Venous irritation from diazepam and lorazepam injections is primarily due to which solvent?

The correct answer is propylene glycol because it is commonly used as a solvent in injectable formulations of diazepam and lorazepam. Propylene glycol can cause venous irritation at the injection site due to its osmotic properties and potential to disrupt the local tissue homeostasis. When medications containing propylene glycol are injected, the high concentration of this solvent can lead to pain, irritation, or even phlebitis.

Water is often used as a solvent but typically does not cause irritation when used in higher volumes compared to propylene glycol. Metabisulfite is primarily a preservative and does not directly cause the irritation associated with the solvents used in these medications. Alcohol, while capable of irritating tissues, is not the solvent responsible for venous irritation in this context. Thus, propylene glycol is identified as the primary cause of venous irritation related to the injections of these benzodiazepines.