A method may comprise (a) inserting an insulin delivery device subcutaneously into a body of a subject, which comprises an amperometric glucose sensor comprising an electrode layer comprising an indicating electrode and underlying a redox-catalytic layer comprising a redox mediator; (b) using said insulin delivery device to deliver an insulin formulation (e.g., comprising a phenol or cresol excipient) subcutaneously to said subject; and (c) using said amperometric glucose sensor to measure a subcutaneous glucose concentration, which comprises using said redox-catalytic layer to allow electron transfer from subcutaneous glucose to said indicating electrode sufficient to cause a response of said amperometric glucose sensor at an applied bias potential of no more than +250 millivolts, wherein (b) and (c) are performed at the same time for at least one hour, while maintaining a sensor sensitivity of at least 50% of an initial sensor sensitivity for up to one hour.
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