Anti-emetics and Drugs Affecting Gastrointestinal Motility MCQs

A laxative that mildly stimulates the gut would be most suitable in a patient taking a smooth muscle relaxant drug such as verapamil. By holding water in the intestine, magnesium hydroxide provides additional bulk and stimulates increased contractions . A helpful mnemonic is magnesium "magnifies" stool, aluminum halts the stool. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 1091

Perception of motion and orientation is determined by input from the vestibular, visual, and somatosensory systems. These 3 systems are usually congruent, but conflicting input can lead to motion sickness, characterized by nausea, dizziness, and autonomic symptoms (eg, diaphoresis). Integration of these sensory pathways occurs in the vestibular nuclei via muscarinic M1 and histaminic H1 neurotransmission. As such, antimuscarinic agents (eg, scopolamine) and first-generation antihistamines (eg, meclizine, dimenhydrinate) are most effective for management of motion sickness. Anticholinergic side effects are common with these medications and may include blurry vision, dry mouth, urinary retention, and constipation. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 1108

Linaclotide is approved for the treatment of chronic constipation and IBS with predominant constipation. Linaclotide activates guanylyl cyclase-C on the luminal intestinal epithelial surface, which leads to activation of the cystic fibrosis transmembrane conductance regulator (CFTR) leading to increased chloride-rich secretion and acceleration of intestinal transit. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 1103

Central anticholinergics These are drugs having a higher central: peripheral anticholinergic action ratio than atropine, but the pharmacological profile is similar. The central anticholinergics act by reducing the unbalanced cholinergic activity in the striatum of parkinsonian patients. These drugs produce 10-25% improvement in parkinsonian symptoms lasting 4-8 hours after a single dose. Generally, tremor is benefited more than rigidity; hypokinesia is improved the least. Sialorrhoea is controlled by their peripheral action. Anticholinergics are the only drugs effective in drug (phenothiazines, other D2 antagonists) induced parkinsonism. The side effect profile is similar to atropine. Impairment of memory and cognition, organic confusional states and blurred vision are more common in the elderly. Urinary retention is possible in elderly males.

Serotonin plays a major regulatory role in the enteric nervous system, and the potent 5-HT3 receptor antagonist alosetron has shown efficacy in treating women with IBS that is accompanied by diarrhoea. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 1093

Of the drugs listed, only metoclopramide is considered a prokinetic agent (i.e., one that increases propulsive motility in the gut) . Alosetron is a 5HT3 receptor blocker, cimetidine is a H2 receptor blocker, loperamide is an opioid, and sucralfate forms a protective layer over an ulcer. Reference: Basic & Clinical Pharmacology by Bertram G. Katzung, 14th Edition, Page number- 1099.

Aprepitant and ondansetron, both are used to treat chemotherapy induced nausea and vomiting. Aprepitant acts by inhibition of NK1 receptors in the solitary nucleus. Central anti-emetic effect B : Bosentan, competitive antagonist of endothelin-1 at the endothelin receptor that decreases pulmonary vascular resistance. Commonly used for treatment of pulmonary arterial hypertension. C: Bradykinin, not a drug but mediator, which releases from ACEi. D : Ondansetron is an antagonist at 5-HT3 receptors. Reference: Basic & Clinical Pharmacology, Fourteenth Edition By Bertram G. Katzung Pg no. 290

Explanation: With better understanding of the impact of multimodality treatment, chemotherapy is used as both definitive and adjuvant regimens. The mechanism of action of the various drugs used in head and neck SCC are as follows. Platinum Compound cisplatin and Carboplatin - form DNA cross links (Option A) Taxanes - paclitaxel and docetaxel - stabilise microtubules to block M phase (Option B) Antifolates - Methotrexate - inhibit DHFR during S phase (Option C) Fluoropyrimidines - 5 Fluorouracil - inhibit DNA synthesis during S phase (Option D)