The effect of a gastric bypass procedure on the pharmacokinetics of citalopram

Mental disorders are common in people with morbid obesity. In Maasstad Hospital
one of the six patients, who because of morbid obesity had a gastric bypass
surgery uses antidepressants (especially SSRIs, selective serotonin reuptake
inhibitors). As a result of the gastric bypass surgery, there is a drastic
change in the gastrointestinal tract; causing changes in drug absorption.
Possibly the reduced solubility of drugs and reduction of the absorption
surface of the gut plays a role. Some small studies show that the
bioavailability for most drugs decreased. There is hardly pharmacokinetic data
available on the effect of gastric bypass surgery on the pharmacokinetics of
SSRIs. Further research is needed to investigate the effect of gastric bypass
surgery on the pharmacokinetics so that an optimal pharmacological treatment
can be given.

Primary objective: to determine to what extent a gastric bypass procedure has
effect on the AUC (area under the serum concentration-time curve), Cmax
(maximum concentration) of citalopram.

Secondary objectives:
- To determine the severity of depressive symptoms in SSRI users before and
after gastric bypass surgery in combination with the observed pharmacokinetic
changes.
- Determine other pharmacokinetic parameters of citalopram (Cmax (maximum serum
concentration), Tmax (time of maximum serum concentration) and T1 / 2
(half-life)).

Before-/after study; observational study

During the five days of research, the participant wille be insterted whith a
flexibele cannula (venflon) Trough this cannula blood can be taken. The risk to
the participant will be limited.
Patients will be using their own medication in the same dosage.