Temsirolimus injection (Torisel), a kinase inhibitor indicated for advanced renal cell carcinoma, is supplied in a kit that includes diluent for reconstitution. The active drug vial contains 30 mg in a volume of 1.2 mL (25 mg/mL, as marked on the label). The correct method for preparing the dose is to add the full 1.8 mL of diluent to the active drug vial for a total volume of 3 mL and concentration of 10 mg/mL (30 mg/3 mL). Because the drug is given at a fixed dose of 25 mg, only 2.5 mL should be withdrawn; although the drug vial label doesn't state so, the 20% overfill is meant to accommodate withdrawing medication from the vial.

While reconstituting the drug, pharmacy staff didn't realize that after adding the diluent, the drug concentration in the vial was 10 mg/mL. Thinking that the concentration was 25 mg/mL as printed on the active drug vial, the clinician withdrew 1 mL from the vial. Because this volume contained only 10 mL of the drug after reconstitution, the patient received less than the ordered dose. The error was later discovered by a staff member who correctly prepared the product according to the instructions in the package insert.

Changing the vial labeling to state that the drug's concentration is 30 mg/3 mL (or 10 mg/mL) after reconstitution may help resolve this confusion. If Torisel is dispensed before the dose is prepared in the pharmacy, the diluent and active drug should be dispensed together with the package insert, highlighting reconstitution instructions and final drug concentration amounts because, at present, the vials contain no instructions.