The studies reported here simulated the administration of IR and LV in most patient care areas. That is, all experimental solutions were continuously exposed to ambient fluorescent light, 3 types of containers simulating different types of tubing (PVC, PAB, and glass [control]) were used, and 6 concentration combinations representing 6 treatment scenarios (Table 1) were evaluated. PABs are made of a polypropylene- polyethylene copolymer and simulate the more rigid non-diethylhexyl phthalate PVC and polyethylene tubing sets used for administration of some drugs.

The final concentration of both drugs in the Y-site line after mixing depends not only on the concentration of the drugs in solution but also the flow rates of each solution. The concentration estimates in Table 1 do not consider bag-overfill volumes or the volume of the drug solution added to the bag and so are slightly higher than might actually be encountered in practice under similar scenarios.

Actual concentrations in clinical practice will also vary because of dose adjustments related to patients’ body weight and because the infusion rate varies with calibration errors. However, the aim was to ensure that the estimated concentrations in Table 1 were closer to the concentrations likely encountered in clinical practice than those produced by the more common method of mixing equal volumes of each solution (scenarios 3a and 3b). Mixing equal volumes would yield LV concentrations 2- to 7-fold higher than those generally seen in clinical practice because of the longer infusion times and smaller bag volumes. To avoid this pitfall, numerous potential concentrations of mixtures were calculated, and concentration scenarios representing and/or encompassing concentrations likely to be observed in clinical practice were selected.
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In all treatment scenarios, IR and LV were physically compatible for 24 h. The HPLC analyses of IR and LV concentrations at 0.5 h support these physical compatibility data. The mean concentrations of LV and IR at 0.5 h, as a percentage of the concentrations at time 0, were greater than 96% for LV and greater than 91% for IR in all treatment scenarios, which indicates that, based on a 10% threshold for degradation, both IR and LV were chemically stable for 0.5 h. In other words, concentrations of IR ranging from 0.30 to 0.59 mg/mL were chemically compatible with LV concentrations from 0.27 to 3.60 mg/mL for 0.5 h. Other treatment scenarios that might be used in clinical practice should have concentrations of IR and LV that fall within the ranges evaluated here. For example, if equal infusion times are used for treatment scenarios 2a and 2b, a concentration of 0.51 mg/mL for IR and 0.45 or 1.20 mg/mL for LV would be produced in the final mixuture. It can therefore be expected that the final mixed solution of IR and LV will be chemically stable at 0.5 h.

The stability of both IR and LV for 0.5 h supports the hypothesis that these 2 compounds can be administered simultaneously via Y-site connection because the contact time in the Y-site will be far less than 0.5 h. In fact, the period of contact will be less than 2 min with standard IV tubing set 81 cm (32 inches) long. Standard IV tubing 165 cm (65 inches) in length with an internal diameter of about 2.5 mm holds 9 mL of fluid (equivalent to 0.135 mL/inch or 0.055 mL/cm). Therefore, even if the Y-site is maximally separated from the site of infusion (32 inches or 81 cm) and the lowest flow rates for IR and LV are employed (Table 1, scenario 3a), the mixing time will be limited to less than 2 min. These data also indicate that container type had no impact on stability, so either PVC or polyethylene-lined tubing could be used for Y-site infusion with IR and LV.
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