Enteroenteric circulation is the secretion back into the intestines of substances previously taken up from it. It occurs when there is a negative relative concentration of substance in the
intestines, making it passively diffuse from the mesenteric circulation into the intestinal lumen and is trapped.

Examples of toxins that exhibit enteroenteric circulation include theophylline

Theophylline

Theophylline, also known as dimethylxanthine, is a methylxanthine drug used in therapy for respiratory diseases such as COPD and asthma under a variety of brand names. Because of its numerous side-effects, the drug is now rarely administered for clinical use. As a member of the xanthine family, it...

, phenobarbital

Phenobarbital

Phenobarbital or phenobarbitone is a barbiturate, first marketed as Luminal by Friedr. Bayer et comp. It is the most widely used anticonvulsant worldwide, and the oldest still commonly used. It also has sedative and hypnotic properties but, as with other barbiturates, has been superseded by the...

, and phenytoin

Phenytoin

Phenytoin sodium is a commonly used antiepileptic. Phenytoin acts to suppress the abnormal brain activity seen in seizure by reducing electrical conductance among brain cells by stabilizing the inactive state of voltage-gated sodium channels...

. Administration of activated charcoal inhibits the enteroenteric circulation of such substances, and is therefore useful in overdose or intoxication.