Interactions

Question 1

Interactions with DOACs
(Apixaban, Dabigtran, Rivaroxaban)

that can an increase in bleeding? (4)

Avoid. But if needed - look out for signs of bleeding and anaemia

Answer 1

1. NSAIDs - increases risk of bleeding. ideally avoid
2. Other DOACs/Heparin/Warfain -
3. Antiplatelets- aspirin/clopidogrel/tricagrelor
4. Selective serotonin reuptake inhibitors - citalopram
   serotonin norepinephrine re-uptake inhibitors - duloxetine and venlafaxine

Question 2

Interactions with DOACs
(Apixaban, Dabigtran, Rivaroxaban)

that can decrease the plasma concentration of doacs? (1 group)

Answer 2

1. Strong enzyme inducers - carbamazepine, phenytoin, rifampicin and st. johns wort

Question 3

Interactions with DOACs
(Apixaban, Dabigtran, Rivaroxaban)

that can increase the plasma concentration of doacs? (2)

Answer 3

1. Strong Cytochrome P450 INHIBITORS e.g. ketoconazole, itraconazole
2. HIV protease inhibitors -ritonavir

for those that aren’t strong inhibitors such as amiodarone, clarithromycin, verapamil no dose adjustment required just monitor

Question 4

Why should beta blockers not be used with verapamil?

Answer 4

Severe Hypotension

Asystole

Question 5

Which drugs can ENHANCE the effect of warfarin ? (15)

What should happen?

Answer 5

1. Alcohol-avoid binge drinking
2. Amiodarone - during loading dose phase check INR. Effect can be seen months after stopping Amiodarone
3. Antibiotics - co-trimoxazole - consider trimethoprim or reduce warfarin
   Metronidazole, erythromycin and clarithromycin - reduce warfarin dose as necessary
4. Antideppressants e.g SSRI, SNRI, TCA & mirtazapine - Avoid.
5. Aspirin/products containing aspirin e.g. topical salicylates . AVOID
6. Azoles - fluconazole, miconazole, voriconazole. Monitor INR 4-7 days after oral azole started and adjust dose based on that
7. Cranberry juice/products - Avoid
8. Clopidogrel or dipyridamole - Avoid
9. Corticosteroids - check INR and adjust if needed
10. Direct acting antivirals for Hep C - changes in liver function, check INR
11. Fibrates - Avoid or reduce warfarin dose
12. Glucosamine - Avoid
13. NSAIDs 0 Avoid. If must take check INR and pt counselled on signs of GI bleeding
14. Tamoxifen - avoid or reduce warfarin dose. Measure INR 1-2 weeks
15. Thyroxine (thyroid hormone) - reduce warfarin dose and weekly monitoring whilst thyroxine is being titrated

Question 6

Which drugs can REDUCE the effect of warfarin ? (1 main group - 6)
What should happen?

Answer 6

1. Enzyme inducers -

Rifampicin - increase W dose if nec

St johns wort - stop St john wart and monitor INR

Carbamazepine -increase W dose if nec

Phenytoin - increase W dose if nec. After stopping phenytoin, INR may be affected for up to 6 weeks.

Phenobarbitone - monitor and affects can be seen upto 6 weeks after stopping

Griseofulvin - increase W dose if nec

Question 7

Important to monitor the INR when warfarin is used concurrently with the following drugs, especially in older people (12)

Answer 7

1. Allopurinol.
2. Azathioprine.
3. Grapefruit juice (it may be easier to completely avoid this).
4. Influenza vaccine.
5. Methylphenidate.
6. Orlistat (may reduce the absorption of vitamin K).
7. Paracetamol or paracetamol-containing products (particularly if prolonged regular use).
8. Proton pump inhibitors.
9. Quinolone antibiotics.
10. Statins (particularly fluvastatin or rosuvastatin; not pravastatin).
11. Stopping smoking (it takes about 1 week for enzyme induction due to smoking to wear off).
12. Zafirlukast (leukotriene receptor antagonists)

Question 8

What are the enzyme inducers?

SCRAP GPS

Answer 8

Sulphonylureas
Carbamazepine
Rifampicin 
Alcohol 
Phenytoin 
Griseofluvin
Phenobarbital 
St johns wort

Question 9

What are the enzyme inhibitors?

SICKFACES.COM

Answer 9

Sodium valproate
Isoniazid
Cimetidine
Ketoconazole
Fluconazole
Alcohol (binge)
Chloramphenicol 
Erythromycin 
Sulfonamide

Ciprofloxacin
Omeprazole
Metronidazole
*Grapefruite juice

Question 10

Which drugs interact with beta blockers and cause severe hypotension? (4)

Answer 10

1. Antipsychotics and antidepressants
2. Baclofen
3. Verapamil
4. Other antihypertensive including nitrates

Question 11

What other drugs need to be careful with beta blockers - mask effects of hypoglycaemia ? (1)

Answer 11

1. Insulin and oral antidiabetic drugs

Question 12

Which drugs need to be used with caution with beta blockers because bradycardia and AV block? (4)

Answer 12

1. Diltiazem
2. Class I antiarrhytmics e.g. flecainide, quinidine
3. Class III antiarrhythmics e.g. amiodarone
4. Digoxin

Question 13

Which drugs interact with ACE Inhibitors and cause severe hypotension? (10)

Answer 13

1. Alcohol
2. Aldosterone antagonists
3. Alpha-blockers
4. Antipsychotics
5. Diuretics - e.g. ppl on 80mg furosemide consider holding diuretic 24 hours before starting ACE. Or ACE to be taken at night
6. Levodopa
7. Nitrates
8. Tricyclic antidepressants
9. Gold injections
10. Sitagliptin

Question 14

Which drugs interact with ACE and cause hyperkalaemia? (4)

Need to monitor K

Answer 14

1. Potassium sparing diuretics & Aldosterone antagonists
2. Heparin
3. Ciclosporin
4. Antibiotics - Tetracyclines avoid
   Trimethoprim -monitor K

Question 15

What can happen if using NSAID and ACE?

Answer 15

risk of deterioration in renal function especially in elderly, dehydrated, chronic kidney disease