GI pharmacology Flashcards
Main drug classes used in GI disease (5)
Acid suppressants Drugs affecting GI motility Laxatives Drugs for IBD Drugs affecting intestinal secretions
Name 3 acid suppressant drugs
Antacids
H2 receptor antagonists
Proton pump inhibitors
Name 3 drugs affecting GI motility
Anti-emetics
Anti-muscarinics/ other anti-spasmodics
Anti-motility agents
Name 4 drugs used for IBD
Aminosalicylates
Corticosteroids
Immunosuppressants
Biologics
Name 2 drugs affecting intestinal secretions
Bile acid sequestrants
Ursodeoxycholic acid
Mechanism of antacids
Contain magnesium or aluminium to neutralise gastric acid
Indications of antacids
When symptoms occur, e.g. heartburn
What are alginates + mechanism of action
Acid suppressant, e.g. gaviscon
-forms a viscous gel that floats on stomach contents and reduces reflux
Name 2 histamine receptor antagonists
Ranitidine
Cimetidine
Mechanism of action of histamine receptor blockers
Block histamine receptor therefore reducing gastric acid secretion
Indications of histamine receptor antagonists (2)
GORD
peptic ulcer
Name a proton pump inhibitor
Omeprazole
Mechanism of action of proton pump inhibitors
Blocking the H+/K+ ATPase (gastric proton pump) so reducing gastric acid secretion
Decreasing gastric acid in stomach can aid the healing of what
aid the healing of duodenal ulcers and reduce the pain from indigestion and heartburn
Indications of PPIs (3)
GORD
Peptic ulcer
H. pylori infection
Complications/prolonged use of PPIs (3)
Predispotion to C. diff infection
Hypomagnesaemia- fatigue, muscle tremor
B12 deficiency - fatigue, muscle tremors
What do prokinetic agents do + name 2
increase gut motility and gastric emptying
metoclopramide, domperidone
What is gastroparesis
nerves controlling stomach muscles/ the muscles themselves don’t work properly –> inadequate grinding –> poor gastric emptying
Mechanism of action of prokinetic agents
Involves parasympathetic nervous system controlling smooth muscle and sphincter tone via ACh
Domperidone is an antagonist of what neurotransmitter + domperidone mechanism
Dopamine
blocking dopamine receptors inhibits post-synaptic cholinergic neurones
Stimulants of the vomiting centre in the medulla
- chemoreceptor trigger zone triggered by what (1)
- vestibular nuclei triggered by what (1)
- cerebral cortex triggered by what (2)
- pharynx & GIT triggered by what (2)
Chemoreceptor trigger zone (in the brain) – triggered by some drugs/toxins
Vestibular nuclei – triggered by excess motion (motion sickness)
Cerebral cortex – triggered by smell or sight of things
Pharynx & GIT – triggered by gastroenteritis, radiotherapy, some drugs
Antimuscarinics act on what centre
Vomiting centre
Anti-spasmodics 3 mechanisms of action
They are anti-cholinergic (muscarinic receptor antagonists)
–> so inhibit smooth muscle contraction in gut wall + ureter –> relaxation and less spasm
Are direct smooth muscle relaxants
Block calcium channels
–> reduce calcium needed for smooth muscle contraction
Name 2 drugs which decrease GI motility + what they are used for
Loperamide
Opioids
Can be beneficial as an anti-diarrhoea agent
Mechanism of drugs which decrease motility
Activate opiate receptors in GI tract, causing them to decrease ACh release decreased smooth muscle contraction of GI tract increased anal sphincter tone
4 types of laxatives
bulk, osmotic, stimulant, softeners
laxatives work by increasing bulk or drawing fluid into gut
Complications of laxatives (3)
Gut obstruction
Need for other measures to allow laxative to work
-Osmotic laxatives won’t work without adequate fluid intake
Misuse – can get addicted
What laxative shouldn’t be used for IBS as it may cause bloating
Lactulose
First-line choice of anti-motility drug for relief of diarrhoea in IBS
Loperamide
Name 2 aminosalicylates used for IBD
Mesalazine
Olsalazine
Aminosalicylates route of administration (2)
Oral or rectal
Aminosalicylates are anti what
Anti-inflammatory
Contraindication of aminosalicylates
Renal impairment - need to be cautious with use
Adverse effects of aminosalicylates (5)
GI upset Blood dyscrasias (disease of blood cells) Renal impairment Headache Pancreatitis
Adverse effects of corticosteroids used in IBD (5)
Osteoporosis Facial puffiness weight gain Increased susceptibility to infection ADDISONIAN (ADRENAL) CRISIS if corticosteroid is abruptly withdrawn
When do you get addisonian (adrenal crisis)
If corticosteroid is abruptly withdrawn
Name corticosteroids used in IBD (2)
Prednisolone
Hydrocortisone
3 routes of administration of corticosteroids in IBD
Oral/IV/rectal
Name 2 immunosuppressants used in IBD
Azathioprine
Methotrexate
Mechanism of action of immunosuppressants
prevents purine formation needed for DNA synthesis so reduces immune cell replication
Adverse effects of immunosuppressants
Bone marrow suppression
Hypersensitivity of azathioprine –> ORGAN DAMAGE (lung, liver, pancreas)
Mechanism of action of biologics (anti-TNFa antibodies)
prevents action of TNFa (important cytokine in inflammatory response)
Name a biologic used in IBD
Infliximab
3 Contraindications of infliximab (a biologic used in IBD)
TB
MS
Pregnancy/breast feeding
Adverse effects of infliximab (5)
Infection risk, especially TB Fever + itch Anaemia Thrombocytopenia (low platelets) Neutropenia (low neutrophils) Malignancy
Mechanism of action of cholestyramine (a drug affecting biliary secretions)
reduces bile salts by binding with them and excreting them as insoluble complex
What is ursodeoxycholic acid (UDCA) used for (2)
Gallstones
Primary biliary cholangitis
Mechanism of action of ursodeoxycholic acid (UDCA)
inhibits an enzyme involved in formation of cholesterol, altering cholesterol content in bile
Reduces cholesterol absorption
How is absorption of drugs affected
pH
Gut length
Transit time of food
GI disease can affect ADME of drugs - what are these
ABSORPTION, DISTRIBUTION, METABOLISM AND EXCRETION
How can distribution of drugs be affected in some GI/liver diseases
Low albumin in some GI/liver diseases –> decreased albumin to bind to drug in blood –> therefore increased free drug concentration
How can metabolism of drugs be affected in some GI/liver diseases (4)
Increased liver enzyme levels –> toxic effects
Increased gut bacteria in some diseases –> metabolise drugs faster? –> so higher dose needed
Disease may reduce gut wall metabolism
Disease can also affect liver blood flow
How can excretion of drugs be affected in some GI diseases
Biliary excretion can be more toxic than usual
Diarrhoea is an adverse effect of what drugs (2)
Cholinergics
Antimicrobials
Constipation is an adverse effect of what drugs (2)
opioids,
anticholinergics
GI bleeds/ulcers are caused by what drugs (2)
Aspirin
NSAIDs
Type A adverse drug reactions are… (2)
Predictable
Dose dependent
What type of ADR can cause intrinsic hepatotoxicity (liver injury)
Type A
Risk factors of adverse hepatic reactions (6)
Young or elderly Female Alcohol Genetics Malnourishment
Severity of liver disease measured with what classification
CHILD-PUGH CLASSIFICATION
Describe the child-pugh classification (a measure of liver disease severity, assesses prognosis of CLD such as cirrhosis) (3)
Classification A = <7
Classification B = 7-9
Classification C = >9
Avoid what drugs in those with liver disease (3)
Methotrexate - hepatotoxic
Benzodiazepines - worsen non-liver aspects of liver disease (precipitate encephalopathy)
Those are toxic due to changes in pharmacokinetics
where to find information about risks with specific drugs in liver disease
BNF guidance
