RECTAL & TOPICAL ROUTE OF DRUG ADMINISTRATION
Rectum has a rich blood supply and drugs can cross the rectal mucosa to be absorbed for systemic effects. Drugs absorbed from the upper part of the rectum are carried by the superior hemorrhoidal vein to the portal circulation (can undergo first pass metabolism), while that absorbed from the lower part of the rectum is carried by the middle and inferior hemorrhoidal veins to the systemic circulation. Drugs like-indomethacin, chlorpromazine diazepam abd paraldehyde can be given rectally. Some irritant drugs are given rectally as suppositories.
- Gastric irritation is avoided
- Can be administered by unskilled persons
- Useful in geriatric patients and others with vomiting and those unable to swallow
- Irritation of the rectum can occur
- Absorption may be irregular and unpredictable
Drugs may also be given by rectal route as enema.
Enema is the administration of a drug in a liquid form into the rectum. Enema may be evacuant or retention enema.
Evacuant enema: In order to empty the bowel, about 600 mL of soap water is administered rectum while soap lubricates. Enema is given prior to surgeries, obstetric procedures and radiological examination of the gut.
Retention enema: The drug is administered with about 100 mL of fluids and is retained in the rectum for local action, e.g. prednisolone enema in ulcerative colitis.
Drugs may be administered as suppository for rectum, bougie for urethra and pessary and douche for vagina. Pessaries are oval shaped tablets to be placed in the vagina to provide high local concentrations of the drug at the site, e.g. antifungal pessaries in vaginal candidiasis.
Drugs may be applied on the skin for action as ointment, cream, gel, powder, paste, etc. Drugs may also be applied on the mucous membrane as in the eyes, ears and nose as ointment, drops and sprays.