At positions 28 and 29 in the B chain are reversed. This results in more rapid absorption after subcutaneous injection than is seen with regular insulin. Consequently, insulin lispro acts more rapidly. Peak levels of insulin lispro are seen at 30 to 90 minutes after injection, as compared with 50 to 120 minutes for regular insulin. Insulin lispro also has a shorter duration of activity. Insulin aspart and insulin glulisine have pharmacokinetic and pharmacodynamic properties similar to those of insulin lispro. They are administered to mimic the prandial (mealtime) release of insulin, and they are usually not used alone but with a longer-acting insulin to ensure proper glucose control. Like regular insulin, they are administered subcutaneously. Insulin lispro is usually administered 15 minutes prior to a meal or immediately following a meal, whereas glulisine can be taken either 15 minutes before a meal or within 20 minutes after starting a meal. Insulin aspart should be administered just prior to the meal or up to 15 minutes following the meal. All of the rapid-acting formulations are suitable for IV administration, although regular insulin is most commonly used when the IV route is needed. Insulin lispro, insulin aspart, and insulin glulisine may also be used in external insulin pumps.