P450 enzyme system

Induction usually requires prolonged exposure to the inducing drug, as opposed to P450 inhibitors, where effects are often seen rapidly

Inducers of the P450 system include "CRAP GPS"

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CRAP GPS induces my rage!

Carbamazepine Rifampicin Alcohol (chronic) Phenytoin, topiramate

Griseofulvin Phenobarbitone St. John’s Wort, Sulfonylurea, smoking

my RAage (topiRAmate)

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smoking affects CYP1A2, reason why smokers require more aminophylline)

Hypericum perforatum, commonly known as St John's Wort is a plant frequently used in alternative medicine, particularly for the management of depression. Although its use remains controversial multiple studies have indicated it may have superiority over placebo on treating mild to moderate depression, with the active ingredients thought to be hypericin and hyperforin.

Overview

• shown to be as effective as tricyclic antidepressants in the treatment of mild-moderate depression
• mechanism: thought to be similar to SSRIs (although noradrenaline uptake inhibition has also been demonstrated)
• NICE advise 'may be of benefit in mild or moderate depression, but its use should not be prescribed or advised because of uncertainty about appropriate doses, variation in the nature of preparations, and potential serious interactions with other drugs'

Adverse effects

• profile in trials similar to placebo
• can cause serotonin syndrome (particularly if use with other antidepressants)
• inducer of P450 system, therefore decreased levels of drugs such as warfarin, ciclosporin. The effectiveness of the combined oral contraceptive pill may also be reduced

Inhibitors of the P450 system “SICKFACES.COM”

This is the "gold standard" mnemonic for inhibitors. If you inhibit the liver, the patient gets "sick" because drug levels rise to toxic levels.

• S – Sodium Valproate
• I – Isoniazid
• C – Cimetidine / Ciprofloxacin