Review of Pharmacology - 9E (2015)

Review of Pharmacology
brain. It is metabolized by CYP3A4 enzymes and can also inhibit the metabolism of
drugs metabolized by this enzyme e.g. warfarin.
• Fosaprepitant is an intravenous prodrug of aprepitant.
• Netupitant is a newer NK1 antagonist approved for chemotherapy induced vomiting
(both acute and delayed in combination with palonosetron)
Drugs for Post Operative Vomiting
5 HT 3
antagonists are preferred over other drugs.
Other Drugs for Vomiting
• Steroids like dexamethasone can be used as anti-emetic agents in chemotherapy
induced vomiting.
• Benzodiazepines like lorazepam and alprazolam may be useful for anticipatory
component of nausea and vomiting before surgery.
• Dronabinol (a cannabinoid) possesses anti-emetic properties and acts by stimulating
CB 1
receptors. It can also stimulate appetite (used for AIDS with anorexia). Central
sympathomimetic (tachycardia, palpitations etc.) effects, paranoid reactions and thinking
abnormalities may appear as adverse effects.
Emetic Drugs
Apomorphine and ipecacuanha can be used to produce vomiting for treatment of poisonings.
Emetics should not be used for kerosene and corrosive (acid and alkali) poisonings.
Gastrointestinal Tract
Gastroesophageal Reflux Disease (Gerd)
It is a condition in which acid in the stomach reaches the esophagus and causes mucosal
inflammation. Two strategies for the management of this condition are either to decrease the acid
production (by PPIs) or to increase the forward movement of GIT (so that the contents do not reflux
upwards). The drugs used for increasing the GI motility are known as prokinetic drugs.
These drugs can also be used for the treatment of gastroparesis, post operative paralytic ileus
and constipation.
Prokinetic Drugs
• ACh is the main excitatory neurotransmitter in the GIT. Cholinergic neurons contain
excitatory (5-HT 4
) as well as inhibitory (5HT 3
, D 2
) presynaptic receptors.
• Thus D 2
and 5HT 3
antagonists and 5 HT 4
agonists will increase the release of ACh and
stimulate the GI motility.
Metoclopramide
It possesses central as well as peripheral D 2
responsible for its antiemetic effects.
blocking action. Central D 2
blocking action is
• It is also a prokinetic drug due to agonistic action at 5HT 4
receptors (main
mechanism) and antagonistic action at 5HT 3
receptors.
• Prokinetic action is due to release of ACh and thus can be antagonized by atropine.
It increases gastric peristalsis (enhances gastric emptying) and LES tone but has no
effect on colonic motility.
• Metoclopramide is mainly used as an antiemetic agent. It can also be used in
GERD and for the treatment of gastroparesis (in diabetic patients). Another
indication of this drug is to enhance gastric emptying for emergency general
anaesthesia (if the patient has taken food within 4 hrs.)
• D 2
blocking action can result in extrapyramidal side effects (muscle dystonia,
Parkinsonism etc.) and hyperprolactinemia (leading to galactorrhoea).
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