JNTU B.Pharmacy III PHARMACOLOGY-III Previous Question Paper (August-2022 - R17)

Mast cell stabilizers, such as sodium cromoglycate and nedocromil, are prophylactic agents used primarily in the management of bronchial asthma and allergic conditions.

The mechanism of action involves the stabilization of the mast cell membrane, which prevents the degranulation process. By inhibiting the influx of calcium ions into mast cells upon antigen-antibody interaction, these drugs block the release of inflammatory mediators like histamine, leukotrienes, and prostaglandins, thereby preventing the early and late-phase allergic responses.

Their pharmacological actions include the inhibition of bronchospasm induced by allergens, exercise, or cold air. They do not possess bronchodilator or anti-inflammatory activity themselves and are ineffective in treating an acute asthma attack.

The adverse effects are generally mild due to poor systemic absorption. Common effects include throat irritation, cough, dry mouth, and transient bronchospasm upon inhalation. Rarely, hypersensitivity reactions may occur.

Anti-emetics acting through 5-HT receptors primarily target the 5-HT3 receptor subtype, which is located on the vagal afferent nerve terminals in the gastrointestinal tract and in the chemoreceptor trigger zone (CTZ) of the area postrema in the brain.

The 5-HT3 receptor antagonists, commonly known as 'setrons', include drugs like ondansetron, granisetron, and palonosetron. These agents competitively block the binding of serotonin to 5-HT3 receptors, thereby inhibiting the emetic reflex triggered by chemotherapy, radiotherapy, or post-operative stimuli.

Key pharmacological features include:

• Efficacy: They are highly effective in controlling acute phase chemotherapy-induced nausea and vomiting (CINV).
• Pharmacokinetics: These drugs have a high therapeutic index and are often administered intravenously or orally. Palonosetron has a significantly longer half-life, providing better protection against delayed emesis.
• Adverse Effects: The most common side effects are headache, constipation, and dizziness. A clinically significant concern is the potential for QTc interval prolongation, which requires caution in patients with cardiac conduction abnormalities.