Drug Classification: Gastrointestinal system

Domperidone

UNDER REVIEW (September 2016)

Mechanism of Action:

Dopamine D2 receptor antagonist.

Lecture and CAL materials:

Hyoscine

UNDER REVIEW (September 2016)

Mechanism of Action:

Peripherally acting muscarinic receptor antagonist (antimuscarinic) that competitively inhibits the action of acetylcholine (ACh) at muscarinic receptors. Muscarinic AChRs are seven-transmembrane G-protein-coupled receptors which are activated by the endogenous neurotransmitter, ACh. They are generally associated with the parasympathetic nervous system, and also cholinergic transmission in the CNS. Hence, antimuscarinics block the effects of parasympathetic nerve stimulation and so dilate pupils, reduce intestinal motility and smooth muscle contraction and reduce secretions from glands (sweat, salivary, bronchial).

Lecture and CAL materials:

Infliximab

UNDER REVIEW (September 2016)

Mechanism of Action:

Infliximab is an injectable antibody that blocks the effects of tumor necrosis factor alpha (TNF alpha). TNF alpha is a pro-inflammatory cytokine, a substance made by cells of the body which has an important role in promoting inflammation.

Lecture and CAL materials:

Azathioprine

Mechanism of Action:

Cytotoxic immunosuppressant- azathioprine is a prodrug. It is metabolized to its active form mercaptopurine, a purine analogue which inhibits DNA synthesis. Clonal proliferation of the immune response is thus inhibited&#059; may also inhibit cytokines and growth factors. Mercaptopurine is released slower from azathioprine and is more effective as an immunosuppressant. (mercaptopurine is more useful as an antineoplastic drug). Drug action is potentiated by allopurinol (gout medication-gout is caused by excessive purine degradation to uric acid) which inhibits xanthine oxidase. This enzyme acts to degrade azathioprine. The dosage of azathioprine should be reduced by 25% with concurrent use of allopurinol. Thiopurine methyltransferase (TMPT) is another enzyme that degrades azathioprine. Individuals homozygous for low TMPT are susceptible to myelosuppression (bone marrow suppression). See comments.

Lecture and CAL materials:

Sulfasalazine

UNDER REVIEW (September 2016)

Mechanism of Action:

An aminosalicylate drug that is a combination of a sulphonamide (an antibiotic) and 5-aminosalicylic acid (5-ASA, an aspirin derivative). Mode of action unknown: sulfasalazine is a prodrug, that is, it is not active in its ingested form but is broken down by bacteria in the colon into its two constituents: 5-aminosalicylic acid (5ASA), and sulfapyridine. There is some controversy as to which of these two products are responsible for the activity of sulfasalasine. It reduces cytokine production and inflammatory activity. The anti-inflammatory action of 5-ASA is at least in part mediated through modulation of the endocannabinoid system via elevation of anandamide levels – anandamide being an endogenous cannabinoid.

Lecture and CAL materials:

Loperamide

Mechanism of Action:
Peripherally acting µ opioid receptor agonist which is negligibly absorbed from gut and does not cross blood-brain barrier. It therefore acts on opioid receptors in the myenteric plexus of the gut, but not in the CNS.

Indications:

  • Non-infective diarrhoea
  • Reducing output of stoma

Mu opioid receptors are transmembrane G-protein coupled receptors. Activation prevents adenylate cyclase from converting ATP to cyclic AMP. This opens potassium channels (potassium leaves the cell), leading to hyperpolarisation and decreased neuronal excitability. It also blocks calcium channels which affects transmission of impulses. Hence, opioid agonists have an inhibitory effect on neurons. The activation of opioid receptors in the enteric nerve plexus enhances tone and regularity of intestinal contractions but inhibits propulsive motor activity

Lecture and CAL materials: (under review)

Glycerol

UNDER REVIEW (September 2016)

Mechanism of Action:

Glycerol is a component of triglycerides that forms the backbone linking fatty acids together. It is soluble in water and has many uses, medically (e.g. as a lubricant, laxative, and in medications to treat cough) and otherwise (e.g. in liquid soap).

Lecture and CAL material:

Ricinoleic Acid

UNDER REVIEW (September 2016)

Mechanism of Action:

Ricinoleic acid is an unsaturated fatty acid that makes up a large part of castor oil. It has long been used as a irritant purative because of its laxative properties. It is also used to treat skin problems like inflammation (anti-inflammatory properties) and infection (bactericidal). It offers some degree of analgesia

Lecture and CAL materials:

Senna

UNDER REVIEW (September 2016)

Mechanism of Action:

Derived from a shrub-like plant that has glycosides of sugar and anthracene (which is oxidized to anthraquinone). Has been used since ancient times as a purgative agent. Bacteria work on senna (the drug) to break the glycosidic bond, releasing anthracene into the colon. There it stimulates enteric nerves that control the GI system to increase smooth muscle activity and also leads to secretion of water and electrolytes.

Lecture and CAL materials: