Oral

This is convenient and is indicated for patients who can ingest and tolerate an oral form of medication. Some medications with short half-lives are administered orally as timed-release or sustained-release forms that get absorbed over several hours.

Advantages:

• Ease of administration
• Widespread acceptance by the patients.

Disadvantages:

• Variable absorption rates
• Degradation of some drugs before reaching the site of absorption into the bloodstream
• The inability of many compounds to effectively traverse the intestinal epithelial membrane cells to reach the bloodstream.
• The insolubility of many drugs at low pH levels prevalent in the digestive tract.
• The inactivation of the drug in the liver on its way to the systemic circulation
• Irritation of the mucous lining of the gastrointestinal tract. This can be prevented to some extent by coating.  

Sublingual and Buccal Routes

These are indicated for medications with high first-pass metabolism that need to avoid clearance by the liver. For instance, nitroglycerin is cleared more than 90% during a single pass through the liver; therefore, it is given in a sublingual form.

Advantages:

• Rapid absorption due to the abundant mucosal network of systemic veins and lymphatics, thereby leading to a rapid onset of action.
• If there is any untoward event, the tablet can be removed.
• Avoids first-pass hepatic metabolism.
• A tablet can be kept for a long duration of time in the buccal cavity which helps the development of formulations having a sustained-release effect.
• This route is useful in patients having swallowing difficulties.
• Low risk of infection
• Convenience

Disadvantages:

• The tablet has to be kept in place in the buccal cavity and neither chewed nor swallowed.
• Excessive salivation may cause quick dissolution and absorption of the tablet.
• Patients may find it difficult to accept an unpalatable tablet. Hence some drugs are applied as a patch or a spray.

Rectal Route

This route is useful for patients with gastrointestinal motility problems such as dysphagia or ileus that can interfere with delivering the drug to the intestinal tract. The rectal route is also often utilized in patients near the end of life undergoing hospice care.

Advantages:

• A relatively big amount of the drug can be administered.
• Those drugs that are destroyed by the acidic medium in the stomach and those metabolized by pancreatic enzymes can be administered effectively.
• Safe and convenient for infants and the elderly.
• Can be used in emergency situations such as in infants having seizures when the intravenous route is unavailable.
• The rate of absorption is uninfluenced by the ingestion of food or the rate of gastric emptying.
• Bypasses hepatic metabolism
• Less degradation of drugs compared to that in the upper gastrointestinal tract.

Disadvantages:

• Some hydrophilic drugs like antibiotics and peptide drugs are not suitable for rectal administration as they are not readily absorbed.
• Some drugs can cause rectal irritation and proctitis leading to ulceration and bleeding.