Gastro drugs Flashcards
Dosage of Ranitidine
150mg BD or 300mg nocte
Dosage of Omeprazole
20-40mg OD
Dosage of Loperamide
Acute diarrhoea: 4mg then 2mg after each loose stool for up to 5 days, usual dose 6-8mg daily
Dosage of Mesalazine
1.2g-4.8g
Fybogel dose
1 sachet BD after meals
Lactulose dose
15ml BD in constipation
30-50ml TDS in hepatic encephalopathy
Macrogol dose
1-2 sachets daily
Senna dose
2-4 tablets ON
Mechanism of Ranitidine
Histamine H2 receptor antagonist in gastric parietal cell. This reduces stimulation of gastric acid secretion
Mechanism of omeprazole
PPI
H+K+ATPase pump at the secretory surface of gastric parietal cells
Inhibits final transport of H+ into gastric lumen, therefore inhibiting acid secretion
Mechanism of loperamide
Slows intestinal motility by targeting opioid mu receptors in the myenteric plexus of the large intestine (agonist), reducing tone of circular muscle
Mechanism of mesalazine
Aminosalicylate (5-aminosalicylic acid)
Inhibits COX enzymes in the colon, inhibiting mucosal production of arachidonic acid metabolites such as prostaglandins, Therefore reduces colonic inflammation
Mechanism of bulk-forming laxatives (e.g. ispaghula husk)
Polysacchiaride polymers, increase stool volume activating the stretch reflex, stimulating peristalsis
Mechanism of osmotic laxatives (e.g. lactulose, macrogol)
Draw water into the bowel. Accelerates transfer of gut contents through the small intestine
Mechanism of Senna
Stimulant. Increases electrolyte and water secretion by the GI mucosa and increase peristalsis. Directly stimulates the myenteric plexus
Cimetidine (H2 receptor antagonist) can cause what side effect in men?
Gynaecomastia and impotence
Cimetidine should be avoided with which other medications?
Warfarine
Theophylline
Phenytoin
(it is a CP450 inh)
What can PPIs and H2 receptor antagonists mask?
Gastric cancer symptoms - rule out red flag symptoms before starting
What group of patients is PPIs and H2 agonists contraindicated in?
Pregnancy and breast feeding
What interactions does omeprazole have?
Warfarin - increases anticoagulant effect
Clopidogrel - reduces antiplatelet effect
What are some important side effects of omeprazole?
Rebound acid hypersecretion
Hepatitis
Interstitial nephritis
Blood disorders
C. diff
Hypomagnesaemia
What electrolyte may you consider monitoring before and during prolonged PPI treatment?
Magnesium
What is an important side effect of loperamide?
paralytic ileus
What are some contraindications to loperamide?
Active colitis or any other condition where inhibition of peristalsis should be avoided
Should not be given to children below age 4
What are important adverse effects of mesalazine?
Acute pancreatitis
Blood disorders including agranulocytosis
Lupus erythematosus-like syndrome (sulfasalazine)
Renal dysfunction (interstitial nephritis, nephrotic syndrome
What haematological condition must you be careful with in prescribing sulfasalazine?
G6PD deficiency - observe closely for signs of haemolytic anaemia
What conditions should you have caution in prescribing aminosalicylates to?
Elderly
Pregnancy
Breastfeeding
Asthma
Hepatic or renal impairment
What are the interactions for aminosalicylates?
Lactulose - reduces 5-ASA efficacy
Azathioprine (increased risk of leucopenia)
Mercaptopurine (increased risk of leucopenia)
Digoxin (absorption may be reduced)
What must you counsel patients on for aminosalicylates such as mesalazine?
To report any unexplained bleeding, bruising, sore throat, fever, malaise
Let them know that sulfasalazine can cause yellow-orange discolouration of skin, urine and other body fluids
Which laxative do you have to use with caution with those who are lactose intolerant?
Lactulose
