A nurse is preparing to administer NPH insulin and regular insulin in the same syringe for a client. Which of the following actions should the nurse take?

Mixing different types of insulin requires a specific sequence to prevent cross-contamination of vials. Regular insulin is short-acting and must remain pure, while NPH is an intermediate-acting isophane suspension containing protamine. Correct technique ensures that the rapid onset of regular insulin is not compromised by the longer-acting NPH components. Rationale: A. Injecting air into the regular insulin vial first is the incorrect order for the air-injection phase of mixing. The nurse should first inject air into the NPH (cloudy) vial without touching the solution, then inject air into the regular (clear) vial. This sequence maintains the pressure in both vials while ensuring the clear insulin remains completely uncontaminated by protamine. B. Shaking insulin vials vigorously is contraindicated because it creates air bubbles that can lead to inaccurate dosing and may denature the protein molecules. Instead, the nurse should gently roll the NPH vial between the palms to re-suspend the particles. Regular insulin does not require agitation as it is a clear solution that does not settle or separate. C. Ensuring that NPH has a clear appearance is incorrect because NPH is a suspension that should normally appear cloudy or milky after gentle agitation. If NPH appears clear, it may have lost its potency or been mislabeled. Conversely, regular insulin must always be clear; any cloudiness in a regular insulin vial indicates contamination or expiration. D. Withdrawing the regular insulin into the syringe first is the correct procedure after air has been injected into both vials. This "clear to cloudy" method ensures that no NPH insulin enters the regular insulin vial. If protamine from the NPH were introduced into the regular insulin, it would alter the drug's rapid-acting pharmacokinetics, potentially leading to unpredictable glycemic control.