appearance, psychosis, osteoporosis, hypokalaemia, hyperglycaemia, infections, leukocytosis, risk of avascular necrosis
  • Azathioprine: myelosuppression
  • Ciclosporin: tremor, chronic interstitial nephritis, hypertrichosis, gum hyperplasia, burning sensation in hands/feet
  • Levodopa: nausea, red urine/other body fluids, postural hypotension, dyskinesias, ‘on-off’ and ‘wearing off’ effects
  • Proton pump inhibitor: tinnitus, GI disturbance, headache, hyponatraemia, hypomagnesaemia
  • Antiarrhythmics
    • Amiodarone: thyroiditis, pulmonary fibrosis, peripheral neuropathy, myopathy, blue-grey skin pigmentation/photosensitivity, hepatitis, metallic taste
    • Digoxin toxicity: xanthopsia (yellow/orange tinge to vision), GI distress, any arrhythmia
    • Adenosine: flushing, sense of impending doom

Drugs causing…

Electrolyte imbalances

  • Hypernatraemia: sodium-containing antibiotics/fluids, sodium bicarbonate, drugs causing diabetes insipidus (e.g. lithium)
  • Hyponatraemia: antidepressants, diuretics, chlorpromazine, carbamazepine, proton pump inhibitors, ACE inhibitors
  • Hyperkalaemia: K+ sparing diuretics, ACE inhibitors/angiotensin receptor blockers, NSAIDs, trimethoprim, ciclosporin/tacrolimus, heparin
  • Hypokalaemia: salbutamol (used in Tx of hyperkalaemia), insulin, diuretics (except K+ sparing), caffeine/theophylline
  • Hypercalcaemia: thiazide diuretics, lithium
  • Hypocalcaemia: loop diuretics, bisphosphonates, phenytoin

Organ toxicity

  • Hepatitis: TB antibiotics (rifampicin/isoniazid/pyrazinamide), sodium valproate, methotrexate, methyldopa, amiodarone, statins, paracetamol, phenytoin, ketoconazole/fluconazole, nitrofurantoin, sulfonylureas/sulfonamides
  • Cholestasis: co-amoxiclav (may be delayed/severe), clarithromycin/erythromycin, carbamazepine, chlorpromazine, contraceptives, flucloxacillin, sulfonylureas/sulfonamides
  • Pulmonary toxicity/fibrosis: nitrofurantoin, amiodarone, methotrexate, cyclophosphamide, sulfasalazine, bleomycin
  • Renal impairment
    • Interstitial nephritis: NSAIDS, penicillins/cephalosporins, calcineurin inhibitors (ciclosporin/tacrolimus), PPIs 
    • Acute tubular necrosis: lithium, contrast, gentamicin, amphotericin B
    • Precipitate renal artery stenosis: ACE inhibitors
    • Glomerular damage: NSAIDs
  • Creatinine rise: trimethoprim, cimetidine/ranitidine             
  • Photosensitivity: tetracyclines, terbinafine, chlorpromazine, amiodarone (→ blue/grey discoloration), chemo (vincristine), ciprofloxacin, psoralens, retinoids, thiazide diuretics, sulphonylureas
  • Hypothyroidism: amiodarone, carbimazole, lithium, propylthiouracil, radio-iodine

Other reactions

  • Stevens-Johnson syndrome/erythroderma: sulphur-based drugs (sulphonamides, sulfonylureas), antiepileptics, allopurinol, antibiotics
  • Vasculitis: allopurinol, penicillin, sulphonamides, thiazides, phenytoin, cephalosporins 
  • Agranulocytosis: C’s – Carbamazepine, Clozapine, Colchicine, Carbimazole, Cytotoxic agents
  • Gynaecomastia: DISCO MTV – Digoxin, Isoniazid, Spironolactone, Cimetidine, Oestrogens, Methyldopa/metronidazole, Tricyclic antidepressants, Verapamil
  • Neuropathy: metronidazole, nitrofurantoin, isoniazid, vincristine, cisplatin, amiodarone, phenytoin
  • Megaloblastic anaemia: methotrexate, phenytoin, ethanol, trimethoprim, sulfonamides, sodium valproate, metformin, antidepressants
  • Dyskinesia: dopaminergic drugs (levodopa, bromocriptine), dopamine-blocking drugs (antipsychotics), antidepressants
  • Clostridium difficile risk: cephalosporins, clindamycin, ciprofloxacin, broad spectrum penicillins
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