Rheological Behavior of Carbopol® 981 in Intravenous Drug Abuse

Nova Southeastern University, Davie, Florida, USA

Objective. Examine the rheological properties of Carbopol 981 in different solvents, varying in polarity and ionic strength, under different shear rates to assess the polymer’s intravenous extraction-resistant capacity. Background. Carbopol 981 is a carbomer homopolymer with wide pharmaceutical applications. Upon neutralization, the polymer forms viscous gels, resisting the withdrawal of opioid drug solutions into a syringe. This in turn deters drug abuse by injection. In this study, we evaluated the rheological behavior of the neutralized polymer under different chemical and physical conditions of drug IV abuse. Methods. 0.5% w/v Carbopol 981 solutions were prepared in water, normal saline, and 40% v/v ethanol. The mixtures were neutralized using NaOH to pH 6–7. A cone & plate rheometer was used to measure the rheological properties of the prepared solutions (Brookfield DV-III Ultra, spindle 2.4 cm, 25°C). The viscosity versus shear rate rheograms were obtained and compared among the different solvents. Results. Viscous solutions were obtained in water and 40% ethanol, while the viscosity of the polymer in normal saline was minimal. The carbomer exhibited a shear thinning behavior in all the solutions, where the viscosity was significantly reduced from 1318 to 140 cP in water, from 253 to 33 cP in saline, and from 2314 to 140 cP in the alcoholic solution over the shear rate of 37-1537 sec-1 . Conclusion. Carbopol 981 produces abuse-deterrent viscous gels in non-ionic solvents, however its deterrent properties is adversely affected under shear and in the presence of ions. Grants. NSU PFRDFG Grant 335081