create an osmotic force in the lumen that draws water into the stool, resulting in more viscosity and more bulk. salts are more potent that sugars, but sugars are especially useful for opiate constipation and the elderly (or both!).
docusate salts are surfactants that allow mixing of aqueous and fatty substances in the stool. they also increases intestinal fluid secretion.
mineral oil MOA
slows absorption of water in the colon and softens the stool.
mineral oil side effects
N/V/D, perianal irritation, abdominal cramps, weakness, dizziness, syncope. messes with absorption of fat-soluble vitamins. do not administer hs due to danger of lipid pneumonitis.
Laxatives -- peripheral opioid antagonists drugs
peripheral opioid antagonists MOA
activation of µ opioid receptors in the gut slows things down. antagonization of these receptors increases peristalsis in the colon.
Cannabinoid agonists drugs
dronabinol (THC), nabilone, cannabidiol
Cannabinoid antagonists drugs
cannabinoid receptors are G-protein-coupled receptors found throughout the body, including in the mesolimbic dopamine pathway (reward pathway), and importantly here CB1 receptors in the hypothalamus are associated with feeding. These receptors are also found in adipocytes.
Cannabinoid agonists pharmacokinetics
oral bioavailability low to due first-pass metabolism. THC and its metabolites are both active.
Cannabinoid antagonists pharmacokinetics
lipophilic with very long half life (6-9 days, 16 days in obese pts due to fatty tissue deposits)