Abstract
Aims: To measure plasma and breast milk levels of olanzapine in a group of mothers and estimate the amount nursing infants are exposed to. Olanzapine has not been measured in this way before, despite it becoming an increasingly popular agent for the treatment of psychosis and used in the post partum population.
Method: Women admitted to the Austin and Repatriation Medical Centre Mother Baby Unit in Melbourne who were receiving olanzapine, in dose range of 2.5–10mg daily, were asked to take part in this study by providing paired plasma and milk samples for analysis. A literature review of similar studies with other antipsychotic agents was performed for comparison.
Results: 5 women provided a total of 9 paired samples including one patient who provided 3 sets across 24 hours and allowed her nursing infant to have a plasma sample taken. The results showed milk concentrations in the range of 2–21ng/ml and Milk/Plasma ratios of 0.2–0.84. These figures compare favourably with other antipsychotic agents. The infant's plasma level was < 1ng/ml, suggesting adequate clearance of the drug. Infants are estimated to receive 1–2% of the maternal dose of olanzapine, adjusted for weight.
There is generally a great shortage of evidence based information to assist clinicians in making their choice of treatments in this patient group. For example, of all other studies reporting levels of antipsychotic agents in breast milk only two have had larger cohorts than that presented here and some popular agents have not been reported on at all. The knowledge base developed so far, and its limitations, is discussed.