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Key drug interactions for PSA JeffreyKey take away point: not about learning every and all the drug interactions, but about learning to use the Interactions checker and knowing which reactions are severe/strongly contra- indicated.Collapse • A 67-year-old male is admitted to the hospital following a collapse Medicine Dose Route Frequency earlier at home this morning. Isosorbide 20mg PO TDS replacement, T2DM, GORD,ion, R hip mononitrate migraines, erectile dysfunction Amlodipine 5mg PO OD • Investigations: BM: 5.7, Hb 146, Metformin 500mg PO OD WCC 7.6, CRP 4 Omeprazole 20mg PO OD • DH: His drug chart is listed below. • Which of the 2 prescriptions are Paracetamol 1g PO QDS most likely to have interacted to cause this man’s collapse? Sildenafil 50mg PO OD PRN Sildenafil and isosorbide mononitrate • Question learning points: using the Interactions checker on Medicines Complete. • Searching all of the above will show as below:Parkinson Disease • An 86-year-old male on the geriatric ward is complaining of 1/7 hx of nausea and vomiting. He has Parkinson’s disease, which was initially well controlled but his symptoms have worsened following his admission for a fall at home. Medicine Dose Route Frequency Co-careldopa 75mg/300mg PO TDS • PMH: Parkinson’s disease, HTN, Entacapone 200mg PO TDS T2DM, hypercholesterolaemia Ramipril 6.25mg PO OD • DH: His drug chart is listed below. Atorvastatin 40mg PO ON • Examination: BP 132/86 mmHg. Examination reveals a resting tremor Codeine 30mg PO 4-hourly phosphate and cogwheel rigidity in the right arm. Metoclopramide 10mg PO TDS • Select the ONE prescription that may exacerbate the patient’s Parkinson’s symptomsAnswer • Metoclopramide • Also aware of haloperidol, clozapine and domperidoneLiver enzyme inducers • A 21-year-old female presents to the GP as she is having recurrent spotting despite taking the combined oral contraceptive pill 3 packets at a time, with a 7-day Medicine Dose Route Frequency break every 3 packets. She Hydroxocobalamin 1 mg IM Every 3 months denies forgetting to take any pills. Phenytoin 200 mg PO OD • DH: Her drug chart is listed Ethinylestradiol with 1 tablet PO OD for 63 desogrestrel days below. Nitrofurantoin 50 mg PO QDS for 3 • PMH: days • B12 deficiency, tonic-clonic Paracetamol 1 g PO QDS PRN seizures, recent UTI. • Which one medication may reduce the efficacy of the COCP?Answer • PhenytoinEnzyme inducers CRAP GPS • Carbamazepine • Rifampicin • Alcohol (chronic) • Phenytoin • Griseofulvin • Phenobarbitone • Sulphonyureas, smoking, St Join’s WortAn 84-year-old male attends his GP for his INR review, which came back as 5.7 (target range 2.5-3.5). He is on warfarin for atrial fibrillation. Medicine Dose Route Frequency He was recently discharged from the hospital for alcohol Warfarin 5 mg PO OD withdrawal and cellulitis. Chlordiazepoxide 20 mg PO QDS for 5 days • PMH: Aortic valve replacement, B12 deficiency, Erythromycin 500 mg PO QDS for 5 chronic liver disease, HTN days Hydroxocobalamin 1 mg IM Every 3 • DH: His drug chart is listed months below. Amlodipine 10 mg PO OD • Which of the following ONE Ramipril 5 mg PO OD prescription is likely to have caused the prolonged INR?Answer • ErythromycinEnzyme inhibitors SICKFACES.COM Group • Chloramphenicol • Erythromycin • Sodium valproate • Isoniazid • Sulfonamides • Cimetidine • Ciprofloxacin • Ketoconazole • Omeprazole • Fluconazole • Metronidazole • Alcohol (binge/acute) • Grapefruit juiceNephrotoxicity • A 72-year-old female is admitted to the hospital following a CAP and delirium. She is treated with a stat dose of IV gentamicincine Dose Route Frequency 3mg/kg and a 5-day course of amoxicillinFurosemide 40 mg PO OD She weighs 62kg. Her recent blood tests reveal the following: Ramipril 2.5 mg PO BD • Hb 127 WCC 13 CRP 113 Na+ 137 K+ 3.8 Urea 10.4 (2.1-8.5 mmol/L) Creatinine 11Paracetamol 1 g PO QDS PRN (53-97 micromol/L) AKI: Stage 1 • PMH: Heart failure, migraines Ibuprofen 400 mg PO STAT PRN • DH: Her drug chart is listed below. • Which three drugs will have most likelyentamicin 186 mg IV STAT contributed to the development of the AKI?oxicillin 500 mg PO TDS for 5/7Answer • Furosemide, Gentamicin, Ibuprofen DAMN: Diuretics, ACEI/ARB/ABX, Metformin, NSAIDsNephrotoxic • Antimicrobial • Immunosuppressants • Aminoglycosides • Azathioprine • Fluroquinolones • Rifampicin • Other medications • Tetracycline • Cephalosporins • Allopurinol • Sulphonamides • NSAIDs • Vancomycin • Penicillamine • ACE inhibitors • Cancer chemotherapy • Mannitol • Bisphosphonates • Cisplatin, carboplatin • Cimetidine • Methotrexate • Doxorubicin• A 38-year-old female is admitted to the hospital with palpitations. An ECG reveals she has a supraventricular tachycardia and she is treated in accordance with the trust guidelines. She is later found to be hypotensive and bradycardic on the ward. • PMH: Migraines, Asthma Medicine Dose Route Frequency • Examination: HR 36 RR 18 BP 86/49 Sats 95% Verapamil 80 mg PO TDS • DH: Her drug chart is listed below. Salbutamol • Which two medications are likely to Propranolol 160 mg PO BD be the cause of the new bradycardia? Ethinylestradiol with 1 tablet PO OD desogrestrel Hydroxychloroquine 200 mg PO ODAnswer • Verapamil and Propranolol • Non-dihydropyridine CCBs (verapamil, diltiazem) and beta blockers should not be given together • Risk of hypotension and bradycardia.Other important points to consider: • NSAID: • Asthma • Beta blockers • Peptic ulcers • Urinary retention • HyperkalaemiaHepatotoxic • Hepatocellular • Cholestatic • Paracetamol • Abx: co-amoxiclav, flucloxacillin, erythromycin • TB medication: Rifampicin, pyrazinamide, isoniazid • Testosterones • Amiodarone • Fibrates • Nitrofurantoin • Chlorpromazine, • Methotrexate prochlorperazine • Methyldopa • Sulphonylureas • StatinsContraception Drug Contraindication COC HTN, smoking, BMI >35, migraine, VTE hx POP PV bleeding Progesterone implant, injection PV bleeding, enzyme inducers Levonorgestrel IUD PID Copper IUD PID, copper allergyAnti-emetics Drug Contraindication Ondansetron Avoid in 1 trimemster pregnancy QT interval prolongation Cyclizine Additive effect with CNS depressations Enhanced SEs with anticholinergic drugs Promethazine Respiratory depression in children Metoclopramide Tardive dyskinesia and EPS Domperidone (dopamine antagonist) Cardiac diseaseHyperkalaemia- K+ ABCD PENS HIT • K+ sparring diuretics • ACE inhibitors, Angiotensin receptor blockers • Beta blockers (non-selective) • Calcineurin inhibitors (tacrolimus, cyclosporin) • Digoxin • Pentamidine • NSAIDs • Succinylcholine • Heparin • TrimethoprimHyponatraemia- ABCDEFGH • ACEi/antidepressants/antipsychotics • Brivaracetam • Carbamazepine • Desmopressin/diuretics • Ethosuximide • Furosemide • Gliclazide • Heparin Neuroleptic malignant syndrome Serotonin syndrome Onset Gradual Sudden Sx Rigidity Tremor and myoclonus Course Prolonged within 7 days Rapid breaking within 24 hours Reflexes Reduced Increased Pupils Normal Mydriasis Lab Increased WCC, increased CK Increased WCC, increased CK Severity More severe (most require ITU) Wide spectrum Specific tx Dopamine agonist, amantadine, Benzodiazepines, cyproheptadine, dantrolene, carbidopa-levodopa chlorpromazine Cx drugs Neuroleptics, metoclopramide, SSRIs, TCAs, MAOIs sudden dopaminergic drug withdrawalClozapine: agranulocytosis • Side effects: • Agranulocytosis • Fever • Myocarditis, cardiomyopathy • PE, pneumonia • Parkinsonian, seizures, dizziness, headache, tremor • Risk of hyperglycaemia • Other • Weight gain, sedation, constipation • Clozapine induced GI hypomotility • PancreatitisTips • Timing is key • Learn the key interactions and mnemonics • Familiarise with the interaction checker