Interactions Flashcards
Name the enzyme inhibitors (SICKFACES.COM)
Sodium valproate Isoniazid / itraconazole Cimetidine Ketoconazole Fluconazole / fluoxetine Alcohol (acute, binge) / Amiodarone Chloramphenicol Erythromycin + clarithromycin Sulphonamides (co-trimoxazole) Ciprofloxacin Omeprazole Metronidazole
Also:
Grapefruit juice
Name the enzyme inducers (SCRAP GPSS)
Sulphonylureas Carbamazepine Rifampicin Alcohol (chronic) Phenytoin
Griseofulvin
Phenobarbital
St John’s Wort
Smoking
What are the main interactions with amiodarone?
- Amiodarone inhibits warfarin metabolism- enhanced anticoagulant effect
- Increased risk of bradycardia, AV block, myocardial depression with beta blockers
- Risk of ventricular arrhythmias with lithium
- Plasma concentration of digoxin increased by amiodarone
Amiodarone has a very long half life so there is potential for drug interactions to occur weeks/months after stopping treatment
What are the common interactions with digoxin?
- Plasma conc of digoxin increased by amiodarone (enzyme inhibitor)
- Plasma conc of digoxin increased by erythromycin (enzyme inhibitor)
- . Plasma conc of digoxin reduced by rifampicin (enzyme inducer)
- Plasma conc of digoxin reduced by St John’s Worst (enzyme inducer)
- Increased toxicity of digoxin if hypokalaemia occurs with loop and thiazide diuretics
- Plasma conc of digoxin increased by CCBs
What are the common interactions with lithium?
- Risk of lithium toxicity with ACEi (excretion reduced)
- Risk of lithium toxicity with NSAIDs (excretion reduced)
- Sodium depletion with loop and thiazide diuretics (excretion of lithium reduced)
- Risk of ventricular arrhythmias with amiodarone
What are the common interactions with methotrexate?
- Increased risk of infection with vaccines
- PPIs at high doses reduce clearance of methotrexate increasing risk of toxicity
- Penicillins increases risk of methotrexate toxicity
- Trimethoprim- both folate antagonists, increased risk of side effects and nephrotoxicity
What are the common interactions with phenytoin?
- Effects of phenytoin enhanced by NSAIDs
- Amiodarone inhibits phenytoin metabolism
- Phenytoin accelerates metabolism of warfarin
- Cimeditine inhibits metabolism of phenytoin
- Plasma conc of phenytoin increased by fluoxetine
- St John’s Wort reduces plasma conc of phenytoin
- Ciprofloxacin affects the concentration of phenytoin
- Decreases efficacy of combined contraceptive pill
- Phenytoin decreases exposure to NOACS
What are the common interactions with theophylline?
- Increased risk of convulsions with quinolones e.g. ciprofloxacin
- Plasma conc of theophylline reduced by St John’s Wort
- Plasma conc of theophylline reduced by rifampicin
- Plasma conc of theophylline increased by cimetidine
- Plasma conc of theophylline increased by fluconazole
- Smoking can increase theophylline clearance and increased doses of theophylline are therefore required
What are the common interactions with warfarin?
- Anticoagulant effect increased by NSAIDs
- Anticoagulant effect increased by fluconazole
- Anticoagulant effect increased by statins
- Anticoagulant effect increased by ciprofloxacin, erythromycin, metronidazole
- Anticoagulant effect reduced by griseofulvin
- Anticoagulant effect reduced by antiepileptics
- Alcohol effects anticoagulant control
- Anticoagulant effect antagonised by Vitamin K
- Anticoagulant effect enhanced by cranberry juice
What is the risk of consuming tyramine based food and drink e.g. cheese if on MAOIs?
Hypertensive crisis
How does alcohol interact with TCAs and mirtazapine?
Increased sedative effect
What are the main interactions with combined oral contraceptives?
- Enzyme inducing drugs increase metabolism of contraceptives. Additional contraceptive precautions should be taken for 4-8 weeks after stopping treatment
- Some ABX may reduce efficacy of the pill by impairing bacterial flora responsible for recycling ethinylestradiol e.g. ampicillin, amoxicillin, doxycycline. Additional precautions are required for duration of treatment and for 7 days after stopping
What are the main interactions with progesterone only contraceptives?
Efficacy reduced by enzyme inducers
Additional protection is needed for duration of treatment and 4 weeks after
What are the main interactions with sympathomimetics e.g. pseudoephedrine?
- MAOI- hypertensive crisis
- Beta blockers- hypertension risk
What are the main interactions with Orlistat?
- Orlistat reduces plasma conc of amiodarone
- Anticoagulants- monitor
- Acarbose for diabetes due to its GI effects
- Reduces absorption of ciclosporin
