Contra-Indications and Interactions Flashcards
Antacids
Can reduce serum concentration of ACEi’s, some Abx, digoxin, levothyroxine and PPI’s
H2 antagonists
Reduce dose in CKD and can disguise symptoms of gastric cancer
PPI
Reduces effect of clopidogrel
Can disguise symptoms of gastric cancer and can increase risk of osteoporotic #
Loperamide
Avoid in acute UC/bloody diarrhoea and in possibility of C-diff
Laxatives
Do not use in obstruction
Aminosalicylate
Don’t use in children < 2 or in renal impairment
Have pH resistant coating so affected by gastric pH modifying drugs (PPI)
Antiemetics
Risk of side effects increased when prescribed with antipsychotics
Loop Diuretics
Effects drugs that are renally excreted
Contraindicated in severe hypovolaemia/dehydration and caution in hepatic encephalopathy
Thiazide diuretics
Avoid in hypokalaemia/natraemia
Can precipitate acute gout attacks - increases uric acid levels
Effectiveness reduced by NSAIDs
Potassium Sparing Diuretics
Contraindicated in severe renal impairment, hyperkalaemia, addisons and pregnant women
Caution when using other K+ elevating drugs - ACE/ARB
Beta Blockers
Do not use in heart block, reduce dose in hepatic failure and dont use with non-dihydropyridine Ca blockers
Calcium Blockers
Caution in those with poor LV function, avoid in AV node conduction delay and unstable angina
Do not use non-dihy…… with B-blockers
ACE inhibitors/ AT1 Blockers
Avoid in those with Renal Artery Stenosis and pregnancy/ breastfeeding
Low doses in CKD
Avoid using with other K+ elevating drugs and risk of renal failure increased when used with NSAIDs
Nitrates
Contraindicated in severe aortic stenosis and if hemodynamically unstable
Cardiac Glycosides
Contraindicated in 2nd degree hear block
Do not use if risk of ventricular arrythmias, reduce dose in renal failure
Duiretics, amiodarone, Ca blockers and quinine can all increase risk of toxicity
Amiodarone
Only use when risk/benefits are balances as can be dangerous particularly in severe hypotension, heart block and active thyroid disease
Increases plasma levels of digoxin, diltiazem and verapamil
Aspirin
Not used in < 16yrs due to Reye’s syndrome
Avoided in 3rd trimester of pregnancy
Caution in peptic ulceration and can cause acute attack of gout
Clopidogrel
Caution in renal/hepatic impairment
CP450 metabolised
Heparin/NOACs
Use in caution with other anticoagulants
Warfarin
Do not give in 1st trimester of pregnancy
Low therapeutic dose and CP450 metabolised
Statins
Caution in hepatic and renal impairment and pregnant/breasfeeding women
Beta-2-agonists
B-blockers reduce effectiveness
Anticholinergics
Caution in those at risk of Angle Closure Glaucoma as can cause rise in IOP
Corticosteoids
Use with NSAIDs increases risk of peptic ulceration + GI bleeding
Enhances hypokalaemia in those taking B2 agonists
CP450 metabolised
Theophylline
Contraindicated in porphyria
Smoking and alcohol increase clearance
CP450 metabolised
O2
Can disturb fine balance between hypoxia and hypercapnia in those with T2 resp failure - leading to rise in blood CO2
Insulin
Increased risk of hypo in renal impairment
Sulphonylureas
Reduce dose in hepatic impairment
Risk of hypo increased when used with other anti-diabetic drugs
Efficacy reduced by prednisolone, thiazides and loop diuretics as increase blood glucose
Biguanides
Contraindicated in severe renal impairment, caution in hepatic impairment
Withhold in acute alcohol intoxication and caution in chronic alcohol
Withhold for 48yrs post IV contrast
Thyroxine
In hypopituitarism, must administer corticosteroids first to avoid addisonian crisis
GI absorption reduced by antacids, calcium and iron salts
Carbimazole
Contraindicated in haematological/hepatic condition
Vit K antagonist so can enhance anticoagulative effects
Bisphosphonates
Avoid in severe renal impairment, hypocalcaemia and upper GI disorders
Absorption reduced with antacids, calcium and iron salts
Mineralocorticoids
Contraindicated in systemic infections, myasthenia gravis, increased eye pressure, cataracts, hypertension,
Caution when used with theophylline, loop and thiazide diuretics as all reduce K+
Penicillin
Reduce dose in severe renal impaiment
They reduce renal excretion of methotrexate and enhance warfarin effect
Cephalosporins
Caution in epilepsy and reduce dose in renal impairment.
Enhances effect of warfarin and can increase nephrotoxicity of aminoglycosides
Trimethoprim
Contraindicated in 1st trimester of pregnancy - foetal abnormalities
Used in caution in folate deficiency and reduce dose in renal impairment
Nitrofurantoin
Do not use in near term pregnancy/ babies < 3months
Contraindicated in patients with renal impairment
Tetracyclines
Dont use in pregnancy, breastfeeding, < 12 yrs or in renal impairment
Do not give within 2 hrs of iron, antacids or calcum as prevent absoption
Aminoglycosides
Avoid in myasthenia Gravis
Ototoxicity more likely if used with loop diuretics or vancomycin
Nephrotoxicity more likely if used with cyclosporin or vancomycin
Macrolides
Caution in renal/hepatic impairment
CP450 inhibitor
Quinolones
Calcium and antacids reduce absorption
CP450 inhibitor
Use with NSAIDs increases risk of seizures and use with prednisolone increase risk of tendon rupture
Metronidazole
CP450 metabolised
Inhibits acetaldehyde dehydrogenase which clears alcohol metabolites so no alcohol to be drunk
Glycopeptides
Dose adjustement in elderly and renal impairment
Increased risk of toxicity when prescribed with aminoglycosides, loop diuretics or ciclosporins
NSAIDs
Aspirin and corticosteroids increase risk of GI ulceration
Anticoagulants and SSRI’s increase risk of bleeding
ACEi’s and diuretics increase risk of renal impairment
Reduce efficacy of antihypertensives and duiretics
Codeine
Caution in sever respiratory disease, reduce dose in renal/hepatic impairment and the elderly
Do not use with other sedating drugs
Morphine
Reduce dose in hepatice failure and renal impairment and elderly
Do not give in resp failure or biliary colic
Paracetamol
Overdose can lead to liver failure due to saturation of pathway leading to build up of NAPQI
Xanthine-Oxidase Inhibitors
Reduce dose in severe hepatic/renal impairment
Reduces efficacy of mercaptopurine + azathioprine as require xanthine oxidase for metabolism
Use with amoxicillin increase risk of rash
Use with ACEi’s and thiazides increase risk of hypersensitivity
Alpha Blockers
Contraindicated if already postural hypotension
5-alpha-reductase inhibitors
Do not use in pregnancy (or even come into contact with) as can cause abnormal development of male external genitalia
L-dopa
Do not use with antipsychotics or metoclopramide as effects contradictory
Phenytoin
Reduce dose in hepatic impairment
In utero exposure associated with craniofacial abnormalities and reduced IQ
Carbamazepine
In utero exposure associated with neural tube defects, cardiac and urinary abnormalities and cleft palate
Contraindicated in previous Antiepileptic Hypersensitivity syndrome
Sodium Valproate
Avoid in women of childbearing age and in 1st trimester as related to foetal abnormalities
Avoid in severe hepatic/ renal abnormalities
Inhibits CP450
Tricyclics
Caution in elderly, those at risk of CV disease and epilepsy and those with constipation, prostatic hypertrophy or raised IOP
SSRI’s
Dose reduction in hepatic impairment
Gastroprotection needed if also taking NSAIDs
Do not prescribe with other drugs that prolong QT interval
Benzodiazepines
Reduce dose in elderly
Avoid in significant resp/neuro impairment
Avoid in liver failure
Acetylcholinesterase Inhibitors
Do not use whilst driving, breastfeeding or pregnant
Itraconazole, erythromycin and fluoxetine inhibit metabolism
Can interfere with anticholinergic medications such as atropine, amitriptyline and codeine
