Lorazepam and clonazepam are both from the benzodiazepine family. I see them both used in clinical practice on a regular basis. While their pharmacology actions are essentially identical, there are some pharmacokinetic, dosage form, and indication differences you should know. I’ll outline some of those differences while comparing lorazepam versus clonazepam.
In addition to its tablet formulation, lorazepam has two different liquid dosage forms. Lorazepam can be used as an injection and given IV or IM. It should be noted that lorazepam liquid is very thick and drawing it up with a syringe can be challenging and take a little patience. The oral liquid dosage form can be useful as well with lorazepam. It is often used in hospice patients and others who may not be able to swallow tablets. Clonazepam does not have a commercially available liquid formulation. It should be noted that clonazepam has an orally disintegrating tablet and can be useful in patients who have difficulty swallowing tablets whole.
The injectable dosage form of lorazepam does allow it to be used for an acute seizure. Since clonazepam doesn’t have an injectable option, this is likely not going to be a consideration with this agent.
Clonazepam’s half-life is considered to be longer than lorazepam in your typical adult patient. Lorazepam’s half-life is most often reported at around 12 hours while clonazepam’s half-life can risk up into the 20-30+ hour range. In the senior population, this is one of the reasons why I prefer to see lorazepam used over clonazepam. There is less risk of that drug lingering around in the bloodstream for long periods of time and continuing to increase the risk for adverse effects and drug interactions.
In rare cases, I have seen clonazepam used to reduce the frequency of seizures. The only situation where I’ve seen this done is when patients have failed numerous other more traditional antiseizure therapies. It makes sense that you would use a benzodiazepine with a longer half-life if you need to maintain stable drug levels. Lorazepam would need to be dosed too frequently and the risk for a rebound seizure would be greater if a dose was missed.
Understanding that the half-life of lorazepam is significantly shorter than clonazepam, one could expect that each of these may be used for different circumstances. For patients needing short-term, all-day relief from their anxiety, using a longer-acting agent like clonazepam may be considered. This would reduce the need for redosing. If a patient is using a benzodiazepine for its sedative purposes to treat insomnia, clonazepam would likely not be used because its effects would linger into the next day. Lorazepam probably has a long enough half-life to linger into the next day as well if it is taken at bedtime but it would be less significant than clonazepam. In the case of insomnia, you would probably be more likely to use a short-acting benzodiazepine as lorazepam and clonazepam are considered intermediate-acting agents.
Looking for more on benzodiazepines? Be sure to check out our benzodiazepine comparison table. What other differences are important in your practice when comparing lorazepam versus clonazepam?