Drug name Nature of interaction with Clinical Advise to patient smoking relevance (BNF category) Warfarin Warfarin is partly metabolised Moderate Advise patient that smoking via CYP1A2 however an cessation may cause a slight (2.8.2) interaction with smoking is not increase in INR and they should clinically relevant in most monitor their INR more closely – patients Clients need to ensure they do not miss their routine blood testing and to tell their GP that they are stopping smoking Theophylline Theophylline is metabolised High Advise patients to have a blood principally via CYP1A2. test when they stop smoking as (3.1.3) Smokers need higher doses of their plasma theophylline theophylline than concentrations may change and smokers due to theophylline’s their dose may require reducing shortened half-life and by about one quarter to one third increased elimination. Some one week after withdrawal. reports suggest may However, it may take several need twice the dose of weeks for enzyme induction to smokers. dissipate. Advise patients to have their theophylline concentration checked periodically. Advise the patient to seek help if they develop of theophylline toxicity such as palpitations or nausea. Chlorpromazine Chlorpromazine is Moderate Advise patient to be alert for metabolised principally via increased adverse effects of (4.2.1) CYP1A2. Smokers have lower chlorpromazine (e.g. dizziness, serum levels of sedation, extra-pyramidal chlorpromazine compared symptoms) when they stop with non-smokers. smoking. Advise patient to see GP if this occurs to review/reduce dose Clozapine Clozapine is metabolised High Advise patients that smoking principally via CYP1A2 and cessation may alter their (4.2.1) clearance is increased in response to clozapine and they Serum clozapine may need additional blood levels are reduced in smokers monitoring they need to – compared with non-smokers; ensure they do not miss their smokers may need higher blood testing. doses. Date and prescriber details to be documented. Advise patient that their blood should be monitored before they stop smoking and one or two weeks after having stopped. Their dose may need reducing
Drug name (BNF category) Nature of interaction with smoking Clinical relevance Advise to patient Warfarin (2.8.2) Warfarin is partly metabolised via CYP1A2 however an interaction with smoking is not clinically relevant in most patients Moderate Advise patient that smoking cessation may cause a slight increase in INR and they should monitor their INR more closely – Clients need to ensure they do not miss their routine blood testing and to tell their GP that they are stopping smoking Theophylline (3.1.3) Theophylline is metabolised principally via CYP1A2. Smokers need higher doses of theophylline than due to theophylline’s shortened half-life and increased elimination. Some reports suggest smokers may need twice the dose of High Advise patients to have a blood test when they stop smoking as their plasma theophylline concentrations may change and their dose may require reducing by about one quarter to one third one week after withdrawal. However, it may take several weeks for enzyme induction to dissipate. Advise patients to have their theophylline concentration checked periodically. Advise the patient to seek help if they develop of theophylline toxicity such as palpitations or nausea. Chlorpromazine (4.2.1) Chlorpromazine is metabolised principally via CYP1A2. Smokers have lower serum levels of chlorpromazine compared with non-smokers. Moderate Advise patient to be alert for increased adverse effects of chlorpromazine (e.g. dizziness, sedation, extra-pyramidal symptoms) when they stop smoking. Advise patient to see GP if this occurs to review/reduce dose Clozapine (4.2.1) Clozapine is metabolised principally via CYP1A2 and clearance is increased in smokers. Serum clozapine levels are reduced in smokers compared with non-smokers; smokers may need higher doses. High Advise patients that smoking cessation may alter their response to clozapine and they may need additional blood monitoring – they need to ensure they do not miss their blood testing. Date and prescriber details to be documented. Advise patient that their blood should be monitored before they stop smoking and one or two weeks after having stopped. Their dose may need reducing