Friday, 27 April 2012

Mnemonics for pharmacology and therapeutics

There's been much discussion of mnemonics for drugs, and just in case other medical students ever come across this blog, I thought I'd post them here (you never know, it might increase traffic to the site). I can't claim authorship of any of these, I got them all from friends - some may have come directly from, or been modified from books.

Enzyme Inhibitors -
Sodium Valproate (anti-epileptic, also used for bipolar disorder)
Isoniazid (used for TB)
Cimetidine (an H2 receptor blocker)
Ketoconazole & fluconazole (anti-fungals)

Fluoxetine (a selective serotonin reuptake inhibitor)
Alcohol - acute consumption & cigarettes
Cardiac failure and liver failure
Erythromycin & clarithromycin (macrolide antibiotics)
Sulphonamides (antibiotics)
Ciprofloxacin (a quinolone antibiotic, which can cause tendonitis and tendon rupture)
Omeprazole (a proton-pump inhibitor)
Metronidazole (antibiotic effective against anaerobes)

These all inhibit enzymes and therefore can increase the amount of a drug that is metabolised by the enzymes that are inhibited, as less of the drug is being metabolised. Therefore, these drugs will increase INR as they inhibit warfarin metabolism.

Apparently amiodarone and grapefruit can also go in this group (which is why patients on some medications are advised not to drink grapefruit juice), and also ritonavir, a protease inhibitor used for HIV. However ritonavir's enzyme inhibition is useful as it increases the amount of other HIV drugs, so is always given in combination with another HIV drug to "boost" it. 

Enzyme Inducers - Crap GPs (not very respectful to GPs I know, but they can't all be good, there must be some crap ones)
Carbamazepine (anti-epileptic)
Rifampicin (antibiotic, particuarly used for TB)
Alcohol - chronic consumption
Phenytoin (anti-epileptic)

Griseolfin (anti-fungal - I've never heard of it, apparently been largely replaced by terbinafine)
Phenobarbitone (old-style anti-epileptic, not commonly used, not first-line)
Sulphonylureas (anti-diabetic drugs, e.g. gliclazide) & St John's Wort (herbal remedy used for depression - available off the shelf in Boots even though it could dangerously interfere with lots of drugs... but I guess so can alcohol)

These all induce enzymes, so will decrease the amount of a drug, as the induced enzymes metabolise more of the drug. They will decrease the INR, possibly below the therapeutic level, as more warfarin is being metabolised.
Worth noting that carbamazepine and phenytoin induce the enzymes that they themselves are metabolised by, so they induce their own metabolism. I think this is why you have to gradually increase the dose of them, as the more they induce the enzymes, the less of the drug you have, so you have to increase the dose. But only up to a point - not sure why that is. Maybe there is a maximum amount that the enzymes can be induced, I don't know.

Drugs metabolised by cytochrome P450 - Cow Pats
Ciclosporin (affects the immune system, used post-transplant and for psoriasis), carbamazepine (anti-epileptic), citalopram (selective serotonin reuptake inhibitor, first-line treatment for depression)
Oral contraceptive pill (contraceptive - very important!)
Warfarin (anti-coagulant)

Phenytoin (anti-epileptic) and protease inhibitors (a type of HIV drug)
Acetylcholinesterase inhibitors (eg Donepezil, used for Alzheimer's disease)
Theophylline (used for severe asthma) and tacrolimus (immune modulator, used for eczema and psoriasis, I think)
Statins (used to decrease cholesterol, particularly LDL) and steroids (used for loads of things! Auto-immune and rheumatological conditions, for example)

The only problem with this one is that you have to remember there are three Cs, two Ps, two Ts, and two Ss, which isn't reflected in the Cow Pats mnemonic.
The inclusion of warfarin in this list reflects what I said above about other drugs affecting INR. Thyroxine also affects warfarin, but maybe not through enzymes and that's why it's not on these lists.
Phenytoin and carbamazepine here, reflect what I said about enzyme induction.
Protease inhibitors here, that's why their metabolism is inhibited by ritonavir, as above.

That's all the therapeutics mnemonics I have for now! Maybe I'll have more mnemonics for something another day. Note mNEmonic, not pneumonic as Podmedics and loads of others pronounce it - these memory aids have nothing to do with air or lungs!

Apologies to the non-medics for the boring nature of this post. Normal waffley service will resume soon. Though I do like the opportunity to write a blog that contributes to the amount of work I've done today!

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