Test: Autacoids - 1 - NEET PG MCQ

• First Generation Antihistamines can cross the blood-brain barrier and have additional anticholinergic effects, which are absent in second generation medications.
• Cyclizine is an example of a first generation antihistamine, while cetirizine, loratadine, and fexofenadine are classified as second generation drugs.

Although both histamine and bradykinin can lead to swelling and heightened permeability, histamine is classified as an amine, while bradykinin is a peptide.

Obstetric uses of ergometrine (Ergonovine) include:

• Managing and preventing postpartum haemorrhage.
• Administered during the delivery of the anterior shoulder.
• Given after a Caesarean section or instrumental delivery to avert uterine atony.
• To promote normal involution in multipara patients.

It is a non-sedating, second-generation antihistamine and is favoured for patients needing continuous attention.

It does not induce sedation or hinder psychomotor abilities.

The other medications mentioned are first-generation antihistamines.

H₃ receptors function as pre-synaptic receptors, leading to a reduction in the release of histamine and various neurotransmitters.

• They counteract H₁-mediated wakefulness and bronchoconstriction.
• They also lower gastrin release and induce a negative chronotropic effect.

The inverse agonist of the H₃ receptor, tiprolisant, has been approved for the treatment of narcolepsy.

Chlorpheniramine and promethazine are first-generation antihistamines.

Both H₁ and H₂ receptors induce vasodilation.

• H₁ receptors, located in the endothelium, promote vasodilation through the release of NO.
• In contrast, H₂ receptors are found on smooth muscle and facilitate direct vasodilation.

Basic medications such as morphine, d-TC, and amphotericin B function as histamine liberators. This can result in an immediate reaction that leads to:

• Itching
• Hypotension

First-generation antihistamines lead to drowsiness and hinder psychomotor abilities.

Anti-motion sickness effects are connected to the anticholinergic characteristic. This feature is displayed by first-generation compounds, while second-generation antihistamines do not possess this capability.

• Autacoids are biologically active substances that function similarly to hormones but are produced locally in tissues.
• They play a crucial role in various physiological processes, including inflammation, pain modulation, and regulation of blood flow.
• Some well-known autacoids include histamine, serotonin, and prostaglandins.
• These compounds are released in response to specific stimuli and act on nearby cells, influencing their activity.
• Due to their localised action, autacoids are significant in maintaining homeostasis and responding to injury or stress.

Ketoconazole, erythromycin, and clarithromycin serve as strong inhibitors of microsomal enzymes.

• Astemizole, terfenadine, and cisapride are medications that can obstruct cardiac K⁺ channels when present in elevated concentrations.
• When these drugs are given alongside microsomal enzyme inhibitors, they may lead to torsades de pointes, a severe form of polymorphic ventricular tachycardia.

Fexofenadine is a metabolite of terfenadine that is active. It does not possess the ability to block K⁺ channels, which means it has no potential to cause arrhythmias. It is offered as an independent second-generation H₁ blocking agent.

All serotonin receptors are G-protein coupled receptors, with the exception of 5-HT₃, which is an ionotropic receptor.

Both cisapride and tegaserod are selective 5HT₄ agonists that are beneficial in the management of GERD.

• Cisapride has the potential to block cardiac K⁺ channels, which can result in torsades de pointes.
• Tegaserod does not have this negative effect.
• However, tegaserod has been withdrawn recently due to a heightened risk of myocardial infarction and stroke.

Adrenaline acts as a physiological antagonist to histamine. It counteracts bronchoconstriction induced by histamine.

Ranitidine is classified as an H₂ antagonist, which reduces gastric acid secretion; however, it does not impact smooth muscles.

In this condition, excessive secretions (such as rhinorrhoea) result from cholinergic overactivity. First-generation antihistamines have anticholinergic properties, making them effective for the common cold.

Conversely, second-generation agents, which do not have anticholinergic effects, are ineffective.

The treatment of these patients with erythromycin, a macrolide antibiotic, involves the following:

• Astemizole and terfenadine are metabolised by microsomal enzymes.
• Erythromycin inhibits these enzymes, resulting in an increased plasma concentration of these medications.
• At elevated levels, these drugs obstruct cardiac K⁺ channels, which may lead to arrhythmias.