Fig. 2. Release rate of the Chronogesic™ Sufentanil Pain Therapy system is shown; these units are designed to deliver sufentanil at a rate of ∼ 25 μg/h for more than 90 days. To estimate the release rate, implants are placed in a physiologic buffer solution at 37°C and samples are obtained at periodic intervals to quantify the sufentanil released. After an initial startup period, sufentanil release is constant until formulation is exhausted from the reservoir. Each line represents the release rate of an individual unit (n = 6). In clinical practice, the implant will be removed or replaced at 90 days, ensuring constant delivery of sufentanil throughout the treatment cycle.