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Clinical guidelines

Supporting smoking cessationA guide for health professionals

Appendix 3

Effect of smoking abstinence on medications

Smoking tobacco can alter the metabolism of a number of medicines. This is primarily due to substances in tobacco smoke, such as hydrocarbons or tar-like products that cause induction (speeding up) of some liver enzymes (CYP 1A2, in particular). Therefore, medicines metabolised by these enzymes are broken down faster and can result in reduced concentrations in the blood (see table below). When a person stops smoking, the enzyme activity returns to normal (slows down), which may result in increased levels of these medicines in the blood. Monitoring and dosage reduction may often be required.

Smoking affects the following medications
MedicationEffect of smoking
Caffeine Increased clearance (by 56%)
Chlorpromazine Decreased serum concentrations (by 24%)
Clozapine Decreased plasma concentrations (by 50%)
Olanzepine Decreased plasma concentrations (by 30%)
Estradiol Possibly anti-estrogenic effects
Flecainide Increased clearance (by 61%)
Fluvoxamine Decreased plasma concentrations (by 47%)
Haloperidol Decreased serum concentrations (by 70%)
Heparin Increased clearance
Imipramine Decreased serum concentrations
Insulin Decreased subcutaneous absorption due to poor peripheral blood flow
Lidocaine Decreased oral bioavailability
Olanzapine Increased clearance (by 30%)
Propranolol Increased oral clearance (by 77%)
Theophylline Increased metabolic clearance (by 58 to 100%); within 7 days of smoking cessation, theophylline clearance falls by 35%
Warfarin Decreased plasma concentrations (by 13%). No effect on prothrombin time
Stopping smoking can result in the opposite of the effects noted above.
Healthcare workers should be aware of the potential for increased blood levels of some of these medicines when smoking is stopped. Blood levels of some (eg. clozapine, olanzapine, theophyline) may need to be monitored.

Used with permission from: Ministry of Health. New Zealand Smoking Cessation Guidelines. Wellington: Ministry of Health. 2007

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