After my first post on this subject, I went off to a lecture on sedation in the ICU so I will now regurgitate what I have just learned. There other reason for preferring lorezepam (Ativan) over midazolam (Versed) besides cost.
The reason midazolam is shorter acting is that it is more lipophilic than lorezepam. Therefore there is more potential for peripheral accumulation of the drug. The intermediate metabolites of midazolam have sedative properties. Therefore with infusions greater than 24 hours a prolongation of the clinical effects of the drug will result.
Compared with midazolam, lorazepam is longer acting, causes less hypotension, causes an equally effective anterograde amnesia, is lower in cost, and with prolonged administration produces more rapid awakening.
Therefore midazolam or propofol are the preferred agents only for the short term (<24 hrs) treatment of anziety in the critically ill adult. Lorazepam is the preferred agent for the prolonged treatment of anxiety in the critically ill adult.
The other interesting tidbit is that Wyeth-Ayerst the only makers of a parenteral form of lorazepam announced last week that they will be raising their price of lorazepam. They apparently realized that they had a lock on the market.