Portacaval Anastomosis: A novel nutraceutical delivery system
Unfortunately, we live in a toxic world. We live in a world in which staying healthy is more difficult to achieve, where near 90 percent of the water is contaminated with plastics,  where our food is genetically modified, sprayed with pesticides and herbicides; and a world where chemicals are being produced and dumped in the environment on a daily basis.
This translates into higher toxic burdens in our bodies and thereby stressed organ systems. Specifically, our gut (gastrointestinal) system takes one of the biggest hits in terms of its predisposition to damage by toxins. When the foundation of our health, the gut, is compromised it impairs proper absorption of nutrients. It also impairs the absorption of various supplements that we take to help boost our body's ability to detoxify and fight cancer.
For instance, when you swallow a capsule it travels through the gastrointestinal system where immune cells, called dendritic cells “police” the contents to decide if it is “acceptable or not.” Often, living in a pernicious environment leads to hyperactivation of our immune gut cells, and what would normally not cause an immune response, now does.
Even in the form of what seems like a harmless capsule containing “beneficial” ingredients, the immune system can block its absorption and/or produce an immune response (inflammation) against it. Also, the cells lining the GI tract called endothelial cells can become “leaky” and dysfunctional from toxic-insult; this can mechanically lead to poor absorption.
Fortunately, we have cells in the lower gut that can absorb nutrients and bypass the issues stated above. A novel approach to the delivery of nutrients and other supplements is via the rectal veins, where there is a unique connection between the portal and systemic circulation. Seemly unharmed by the environment, rectal absorption via the portacaval anastomosis has promise as a new method for better absorption of many traditionally orally-dosed nutraceuticals.
Delivery of various nutraceuticals via the rectal route bypasses nearly two-thirds of the first-pass metabolism as the rectum’s venous drainage is two-thirds systemic (middle and inferior rectal vein to the body) and one-third hepatic (direct to the liver) portal system (superior rectal vein). This means the substance will reach the circulatory system with significantly less alteration and in greater concentrations. 
“A drug that is administered rectally will in general (depending on the drug) have a faster onset, higher bioavailability …” [2, 3] Another advantage of administering substances rectally is that it tends to produce less nausea compared to the oral route and prevents any amounts from being lost due to vomiting, degradation due to stomach acid, and loss due to bile and/or pancreatic enzyme activation.
Important in cancer care, rectal delivery may be a better fit for those doing Time Restricting Eating (TRE). Briefly, this is the method where eating is restricted to a window of around 7-10 hours. The goal is to give the gut an extended period of time of rest in order to repair itself from daily damage from toxins. Scientific research supporting TRE is robust, especially regarding cancer.
When eating time is shortened it can be difficult to find time to take daily supplements inside the restricted time. Rectal administration of nutraceuticals does not affect the resting period which is critical for repair. A large portion of the body’s immune system also resides in the gastrointestinal system; encouraging other methods and sites of absorption may help decrease aberrant immune activation and sensitization.
Independent of the positive effects of absorption, the rectal administration can allow patients to remain in the home setting when the oral route is compromised or utilized when cancer (or treatment) affects the ability to use an oral administration route. Unlike intravenous lines, which need to be placed in an inpatient environment and also require costly formulations of sterile medications,  a rectal catheter can typically be placed at home. Many oral forms of medications and supplements can be crushed and suspended in water to be given via a rectal catheter or another mode of delivery.
1 Tyree, C, et al. (2017). Invisibles – The Plastic Inside Us. Extracted from https://orbmedia.org/stories/Invisibles_plastics
2 De Boer AG, Moolenaar F, de Leede LG, Breimer DD. (1982) “Rectal drug administration: clinical pharmacokinetic considerations.” Clin Pharmacokinetics. 7(4):285–311
3 Moolenaar F, Koning B, Huizinga T. (1979) “Biopharmaceutics of rectal administration of drugs in man. Absorption rate and bioavailability of phenobarbital and its sodium salt from rectal dosage forms.” International Journal of Pharmacaceutics, 4:99–109
4 Plumer AL. 2007. Plumer’s Principles and Practices of Intravenous Therapy. Lippincott Williams & Wilkins. 753 pp.
5 A Quality Improvement Study: Use of a Rectal Medication Administration Device Intervention to manage end-stage symptoms in hospice patients when the oral route fails. Poster Presentations. 6th Annual Hospice Palliative Nurses Association Clinical Practice Forum, Pittsburgh, PA, September 15-15, 2012