Patients with OCD usually require higher dosages of serotonin reuptake inhibiting (SRI) drugs than is used for the treatment of depression. This observation resulted in treatment-refractory patients being occasional prescribed selective SRI drugs above the normal upper limit of prescribing. Previous studies have shown that these high doses are well tolerated.

We decided to investigate the blood levels of patients on dosages of sertraline that were above the normal therapeutic range.

Successive patients treated by the National Inpatient Service for OCD/BDD who were treatment refractory and prescribed > 200 mg sertraline per day were included. All had previously received 2+ trials of different SRIs for > 3months each as well as been offered augmentation with dopamine blockers and at 2+ trials of exposure and response-prevention. All patients scored in the profoundly ill range of the Yale Brown Obsessive Compulsive Scale.

Sertraline was titrated in 50 mg increases every 2–4 weeks up to a maximum of 400 mg. Blood samples were taken after their morning dose. This was after the patients had stabilised for at least 2 weeks on the higher doses.

Seventeen patients were included in the study and received sertraline dosages ranging from 225 mg to 400 mg per day. Blood levels were within therapeutic range or below for all patients. Following treatment within the service, these patients generally showed an improvement of an average of improvement of 43% on the YBOCS.

A subgroup of patients with profound refractory OCD seem to either malabsorb or rapidly metabolise sertraline resulting in lower than therapeutic blood levels.

The authors have not supplied their declaration of competing interest.