The rectum: a useful back door
Rectal delivery is the route of choice when the mouth is unavailable — a patient who is vomiting, unconscious, or an infant who will not swallow. A [[suppository|suppository]] is a solid, bullet-shaped dose that melts at body temperature (a fatty base) or dissolves in the rectal fluid (a water-soluble base), releasing its drug to act locally on haemorrhoids or be absorbed for a whole-body effect such as fever or seizure control.
The vagina: mostly local, sometimes more
Vaginal delivery is used mostly for local action — antifungal creams, antibacterial gels, pessaries (vaginal suppositories) and hormone preparations for local symptoms. Like the rectum it drains partly around the liver, so it can also give a systemic effect, used for some hormones and labour-inducing drugs. Because the tissue is a mucous membrane, mucoadhesive gels and rings are popular here too, holding the drug in place for hours or even weeks.
Choosing a door: one way of thinking
Step back and the whole track collapses into a single decision. Picking a route of administration is a conversation between the drug, the target and the patient. Ask in order: where does the disease live, what will survive the journey, and what can this particular person actually use?
- Where is the target? If the disease is local — airway, eye, skin, vagina — deliver there directly for site-specific action and small doses.
- Does the drug survive the gut and liver? If it is destroyed by stomach acid, gut enzymes or the first-pass effect, pick a route that bypasses them — transdermal, sublingual, nasal, pulmonary or rectal.
- How fast must it act? Sublingual and nasal are minutes; a transdermal patch is hours-to-days of steady level; choose the kinetics the therapy needs.
- Can the patient use it? Weigh compliance: a confused elder cannot coordinate an MDI; a vomiting child needs a suppository; a forgetful adult may do better on a weekly patch than a daily pill.