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Flashcards in Interactions Deck (67)
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1

Phenytoin and Amiodarone

Amiodarone increases phenytoin concentration

NB: Amiodarone is an enzyme inhibitor.
Due to amiodarones long half life: potential for interaction several months after discontinuation

2

Phenytoin and Warfarin

Phenytoin (p450 enzyme INDUCER) induces warfarins metabolism, decreases warfarin concentration, reduced anti-coagulation effect, decreases INR

3

Phenytoin and COC

Phenytoin (a p450 enzyme inducer) accelerates metabolism of Oestrogens, reducing their effectiveness

Patient should be changed to an IUD

4

Phenytoin and Fluoxetine

Fluoxetine increases phenytoin concentration

5

Phenytoin and Theophylline

Theophylline decreases phenytoin concentration

6

Phenytoin and St Johns Wort

St Johns Wort decreases phenytoin concentration
(St Johns Wort is an enzyme inducer)

7

Phenytoin and Fluconazole

Fluconazole increases phenytoin concentration (Fluconazole enzyme inhibitor part of SICKFACES)

8

Phenytoin and Cimetidine

Cimetidine increases phenytoin concentration (Cimetidine enzyme inhibitor part of SICKFACES)

9

Phenytoin and Diltiazem

Diltiazem increases phenytoin levels, and diltiazems own effects are decreased by phenytoin

10

Phenytoin and Rate limiting CCB's

Phenytoin decreases effects of Verapamil and Diltiazem and also Felodipine

11

Amiodarone and Grapefruit Juice

Grapefruit Juice increases levels of Amiodarone

Grapefruit Juice is an enzyme inhibitor

12

Amiodarone and warfarin

Amiodarone increases warfarin levels
Enhances anti-coagulant effects, increased bleed risk

Amiodarone is an inhibitor of some of the CYP450 enzymes.

13

Amiodarone and Simvastatin

Increased risk of Myopathy
Max dose of Simvastatin: 20mg

This is not the same with Atorvastatin etc but still monitor for mypopathy

14

Amiodarone and beta blockers and Rate-limiting CCB's diltiazem and verapamil

Increased risk of
Bradycardia
Myocardial depression
AV block

When given with beta blockers/ rate limiting CCB

15

Amiodarone and Lithium

Increased risk of Ventricular Arrhythmias
(poss associated with QT prolongation)

Also both effect THYROID function

16

Amiodarone and Digoxin

Amiodarone increases plasma level of Digoxin, leading to digoxin toxicity

17

Theophylline + enzyme inhibitors:
Cimetidine, Fluconazole, Ketoconazole, Ciprofloxcin, Erythromycin

Theophylline levels increased as it is metabolised by the CYP450 enzymes

18

Theophylline + enzyme Inducers:
Carbamazepine, Alcohol, Phenobarbital, Phenytoin, Rifampicin, St Johns Wort
(SCRAP GP's)

Theophylline levels decreased

19

Theophylline and Quinolone antibiotics e.g. Ciprofloxaxin, Levofloxacin

Increased risk of SEIZURES
These BOTH lower seizure threshold

20

What do diltiazem and Verapamil (rate limiting CCBs) do to Theophyllines concentration?

Increase it
these are CYP3A4 enzyme inhibitors!

21

NSAIDs and warfarin/ phenindione

NSAIDs increase warfarin levels- increased anticoagulant effect

NSAIDs, like warfarin, have a high affinty for Albumin. They displace warfarin off the protein= more free warfarin

So remember the interaction is not because both drugs can increase bleed risk- NSAIDs actually increase the levels of warfarin

22

SSRI's and TCA's and warfarin

SSRI's and TCA's will increase warfarin levels- increased anticoagulant effect

23

Statins and warfarin

Only statin that interacts: Rosuvastatin
Increased effects of warfarin

24

Clopidogrel and warfarin

Anti-coagulant effect enhance (both thin blood)- increased risk of bleeds

25

Orlistat + Antiepileptics

Possible increased risk of convulsions- orlistat lowers seizure threshold

26

Methotrexate and Phenytoin

Do not use together- both deplete Folate

27

Methotrexate and Trimethoprim/ Co-trimoxazole (trimethoprim + Sulfamethoxazole)

Do not use together- both deplete folate- haematological blood toxicity risk

Sulfamethoxazole also increases methotrexate toxicity

28

Methotrexate and Ibuprofen

Methotrexate toxicity increased by NSAIDs due to decreased renal excretion

29

Methotrexate and Flucloxacillin

Methotrexate toxicity increased by all penicillins due to decreased renal excretion

30

Methotrexate and Clozapine

Neutropenia risk increased