#prescribing

The main ones can be remembered using "CRAP GPs spend all day on SICKFACES.COM".

Cytochrome P450 Inducers

These induce CYP450 activity, and thus reduce the concentration of drugs which are metabolised by this system.

Carbemazepine Rifampicin Alcohol (chronic use) Phenytoin Griseofulvin Phenobarbitone Sulphonylureas, St John's Wort, Smoking

Also topiramate.

Cytochrome P450 Inhibitors

These inhibit CYP450 enzyme activity and thus increase the concentration of drugs which are metabolised by this system.

Sodium valproate Isoniazid Cimetidine Ketoconazole Fluconazole Alcohol (acute use), Amiodarone, Allopurinol Chloramphenicol Erythromycin Sulfonamides, SSRIs Ciprofloxacin Omeprazole Metronidazole

Also grapefruit, cranberry juice, diltiazem, verapamil, clarithromycin.

Common Interactions

Medications which commonly interact with CYP450 inhibitors and inducers are:

Warfarin

Phenytoin

Combined Oral Contraceptive Pill (COCP)

Theophylline

Corticosteroids

Tricyclic antidepressants

Statins

Lamotrigine

In med school: phenytoin of course works by reducing neuronal excitability and the electrical conductance of the brain cells, thus reducing seizure activity. This is usually given by slow IV injection :)

Ok PSA post incoming, cos I’ve got a few questions about this!

First of all, try not to worry too much. This exam is different to other exams in that if you don’t know something, you can look it up. 

This is how I revised for it and I got 85%:

1. In the months leading up to the exam, just try to do a bit of revision on drugs in general - I wrote summary sheets on the most common drugs. It’s good to do this anyway for finals. I recommend the book ‘the top 100 drugs’. Things like indications, side effects, common interactions blah de blah.

2. When it gets to 1-2 months before the exam, start proper PSA-focused revision. I recommend getting the ‘pass the PSA’ textbook because that’s good for familiarising yourself with the type of questions they ask. However, bear in mind that the questions in this book are slightly easier than the real thing.

3. A few weeks before the exam, start doing the practice papers on the PSA website. These are very similar to the real thing, so do them properly, and review your answers, note the sections where you lost the most marks. I think there’s 3, I did them all twice.

Some tips:

- especially make sure you practice the calculations, because they’re not too bad but it’s easy to get in a tizz about them in the real thing. Definitely learn the main types of calculations like the back of your hand!

- practice looking things up in the online BNF. This is practically the whole exam, because unless you’ve got a photographic memory you probably will have to look up drugs for at least half the questions. Being fast on the online BNF will gain you marks. The test is quite time-pressured. Remember to use control+F to find words!

- However, I’d recommend learning some lists of drugs which cause common side effects. There’s almost always questions on drugs that cause hypo or hyperkalaemia, so learn those. Also drugs that cause confusion/drowsiness e.g. diazepam, opioids. You won’t have time to check every drug in the BNF to see if it has a certain side effect so definitely try to learn which drugs cause which common side effects! Again, the Pass the PSA book will help you with that.

- revise fluid prescribing as well, because there’s usually a big question on that