Irritability rather than depression during interferon treatment is linked to increased tryptophan catabolism.

OBJECTIVE

Treatment with recombinant interferon is associated with high rates of psychiatric comorbidity. We investigated the relation between catabolism of the essential amino acid tryptophan, being rate-limiting of peripheral and cerebral serotonin formation, and psychiatric symptoms in patients undergoing combination treatment with interferon-alpha and ribavirin.

PATIENTS AND

METHODS

Eighteen patients with viral hepatitis C who received interferon were included. A psychiatrist screened patients before and while on interferon-alpha treatment for 2 months, using a structured diagnostic interview. Fasting plasma tryptophan and platelet serotonin levels were measured at each visit.

RESULTS

At baseline no evident psychopathology was observed. After 2 months of interferon treatment, 10 patients experienced increased irritability. No other structural psychopathology was observed. Decreased plasma tryptophan level correlated with the presence of irritability (p = .047). Platelet serotonin levels were found to be decreased during treatment (p = .002).

CONCLUSIONS

Aggressive impulse dysregulation is highly prevalent in patients receiving interferon treatment. This is associated with decreased plasma tryptophan levels which may lead to attenuated peripheral and central serotonergic neurotransmission.