Mr Isoniazid is sitting at a cafe playing cards over a bottle of wine and a Guinness with his best pal Dave. Dave is taking oestrogens because he wanted a pair of breasts to complement his favourite mushroom hat, and Mr Isoniazid recently bought a plastic halo that he wears on a stick above his […]
Isotretinoin Steroids Lithium Tetracyclines Levothyroxine Combined oral contraceptive Cimetidine
Lithium is an interesting drug with some important side effects. It’s one of those drugs that has a very narrow therapeutic window (0.4-1.0mmol/L) and above 1.5mmol/L you’re at significant risk of developing toxicity. It’s used primarily as a mood stabiliser in conditions such as Bipolar disorder and refractory depression, and it is important to […]
Which common drugs inhibit CYP450 enzymes and which induce them?
Here’s a couple of stories to help remember them – it’s by no means a comprehensive list, but should highlight the common drugs to remember.
Inducers – Mr Rifampicin
Mr Rifampicin tries St John’s Wort for the first time, which causes him to have two seizures.
He then rolls over and gets caught in barbed wire, where he proceeds to stay, and passes the time by having a long drinking session.
A wandering grizzly bear then mauls him to death.
- St John’s Wort
- Phenytoin, Carbamazepine
- Chronic alcohol use
- (also smoking, but via CYP1A2)
Inhibitors – Mrs Isoniazid
Mrs Isoniazid rolls in the New Year with a whopper of a booze binge.
This sets off her gout and causes her to vomit twice.
This then makes her feel depressed, despite the two antidepressants that she’s taking, and gives her palpitations.
She attempts to remedy the situation by having unprotected sex, which gives her HIV and a nasty infection.
She’s prescribed four separate antibiotics and two antifungals to clear everything up.
- Acute alcohol use
- Cimetidine, Omeprazole
- Fluoxetine, Sertraline
Just remember than in questions they’ll often ask something like, “which of the following drugs would increase a warfarin patient’s INR” – an increased INR implies the enzymes have been inhibited so you need to think about the inhibitors…
Don’t get fooled!
How to remember the DMARDS commonly used in rheumatoid disease?
There’s a special place, where all of the people suffering from crippling rheumatoid arthritis can go for treatment. It’s a huge golden pyramid with a log flume running down from the top.
- Leflunemide (pyrimidine synthesis inhibitor)
- pyramid also describes the therapeutic pyramid of drugs in rheumatoid arthritis
At the top is a meth addict with spina bifida who tells you when you can ride the flume. He shouts go, and turns on a huge hydro-chlorine hose that fires you down the chute. The chlorine is to keep the mosquitos away.
- Methotrexate (folate antagonist)
- Hydroxychloroquine (antimalarial)
At the bottom you land in a huge pit full of aspirin pills that stink of sulphur, each of which is the same size as a thigh of pure chicken.
- Sulfasalazine (5-ASA salicylate)
- Azathioprine (purine analogue)
It’s a suitably weird story, feel free to make up your own….