178974 Modeling longitudinal trajectories of ketamine injection among young injecting drug users

Tuesday, October 28, 2008

Stephen E. Lankenau, PhD , Department of Pediatrics, University of Southern California, Hollywood, CA
Jennifer Jackson Bloom, MPH , Division of Research on Children, Youth and Families, Childrens Hospital Los Angeles, Hollywood, CA
Bill Sanders, PhD , Department of Pediatrics, University of Southern California, Hollywood, CA
Dodi Hathazi, BS , Division of Research on Children, Youth and Families, Childrens Hospital Los Angeles, Hollywood, CA
Background: No previous studies have modeled trajectories of ketamine injection longitudinally, which may offer important insights into patterns of cessation and continuation. Methods: A sample of 68 young ketamine injecting drug users (IDUs) – aged 16 to 29 - was interviewed about ketamine injection every three to four months over a two-year period. Longitudinal models of ketamine injection were developed using Proc Traj (SAS). Trajectories of ketamine injection frequency were illustrated using a censored normal model of standardized rates of use at each follow-up. Trajectories of ketamine injection likelihood were illustrated using a logistic model of use (yes/no) at each follow-up. Findings: Approximately 50% did not inject ketamine at any follow-up. A censored normal model indicated that 42.5% followed a flat linear, low-use trajectory – injecting ketamine approximately once per year during follow-up, while 7.8% followed a declining linear, high-to-low use trajectory – decreasing ketamine injection from a mean rate of once per month to once per year. A logistic model revealed that 33.9% – nearly all injected ketamine in the year prior to first interview - had a 50% likelihood of injecting ketamine at each follow-up (declining linear trajectory) while 16.3% - none injected ketamine in the year prior to first interview – increased to a 10% likelihood of injecting ketamine at each follow up (slightly increasing linear trajectory). Co-variates, including gender and homeless status, improved model fit but were not statistically significant. Conclusions: Longitudinal models indicated that most IDUs ceased ketamine injection or injected sporadically, while frequent injectors decreased use during the study.

Learning Objectives:
1) Describe different patterns of ketamine use among young IDUs. 2) Discuss particular techniques for modeling ketamine injection. 3) Understand the utility of longitudinal studies for researching young IDUs.

Keywords: Drug Injectors, Methodology

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: I am the principal investigator of the study described in the abstract.
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.