Common Interacting Drugs

Question 1

Drugs with a narrow therapeutic index

Answer 1

Warfarin, Digoxin, Phenytoin, Theophylline

Question 2

Drugs which require careful dosage control

Answer 2

Antihypertensives (due to risk of hypotension)
Antidiabetic drugs (due to risk of hypoglycaemia)

Question 3

Cytochrome P450 Enzyme Inducers

reduce concentrations of these drugs - e.g. with warfarin, reduces INR

Answer 3

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Carbamazepine
Rifampicin
Alcohol (chronic)
Phenytoin
Griseofulvin
Phenobarbitone
Sulphonylureas
\+St John's wort

Question 4

Cytochrome P450 Enzyme Inhibitors

increase concentrations, e.g. in warfarin they increase INR

Answer 4

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Sodium valproate
Isoniazid
Cimetidine
Ketoconazole
Fluconazole and other anti-fungals
Alcohol (acute), amiodarone, allopurinol
Chloramphenicol
Erythromycin
Sulfonamides , SSRIs
Ciprofloxacin
Omeprazole
Metronidazole
\+grapefruit juice
\+disulfiram

Question 5

P450 Metabolised Drugs

Answer 5

CCCOWPPATSS
Ciclosporin
Carbamazepine
Citalopram
OCP
Warfarin
Phenytoin
Protease inhibitors (HIV drugs)
ACh inhibitors (e.g. donepezil for Alzheimer's)
Theophylline
Tacrolimus
Steroids

Question 6

Drugs with interactions with alcohol causing:

1. GI bleeding
2. Anticoagulation changes
3. Sweating, flushing, nausea and vomiting
4. Lactic acidosis
5. Hypertensive crisis
6. Sedation

Answer 6

1. NSAIDs, inc. aspirin
2. Warfarin - acute intoxication causes enzyme inhibition and so increased effect, chronic causes enzyme infucion and so reduced effect
3. Metronidazole, disulfiram
4. Metformin
5. Monoamine Oxidase inhibitors
6. Barbiturates, opioids and benzodiazepines