Pathophysiology
Clinical meaning
Rectal medication administration delivers drugs through the richly vascularized rectal mucosa. The lower and middle rectal veins drain into systemic circulation (IVC), bypassing hepatic first-pass metabolism, while the upper rectal vein drains into the portal system. Medications inserted low achieve higher bioavailability than oral. This route is valuable when oral is unavailable (nausea/vomiting, unconsciousness, seizures, NPO). Common formulations: suppositories (solid drug in wax/glycerin base melting at body temperature), enemas, and rectal foams. Onset typically 15-30 minutes. Contraindications: rectal surgery, active rectal bleeding, diarrhea, neutropenia, and thrombocytopenia.