Expert psychopharmacologists like our readers should make sure they are well-versed in prescribing medications that may be helpful for difficult-to-treat illness.
One such medication is clomipramine (Anafranil®). Since clomipramine can be toxic at higher serum levels, a serum level should be checked.
There are a few special things to remember regarding how to check the serum clomipramine level:
1. There is usually little point checking the level until a dose of 150 mg/day is reached.
2. However, the level should be checked at a lower dose if a drug interaction is present that could raise the clomipramine level (Grant, 2014).
3. The half life of desmethylclomipramine, the main metabolite of clomipramine is about three to four days. So, it takes two to three weeks to reach steady levels. Unless there is some urgency, levels should be checked two to three weeks after the last dose change. Yes, that’s a lot more than what we are used to for other medications.
4. The blood should be drawn no less than 12 hours after the last dose of clomipramine. Otherwise, it will appear to be falsely elevated since it will not have come down to the trough level.
5. After the trough level is reached at about 12 hours, there is not as much of a further decrease in the level. So, we should tell the patient that it is better for the time since the last dose to be more than 12 hours rather than less. And, that more than 12 hours is OK.
The laboratory results will show a serum level for clomipramine, a level for desmethylclomipramine, and a total of the two.
“Normal” or desirable ranges for these are as follows:
– Clomipramine 50 to 250 mcg/L
– Desmethylclomipramine 150 to 350 mcg/L
– Total 200 to 500 mcg/L
Important! The combined trough plasma levels of clomipramine and desmethylclomipramine should not exceed 500 ng/mL because the risk of seizures and of cardiac conduction delay is clearly higher above that level (Fineberg et al 2012).
How to interpret the clomipramine level
At lower serum levels, response to clomipramine is inadequate. At high levels, there is no additional benefit and side effects tend to increase. So, we should aim for the recommended levels mentioned above.
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