Unfortunately no
one really knows the true incidence of this complication. To our
knowledge, there is no good or convincing data about the incidence of this drug
interaction resulting in patients developing serotonin syndrome. The
majority of literature linking serotonin syndrome with tramadol and selective
serotonin reuptake inhibitors (SSRI) are in the form of case reports which are
considered insufficient to determine causality.1-7 However, having
several case reports and/or case series showing similar time related
occurrences of this condition can be helpful in the absence of better
evidence. One study using claims data in an Australian VA population
identified 1811 (0.7%) patients who were receiving potentially life-threatening
serotonergic medication combinations, most of which were an SSRI and tramadol.8 They
were unable to determine if those cases resulted in the development of
serotonin syndrome. Furthermore, the mechanism for how this occurs is multifactorial.9-12 To learn more about the mechanism for tramadol induced serotonin syndrome in patients taking SSRIs ... click here
Why is this condition difficult to assess?
The
first point about the broad spectrum of signs and symptoms is certainly a
contributing factor. In addition, the strict application of the Sternbach
criteria may cause the clinician to exclude mild or subacute cases of serotonin
syndrome.9,13 To complicate things further there has been such debate
over the Sternbach criteria that another criteria set, called the Hunter
Serotonin Toxicity Criteria, have been developed.14 The Hunter criteria
have been proposed to be easier for clinicians to use. However, this may also
result in an inconsistency in the diagnosis rates, depending on which criteria
set a clinician uses.14
A
third and final influencing factor (especially given the above factors) is the
fragmented nature of healthcare delivery to patients. It is not uncommon
for a patient to be treated or followed by 2 or more physicians of different
specialties, all of whom prescribe medications related only to their respective
areas of expertise, and often without regard to medications prescribed by others.
This leaves the patient's primary care physician (if they even have one) to
factor in all of these issues on top of any other comorbidities they may be
trying to manage for that patient.
Given
all of these influencing factors, it understandable why this condition may be
underreported and therefore, not perceived as being a clinically significant
adverse drug reaction that affects the quality of life. This is relevant
given the number of other treatment options for pain management in patients who
also require serotonergic medications for another problem. In addition,
there are enough case reports and regulatory warnings about this drug
interaction that clinicians should take it into consideration.15.
