Therefore, if you inhibit the enzyme that metabolises them, you will decrease the plasma concentration of the active compound, and thus not get enough pain relief or enough antiplatelet effect. codeine (into morphine), and clopidogrel. It's also important to know that some drugs are activated by CYP450 enzymes too, e.g. Counselling point for simvastatin: avoid grapefruit and grapefruit juice altogether. This has caused the plasma simvastatin concentration to increase with successive dosing, causing myopathy (unexplained muscle pains). Simvastatin is metabolised into an inactive compound by CYP3A4, which is inhibited by grapefruit (juice and whole fruit). He starts to get muscle pains (without any obvious causes).

The best thing to do, again, would be to dose the warfarin according to INR, if this antibiotic is essential - if not, try and find a suitable alternative that won't interact with warfarin.*Īnother example: a patient is on simvastatin, and drinks a glass of grapefruit juice with breakfast every morning.

This will lead to an increased risk of side effects, e.g.

erythromycin, will inhibit the production of the enzyme CYP2C19, meaning that warfarin will be metabolised very slowly, so its plasma concentration will increase with successive dosing, and hence the INR will increase. The easiest thing to do would probably be to increase the dose of warfarin whilst the patient is on rifampicin (dose according to INR) and keep a close eye on the INR and potential side effects of warfarin, like haemorrhage.Īn inhibitor of the enzyme, e.g. This will mean that the patient will be at an increased risk of DVT, PE etc. This means that the plasma concentration of warfarin will decrease, meaning that the INR will decrease (as the anticoagulant effect of warfarin is lessened). warfarin is metabolised (into an inactive compound) by this enzyme, then warfarin will be metabolised more quickly under the influence of rifampicin. rifampicin = a drug that stimulates the production of a CYP450 enzyme, e.g. P450 inducers stimulate metabolism, say for example they are co-administered with warfarin, does this mean that they will make warfarin less potent and increase the risk of DVT? Hello, I hope you wont mind clarifying this for me please

Doctors in training cyp450 inducer