Our 2nd article on Smoking to help you "Stay stopped" - Interesting information highlighting adverse interaction between tobacco smoke and medications
Posted by Eamonn Brady on
Smoking Cessation Part 2
Drug interactions with smoking
Drug interactions between tobacco smoke and drugs are often underestimated by patients and clinicians alike. Tobacco smoke affects the absorption, distribution, metabolism (or elimination) of drugs thus potentially giving an altered response. Tobacco smoke accelerates the metabolism of certain drugs by inducing hepatic cytochrome P450 enzymes (primarily CYP1A2). It is believed the polycyclic aromatic hydrocarbons in tobacco smoke are responsible for the induction of cytochrome P450 rather than nicotine meaning that nicotine replacement products do not have the same degree of drug interactions
The HSE’s Brief Intervention for Smoking Cessation programme (Table 1) documents the main tobacco drug interactions with caffeine and fluvoxamine being considered the most clinically significant interactions.
Table 1:
|
Drug |
Possible Effects when giving up smoking versus when smoking |
|
Benzodiazepines (used for anxiety) |
• Decreased sedation and drowsiness. • |
|
Beta-blockers (used for fast heart rate, high blood pressure, heart failure and less often for anxiety and migraine) |
• Less effective antihypertensive (blood pressure control) and heart rate control. • |
|
Caffeine (stimulant) |
• Clearance increased by 56% so may be over 50% less effective. • |
|
Chlorpromazine (Anti-psychotic drugs used for mood disorders) |
• • Smokers may experience less sedation and hypotension (lower blood pressure) and require higher dosages than nonsmokers. |
|
Clozapine (Anti-psychotic drugs used for mood disorders) |
• Blood concentrations decreased by 28%. |
|
Flecainide (used for irregular heart rate, especially fast heart rate) |
• Clearance increased by 61%; blood levels decreased by 25%. • Smokers may require higher dosages. |
|
Fluvoxamine (Anti-depressant) |
• Clearance increased by 25%; decreased blood concentrations (47%). • Dosage modifications not routinely recommended but smokers may require higher dosages. |
|
Haloperidol (Anti-psychotic drugs used for mood disorders) |
• Clearance increased by 44%; blood concentrations decreased by 70%. |
|
Heparin (Blood thinner) |
• Mechanism unknown but increased clearance and decreased half-life observed. • Smokers may require higher dosages. |
|
Insulin (used for diabetics) |
• Insulin absorption may be decreased due to peripheral vasoconstriction (narrowing of blood vessels); smoking may cause release of endogenous substances that antagonise the effects of insulin. Smokers may require higher dosages. |
|
Olanzapine (Anti-psychotic drugs used for mood disorders) |
• Clearance increased by 40-98%. Dosage modifications not routinely recommended but smokers may require higher dosages. |
|
Opioids (propoxyphene, pentazocine)- used for severe pain |
• Decreased analgesic effect; higher dosages necessary in smokers. • Mechanism unknown. |
|
Propranolol (older beta blocker; uses described above) |
• Clearance (via side chain oxidation and glucuronidation) increased by 77%. |
|
Oral contraceptives |
• Increased risk of cardiovascular adverse effects (e.g., stroke, myocardial infarction, thromboembolism) in women who smoke and use oral contraceptives. • Risk increases with age and with heavy smoking (15 or more cigarettes per day) and is quite marked in women over age 35 years. |
|
Theophylline (used for asthma and COPD) |
• Clearance increased by 58-100%; half-life decreased by 63%. • Theophylline levels should be monitored if smoking is initiated, discontinued, or changed. • Maintenance doses are considerably higher in smokers. |
Table 1 Reference: Significant tobacco/ drug interactions (Reference: Brief Intervention for Smoking Cessation (HSE) 2012
Many of the tobacco/ drug interactions involve drugs used for mental health disorders. It is well documented that people with mental health disorders have a higher propensity to smoke so drug interactions can be more of an issue for these patients and need to be considered when patients are giving up smoking as the concentration of the drug in the blood stream may be increased. However, many of the drugs which tend to have the more significant interactions are used less frequently nowadays
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To be continued…next week
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