A nurse is teaching a client how to self-administer insulin. The client has a prescription for 5 units of NPH insulin and 15 units of regular insulin. Identify the sequence in which the nurse should perform the following steps. (Move the steps into the box on the right, placing them in the order of performance. Use all the steps.)

Inject 5 units of air into the NPH insulin vial. Inject 15 units of air into the regular insulin vial. Withdraw 15 units of medication from the regular insulin vial. Withdraw 5 units of medication from the NPH insulin vial. Brief Introduction: Insulin mixture preparation requires a specific sequence to prevent cross-contamination of vials and ensure dosage accuracy. Regular insulin is a short-acting, clear solution, while NPH insulin is an intermediate-acting, cloudy suspension. Maintaining the "clear before cloudy" withdrawal rule is a critical safety standard in clinical pharmacology to avoid contaminating the fast-acting clear vial with the protein-binding agents found in the NPH suspension. Rationale: A. Injecting 15 units of air into the regular insulin vial is the second step in the sequence. After the NPH vial has been pressurized with air, the needle is withdrawn and inserted into the clear vial. This ensures that the clear insulin vial is ready for immediate withdrawal without needing to re-enter the cloudy vial later, which maintains the chemical purity of the short-acting insulin. B. Withdrawing 5 units of medication from the NPH insulin vial is the final step of the procedure. Because NPH contains protamine, any accidental backflow into the regular vial would alter the clear insulin's pharmacokinetic properties. By withdrawing the cloudy insulin last, the nurse ensures the integrity of the fast-acting dose, which is essential for managing postprandial glucose spikes. C. Withdrawing 15 units of medication from the regular insulin vial occurs after air has been injected into both vials. The clear insulin is always drawn up first into the syringe to ensure that no cloudy suspension enters the clear vial. This order is a standard nursing competency designed to prevent the modification of the onset and peak action of the clear insulin dose. D. Injecting 5 units of air into the NPH insulin vial is the initial step in preparing a mixed dose. Vials are sealed vacuum environments; therefore, air equal to the dose must be injected to allow for the easy displacement of fluid. Starting with the cloudy vial for air injection (without the needle touching the solution) allows the nurse to then move to the clear vial for the withdrawal phase.