A 32 year old woman with chronic schizophrenia and type 1 diabetes complains that in the last 5 months she has gained 6kg in weight. She is concerned that her blood glucose measurements have been raised despite following dietary recommendations made by the dietician and taking the prescribed insulin regularly.
Although she has a long history of agitation and hallucinations, her schizophrenia is now well controlled. She used to take trifluoperazine, but 10 months ago this was switched to olanzapine because she developed tardive dyskinesia.
She was recently involved in a car accident and is taking analgesia for the back pain.
Her current medications are:
Insulin Comb® 25
Olanzapine 15mg daily
Naproxen 500mg twice daily
Omeprazole 20mg daily
Fasting blood glucose = 8mmol/litre
HbA1c = 75mmol/mol (units for expressing HbA1c values have changed, see section 6.1)
Body-weight = 64kg
Body mass index = 26kg/m2
According to the prescribing note on Antipsychotic Drugs (section 4.2.1, BNF 62), hyperglycaemia and sometimes diabetes can occur with olanzapine. Also, it commonly causes weight gain, usually during the first 6-12 months of treatment.
The prescribing notes on Antipsychotic Drugs (section 4.2.1, BNF 62) recommend that second-generation antipsychotic drugs should be prescribed if extrapyramidal side-effects are a particular concern. Of these, aripiprazole, clozapine, olanzapine, and quetiapine are least likely to cause extrapyramidal effects.
According to the prescribing note on Antipsychotic Drugs (section 4.2.1, BNF 62), schizophrenia itself is associated with insulin resistance and diabetes; the risk of diabetes is increased in patients with schizophrenia who take antipsychotic drugs. Of the second-generation antipsychotic drugs, amisulpride and aripiprazole have the lowest risk of diabetes and are least likely to cause weight gain.
According to the prescribing notes on Antipsychotic Drugs (section 4.2.1, BNF 62), with the exception of clozapine, there is little meaningful difference in efficacy between the different antipsychotic drugs, and response and tolerability to each drug varies. Choice is influenced by the patient's medication history, the degree of sedation required, and consideration of individual patient factors such as risk of extrapyramidal side-effects, weight gain, impaired glucose tolerance, QT interval prolongation, or the presence of negative symptoms.
Aripiprazole would be a more suitable choice for this patient because it has a low risk of extrapyramidal effects and, unlike olanzapine, it has a lower risk of hyperglycaemia and weight gain. Aripiprazole has negligible effect on the QT interval and hyperprolactinaemia is not usually clinically significant.
The prescribing notes on Antipsychotic Drugs (section 4.2.1, BNF 62) advise that full blood count, urea and electrolytes, and liver function tests should be checked before starting treatment, and then annually thereafter.
Blood lipids and weight should be measured at baseline, at 3 months (weight should be measured at frequent intervals during the first 3 months), and then yearly.
Although this patient with diabetes will be self monitoring her blood glucose, her fasting blood glucose and HbA1c should be monitored regularly, particularly while unstable.
The physical health of patients with schizophrenia should be monitored at least once per year and this should include assessment of cardiovascular disease risk; patients with diabetes are at increased risk of cardiovascular disease. An ECG may be performed before initiating treatment, particularly if physical examination reveals specific cardiovascular risk factors.
As aripiprazole is not normally associated with symptomatic hyperprolactinaemia, monitoring of prolactin concentration should only be considered if symptoms occur.
She should also be monitored for any signs of relapse of her schizophrenia.