A 47-year-old woman has been treated with Paraflex comp (chlorzoxazone + aspirin + dextropropoxyphe

Fråga: A 47-year-old woman has been treated with Paraflex comp (chlorzoxazone + aspirin + dextropropoxyphene) for several years due to backpain. She is in a depressive state and has been treated earlier with TCA but half a year ago this was changed to Aurorix (moclobemide). The patient experiences some sexual disturbances and uses Aurorix only now and then. The pharmacy warns about an interaction between moclobemide and dextropropoxyphene. Is this interaction of any clinical importance?

Sammanfattning: Limited information concerning an interaction between moclobemide and dextropropoxyphene is found in the literature. The only clinical observation seen was moderate agitation in one patient out of three who received moclobemide together with codeine or dextropropoxyphene. The D-classification in FASS is based on the analogy with the well-documented serious interactions between the older MAO-inhibitors and pethidine-like compounds.

Svar: The statement in the Swedish catalogue of approved medical products is the following; "On the basis of experimental observations in animals and the clinical experience with classical MAO-inhibitors it is adviced against the simultaneous use of moclobemide and pethidine or dextropropoxyphene" (1,2). This interaction is classified as D which means that a combination may lead to serious clinical consequences and the combination should be avoided.

A thorough literature search, covering pharmacological handbooks and Medline, of any drug interaction with moclobemide in combination with an analgesic drug, has resulted in very scant documentation. According to reference 2, data are available on three patients who received moclobemide together with opioids, two of them with codeine and one with dextropropoxyphene. In one patient, moderate agitation occurred as an adverse event, but otherwise no adverse event or change of vital signs indicative of a relevant interaction was recorded (2).

A handbook in drug interactions states that until additional information shows that the combination may be used safely, the combination of moclobemide and dextropropoxyphene should be avoided (3). A review article mentions that moclobemide has been shown to potentiate the effect of pethidine and dextropropoxyphene (4). These two articles are referring to reference 2.

No further information could be found in the literature.

The classifying of this interaction as category D is based on the analogy with the well-documented serious interactions between the older MAO-inhibitors and pethidine-like compounds (5).

In the present case, the patient has already used the two drugs concomitantly for some time without any negative effects. In view of the weak documentation of a serious interaction between moclobemide and dextropropoxyphene and the experience in this patient, it seems reasonable to continue with the two drugs concomitantly.