Oh Steve, I do apologize. I somehow missed this earlier.

Durahist-D is dexchlorpheniramine. It is the "active" isomer of chlorpheniramine. Molecularly, Durahist has the interaction potential you were concerned about chlorpheniramine.

If you didn't see a panic problem with the Durahist-D, I'd have to suggest that the worsening you saw in the panic disorder was more than likely coincidence. I'd say, if the Durahist worked for you, then try the chlorpheniramine again.

Another possibility is how often did you take the Durahist? Every four hours? You should get a formulation of chlorpheniramine that is to be taken at the same intervals... dosages affect peak drug levels. An extended release version could produce different side effects than an immediate release, and vice versa.

Chlorpheniramine used to be available in immediate release,(4-hour dosing, intermedieate (8-hour) and extended (12-hour) dosing. For the 8- and 12-hour release versions, you might have to get a hold of Chlor-Trimeton brand and I don't know if that's available still. The 4-hour version is standard and is available in all generics.