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Table 2 Inclusion criteria and rationale

From: Improving metabolic parameters of antipsychotic child treatment (IMPACT) study: rationale, design, and methods

Criterion Rationale
Ages 8 to 19 years Even young children are frequently treated with SGAs and experience severe weight gain. The FDA has approved metformin for use in type 2 diabetes in children ≥ 10 years, it appears 8 year olds could safely use metformin based on available toxicology literature (Spiller et al. 2000; Benavides et al. 2005), use in previous clinical trials (Ibanez et al. 2004; Lutjens and Smit 1977), and advice from our pediatric endocrinology consultant.
Primary DSM-IV diagnosis of Early Onset Schizophrenia Spectrum disoder, Bipolar Spectrum disorder, Major Depression with psychotic features, Major Depressive Disorder (only for participants aged 18–19 years), or Autism with irritability Most diagnoses or symptom clusters for which a SGA is prescribed in clinical practice are included to enhance ecological validity.
Clinically stable on current treatment regimen for ≥ 30 days Stability is required to reduce risk of psychiatric decompensation
Stable dose of current SGA and psychotropic co-medications for ≥ 30 days
BMI ≥ 85th percentile for age and gender (i.e., at least “at risk for overweight”) Youth at greatest risk for harm from SGA weight gain need intensive side effect monitoring. Current vulnerability to overweight/obesity-related health problems balances the risk of being randomized to an intervention that is not yet widely used in child psychiatry clinical settings (i.e. addition of metformin).
Substantial weight gain over the previous 3 years, while taking a SGA (aripiprazole, asenapine, iloperidone, lurasidone, olanzapine, paliperidone, quetiapine, risperidone, or ziprasidone) All SGAs other than clozapine were included because all have been associated with substantial weight gain Clozapine was not included because of unique benefits and it is generally reserved for youth with severe illness that has not been adequately controlled with other antipsychotics.
Sexually active girls must agree to use two effective forms of birth control (i.e., hormonal o r spermicidal and barrier) or be abstinent Risk of study agents to unborn babies.
Participant has a primary caretaker (defined as parent(s), close relative functioning in loco parentis, legal guardian, or foster parent) who has known the child well for at least 6 months before study entry Legal authority to make medical decisions including participation in research study. Ability to accurately report on past and current functioning.
Primary caretaker is able to participate in study appointments as is clinically indicated. Most participants are minor children.
Ability of child to participate in all aspects of the protocol per investigator clinical judgment. Child must demonstrate awareness of study procedures and assent to participate.
After considering all aspects of study participation, including random assignment, guardian and the child must agree (legally consent and assent) to participation Study participation is voluntary but requires consent.