USE OF MIRTAZAPINE IN PREGNANCY

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(Date of issue: September 2015, Version: 2.1)

This is a UKTIS monograph for use by health care professionals. For case-specific advice please contact UKTIS on 0344 892 0909. To report an exposure please download and complete a pregnancy reporting form. Please encourage all women to complete an online reporting form.

A corresponding patient information leaflet on mirtazapine use in pregnancy is available at www.medicinesinpregnancy.org.

Summary

Mirtazapine is a benzazepine tetracyclic antidepressant licensed for use in the treatment of depression and mood disorders. It is also used off-licence in the treatment of anxiety and as an antiemetic. Its mechanism of action is related to that of selective-serotonin reuptake inhibitors (SSRIs).

The data regarding exposure to mirtazapine in human pregnancy are limited and comprises around 700 exposures, derived from case reports, case series, cohort studies and registry studies. Use of mirtazapine in pregnancy should therefore be limited to situations where use of another antidepressant, for which there is more pregnancy safety data, is not considered clinically appropriate and where prescriber and patient feel that the benefits of use outweigh any potential risks. Women should be counselled regarding the limited available human pregnancy safety data.  

Whilst these data do not suggest a significantly increased risk of congenital malformation they are too limited to exclude any increase in risk. Data regarding risk of spontaneous abortion and preterm delivery are conflicting. Risk of neonatal hypoglycaemia may be increased.  Data regarding the risk of neonatal withdrawal is lacking, however there are theoretical concerns with exposure to centrally acting drugs and monitoring for neonatal effects is advised following use near delivery.

There are no epidemiological studies which investigate risk of PPHN following mirtazapine use in pregnancy. However, as mirtazapine increases serotonin concentration and PPHN has been associated with in utero exposure to SSRIs, there are theoretical concerns that in utero mirtazapine exposure may also increase the risk of PPHN in the neonate. 

The effects of mirtazapine exposure on neurodevelopment have not been studied. Preliminary findings suggest that children of women with untreated depression, as well as children exposed to antidepressants in utero, have lower IQs and exhibit more behavioural problems than those of non-exposed children of non-depressed women.

Infants exposed to antidepressants in utero should ideally be delivered in a unit with adequate neonatal support and the delivery team made aware of the exposure. In the non-pregnant adult patient mirtazapine has a half life of 20 to 40 hours which is extended in cases of liver or renal impairment. Neonatal clearance of mirtazapine following in utero exposure may be longer, and neonatal postnatal effects may therefore be delayed.

Exposure to mirtazapine at any stage in pregnancy would not usually be regarded as medical grounds for termination of pregnancy or any additional fetal monitoring. However, other risk factors may be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments.

This document is regularly reviewed and updated. Only use full UKTIS monographs downloaded directly from TOXBASE.org to be sure you are using the most up-to-date version. The summaries of these monographs are openly available on UKTIS.org.

This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to health care professionals at www.toxbase.org.

If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.

If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.

Disclaimer: Every effort has been made to ensure that this monograph was accurate and up-to-date at the time of writing, however it cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes of the measures recommended. The final decision regarding which treatment is used for an individual patient remains the clinical responsibility of the prescriber. This material may be freely reproduced for education and not for profit purposes within the UK National Health Service, however no linking to this website or reproduction by or for commercial organisations is permitted without the express written permission of this service. This document is regularly reviewed and updated. Only use UKTIS monographs downloaded directly from TOXBASE.org or UKTIS.org to ensure you are using the most up-to-date version.