Antihistamines Pharmacology Exam Quiz

The most frequent side effect of H1 antihistamines that is less common with second-gen antihistamines is sedation. Sedation refers to the feeling of drowsiness or sleepiness that can occur as a result of taking antihistamines. Second-gen antihistamines are designed to be less sedating compared to first-gen antihistamines, making them a preferred choice for individuals who need relief from allergies or other conditions without experiencing excessive drowsiness.

Histamine is released in response to various stimuli and can bind to four types of receptors: H1, H2, H3, and H4. However, the group of receptors that are widely expressed and targeted by clinically useful drugs are H1 and H2 receptors. These receptors are involved in mediating allergic reactions, inflammation, and gastric acid secretion. Drugs that target these receptors are commonly used to treat allergies, motion sickness, and gastric acid-related conditions like heartburn and ulcers.

Histamine is mostly produced in mast cells. Mast cells are a type of white blood cell that are found in connective tissues throughout the body, particularly in areas near blood vessels and nerves. When mast cells are activated, they release histamine, which plays a key role in allergic reactions and inflammation. Eosinophils are also involved in allergic reactions, but they do not primarily produce histamine. Basophils release histamine as well, but mast cells are the main source. Cytokines are signaling molecules that regulate immune responses and do not directly produce histamine.

Diphenhydramine and meclizine are H1 antihistamines that are commonly used for motion sickness and nausea. These medications work by blocking the action of histamine, a chemical in the body that is involved in allergic reactions and can contribute to symptoms of motion sickness and nausea. By blocking histamine, diphenhydramine and meclizine help to alleviate these symptoms and provide relief. Toradol is a nonsteroidal anti-inflammatory drug (NSAID) used for pain relief, while epinephrine is a medication used for severe allergic reactions. Loratadine is another H1 antihistamine, but it is not typically used for motion sickness and nausea.

Diphenhydramine is a sedating antihistamine that can cause drowsiness and impair cognitive and motor skills, making it significantly impair the ability to drive an automobile. Ergotamine is a medication used to treat migraines and does not have significant sedating effects. Fexofenadine is a non-sedating antihistamine that does not impair driving ability. Ranitidine is an acid reducer and does not have sedating effects that would impair driving.

Prostaglandins, histamine, and serotonin are all examples of autacoids. Autacoids are endogenous compounds that are produced by various cells in the body and act locally to regulate physiological processes. These compounds have diverse functions, such as inflammation, pain perception, and regulation of blood flow. Therefore, the correct answer is autacoids.

Histamine is not distributed equally among the tissue. Histamine is released by mast cells and basophils in response to an allergic reaction or inflammation. It acts locally on nearby tissues, causing symptoms such as itching, redness, and swelling. Therefore, histamine is not distributed equally among the tissues, but rather is released in specific areas where it is needed.

Fexofenadine would be indicated for the ship captain's seasonal allergies. Fexofenadine is a second-generation antihistamine that is commonly used to treat allergies. It works by blocking the action of histamine, a substance in the body that causes allergic symptoms such as sneezing, itching, and runny nose. Fexofenadine is known for its effectiveness in relieving symptoms without causing drowsiness, which is important for a ship captain who needs to remain alert and focused while working.

Histamine stimulates parietal cells in the stomach. Parietal cells are responsible for producing and secreting gastric acid, which plays a crucial role in the digestion process. Histamine binds to specific receptors on parietal cells, triggering the release of gastric acid. This acid helps break down food and aids in the absorption of nutrients.

Second-generation H1 antihistamines are relatively free of adverse effects. This statement is correct because second-generation H1 antihistamines have been developed to have a reduced ability to cross the blood-brain barrier compared to first-generation antihistamines. This reduced penetration into the central nervous system results in fewer adverse effects such as sedation and drowsiness. Second-generation antihistamines are therefore preferred in the treatment of allergies and other conditions where histamine release is involved, as they provide effective relief with minimal side effects.

The pK of many oral antihistamines allows for once-daily dosing. This means that these medications can be taken only once a day, which is convenient for patients and improves medication adherence. Once-daily dosing also ensures that the drug remains effective throughout the day, providing consistent relief from allergy symptoms. This benefit is not available with twice-daily dosing or sub injections.

H1 and H2 receptor blockers can cause a classic "triple response" on the skin, which includes a wheal (swelling), reddening (erythema), and flare (spreading of redness). This response is a result of the release of histamine and other inflammatory mediators in response to the blocking of H1 and H2 receptors. These mediators cause blood vessels to dilate, resulting in the wheal and reddening, and also cause the surrounding blood vessels to become more permeable, leading to the flare.

The drug of choice in systemic anaphylactic shock is not H1 receptor blockers. The correct drug of choice is epinephrine, which acts as a vasoconstrictor and bronchodilator to counteract the severe allergic reaction. H1 receptor blockers, such as antihistamines, may be used as adjunctive therapy to help relieve symptoms such as itching and hives, but they are not the primary treatment for anaphylactic shock.

When antihistamines are taken with MAOIs (monoamine oxidase inhibitors), it can lead to an exacerbation of anticholinergic effects. Anticholinergic effects refer to the side effects caused by drugs that block the action of acetylcholine, a neurotransmitter in the central and peripheral nervous systems. These effects can include dry mouth, blurred vision, constipation, urinary retention, and cognitive impairment. MAOIs inhibit the breakdown of certain neurotransmitters, including acetylcholine, leading to an increase in its levels. When antihistamines are combined with MAOIs, the anticholinergic effects of antihistamines can become more pronounced, potentially causing more severe side effects.

H1 receptor blockers, commonly used as antihistamines, can have effects on other receptors in the body. One of the effects of these drugs on serotonin receptors is an increased appetite. Serotonin is a neurotransmitter that plays a role in regulating appetite, mood, and other physiological processes. By blocking H1 receptors, these drugs can indirectly increase the activity of serotonin receptors, leading to an increase in appetite.

Histamine, while often associated with allergic reactions, does have clinical indications. It plays a role in gastric acid secretion, and histamine receptor antagonists (H2 blockers) are used to treat conditions like peptic ulcers and gastroesophageal reflux disease (GERD). Histamine is also involved in neurotransmission in the brain, and research is ongoing regarding its potential role in conditions like Alzheimer's disease and multiple sclerosis.

H1 receptor blockers are actually more effective in preventing symptoms rather than reversing them. These medications work by blocking the action of histamine, a chemical that is released during an allergic reaction and causes symptoms such as itching, sneezing, and runny nose. By blocking the H1 receptors, these medications can help prevent the histamine from binding to its receptors and triggering the allergic response. Therefore, taking H1 receptor blockers before exposure to allergens can help prevent symptoms from occurring in the first place.

H1 receptor blockers, also known as antihistamines, have various effects on cholinergic receptors. They can cause increased dry mouth and increased urinary retention due to their anticholinergic properties. Sinus tachycardia, an increased heart rate, can also occur as a side effect. However, increased hypotension is not an effect of H1 receptor blockers on cholinergic receptors. Hypotension refers to low blood pressure, and antihistamines typically do not have a significant impact on blood pressure.

Rhinitis medicamentosa is the term used to describe rebound nasal congestion that occurs as a result of overuse or prolonged use of nasal decongestant sprays or drops. These medications work by constricting blood vessels in the nasal passages, providing temporary relief from congestion. However, with prolonged use, the blood vessels become dependent on the medication, leading to worsening congestion when the medication is stopped or its effects wear off. This condition can be resolved by gradually reducing the use of nasal decongestants and using alternative treatments for nasal congestion.

Using nasal decongestants for more than three days can lead to a condition known as rebound congestion. Rebound congestion occurs when the nasal passages become even more congested after the effects of the decongestant wear off. This can create a cycle of dependency on the decongestant, making it difficult to breathe without using it. Therefore, it is recommended to limit the use of nasal decongestants to three days to avoid this rebound effect.