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TPTC2 > Constipation 2 - Pharmacology > Flashcards

Constipation 2 - Pharmacology Flashcards

1
Q

Treatment of Constipation

A

•Usually effectively treated with dietary modification (increasing fibre, hydration, exercise)

•Only if this fails should laxatives be used.
Therapy Classes:
1. Bulk-forming laxatives
2. Osmotic laxatives
3. Stimulant laxatives
4. Stool softeners
5. Other agents
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2
Q
  1. Bulk-forming laxatives
A

increase volume of matter in GI tract

bulk forming laxative - increases volume of substance in colon by doing that they activate stretch receptor and tactile receptor in wall of colon and that acts to increase colonic activity and peristalsis

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3
Q
  1. Osmotic laxatives
A

increase the volume of liquid in GI tract

has a dual purpose - by increasing fluid content it makes the stools softer and by increasing volume in the colon it activates stretch receptors and the tactile receptors then increases activity

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4
Q
  1. Stimulant laxatives
A

increase activity of colon

direct stimulants increase activity of muscles in the colon wall and increase peristalsis

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5
Q
  1. Stool softeners
A

act to allow the colon to do its job more efficiently

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6
Q
  1. Other agents
A

viewed as separate due to their mechanism of action

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7
Q

Laxatives: Broad Mechanisms of Action

A
  • fibre increases bulk of stools
  • faecal softener lubricates the stool
  • stimulant increases peristalsis
  • stimulant increases peristalsis
  • osmotic laxative increases fluid content of stool
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8
Q

General Contraindications to Use

A
  • Broadly, laxatives should not be used in the presence of undiagnosed abdominal pain
  • The danger is that the drugs may cause an inflamed organ (eg, the appendix) to rupture and spill GI contents into the abdominal cavity with subsequent peritonitis, a life-threatening condition.
  • Oral drugs also are contraindicated when a diagnosed GI disturbance is likely to be worsened by increased motility (e.g. with intestinal obstruction and fecal impaction or inflammatory bowel diseases)
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9
Q

Bulk Laxatives

A
  • Insoluble Non digestible and non-absorbable (pass into the colon whole and unaffected)
  • Increase in bowel content volume triggers stretch receptors in the intestinal wall
  • Causes reflex contraction (peristalsis) that propels the bowel content forward
  • May take several days – 2 weeks to have full effect
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10
Q

Classes of Bulk Laxatives

A
  • Isphagula (Psyllium)
  • Methylcellulose
  • Sterculia
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11
Q

Bulk laxatives

• ADR’s

A

– Bloating and flatulence; GI obstruction & impaction

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12
Q

Bulk laxatives

• Cautions

A

– Adequate fluid intake should be maintained to avoid obstruction
• May need management in elderly & debilitated patients

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13
Q

Bulk laxatives

• Contraindications

A
  • Colonic atony – colon will not be stimulated by activation of stretch receptors
  • Faecal impaction & intestinal obstruction – increased motility will not lead to defecation
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14
Q

Atony definition

A

muscles in colon are not activated

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15
Q

Osmotic Laxatives

A

-work more rapidly than bulk forming laxative
• Effective in 1-3 hours
• Used to purge intestine (e.g. prior to surgery, poisoning)
• Fluid is drawn into or retained in the bowel by osmotic force, increasing volume and triggering peristalsis (makes stools wetter and softer)

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16
Q

Osmotic Laxatives classes

A

• Nondigestible sugars and alcohols
- Lactulose (broken down by bacteria to acetic
and lactic acid, which causes the osmotic effect)
• Macrogol 3350– polymer of ethylene glycol (acts to retain water in colon)
• Salts
• Magnesium hydroxide (Mg(OH)2) (Milk of Magnesia)
• Sodium Phosphates (used as enema)
• (Epsom Salt (MgSO4)) - very strong and causes very rapid evacuation of colon - not recommended anymore

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17
Q

Two main issues associated with osmotic laxatives

A

– Increased GI activity

– Electrolyte & osmotic imbalances (in danger of dehydration)

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18
Q

Osmotic Laxatives

• ADR’s

A

–abdominal discomfort; diarrhoea

19
Q

Osmotic Laxatives

• Cautions

A

– Broadly those at danger of dehydration (elderly, debilitated); and those at risk of electrolyte imbalance (cardiac diseases)

20
Q

Osmotic Laxatives

Contraindications

A

Acute GI conditions; intestinal obstruction & inflammation

21
Q

Stimulant Laxatives

A
  • Irritate the GI mucosa and Increases intestinal motility
  • Indicated for severe constipation where more rapid effect is required (6-8 hours) or where bulk forming laxatives haven’t had the required effect
22
Q

Stimulant Laxatives classes

A
  • Bisacodyl
  • Anthraquinones – Co-danthramer, Co-danthrusate, Senna
  • (Cascara, Castor Oil - From the Castor Bean – obsolete) NOT RECOMMENDED
23
Q

Pharmacology of Stimulant Laxatives

A

draw chart

Galenic form

  • Bisacodyl -> activated by colonic hydrolases -> activated by bis-(p-hydroxyphenyl)-pyridyl-2-methane
  • Sodium picosulfate -> activated by colonic flora -> activated by bis-(p-hydroxyphenyl)-pyridyl-2-methane
  • Senna -> activated by colonic flora -> activated by rhein anthrone
24
Q

Pharmacology of Stimulant Laxatives - what is galenic form

A

is the formulated form which patients take the medicine in

25
Q

Pharmacology of Stimulant Laxatives: bisacodyl

A

has to be formulated so it reaches the colon before the active ingredient becomes available

26
Q

Pharmacology of Stimulant Laxatives: sodium picosulfate

A

almost a pro drug of bisacodyl

27
Q

Pharmacology of Stimulant Laxatives: colonic hydrolases

A

in the gut wall

28
Q

Pharmacology of Stimulant Laxatives: colonic flora

A

only bacteria found in the colon

29
Q

Pharmacology of Stimulant Laxatives: bis-(p-hydroxyphenyl)-pyridyl-2-methane

A

irritates and activates wall of GI tract

30
Q

Stimulant Laxatives

- main issues

A

• Do what they say on the tin…
– ADR’s, cautions & contraindications similar to osmotic laxatives

Two main issues
– Increased GI activity
– Electrolyte & osmotic imbalances

31
Q

Stimulant Laxatives

• Cautions

A

– Those at risk of dehydration or hypokalaemia

32
Q

Stimulant Laxatives

• CI’s

A

– Inflamed & obstructed intestines; undiagnosed abdominal pain

33
Q

Co-danthrusate and Co- danthramer

A

-very effective laxative
• Evidence of carcinogenicity & genotoxicity in animal studies
• Use limited to patients with terminal illnesses

34
Q

genotoxicity

A

destructive effect on a cell’s genetic material (DNA, RNA) affecting its integrity.

35
Q

carcinogenicity

A

Ability of a carcinogen to produce invasive cancer cells from normal cells.

36
Q

Stool Softners - Emollients (types)

A

• Docusate sodium (surfactant and stimulant) main one used
• Arachis oil (enema) help with fecal impaction
- Peanut oil (allergies)
• Liquid Paraffin (oral solution)
- Extemporaneous preparation

37
Q

Docusate sodium

A

Surfactant and bulking agent (stimulates wall of GI tract)
• Oral: up to 500mg daily in divided doses
– Acts within 1-2 days
• Rectal (enema): 120 mg for 1 dose
– Acts within 20 minutes
• ADRs: Abdominal pain, diarrhoea; hypokalaemia
• Cautions: Patients where hypokalaemia to be avoided; Rectal preparation not indicated with haemorrhoids
• Contraindications :Intestinal blockage

38
Q

Opioid Antagonists for Opioid-Induced constipation - draw diagram and explain

A

draw diagram

  • Endogenous opioids act at opioid receptors in brain and periphery.
  • In the brain activation of central u opioid receptors can provide analgesia (pain relieve).
  • Exogenous opioids such codeine and morphine are used as analgesics for patients in palliative care or patients with cancer.
  • u opioid receptors in GI tract activation leads to changes in muscle tone and sensitivity.
  • Opioid antagonists can be given to block u opioid receptors in GI tract but not all opioid antagonists will be suitable as they may cross the BBB and block action of opioid agonist in the brain aswell.
  • Instead we want Peripheral opioid antagonist to act at gut only and not brain.
39
Q

Methylnaltrexone

A
  • Peripherally acting opioid antagonist
  • Subcutaneous injection; 8-12 mg 4-7 doses/week
  • Tmax: 0.5hr; T1⁄2 8hrs (rapid t max but long half life - leads to well above therapeutic threshold)
  • ADRs: Abdominal pain, diarrhoea; flatulence
  • Cautions: Patients with damaged GI tract
  • Contraindications:Acute surgical abdominal conditions; Intestinal blockage
40
Q

Prucalopride

A
  • Selective 5HT-4 agonist with prokinetic properties (increase activity, decrease GI transit time)
  • 2mg once daily, review after 4 weeks
  • ADRs - wide range of abdominal side effects associated with action
  • Cautions – arrythmias & ischaemic heart disease (hERG) affects QT interval
  • Contraindications – Crohn’s disease, abdominal obstruction and other serious GI conditions
41
Q

Lubiprostone (trade name - Amitiza)

A
  • Chloride channel blocker – acts locally to increase fluid secretion and motility
  • 24 μg (micrograms) twice daily for 2-4 weeks
  • PK – low oral bioavailability – actions in GI tract (limits the ADR to abdominal ADRs)
  • ADR’s – wide range of abdominal side effects associated with action
  • Contraindications – GI obstruction
42
Q

• ALWAYS bear in mind potential for damage

A

– when a diagnosed GI disturbance is likely to be worsened by increased motility
– When undiagnosed abdominal pain is present

43
Q

What does peripheral opioid antagonist do?

A

Peripheral opioid antagonist dislodges opioid from u-opioid receptors in GI tact and this leads to reduction in adverse gastrointestinal effects of exogenous opioid analgesics

TPTC2 (8 decks)

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