Assessment of adherence to carbamazepine using plasma and saliva samples, a study from Jordan

The measurement of carbamazepine levels in a biological sample is required to guide dosing, and prevent toxicity, and can be useful to assess medication adherence.

The primary aim of the presented study is to analyze carbamazepine levels in saliva and plasma samples of outpatients and to assess adherence to carbamazepine using saliva and plasma levels.

Adults who used carbamazepine for at least one month were recruited from the outpatient clinic department of Princess Basma Hospital, a public hospital in Irbid. Saliva and blood samples (1 ml) were collected simultaneously from subjects, and using a microanalytical method with high-performance liquid chromatography coupled with an ultraviolet detector, the level of carbamazepine (in micrograms per milliliter) was ascertained. Analysis of adherence to carbamazepine was carried out using plasma and saliva levels.

A total of 69 consecutive patients attending the neurology clinic were recruited, of whom 85.5% had epilepsy. Approximately one-third (34.8%) used carbamazepine as monotherapy, whereas the remainder used a combination of antiepileptic drugs to control seizures. Overall, about two-thirds (71.9%) of the studied samples were non-adherent in either plasma or saliva samples. By referring to the plasma sample carbamazepine concentration, 75.4% of the respondents were adherents, 15.9% had under-adherence, and 8.7% had over-adherence. A total of 85.9% of the responders were adherent using the carbamazepine level in saliva samples. Plasma and saliva carbamazepine levels were linearly correlated to one another. Polypharmacy was commonly utilized with the patients, as 42% of the patients used two medications, with a range of 1-7 drugs used concomitantly. The predictor associated with higher plasma and saliva carbamazepine levels, as determined by multiple linear regression analysis, was the occurrence of seizures less than once a month, as compared to seizures with higher frequencies.

Saliva carbamazepine levels show the potential to be used as an alternative matrix to assess medication adherence, with a considerable correlation with the plasma carbamazepine level. Healthcare professionals can address routine care non-adherence through such measures.