Enzyme inducers and Inhibitors

Question 1

What is an enzyme inducer?

Answer 1

An enzyme inducer will increase the P 450 enzyme activity and reduce the available drug concentration in the body

Question 2

What is an enzyme inhibitor?

Answer 2

An enzyme inhibitor will decrease the P 450 enzyme activity and cause an increase in drug concentration available in the body.

Question 3

List some common enzyme inhibitors

Answer 3

SAMDIJuiceFail.COM

Sodium Valporate/sulphonamides/SSRIs

Amiodarone

Macrolides

Diltiazem

Imidazoles (fluconazole, Miconazole), Isoniazid, Inhibitors (protease inhibitors)

Juice (grapefruit and cranberry)

Failures (Heart and Liver)

Ciprofloxacin

Omeprazole

Metronidazole

Inhibitors act quickly (within 24hrs)

Question 4

List some enzyme inducers

Answer 4

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Barbituates

St john’s wart

Carbamezapine (anti-epileptic)

Rifampicin/Rifabutin (abx - used for TB)

Alcohol - chronic consumption

Phenytoin (anti-epileptic)

Griseofulvin (anti-fungal)

Phenobarbitone (old-style anti-epileptic) + topiramate (AED +migrane prophylaxis)

Sulphonylureas (anti-diabetic drugs, e.g. gliclazide)

Inducers take 1-4 weeks to work

Carbamezapine and phenytoin induce their own metabolism. Therefore, must titrate up dose.

Basically all anti-epileptics are enxyme inducers, except valporate and levetiracetam

Question 5

What common drugs are metabolised by cytochrome P450?

Answer 5

4COWs & 2PATS

CCCCOW PPATTSS

• Ciclosporin
• Carbamazepine
• Citalopram
• Calcium channel blockers
• Oral Contraceptive pill
• Warfarin
• Phenytoin
• Protease inhibitors (a type of HIV drug)
• Acetylcholinesterase inhibitors (e.g. Donepezil - for alzheimers disease)
• Theophylline (used for severe asthma)
• Tacrolimus (immune modulator, used for eczema and psoriasis)
• Statins - If enxyme inhibitor, statins accumulate and lead to myopathy and rhabdomyolysis. This effect reduced in atorvastatin an eliminated pravastatin
• Steroids