Gastrointestinal tract (GIT) medications Flashcards
Oral cavity
Substances enter the digestive system through the mouth. As food enters, the salivary glands release saliva, which mixes with the food to form a bolus (a wet mass). The mouth is the first site of chemical digestion, while chewing (mastication) breaks down food into smaller pieces for swallowing.
Drugs can enter the mouth as tablets, capsules, or liquids and are usually swallowed to enter the digestive tract. However, not all drugs are swallowed. Some, given by the buccal (inside the cheek) or sublingual (under the tongue) routes, are absorbed quickly through the mouth lining, bypassing the rest of the digestive system.
Oesophagus
The pharynx connects to the stomach through the esophagus, a long tube. Two muscular sphincters, at the top and bottom of the esophagus, open during swallowing to let food pass from the pharynx to the stomach.
The esophagus doesn’t play a big role in drug absorption. However, if the upper sphincter is weak or relaxed, stomach acid can flow back into the esophagus, causing heartburn or acid reflux. Some gastrointestinal medications are designed to neutralize this acid and relieve symptoms of reflux.
Stomach
When the bolus reaches the stomach, it is mixed with stomach secretions and broken down into chyme, a semifluid mass. While some protein and fat digestion happens here, very little absorption occurs in the stomach. After 2-6 hours, the chyme is slowly released into the small intestine.
The stomach lining has five types of cells that aid digestion. Four of them (surface mucous cells, mucous neck cells, parietal cells, and chief cells) produce gastric secretions, which include mucin (protects the stomach), intrinsic factor (helps absorb vitamin B12), hydrochloric acid, and pepsin. The fifth cell type, G cells, releases gastrin, which helps with stomach movement and secretion.
Though the stomach doesn’t absorb much food, it can absorb drugs, especially acidic ones like aspirin. To prevent disintegration in the stomach’s acidic environment, some drugs are enteric coated so they dissolve in the intestines instead. The speed at which the stomach empties can also impact how quickly a drug is absorbed, with faster emptying leading to quicker absorption.
Small intestine: Duodenum, jejunum and ileum
Chyme leaves the stomach in small amounts and enters the duodenum, the first part of the small intestine. In the small intestine, it mixes with bile and pancreatic juices from the gallbladder and pancreas. These secretions are controlled by two hormones, CCK and secretin. The chyme then moves to the jejunum for digestion and absorption, and this continues in the ileum, the last part of the small intestine.
Most drugs are absorbed in the intestines due to their large surface area. Food in the gut can affect drug absorption, which is why some drugs are taken before meals (for faster absorption) and others with food (to prevent stomach irritation). Gastrointestinal issues like vomiting, diarrhea, or constipation can also affect how well drugs are absorbed.
Large intestine
The watery chyme moves from the small intestine into the large intestine, which extends from the ileum to the anus. The large intestine includes the caecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anus. Its main job is to absorb water and electrolytes (like sodium and chloride), turning the chyme into faeces. Bacteria in the large intestine help break down leftover carbohydrates, proteins, and fats.
Inflammation can change the structure and function of the gut wall, which may affect drug absorption, depending on the affected area. The GIT also plays a role in drug excretion, with some drugs being excreted in bile and removed with faeces.
Introducing solids/liquids into the oral cavity
Ingestion
Mixing and moving material through the GIT
Motility
Manufacturing and releasing substances that facilitate digestion
Secretion
Breaking down (mechanically or chemically) ingested food into smaller structures
Digestion
Transporting digested molecules, electrolytes, vitamins, water from the GIT into the blood or lymph
Absorption
Expelling indigestible or unabsorbed material
Elimination
An introduction to gastrointestinal tract conditions
Good bowel function relies on a diet with enough fiber, proper fluid intake, and regular physical activity, which may also help prevent some gastrointestinal diseases. Some GIT issues, like nausea, vomiting, diarrhea, and constipation, are temporary and linked to infections or diseases, while others are chronic and need ongoing treatment.
Nausea and vomiting
Definition
Nausea is an uneasiness of the stomach
Vomiting is the forcible voluntary or involuntary emptying of stomach contents through the mouth
Processes at play
Causes include food allergies, seasickness, morning sickness, GIT infections, and some medications, including cancer treatments
Gastric reflux (Heartburn)
Definition
Excessive activity of the stomach acid
Processes at play
Stomach produces hydrochloric acid or HCl and this acid flows up into the oesophagus
If prolonged is referred to as gastro-oesophageal-reflux disease (GORD)
Peptic ulcers
Definition
An erosion or break in the stomach mucosa - allows contacts between eroded area and the stomach’s acid (HCl)
Processes at play
Erosions may be caused by bacteria e.g. Helicobacter pylori (a spiral-shaped bacteria)
May occur from overproduction of acid (rare) e.g. from gastrin-producing tumours
Diarrhoea
Definition
An increase in number of stools (usually three or more per day) and passage of unformed faeces
Processes at play
Can be caused by a range of conditions/medical interventions including emotional stress, anxiety, colon disease (e.g. Crohn’s disease), food allergies or intolerances, intestinal infection, medications (e.g. iron, antibiotics), surgery of colon, enteral nutritional therapy
Constipation
Definition
A decrease in frequency of normal bowel movements
Processes at play
Causes include low fibre diet, poor fluid intake, ignoring urge to defecate, cognitive disorders, neurological disorders
Irritable bowel syndrome
Definition
A condition where the colon contracts more or less often than “normal”
Processes at play
Exact cause is unknown
May be associated with bacterial overgrowth, can develop after severe diarrhoea
Colitis
Definition
A condition where the colon contracts more or less often than “normal”
Processes at play
Several types including ulcerative colitis, infectious colitis and Chron’s disease
Colon polyps
Definition
Benign (non-cancerous) growths in the tissues of the lower GIT
Processes at play
Exact cause is unknown
Colorectal (bowel) cancer
Definition
Abnormal cells develop and start to invade surrounding tissues of the lower GIT
Processes at play
Abnormal cancerous cells may develop from precancerous polyps
Risk factors for colorectal cancer include family history, diet low in fibre, lack of physical activity, obesity and high alcohol intake
Upper gastrointestinal tract medications
Drugs used to treat gastric reflux and GORD include antacids, H2 receptor antagonists, and proton pump inhibitors (Bullock & Manias, 2022). Peptic ulcers are treated by antibiotics and other medications (such as proton pump inhibitors, antacids, and histamine H2 receptor antagonists) in order that the underlying infection can be eliminated, and the stomach acid minimises or neutralised to promote healing
Histamine H2 antagonists
Examples
Ranitidine (Zantac)
Nizatidine (Tazac)
Famotidine (Ausfam)
NB: Cimetidine (Tagamet) was a commonly used H2 antagonists however it was removed from the Australian Register of Therapeutic Goods in July 2022 (Health Direct, 2022).
Action
Block the release of gastric acid
Processes at play
H2 receptor antagonists target the three receptors in the stomach wall responsible for stomach acid production (histamine H2 receptors, muscarinic receptors and gastrin receptors).
By interacting with the receptors, histamine H2 receptor antagonists block the production of stomach acid.
Important nursing knowledge
Long term side effects of medications that influence stomach acid levels is disruption of the absorption of various substances in the stomach (such as vitamin B12 and magnesium).
Regular testing of these substances in the blood and possible supplementation of these substances may be required
Administration is not affected by food.
Antacids
Examples
Mylanta
Gaviscon
Action
Combine with hydrochloric acid and neutralise it
Indication / Processes at play
Made from magnesium hydroxide and aluminium hydroxide (weak bases)
Important nursing knowledge
Antacids may interact with the absorption (and therefore impact) of other medications
Take 2 hours before or after other medications.
Proton pump inhibitors
Examples
Omeprazole (Losec)
Action
Reduce the production of hydrochloric acid
Processes at play
Inhibit the production of the hydrogen (H+) proton needed to make it
Important nursing knowledge
Side effects include dry mouth, nausea, vomiting and abdominal discomfort
Increases the risk of developing upper respiratory tract infections.
Serotonin antagonists
Examples
Ondansetron (Zofran)
Action
Blocks the HT3 receptor
Indication
Anti-emetic (stops nausea and vomiting)
Important nursing knowledge
Side effects include confusion, dizziness, tachycardia
Lower gastrointestinal tract medications
Constipation is also caused by a range of conditions and is a side effect of many medications. Laxatives (also called aperients) are medications used to ease constipation and they are grouped into categories based on their mode of action
Osmotic laxatives
Method of action
Water is retained, or even pulled back into the colon through osmosis
Examples
Glycerol
Lactulose
Onset of action
24 - 72 hours
Faecal softener
Method of action
Hold water molecules in the faecal matter, rendering them softer and easier to pass
Examples
Docusate (Coloxyl)
Paraffin (Agarol)
Onset of action
24 - 72 hours
Stimulant laxatives
Method of action
Causes an increase in peristalsis by irritating the smooth muscle of the intestinal wall
Examples
Caster oil
Sennosides
Onset of action
6 - 12 hours
Bulk forming laxatives
Method of action
Dietary fibre, found in the outer coatings of seeds and grains is not digestible in humans
This adds bulk to the colonic contents, which stimulates movements and the defecation reflex
Examples
Fybogel
Metamucil
Onset of action
48 - 72 hours
What is an aperient?
An aperient (also termed a laxative) is a medication used in the management of constipation.
Aperients can be classified into four (4) groups based on their mode of action.
Name the four types of aperients.
- Osmotic laxatives
- Stimulant laxatives
- Faecal softeners
- Bulk forming laxatives
What is the mechanism of action of an osmotic laxative?
An osmotic laxative draws water into the colon by osmosis, softens stool and increases peristalsis.
What is the mechanism of action of a stimulant laxative?
A stimulant laxative increases peristalsis by irritating smooth muscles of the intestinal wall.
What is the mechanism of action of a faecal (stool) softener?
A stool softener holds water molecules in faecal matter to soften faeces and allow it to pass.
What is the mechanism of action of a bulk forming laxative?
A bulk forming laxative adds bulk to colonic contents and stimulates peristalsis and reduces transit time.
