Overdoses of TCAs are frequently encountered in emergency departments in the UK. The management of TCA overdose is well known to emergency department physicians but rectal overdose is infrequently encountered. At present, there are no case reports or other information in the literature on rectal overdose of a tricyclic and the best management in such cases is unclear.
Tricyclics are absorbed rapidly from the gastrointestinal tract and undergo first pass metabolism. They are also highly protein bound and have a large volume of distribution resulting in a long half-life that usually exceeds 24 h.2
It is not known how rectal administration effects the pharmacokinetics of the drug but it could be hypothesised that as a minimum some of the drug will bypass the liver as at least some of the lower haemorrhoidal veins drain not to the portal system but instead directly to the inferior vena cava.
Tricyclics are known to have some absorption rectally and such a route of administration has been shown to successfully treat depression and improve sleep in one study.3
In another study tricyclic suppositories were shown to reach therapeutic levels and the authors noted an improvement in neuropathic pain.4
A recent literature review highlighted the potential non-oral routes of administration of antidepressants including the use of rectal TCAs.5
- Although the absorption of tricyclic drugs are altered by the rectal route it is still a valid mode of administration.
- A rectal examination should be considered when assessing patients who have taken an overdose.
- At present no data are available on how treatment of a rectal overdose of a tricyclic antidepressant should differ from that of an oral overdose.
- It seems reasonable to attempt careful removal of the drug from the rectum and if that fails to consider phosphate enemas and whole bowel irrigation.