The association between self-reported varenicline adherence and varenicline blood levels in a sample of cancer patients receiving treatment for tobacco dependence

Abstract

IntroductionThe degree to which smokers quit successfully with varenicline is strongly associated with their adherence to the medication regimen. Thus, measuring varenicline adherence to identify smokers needing additional intervention is a priority. Few studies, however, have examined the validity of self-reported varenicline adherence, using a biological assessment of adherence as a reference. No study has examined this issue among cancer patients trying to quit smoking, who may show unique patterns of adherence given their medical comorbidity.MethodsThis study used data from 76 cancer patients who received varenicline and provided self-reported varenicline adherence data (pill count) and a blood sample to determine varenicline metabolites 4 weeks after initiating varenicline.ResultsReceiver operating characteristic (ROC) curve analyses of plasma varenicline levels showed that 4 ng/ml was the optimal cut-point for differentiating adherence with significant (p's < 0.04) area under the curve values, ranging from 0.73–0.80 for 3-day, 7-day, and 4-week self-reported pill count; specificity values ranged from 0.63–0.78 and sensitivity values ranged from 0.82–0.94. Using this cut-point, adherence was high (88%). However, plasma varenicline levels were weakly correlated with 3-day and 4-week pill count and total pill count (12 weeks) was not correlated with plasma varenicline levels. Patients with head and neck cancer, gastrointestinal cancer, and more advanced disease showed lower varenicline adherence and lower plasma varenicline.ConclusionsUsing the 4 ng/ml cut-point, this study suggests validity of short-term self-reported varenicline adherence among cancer patients undergoing tobacco dependence treatment in contrast to studies in the general population, which supported 12-week pill count.

A randomized controlled trial of 24 weeks of varenicline for tobacco use among cancer patients: Efficacy, safety, and adherence

“…A pill adherence measure represented the proportion of total dose taken over the 24 weeks (adherence: greater than or equal to 80% of 333 pills prescribed). We also collected a blood sample at week 4 among Penn participants who agreed to provide a blood sample and attended this session (N = 76) to determine varenicline plasma levels …”

“…We also collected a blood sample at week 4 among Penn participants who agreed to provide a blood sample and attended this session (N = 76) to determine varenicline plasma levels. 32 Smoking was assessed using TLFB and breath CO. 23 The primary outcomes were 7-day point prevalence abstinence at weeks 24 and 52 and a CO less than 10 ppm. 33,34 Continuous abstinence (with CO) from weeks 9 to 24 and 9 to 52 were secondary outcomes consistent with past varenicline trials.…”

“…Overall plasma varenicline levels at week 4 were 7.27 ng/mL (SD = 3.6) and did not differ across ST (6.9 ng/mL) and ET (7.6 ng/mL) ( F 1,75 = 0.85, P = 0.36). Based on the 4.0 ng/mL varenicline cut‐point, 90% of the sample were adherent and this did not differ across ST (95%) and ET (85%) ( χ 2 [1] = 2.1, P = 0.26). Using the pill count data, varenicline adherence was strongly associated with point prevalence and continuous abstinence at weeks 24 and 52 ( P 's < 0.01).…”