Histamine and Antihistamines

HISTAMINE

• Histamine is an autacoid present at high levels in the lungs, skin, and the

gastrointestinal tract and is released from mast cells and basophils by type

I hypersensitivity reactions, drugs, venoms, and trauma.

• Histamine receptors are of the serpentine family, with seven transmembrane-

spanning domains with G-protein-coupled second messenger

effectors.

- H1 activation

+ ↑ capillary dilation (via NO) -→ ↓ BP

+ ↑ capillary permeability -→ ↑ edema

+ ↑ bronchiolar smooth muscle contraction (via IP 3 and

DAG release)

+ ↑ activation of peripheral nociceptive receptors -→ ↑  pain and

pruritus

+ ↓, AV nodal conduction

- H2 activation

+ ↑ gastric acid secretion → ↑  gastrointestinal ulcers

+ ↑ SA nodal rate, positive inotropism, and automaticity

H1 ANTAGONISTS

• Mechanism of action:

- H1 antagonists act as competitive antagonists of histamine and therefore

may be ineffective at high levels of histamine.

- Vary in terms of both pharmacologic and kinetic properties, but all

require hepatic metabolism and most cross the placental barrier.

Properties o f Major Antihistamines

Drug	M block	Sedation	Antimotion	Other Characteristic
Dyphenhydramine	+++	+++	+++	Widely used OTC drugs
Promethazine	+++	+++	++	Some alpha Block and local anesthetic action
Chlorpheniramine	++	++	++	Possible CNS stimulation
Meclizin	++	++	++++	Highly effective in motion sickness
Cetirizine	+/-	+	0
Loratadine	+/-	0	0	No CNS entry
Fexofenadine	+/-	0	0	No CNS entry

• Uses:

- Allergic reactions: hay fever, rhinitis, urticaria

- Motion sickness, vertigo

- Nausea and vomiting with pregnancy

- Preoperative sedation

- OTC: sleep aids and cold medications

- Parkinson disease

- Acute EPSs

• Side effects:

- Extensions of M block and sedation (additive with other CNS

depressants)

Chapter Summary

• Histamine is an autacoid released from mast cells and baso phils by type I

hypersensitivity reactions or under the i nfluence of d rugs, venoms, or trauma.

H istamine receptors a re the G-protein-coupled, seven-transmembrane type.

Three different receptors are recognized: the well-characterized H 1 and H 2

types and an H 3 variant.

• The sequence of reactions leading to H 1 and H 2 activation is presented.

•  H1 antagonists are competitive inhibitors with varying pharmacologic and kinetic

properties. All require hepatic metabolism and cross the placental barrier.

•  The H 1 antagonists are used to treat a llergic reactions, motion sickness,

vertigo, nausea and vom iting in pregnancy, and p reoperative sedation, and

are in over-the-counter sleeping pills.

•  The adverse effects a re excess M block and sedation. Table Vl-1-1

summarizes the properties of some of the m ajor type 1 antih istamines.

KAPLAN medical USMLE step 1- Pharmacology- Lecture Notes (2013)

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Chvostek's and Trousseau's Sign

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Varicella (bệnh thủy đậu) & Herpes Zoster (bệnh Zona, giời leo)

 Phân biệt nhiễm Varicella (bệnh thủy đậu) và nhiễm Herpes Zoster (bệnh Zona, giời leo)

https://www.facebook.com/TTYKMedic/

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The four pillars of learning are fundamental principles for reshaping education

The four pillars of learning are fundamental principles for reshaping education:

Learning to know: to provide the cognitive tools required to better comprehend the world and its complexities, and to provide an appropriate and adequate foundation for future learning.

Learning to do: to provide the skills that would enable individuals to effectively participate in the global economy and society.

Learning to be: to provide self analytical and social skills to enable individuals to develop to their fullest potential psycho-socially, affectively as well as physically, for a all-round ‘complete person.

Learning to live together: to expose individuals to the values implicit within human rights, democratic principles, intercultural understanding and respect and peace at all levels of society and human relationships to enable individuals and societies to live in peace and harmony.

http://www.unesco.org/new/en/education/networks/global-networks/aspnet/about-us/strategy/the-four-pillars-of-learning/

http://www.bluemountainsschool.com/academics/overview/

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Beck's triad

Beck's triad is a collection of three medical signs associated with acute cardiac tamponade, an emergency condition wherein fluid accumulates around the heart and impairs its ability to pump blood. The signs are low arterial blood pressure, distended neck veins, and distant, muffled heart sounds.

Narrowed pulse pressure might also be observed. The concept was developed by Claude Beck, a resident and later Professor of Cardiovascular Surgery at Case Western Reserve University.

Physiology

The fall in arterial blood pressure results from pericardial fluid accumulation increasing pressure on the outside of the heart that limits the maximum size the ventricles can stretch to. This limits diastolic expansion (filling) which results in a lower EDV (End Diastolic Volume) which reduces stroke volume, a major determinant of systolic blood pressure. This is in accordance with the Frank-Starling law of the heart, which explains that as the ventricles fill with larger volumes of blood, they stretch further, and their contractile force increases, thus causing a related increase in systolic blood pressure.

The rising central venous pressure is evidenced by distended jugular veins while in a non-supine position. It is caused by reduced diastolic filling of the right ventricle, due to pressure from the adjacent expanding pericardial sac. This results in a backup of fluid into the veins draining into the heart, most notably, the jugular veins. In severe hypovolemia, the neck veins may not be distended.

The suppressed heart sounds occur due to the muffling effects of the fluid surrounding the heart.

Clinical use

Although the full triad is present only in a minority of cases of acute cardiac tamponade, presence of the triad is considered pathognomonic for the condition.

https://en.wikipedia.org/wiki/Beck%27s_triad_(cardiology)

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Body mass index (BMI)

Body mass index

The body mass index (BMI) or Quetelet index is a value derived from the mass (weight) and height of an individual. The BMI is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m², resulting from mass in kilograms and height in metres.

The WHO regards a BMI of less than 18.5 as underweight and may indicate malnutrition, an eating disorder, or other health problems, while a BMI equal to or greater than 25 is considered overweight and above 30 is considered obese.^[1] These ranges of BMI values are valid only as statistical categories.

Category	BMI (kg/m2)
	from	to
Underweight		18.5
Normal Range	18.5	23
Overweight—At Risk	23	25
Overweight—Moderately Obese	25	30
Overweight—Severely Obese	30

Japan Society for the Study of Obesity (2000):

Category	BMI (kg/m2)
	from	to
Low		18.5
Normal	18.5	25
Obese (Level 1)	25	30
Obese (Level 2)	30	35
Obese (Level 3)	35	40
Obese (Level 4)	40

In Singapore, the BMI cut-off figures were revised in 2005, motivated by studies showing that many Asian populations, including Singaporeans, have higher proportion of body fat and increased risk for cardiovascular diseases and diabetes mellitus, compared with Caucasians at the same BMI. The BMI cut-offs are presented with an emphasis on health risk rather than weight.

Health Risk	BMI (kg/m2)
Risk of developing problems such as nutritional deficiency and osteoporosis	under 18.5
Low Risk (healthy range)	18.5 to 23
Moderate risk of developing heart disease, high blood pressure, stroke, diabetes	23 to 27.5
High risk of developing heart disease, high blood pressure, stroke, diabetes	over 27.5

 https://en.wikipedia.org/wiki/Body_mass_index

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