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Biomedical subjects

Steven Shoptaw

Publications and source records attributed to Steven Shoptaw.

At least 19 recordsLinked to original sources
PubMed2007

A random-effects Markov transition model for Poisson-distributed repeated measures with non-ignorable missing values.

In biomedical research with longitudinal designs, missing values due to intermittent non-response or premature withdrawal are usually 'non-ignorable' in the sense that unobserved values are related to the patterns of missingness. By drawing the framework of a shared-parameter mechanism, the process yielding the repeated count measures and the process yielding missing values can be modelled separately, conditionally on a group of shared parameters. For chronic diseases, Markov transition models can be used to study the transitional features of the pathologic processes. In this paper, Markov Chain Monte Carlo algorithms are developed to fit a random-effects Markov transition model for incomplete count repeated measures, within which random effects are shared by the counting process and the missing-data mechanism. Assuming a Poisson distribution for the count measures, the transition probabilities are estimated using a Poisson regression model. The missingness mechanism is modelled with a multinomial-logit regression to calculate the transition probabilities of the missingness indicators. The method is demonstrated using both simulated data sets and a practical data set from a smoking cessation clinical trial.

Algorithms↗
PubMed2007

Functional regression analysis using an F test for longitudinal data with large numbers of repeated measures.

Longitudinal data sets from certain fields of biomedical research often consist of several variables repeatedly measured on each subject yielding a large number of observations. This characteristic complicates the use of traditional longitudinal modelling strategies, which were primarily developed for studies with a relatively small number of repeated measures per subject. An innovative way to model such 'wide' data is to apply functional regression analysis, an emerging statistical approach in which observations of the same subject are viewed as a sample from a functional space. Shen and Faraway introduced an F test for linear models with functional responses. This paper illustrates how to apply this F test and functional regression analysis to the setting of longitudinal data. A smoking cessation study for methadone-maintained tobacco smokers is analysed for demonstration. In estimating the treatment effects, the functional regression analysis provides meaningful clinical interpretations, and the functional F test provides consistent results supported by a mixed-effects linear regression model. A simulation study is also conducted under the condition of the smoking data to investigate the statistical power for the F test, Wilks' likelihood ratio test, and the linear mixed-effects model using AIC.

Behavior Therapy↗
PubMed2006

A public health response to the methamphetamine epidemic: the implementation of contingency management to treat methamphetamine dependence.

BACKGROUND: In response to increases in methamphatemine-associated sexually transmitted diseases, the San Francisco Department of Public Health implemented a contingency management (CM) field program called the Positive Reinforcement Opportunity Project (PROP). METHODS: Methamphetamine-using men who have sex with men (MSM) in San Francisco qualified for PROP following expressed interest in the program, provision of an observed urine sample that tested positive for methamphetamine metabolites and self-report of recent methamphetamine use. For 12 weeks, PROP participants provided observed urine samples on Mondays, Wednesdays and Fridays and received vouchers of increasing value for each consecutive sample that tested negative to metabolites of methamphetamine. Vouchers were exchanged for goods and services that promoted a healthy lifestyle. No cash was provided. Primary outcomes included acceptability (number of enrollments/time), impact (clinical response to treatment and cost-effectiveness as cost per patient treated). RESULTS: Enrollment in PROP was brisk indicating its acceptability. During the first 10 months of operation, 143 men sought treatment and of these 77.6% were HIV-infected. Of those screened, 111 began CM treatment and averaged 15 (42%) methamphetamine-free urine samples out of a possible 36 samples during the 12-week treatment period; 60% completed 4 weeks of treatment; 48% 8 weeks and 30% 12 weeks. Across all participants, an average of $159 (SD = $165) in vouchers or 35.1% of the maximum possible ($453) was provided for these participants. The average cost per participant of the 143 treated was $800. CONCLUSION: Clinical responses to CM in PROP were similar to CM delivered in drug treatment programs, supporting the adaptability and effectiveness of CM to non-traditional drug treatment settings. Costs were reasonable and less than or comparable to other methamphetamine outpatient treatment programs. Further expansion of programs like PROP could address the increasing need for acceptable, feasible and cost-effective methamphetamine treatment in this group with exceptionally high rates of HIV-infection.

Adolescent↗
PubMed2006

Hepatitis C virus infection among methamphetamine-dependent individuals in outpatient treatment.

Research on the relationship between illicit drug use and infectious diseases have primarily focused on the major problem of heroin injection and HIV transmission. Over the past decade, however, research have shown that rates of hepatitis C infection among injection drug users have surpassed those of HIV infection. There has been little systematic study on the relationship between hepatitis C virus (HCV) and the role of methamphetamine (MA) use in the transmission of the virus. This study examined the prevalence of hepatitis C infection among a sample of 723 MA-dependent individuals who sought outpatient treatment from 1999 through 2005. Roughly 15% of the total sample and 44% of the injectors were found to be infected with HCV. Controlling for participant characteristics, we found through multiple logistic regression analyses that HCV infection was more associated with injection use, older age, and female sex. Findings suggest a need for targeted education and prevention efforts about hepatitis C among high-risk MA users, including HCV testing coupled with referrals to HCV treatments.

Adult↗
PubMed2006

Randomized, placebo-controlled trial of baclofen and gabapentin for the treatment of methamphetamine dependence.

OBJECTIVE: To conduct a 16-week, randomized, placebo-controlled, double-blind trial of two GABAergic medications, baclofen (20 mg tid) and gabapentin (800 mg tid), for the treatment of methamphetamine dependence. METHODS: Adults with methamphetamine dependence were randomized to one of three conditions for 16 weeks: baclofen (n = 25), gabapentin (n = 26) or placebo (n = 37). All participants attended clinic thrice weekly to receive study medication and psychosocial counseling, complete study assessments, and provide urine samples. RESULTS: No statistically significant main effects for baclofen or gabapentin in reducing methamphetamine use were observed using a generalized estimating equation (GEE). A significant treatment effect was found in post hoc analyses for baclofen, but not gabapentin, relative to placebo among participants who reported taking a higher percentage of study medication (significant treatment group and medication adherence interaction in GEE model of methamphetamine use). CONCLUSIONS: While gabapentin does not appear to be effective in treating methamphetamine dependence, baclofen may have a small treatment effect relative to placebo. Future studies evaluating the effectiveness of baclofen and other GABAergic agents for treatment of methamphetamine may be warranted.

Adult↗
PubMed2006

Randomized, placebo-controlled trial of sertraline and contingency management for the treatment of methamphetamine dependence.

BACKGROUND: Methamphetamine dependence and associated medical and psychiatric concerns are significant public health issues. This project evaluated the efficacy of sertraline (50mg bid) and contingency management (CM) for the treatment of methamphetamine dependence. METHOD: In this randomized, placebo-controlled, double-blind trial, participants completed a 2-week non-medication baseline and were randomized to one of four conditions for 12 weeks: sertraline plus CM (n=61), sertraline-only (n=59), matching placebo plus CM (n=54), or matching placebo-only (n=55). All participants attended clinic thrice-weekly for data collection, medication dispensing, and relapse prevention groups. Outcomes included methamphetamine use (urine drug screening and self-reported days of use), retention (length of stay), drug craving (visual analogue scale), and mood symptoms (Beck Depression Inventory). RESULTS: No statistically significant main or interaction effects for sertraline or CM in reducing methamphetamine use were observed using a generalized estimating equation (GEE), although post hoc analyses showed the sertraline-only condition had significantly poorer retention than other conditions (chi(2) (3)=8.40, p<0.05). Sertraline conditions produced significantly more adverse events than placebo conditions. A significantly higher proportion of participants in CM conditions achieved three consecutive weeks of methamphetamine abstinence than those in non-CM conditions. CONCLUSIONS: These data do not demonstrate improved outcomes for sertraline versus placebo for treatment of methamphetamine dependence; indeed, they suggest sertraline is contraindicated for methamphetamine dependence. Findings provide support for the use of contingency management for treatment of methamphetamine dependence.

Adult↗
PubMed2006

Associations between methamphetamine use and HIV among men who have sex with men: a model for guiding public policy.

Among men who have sex with men (MSM) in Los Angeles County, methamphetamine use is associated with high rates of HIV prevalence and sexual risk behaviors. In four separate samples of MSM who differed in the range of their intensity of methamphetamine use, from levels of recreational use to chronic use to those for MSM seeking drug abuse treatment, the association between methamphetamine use and HIV infection increased as the intensity of use increased. The lowest HIV prevalence rate (23%) was observed among MSM contacted through street outreach who mentioned recent methamphetamine use, followed by MSM who used at least once a month for six months (42%), followed by MSM seeking intensive outpatient treatment (61%). The highest rate (86%) was observed among MSM seeking residential treatment for methamphetamine dependence. The interleaving nature of these epidemics calls for comprehensive strategies that address methamphetamine use and concomitant sexual behaviors that increase risk of HIV transmission in this group already at high risk. These and other data suggest that MSM who infrequently use methamphetamine may respond to lower intensity/lower cost prevention and early intervention programs while those who use the drug at dependence levels may benefit from high intensity treatment to achieve goals of reduced drug use and HIV-risk sexual behaviors.

Amphetamine-Related Disorders↗
PubMed2006

A comparison of contingency management and cognitive-behavioral approaches for stimulant-dependent individuals.

AIMS: Previous research has reported that both contingency management (CM) and cognitive-behavioral therapy (CBT) are efficacious interventions for the treatment of stimulant abusers. The present study sought to directly compare the effectiveness of (CM) and (CBT) alone and in combination in reducing stimulant use. DESIGN: Randomized clinical trial. PARTICIPANTS: Stimulant-dependent individuals (n = 171). INTERVENTION: CM, CBT or combined CM and CBT, 16-week treatment conditions. CM condition participants received vouchers for stimulant-free urine samples. CBT condition participants attended three 90-minute group sessions each week. MEASUREMENTS: Participants were interviewed at baseline and weeks 17, 26 and 52. Measures included psychiatric disorders and alcohol and drug use and concomitant social problems. FINDINGS: CM procedures produced better retention and lower rates of stimulant use during the study period. Self-reported stimulant use was reduced from baseline levels at all follow-up points for all groups and urinalysis data did not differ between groups at follow-up. While CM produced robust evidence of efficacy during treatment application, CBT produced comparable longer-term outcomes. There was no evidence of an additive effect when the two treatments were combined. CONCLUSIONS: This study suggests that CM is an efficacious treatment for reducing stimulant use and is superior during treatment to a CBT approach. CM is useful in engaging substance abusers, retaining them in treatment and helping them achieve abstinence from stimulant use. CBT also reduces drug use from baseline levels and produces comparable outcomes on all measures at follow-up.

Adult↗
PubMed2005

Assessing missing data assumptions in longitudinal studies: an example using a smoking cessation trial.

Due to the chaotic nature of the clinical disorder, longitudinal data analysis in substance abuse research is plagued by missing values. To obtain an unbiased estimation on intervention effects, different longitudinal modeling strategies require various assumptions on the patterns and mechanisms of missing data. By defining missingness as intermittent missingness (occasional omission) and dropout (premature withdrawal), this article demonstrates statistical ways for assessing missing data assumptions using evidence from a clinical trial. Within the framework of multiple imputation, intermittent missing data are imputed first so that dropouts can be isolated and treated specifically. A computational tool called "pattern reduction resampling" is proposed to simplify missing data methods when the number of intra-subject repeated measures is large. To test whether missingness patterns are nondifferential across treatment conditions, a formal testing approach treats indicators of missingness as a special type of repeated measures (e.g., 0: intermittent missing, 1: observed, and 2: dropout missing). After reviewing the idea of ignorability for missing data and of classifying missingness mechanisms into subcategories, the article provides an example for assessing common assumptions on missingness mechanisms and how these assumptions affect model selection for significance testing. A carbon monoxide longitudinal data set in a smoking cessation study is used for illustration.

Bias↗
PubMed2005

Sustained reductions in drug use and depression symptoms from treatment for drug abuse in methamphetamine-dependent gay and bisexual men.

Methamphetamine abusers often complain of feelings of depression that can complicate accurately diagnosing these individuals during treatments for methamphetamine abuse. This article presents an examination of temporal associations between documented methamphetamine use and reported ratings of depression among 162 gay and bisexual male methamphetamine abusers who participated in a 16-week randomized clinical trial of four behavioral therapies for methamphetamine abuse. Methamphetamine use was measured using thrice-weekly urine samples analyzed for drug metabolite. Self-reported depressive symptoms were collected weekly using the Beck Depression Inventory (BDI). At treatment entry, 73.2% of participants rated their depressive symptoms as mild or higher in severity (BDI>or=10), with 28.5% reporting BDI scores in the moderate to severe range (BDI>or=19). All participants reported significant decreases in depressive symptoms from baseline through the end of treatment, regardless of treatment condition, HIV status, or mood disorder diagnosis. A mixed regression model showed methamphetamine use for up to 5 days prior to the BDI score strongly predicted depressive symptoms (F1, 968=18.6, P<.0001), while BDI scores had no significant association with subsequent methamphetamine use. Findings show that behavioral methamphetamine abuse treatment yields reductions in methamphetamine use and concomitant depressive symptom ratings that are sustained to 1 year after treatment entry.

Adolescent↗
PubMed2005

Recruiting drug-using men who have sex with men into behavioral interventions: a two-stage approach.

Drug-using men who have sex with men (MSM) are at high risk of acquiring or transmitting HIV infection. Efforts to change behaviors in this population have been hampered by difficulties in recruiting drug-using MSM into behavioral interventions. This study sought to develop an effective strategy for recruiting drug-using MSM into behavioral interventions that consist of motivational interviewing alone or motivational interviewing plus contingency management. MSM were recruited through advertising and community outreach into groups to discuss party drugs, party burnout, and sexual behavior, with the intervention subsequently described and enrollment offered in the group setting. Many more eligible MSM responded to advertisements for the discussion groups than advertisements for the interventions, and 58% of those who participated in the discussion groups volunteered for counseling. Men who entered counseling reported high levels of drug use and sexual activity and were racially and ethnically diverse; only 35% were willing to accept drug treatment. Results demonstrate that a two-stage strategy in which drug-using MSM are first recruited into discussion groups before they are offered a behavioral intervention can be an effective way to induce voluntary acceptance of an intervention employing a behavioral risk-reduction approach.

Adolescent↗
PubMed2005

The methamphetamine epidemic: implications for HIV prevention and treatment.

Methamphetamine and related amphetamine compounds are among the most commonly used illicit drugs, with over 35 million users worldwide. In the United States, admissions for methamphetamine treatment have increased dramatically over the past 10 years. Methamphetamine use is prevalent among persons with HIV infection and persons at risk for HIV, particularly among men who have sex with men. In addition to being associated with increased sexual risk behavior, methamphetamine causes significant medical morbidity, including neurologic deficits, cardiovascular compromise, dental decay, and skin infections, all of which may be worsened in the presence of HIV/AIDS. Methamphetamine use may also result in decreased medication adherence, particularly during "binging" episodes. Behavioral counseling remains the standard of treatment for methamphetamine dependence, although the effectiveness of most counseling interventions has not been rigorously tested. Pharmacologic and structural interventions may prove valuable additional interventions to reduce methamphetamine use.

Amphetamine-Related Disorders↗
PubMed2005

Randomized controlled pilot trial of cabergoline, hydergine and levodopa/carbidopa: Los Angeles Cocaine Rapid Efficacy Screening Trial (CREST).

AIM: This study tested three dopaminergic medications against a common unmatched placebo condition: hydergine 1 mg three times daily (n = 15); levodopa/carbidopa 25/100 mg three times daily (n = 15); cabergoline 0.5 mg per week (n = 15); and placebo three times daily (n = 15) as potential pharmacotherapies for cocaine dependence. DESIGN: The four-parallel group, Cocaine Rapid Efficacy Screening Trial (CREST) design featured a 2-week baseline period followed by randomization to an 8-week medication condition that included 1 hour per week of cognitive behavioral drug counseling. A safety evaluation was conducted 4 weeks after termination. MEASURES: Outcomes included cocaine metabolites measured in urine, retention and self-reports for drug use, cocaine craving, clinical improvement, mood and HIV risk behaviors. RESULTS: Participants assigned to receive cabergoline provided more urine samples negative for cocaine metabolites (42.4%) than those assigned to receive placebo (25.0%), a statistically significant difference after controlling for baseline differences in self-reported cocaine use (F = 2.95, df = 3; P = 0.05). Cabergoline-treated participants demonstrated a significant improvement over placebo from baseline to week 8 when measured using the Addiction Severity Index (ASI) employment subscale (overall change = - 0.09, SD = 0.10, t = 2.36, P < 0.05). Safety and adverse event measures showed similar rates and types of complaints by treatment condition. CONCLUSIONS: These results, combined with the apparent safety of cabergoline when used with this population, provide empirical support for conducting a larger study of the medication.

Adult↗
PubMed2005

HIV-associated medical, behavioral, and psychiatric characteristics of treatment-seeking, methamphetamine-dependent men who have sex with men.

This paper examines medical and psychiatric symptoms and disorders associated with reported HIV serostatus among methamphetamine-dependent, treatment-seeking men who have sex with men (MSM) in Los Angeles. Baseline data from a NIDA-funded, randomized clinical trial of behavioral drug abuse therapies included medical examinations and behavioral interviews of the 162 randomized participants. Variables identified as significantly associated with HIV infection were entered into a multivariate, hierarchical logistic regression analysis to optimally predict HIV serostatus. The disturbingly high 61% of the sample with reported HIV-seropositive status represents 3-4 times the prevalence for all MSM in Los Angeles County. HIV infection status strongly associated with prior treatment for methamphetamine dependence; unprotected receptive anal intercourse; history of sexually transmitted infections; and health insurance status. Findings demonstrate the powerful connection between methamphetamine dependence and HIV infection, and strongly suggest a need for development of interventions that function as both substance abuse treatment and HIV prevention for this population.

Adult↗
PubMed2004

Behavioral treatment approaches for methamphetamine dependence and HIV-related sexual risk behaviors among urban gay and bisexual men.

BACKGROUND: Methamphetamine-dependent gay and bisexual men (GBM) are at high risk for HIV transmission, largely due to drug-associated sexual risk behaviors. This project evaluated the efficacy of four behavioral drug abuse treatments for reducing methamphetamine use and sexual risk behaviors among this population. METHODS: In this randomized controlled trial, 162 methamphetamine-dependent (SCID-verified) GBM in Los Angeles County were randomly assigned to one of four treatment conditions for 16 weeks: standard cognitive behavioral therapy (CBT, n=40), contingency management (CM, n=42), combined cognitive behavioral therapy and contingency management (CBT+CM, n=40), and a culturally tailored cognitive behavioral therapy (GCBT, n=40). Stimulant use was assessed thrice-weekly during treatment using urine drug screens (48 measures). Sexual risk behaviors were monitored monthly (four measures). Follow-up assessments were conducted at 6 (80.0%) and 12 months (79.9%). RESULTS: Statistically significant differences in retention (F(3,158)=3.78, p<.02), in longest period of consecutive urine samples negative for methamphetamine metabolites (F(3,158)=11.80, p<.001), and in the Treatment Effectiveness Score were observed by condition during treatment (F(3,158)=7.35, p<.001) with post hoc analyses showing the CM and CBT+CM conditions to perform better than standard CBT. GEE modeling results showed GCBT significantly reduced unprotected receptive anal intercourse (URAI) during the first 4 weeks of treatment (X2=6.75, p<.01). During treatment between-group differences disappeared at follow-up with overall reductions in outcomes sustained to 1-year. CONCLUSIONS: Among high-risk methamphetamine-dependent GBM, drug abuse treatments produced significant reductions in methamphetamine use and sexual risk behaviors. Drug abuse treatments merit consideration as a primary HIV prevention strategy for this population.

Acquired Immunodeficiency Syndrome↗
PubMed2004

Impaired performance in a test of decision-making by opiate-dependent tobacco smokers.

This study tested whether opiate dependence, tobacco smoking, or their combination accompanied impaired performance on the gambling task (GT), which tests decision-making. GT previously detected impairments in patients with lesions of the ventromedial prefrontal cortex and in substance abusers. Four groups were matched on demographic characteristics and intelligence: methadone-maintained smokers (n = 9) and nonsmokers (n = 9), and control (i.e., not opiate-dependent) smokers (n = 9) and nonsmokers (n = 10). The Wisconsin Card Sorting Task (WCST) was administered to test whether differences in GT performance reflected generalized deficits in prefrontal cortical function. While there were no significant group differences on the WCST, groups differed significantly on GT performance (F(3,31) = 2.95, P = 0.048), controlling for depressive symptom ratings and childhood attention deficit hyperactivity disorder. Methadone-maintained smokers (but not nonsmokers) performed more poorly than either of the two control groups (P = 0.007 versus smokers; P = 0.024 versus nonsmokers). In a planned analysis of methadone-maintained subjects, smokers scored more poorly on GT than nonsmokers (F(1,18) = 5.64, P = 0.032) and had more treatment failures (67% heroin use during the last 30 days versus 20%). The findings suggest that among opiate-dependent individuals, tobacco smoking may be a marker for a more severe form of substance abuse disorder, reflecting impaired decision-making, as modeled by GT.

Adult↗
PubMed2004

Changes in the meaning of sexual risk behaviors among gay and bisexual male methamphetamine abusers before and after drug treatment.

Methamphetamine is widely used among gay and bisexual men in the West Coast of the United States, and is often used in combination with high-risk sexual activities. This study combined quantitative and qualitative research methodologies to examine sexual risk behaviors among gay and bisexual male methamphetamine abusers as they entered treatment and at 1-year follow-up evaluations. Findings from the quantitative follow-up data demonstrate that gay and bisexual men reduce sexual risk behaviors and sustain those reductions following substance abuse treatment, and qualitative data reveal the meaning of these behavior changes from the perspective of the participant. At 1-year evaluations, associated behaviors of methamphetamine use and sexual risk behaviors were lessened. Although condom use decreased slightly, participants reported fewer anonymous sexual partners, reductions in episodes of both receptive and insertive anal intercourse, and an increased sense of responsibility to disclose their HIV status. This study further demonstrates the value of coupling quantitative with qualitative data in understanding the meanings behind reductions in high-risk behaviors.

Adult↗