Clonidine - importance of dosing compliance and safe storage

Health professionals are reminded that serious adverse events can occur in children who are accidentally overdosed with clonidine either when receiving treatment for behavioural disorders, or obtaining access to a family member's medication. Even relatively minor overdoses (for example, double dosing) can result in toxicity, particularly in young children. You are advised to counsel patients and their parents/carers to pay close attention to dosing and remind them of the need for safe storage and other safety precautions.

Clonidine, marketed in Australia under the brand name Catapres and various generic brands, is approved for indications relating to the cardiovascular effects of the drug (for example, high blood pressure, migraine and menopausal flushing).

Clonidine is also being prescribed off-label under careful medical supervision for behavioural disorders in children, including attention deficit hyperactivity disorder (ADHD), tic disorders and sleep disturbances. Clonidine is not approved for the treatment of these conditions in children and the Product Information (PI) - external site does not recommend its use in children due to the lack of supporting evidence in this population. The PI also advises against using clonidine off-label in combination with methylphenidate for this indication due to the risk of serious adverse reactions.

Accidental overdoses

The TGA and the NSW Poisons Information Centre have received reports of clonidine overdose involving children relating to accidental poisoning and dosing errors, including unintentional double-dosing. Many of these events required medical intervention and/or hospitalisation. The number of reports of poisoning has increased in recent years and similar trends have been observed overseas.

To 23 April 2021, there are 43 adverse drug reaction reports included on the TGA Database of Adverse Event Notifications (DAEN) relating to overdose, incorrect dose, or off-label use of clonidine in children. Of these, 27 reports were received in 2020, which is a significant increase from eight reports received in 2019. Accidental administration of a double-dose of clonidine to a child who subsequently required medical intervention has been reported in five cases. Adverse events in these cases include slow heart rate, low blood pressure and reduced level of consciousness. There have also been 11 reports confirming accidental ingestion of clonidine by a sibling for whom it had not been prescribed.

A publication by the NSW Poisons Information Centre - external site states that during 2018, 415 cases of clonidine poisoning in children under 6 years of age were recorded by the NSW Poisons Information Centre. This represented a 50% increase over the previous four years. Off-label prescription of clonidine to the poisoning victim was noted in 28% of those cases. The authors note that clonidine has a narrow therapeutic window, meaning that relatively minor dosing errors (including double-dosing) can lead to toxicity.

In cases of accidental poisoning, clonidine may have been prescribed to the child, or other members of the household (including older siblings treated for ADHD, or adults with high blood pressure).

Clonidine poisoning presents with acute toxicity as early as 30 minutes and up to three hours after ingestion. Symptoms include coma, respiratory depression, bradycardia, hypotension and hypothermia. Milder side effects include constricted pupils, dry mouth, drowsiness, gastrointestinal upsets and dizziness.

The risk of poisoning is greater for younger children with low bodyweight where the low toxic threshold of the drug can be easily exceeded. Significant overdose can occur with ingestion of a single tablet.

Information for health professionals

When you are prescribing clonidine, you are advised to counsel patients and their caregivers about the importance of following dosing instructions carefully and precisely, and ensuring that the medicines are stored safely and out of reach from children. Extra vigilance is recommended when administering clonidine to ensure double-dosing does not occur.

Off-label prescribing should only be considered when other options are unavailable, exhausted, not tolerated or unsuitable, and you should always discuss the risks and benefits of the proposed treatment with the patient and/or their parents/carers so that they are capable of providing informed consent. Additionally, the treatment should be monitored and any adverse events should be reported to the TGA.

Disclaimer

Medicines Safety Update is aimed at health professionals. It is intended to provide practical information to health professionals on medicine safety, including emerging safety issues. The information in Medicines Safety Update is necessarily general and is not intended to be a substitute for a health professional's judgment in each case, taking into account the individual circumstances of their patients. Reasonable care has been taken to ensure that the information is accurate and complete at the time of publication. The Australian Government gives no warranty that the information in this document is accurate or complete, and shall not be liable for any loss whatsoever due to negligence or otherwise arising from the use of or reliance on this document.

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For correspondence or further information about Medicines Safety Update, contact the TGA's Pharmacovigilance and Special Access Branch at ADR.Reports@tga.gov.au.

Medicines Safety Update is written by staff from the Pharmacovigilance and Special Access Branch.

Acting Editor: Dr Catherine Brogan

Deputy Editor: Mr Michael Pittman

Contributor: Dr Neillan Nandapalan and Dr Margaret Wilson