Midazolam/Diazepam (Benzodiazepines)

Benzodiazepines work by modulating GABA-mediated neurotransmission. They are regarded as having a wide margin of safety due to their minimal cardiovascular and respiratory effects and because they have a reversal agent, flumazenil. Benzodiazepine agonists frequently used in veterinary medicine include diazepam, midazolam and zolazepam (sold in combination with tiletamine as Telazol®[Zoetis]). They provide muscle relaxation and anticonvulsant properties with unreliable sedation. 

Benzodiazepines, when used a co-induction agent with another GABA agonist like propofol or alfaxalone, have the potential to significantly decrease the dose requirement of the primary induction agent33,34,35. Benzodiazepines are also routinely administered as co-induction agent with a dissociative like ketamine. 

Diazepam was approved for use in humans in 1960. Diazepam is 40% propylene glycol and 10% ethanol making it incompatible for mixing with other agents.  It is known to be painful and inconsistently absorbed when administered intramuscularly. It is light sensitive and can adhere to soft plastics. 

Midazolam, in comparison, is water soluble and becomes lipid soluble in physiological pH. It will not cause irritation when used intramuscularly and is consistently absorbed. Midazolam is like diazepam in that it does not provide reliable sedation when used as a premedicant in dogs and cats.  However, it can produce reliable sedation in other species such as ferrets, rabbits, pigs, birds and rodents. It can also produce better sedation in geriatric dogs and cats.