Inline fluid dynamics in piggyback and manifold drug delivery systems

Inline mixing characteristics of primary and secondary i.v. solutions were evaluated for the piggyback and manifold systems. Dextrose (5%) and sodium chloride (0.9%) were used as markers for the primary and secondary solutions, respectively. With a 120-mL/hr flow rate, samples (up to 180) were collected over 36 minutes to quantify the change in concentration of each marker when the primary solution was changed to the secondary solution (phase 1) and when the secondary solution was changed to the primary solution (phase 2). The relative concentration data for each marker were fitted to a Weibull mathematical model to describe the disappearance and appearance of the two solutions over time. These data were then used to calculate the volume of secondary solution that was mixed with the primary solution in phases 1 and 2. With the piggyback system, the total mixing volume was 13.5 mL, with 11.1 mL contributed by the secondary solution (phase 1). In phase 2, the total mixing volume decreased to 6.6 mL, with 2.0 mL contributed by the secondary solution. The mixing volumes for the manifold system were markedly reduced; 5.8 mL of the secondary solution became mixed with 1.9 mL of the primary solution. The total mixing volume during phase 1 was reduced from 13.5 to 5.6 mL. The mixing volumes for the primary, secondary, and total solutions in phase 2 were comparable to those with the piggyback system. The use of manual clamps or automated line closures as part of a manifold system can substantially reduce the mixing of solutions inline, compared with a piggyback system.