I take 2mg clonazepam daily for severe anxiety. I read somewhere that phenobarbital can change the effectiveness of how clonanazepam works. Can the small amount of phenobarbital in each Donnatal tablet (16.2mg) Have any effect on the clonazepam I am taking or must it be a larger dose?
I found the following in the literature about clonazepam:
Effect of Clonazepam on the Pharmacokinetics of Other Drugs
Clonazepam does not appear to alter the pharmacokinetics of phenytoin, carbamazepine or phenobarbital. The effect of Clonazepam on the metabolism of other drugs has not been investigated.
Furthermore I checked the interactions between these two drugs and found the following:
Interactions between your selected drugs
clonazepam ↔ phenobarbital
Applies to: clonazepam, phenobarbital
MONITOR: Barbiturates may increase the plasma clearance of clonazepam and thereby reduce its clinical effectiveness. Phenobarbital is the only barbiturate specifically implicated in this interaction. However, other barbiturates may behave in a similar fashion. Also, clonazepam may increase the effectiveness of barbiturates. A case of respiratory depression and coma has been reported in a patient receiving high doses of both clonazepam and amobarbital.
MANAGEMENT: If these drugs are used together, close observation for altered clonazepam and barbiturate effects is indicated.
It would appear that clonazepam does not affect the phenobarbital but phenobarbital may reduce the clinical effectiveness of clonazepam. What quantity of phenobarbital is required to cause this reduced effect of clonazepam, I don't know. Might have to ask the pharmacist this one.
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