Clinical improvement in schizophrenia during antipsychotic treatment in relation to changes in glucose parameters: A systematic review

Antipsychotics (APs) are the cornerstone of treatment for schizophrenia (SCZ) spectrum disorders. Previous research suggests that there may be a positive association between AP-induced weight gain and/or dyslipidemia and improvement in psychiatric symptoms, often referred to as a "metabolic threshold". To determine whether a similar relationship exists for glucose parameters, we conducted a systematic search in six databases from inception to June 2022 for all longitudinal studies that directly examined the relationship between changes in glucose-related outcomes and changes in psychopathology among patients with SCZ treated with APs. We identified 10 relevant studies and one additional study that considered cognition. In most cases, we found that increased levels of fasting glucose and insulin following treatment were associated with clinical improvement. These findings contribute to existing literature that could suggest a common mechanism between AP action and metabolic side effects and support a need for additional work aimed at exploring the validity of a glucose-psychopathology relation in SCZ.

Association between antipsychotic-induced metabolic side-effects and clinical improvement: a review on the Evidence for "metabolic threshold"

Over the last two decades, several studies have reported an intriguing association between clinical improvement with antipsychotics and metabolic side effects. In this review, we attempt a critical evaluation of fifteen such studies. The following are the summary observation from these studies: weight gain over a period of few weeks to more than a year, has been consistently found to be associated with clinical improvement. In addition, serum triglyceride changes have also been found to demonstrate this association. This relationship was not affected by socio-demographic factors, duration of illness or baseline body mass index. Findings from these studies depict changes mainly in schizophrenia patients on treatment with clozapine or olanzapine. Other drugs and diagnoses are poorly represented. Moreover, appetite, physical activity, other metabolic parameters have not been adequately examined. This review raises an important question - "Is there a metabolic threshold for antipsychotics?" i.e. is response to antipsychotics contingent upon the production of metabolic side effects. Current research proposes the involvement of insulin, leptin and phospholipid pathways in pathogenesis as well as therapeutics of psychosis. Though knowledge in this area is preliminary, it clearly warrants further systematic evaluation.