Does Duration of Nicotine Replacement Therapy Use Matter. in Quitting Smoking? A Longitudinal Study of Smokers. in the General Population

Does Duration of Nicotine Replacement Therapy Use Matter in Quitting Smoking? A Longitudinal Study of Smokers in the General Population by BO ZHANG ...
Author: Oswin McCoy
2 downloads 0 Views 981KB Size
Does Duration of Nicotine Replacement Therapy Use Matter in Quitting Smoking? A Longitudinal Study of Smokers in the General Population

by

BO ZHANG

A thesis submitted in conformity with the requirements for the degree of

Doctor of Philosophy in Epidemiology (PhD)

Dalla Lana School of Public Health The University of Toronto

© Copyright by Bo Zhang, 2013

   

Does Duration of Nicotine Replacement Therapy Use Matter in Quitting Smoking? A Longitudinal Study of Smokers in the General Population Bo Zhang Doctor of Philosophy in Epidemiology (PhD) Dalla Lana School of Public Health The University of Toronto 2013

Abstract Background and Objectives: Little is known about the impact of nicotine replacement therapy (NRT) use duration on smoking cessation in the general population. This study determines whether duration of NRT use is associated with smoking cessation. Methods: Data were from the Ontario Tobacco Survey longitudinal study of a population-based cohort of baseline smokers who made serious quit attempts during 18 months of follow-up. The association between NRT (any NRT, patches, or gum) use duration and smoking cessation outcomes (short-term abstinence ≥1 month and long-term abstinence ≥12 months) was estimated by Poisson regression, adjusting for all confounding variables. Results: Among the 1,590 eligible smokers, 933 (59%) did not use any NRT, 535 (34%) used NRT 24 hours, rather than long-term quit.

Swartz et al.65 assessed quitting outcomes (7-day and 30-day point prevalence and 6-month abstinence) among those with NRT plus counselling and those with counselling alone in smokers who registered with the Tobacco HelpLine in Maine November 2003 to January 2004 (n=535), six months after assistance. The study reported that intent-to-treat quit rates (30-day point prevalence) at 6 months were 12.3% (95% CI 8.1–17.6) for counselling alone, and 22.5% (95% CI 19.1–26.3) for counselling plus NRT, and the 6-month abstinence rates were 6.9% for counselling alone and 12.5% for counselling plus NRT. This is a descriptive study, in which there was no adjustment for differences of demographics and tobacco dependence. In addition, those who received NRT obtained more counselling service than those not receiving NRT. The study participants were not a representative sample of the general population.

Miller et al.66 assessed the smoking status of 1,305 randomly sampled NRT recipients and a nonrandomly selected comparison group of eligible smokers who, because of mailing errors, did not receive the treatment from a large-scale distribution program of free nicotine patches. The study found that at 6 months, more NRT recipients than comparison group members successfully quit smoking (7-day point prevalence) (33% vs. 6%, p6 weeks) and relapse. The study68 found that the odds of relapse were unaffected by the use of NRT for >6 weeks either with (p=0.117) or without (p=0.159) professional counselling and were highest among prior heavily dependent persons who reported NRT use for any length of time without professional counselling (OR=2.68). However the study did not use the recommended duration of 8 weeks to categorize the NRT use groups; and the commonly used forms of nicotine patches and gum were not examined separately. According to the 2009 Cochrane review,54 it appears that nicotine patches may be more effective than nicotine gum (Summary of the NRT effect in the population-based studies can be found in Appendix 1). The very common flaws in past observational studies are presented below (Table 1).

Table 1. Summary of very common flaws in the past observational studies that have investigated the association between NRT and smoking cessation Common Flaws Explanation Misclassification NRT use was measured as ever use, (e.g., recall bias) for the last quit attempt, and for the most recent quit attempt in the last year. Those who quit long time ago might not be able to recall NRT use. Even for those who tried to quit in the last year might not recall NRT use for a very short period of NRT use. Those who had serious side effects and discontinued use of NRT might be able to recall NRT use.

Selection bias

1) Studies failing to detect a longterm NRT benefit may be explained at least partly by self-selection of NRT use, if NRT is used by more failure-prone smokers; 2) On the other hand, participants who are highly motivated to be helped are more likely to quit smoking among studies that use nonrepresentative samples, especially in free NRT programs.

   

Potential effect on the outcome If those who used NRT and quit but did not recall use of NRT, the association between NRT use and smoking cessation would be attenuated toward null. If more people with side effects from NRT use could recall NRT use than those who used NRT and quit without side effects, the association between NRT use and smoking cessation would be attenuated too. Among NRT users, if more people who quit could recall of NRT use than those who did not quit, the association between NRT use and smoking cessation would be moved away from null (i.e., higher smoking cessation rate in NRT users than non-users). 1) The association between NRT use and cessation would be attenuated toward null.

2) Those who use NRT to quit smoking with high expectation and motivation are more likely to have a higher likelihood to quit than those with low expectation and motivation. Thus, the association between NRT use and cessation would be moved away from null.

  9    Confounding effect

Several studies included behavioural support as part of the intervention and NRT recipients were provided more behavioural support than those who did not receive NRTs. In addition, tobacco dependence is a potential confounding factor, but was not controlled for in several studies.

Generalization issue

Several studies used a nonrepresentative sample, especially among those studies providing free NRTs.

Those who used NRTs but received more behavioural support than those who did not use NRTs would overestimate the effect of NRTs on cessation, if the confounding effect of behavioural support was not controlled for. If those who used NRTs were those who had higher tobacco dependence than those who did not use NRTs, the effect of NRTs would be underestimated, if this confounding factor was not controlled for and high dependence would make quitting more difficult. Generalizability (external validity) may be questionable. Findings of the study may only reflect a unique population and therefore cannot be generalized to others. However, this is not a critical problem in studies assessing the association between NRT use and smoking cessation, because the scientific goal is to move from timeand place-specific observations to an abstract “universal” hypothesis, such as “NRT increases smoking cessation”.

1.7 Measures of Smoking Cessation in the Literature The majority of outcome measures for smoking cessation in clinical trials included in the 2009 Cochrane review54 was continuous or sustained abstinence at 12 months (n=64, including two studies counted as four trials), followed by continuous or sustained abstinence at 6 months (n=15), point prevalence at 6 months (n=15) and at 12 months (n=13), undefined abstinence at 6 months (n=7) and at 12 months (n=8), and others (e.g., prolonged abstinence at 6 or 12 months, sustained abstinence at 2 years). The majority of the cessation outcomes were validated with expired CO (n = 99), others by plasma thiocyanate, independent observers, cotinine, blood carboxyhemoglobin, and non-validation (n=10).

In general population studies, outcome measures consisted of unclearly defined, point prevalence abstinence (7 or 30 days), quit attempt (≥24 hrs), abstinence at 3 and 6 months, and sustained abstinence at 52 weeks. Only one study used CO validation. The outcome measures for smoking cessation are summarized in the table below (Table 2).    

  10   

Table 2. Outcome measures of smoking cessation in the literature Study type Clinical trials

Cross sectional study Cohort study

Outcome measure Abstinence† (>1 wk or not defined) at 6m,69-75 12m,76-83 and 13m84 Continuous or sustained abstinence‡ at 5m,85 6m,86, 87 88-100 10.5m,101 12m102-110 111-160,161-163 (up to 3 cigs/wk allowed in 3 studies,86, 163, 164 or lapse-free), 13m,165 and 2 yr166 Point prevalence (PP) abstinence§ (7day or not stated) at 6m (incl. 26wks),167-181 36wks,182 12m,183-195 and 16m196 Prolonged abstinence# at 6m197, 198and 12m199 Quitters at interview (not clearly defined), cessation attempts (≥ 1 day), and duration of cessation (last date of regular smoking to the date of interview)63, 64 Quitters (not clearly defined),61 sustained cessation at 52 wks,62 7d, 30d, and continuous abstinence at 6m,65 successful quit attempt (≥24h) and 7d point prevalence abstinence,66 and abstinence for 3m and 6m67

Validation etc. Carbon monoxide (CO), plasma thiocyanate, or no validation CO

Suggest Documents