Common interactions Flashcards
What is the interaction between microgynon 30 and phenytoin?
COC interacts with many anti-epileptic drugs.
Reduce the efficacy of pregnancy prevention due to phenytoin inducing the metabolism of oestrogens.
How is the interaction between COC and antiepileptic drugs managed?
Adjust dose of COC to at least 50 microgram daily and use tricycling regimen with four day pill free break.
Take OC for three consecutive cycles without a break, then have a four-day pill free interval.
What is the interaction between amiodarone and digoxin?
Amiodarone reduces the excretion of digoxin.
Levels of digoxin will rise and toxicity can occur.
BNF and s
Stockleys recommend reducing digoxin doses by half.
What is the interaction between amiodarone and warfarin?
Amiodarone inhibits the metabolism of warfarin through the inhibition of cytochrome p450 enzymes.
Need to monitor the INR and adjust the dose of warfarin accordingly.
What is the interaction between clarithromycin and simvastatin?
Macrolides: alarm bells.
Clarithromycin is CYP inhibitor: increased levels of simvastatin and increased risk of myopathy.
Can either stop statin for duration of clarithromycin course + 3 days or we could change to metronidazole.
What is the interaction between itraconazole and sildefanil?
azoles: CYP inhibitors.
Increased levels of viagra result.
Dose should be halved.
What is the interaction between lithium and NSAIDs?
NSAIDs inhibit prostaglandin synthesis, this leads to reduced renal perfusion and reduced excretion of lithium.
Toxicity could result as lithium has a very narrow therapeutic window.
When dispensing lithium what needs to be checked?
That it is the same brand the patient has had before as the therapeutic window is so narrow.
What should be checked for methotrexate?
ONCE WEEKLY.
Can be used alongside NSAIDs.
How should hypertension be treated in pregnancy?
Atenolol = no.
Labetolol = yes outside of first trimester.
Methyldopa also is fine.
Why can quinolone antibiotics not be used in epileptics?
Quinolones lower the seizure threshold.
Can trimethoprim be used in pregnancy?
Should be avoided in pregnancy.
Especially in 1st semester.
It has an antifolate effect and can lead to neural tube defects.
Can metoclopramide be used in parkinsons?
No.
Why can metoclopramide not be used in Parkinsons?
Induces acute dystonic reactions.
Should be changed to domperidone 10mg tablets 1 tds.
Domperidone does not cross BBB.
What occurs when tramadol are used as well as SSRIs?
Increased risk of CNS toxicity.
SSRIs and tramadol also lower the seizure threshold.
Why can erythromycin and domperidone not be taken at the same time?
Erythromycin increases domperidone levels 3x through inhibition of CYP3A4 and also there is prolongation of the QT interval.
For who are ACEI not recommended?
Afro-caribbean patients because they have lower renin levels.
Therefore, less responsive.
CCBs are better.
Why can Calcichew D3 forte not be used in renal failure patients?
Calcium salts are used as a phosphate binder in renal patients. Calcichew D3 forte contains colecalciferol which requires hydroxylation by the kidney. This conversion is limited in patients with renal impairment. Calcichew should be used.
What should not be dispensed due to the possibility of mechanical trauma to fetus?
Applicator with canestan pessary.
