Use of refractometers to detect controlled-substance tampering

Hospital pharmacies presently lack a simple and cost-effective procedure to monitor the integrity of solutions of controlled substances that they distribute. Thus, the use of refractive-index values, measured by inexpensive hand-held refractometers, in monitoring such solutions was studied. Four refractometers were used to measure the refractive index or % Brix (an index of the percentage of solid in solution) of solutions of a number of controlled substances, including fentanyl citrate, morphine sulfate, hydromorphone hydrochloride, and meperidine hydrochloride. The hand-held refractometers provided precise readings with small variabilities. Although this method does not determine the actual drug concentration per se, subversion of the monitoring procedure for many solutions would require considerable forethought and scientific knowledge. A refractometric survey of 83 controlled-substance solutions returned to the hospital pharmacy showed the procedure to be capable of identifying a solution of unexpected concentration. The described refractometric procedure is rapid, simple, reproducible, inexpensive, and applicable to a wide array of drug solutions. Hospital pharmacies may consider using the procedure for routine monitoring of solutions of controlled substances.