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Early metformin minimizes antipsychotic-induced weight gain


Psychiatrists should prescribe metformin early to patients who experience rapid weight gain after they begin taking antipsychotic drugs, according to a new evidence-based Irish guideline for the management of this common complication in adults with psychoses who are taking medications.

The document was discussed during one of the sessions of the XXXV Argentine Congress of Psychiatry of the Association of Argentine Psychiatrists. The document also was presented by one of its authors at the European Congress on Obesity 2022.

The guideline encourages psychiatrists not to underestimate the adverse metabolic effects of their treatments and encourages them to contemplate and carry out this prevention and management strategy, commented María Delia Michat, PhD, professor of clinical psychiatry and psychopharmacology at the APSA Postgraduate Training Institute, Buenos Aires.

“Although it is always good to work as a team, it is usually we psychiatrists who coordinate the pharmacological treatment of our patients, and we have to know how to manage drugs that can prevent cardiovascular disease,” Dr. Michat said in an interview.

“The new guideline is helpful because it protocolizes the use of metformin, which is the cheapest drug and has the most evidence for antipsychotic-induced weight gain,” she added.

Avoiding metabolic syndrome

In patients with schizophrenia, obesity rates are 40% higher than in the general population, and 80% of patients develop weight gain after their first treatment, noted Dr. Michat. “Right away, weight gain is seen in the first month. And it is a serious problem, because patients with schizophrenia, major depression, or bipolar disorder already have an increased risk of premature mortality, especially from cardiovascular diseases, and they have an increased risk of metabolic syndrome. And we sometimes give drugs that further increase that risk,” she said.

Being overweight is a major criterion for defining metabolic syndrome. Dr. Michat noted that, among the antipsychotic drugs that increase weight the most are clozapine, olanzapine, chlorpromazine, quetiapine, and risperidone, in addition to other psychoactive drugs, such as valproic acid, lithium, mirtazapine, and tricyclic antidepressants.

Several clinical trials, such as a pioneering Chinese study from 2008, have shown the potential of metformin to mitigate the weight gain induced by this type of drug.

However, Dr. Michat noted that so far the major guidelines (for example, the Canadian Network for Mood and Anxiety Treatments [CANMAT]/International Society for Bipolar Disorders [ISBD] for bipolar disorder and the American Psychiatric Association [APA] for schizophrenia) “say very little” on how to address this complication. They propose what she defined as a “problematic” order of action in which the initial emphasis is on promoting lifestyle changes, which are difficult for these patients to carry out, as well as general proposals for changing medication (which is not simple to implement when the patient’s condition is stabilized) and eventual consultation with a clinician to start therapy with metformin or other drugs, such as liraglutide, semaglutide, and topiramate.

The new clinical practice guideline, which was published in Evidence-Based Mental Health (of the BMJ journal group), was written by a multidisciplinary team of pharmacists, psychiatrists, and mental health nurses from Ireland. It aims to fill that gap. The investigators reviewed 1,270 scientific articles and analyzed 26 of them in depth, including seven randomized clinical trials and a 2016 systematic review and meta-analysis. The authors made a “strong” recommendation, for which there was moderate-quality evidence, that for patients for whom a lifestyle intervention is unacceptable or inappropriate the use of metformin is an “alternative first-line intervention” for antipsychotic drug–induced weight gain.

Likewise, as a strong recommendation with moderate-quality evidence, the guidance encourages the use of metformin when nonpharmacologic intervention does not seem to be effective.

The guideline also says it is preferable to start metformin early for patients who gain more than 7% of their baseline weight within the first month of antipsychotic treatment. It also endorses metformin when weight gain is established.

Other recommendations include evaluating baseline kidney function before starting metformin treatment and suggest a dose adjustment when the estimated glomerular filtration rate (eGFR) is < 60 mL/min/1.73 m2. The guidance says the use of metformin is contraindicated for patients in whom eGFR is <30 mL/min per 1.73 m2. The proposed starting dosage is 500 mg twice per day with meals, with increments of 500 mg every 1-2 weeks until reaching a target dose of 2,000 mg/day. The guidance recommends that consideration always be given to individual tolerability and efficacy.

Treatment goals should be personalized and agreed upon with patients. In the case of early intervention, the guideline proposes initially stabilizing the weight gained or, if possible, reverse excess weight. When weight gain is established, the goal would be to lose at least 5% of the weight within the next 6 months.

The authors also recommend monitoring kidney function annually, as well as vitamin B12 levels and individual tolerability and compliance. Gastrointestinal adverse effects can be managed by dose reduction or slower dose titration. The risk of lactic acidosis, which affects 4.3 per 100,000 person-years among those taking metformin, can be attenuated by adjusting the dose according to kidney function or avoiding prescribing it to patients who have a history of alcohol abuse or who are receiving treatment that may interact with the drug.


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