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Hypersensitivity

It refers to the undesirable reactions produced by the normal immune system that can damage,

cause discomfort or sometimes be fatal to an individual. These reactions are produced in the

presence of certain antigens and are considered to be abnormal. There are 4 different types of

hypersensitivity depending on the altaration in the immune system, they are:

1. Type I: Immediate Hypersensitivity2. Type II: Cytotoxic Hypersensitivity3. Type III: Immune Complex Hypersensitivity4. Type IV: Delayed Hypersensitivity

Example

Many different examples of hypersensitivity have been recognized in animals and humans.

These are often referred to collectively as allergies, and clinically may take such forms as

asthma, hives, hay fever, anaphylactic reactions to certain foods or insect venoms, some forms of

eczema and kidney diseases, and skin reactions to poison ivy antigens and many other

substances.

Tachyphylaxis

It is a rapid decrease in the response to a drug after repeated doses over a short period of time.

Hence increasing the dosage of the drug will not increase the desired pharamcological response.

The drug causing tachyphylaxis acts indirectly by causing release of the stored neurotransmitter

from the nerve terminal. After a few doses the neurotransmitter stores are depleted and no more

reponse is obtained.

Example

Repeated doses of ephedrine may display tachyphylaxis, since it is an indirectly acting

sympathomimetic amine which will deplete noradrenaline from the nerve terminal. Thus

repeated doses result in less noradrenaline being released than the initial dose.

Idiosyncrasy

It is a non-immunological hypersensitivity to a substance, without a connection to

pharmacological toxicity. It explores the fact that every individual reacts in an unusually

different way to a given substance, and this difference is based on the condition that theindividual suffers from. This reaction usually occurs in a small group of individuals.

Example

Antipsychotic drugs such as chlorpromazine and clozapine causeinfrequent reactions such as

rhabdomyolysis or breakdown of striatedmuscle and liver toxicity which can be seen by by

an

increase in serum -glutamyl transferase (GGT) activity.

http://en.wikipedia.org/wiki/Ephedrinehttp://en.wikipedia.org/wiki/Sympathomimetichttp://en.wikipedia.org/wiki/Sympathomimetichttp://en.wikipedia.org/wiki/Ephedrine

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Allergy

Allergy is a disorder of the immune system often also referred to as atopy. Allergic reactions

occur to normally harmless environmental substances known as allergens; these reactions are

acquired, predictable, and rapid

Example

Many allergens such as dust or pollen are airborneparticles. In these cases, symptoms arise in

areas in contact with air, such as eyes, nose and lungs. For instance, allergic rhinitis, also known

as hay fever, causes irritation of the nose, sneezing, and itching and redness of the eyes. Inhaled

allergens can also lead to asthmatic symptoms, caused by narrowing of the airways

(bronchoconstriction) and increased production of mucus in the lungs, shortness of breath

(dyspnea), coughing and wheezing.

Tolerance

Tolerance is defined either as getting less and less response to the drug at the usual dosage, or ashaving to administer more and more of the drug to get the same effect.

Example

Long-term benzodiazepine usage, in general, leads to some form of tolerance and/or drug

dependence with the appearance of a benzodiazepine withdrawal syndrome when the

benzodiazepines are stopped or the dose is reduced. Long term use of benzodiazepines can cause

a range of health problems in a proportion of people. The long term effects of benzodiazepines

include impaired concentration and memory, sleep problems, depression, anxiety and panic

attacks as well as agoraphobia

Hyper-reactivity

The quality of being hyperreactive.

Example

Bronchial Hyperreactivity: a condition where the individual is 100- to 1000-fold more sensitive

to histamine than a normal individual.

Supersensitivity

Abnormally increased sensitivity

Example

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Addiction

Strong physiological and psychological dependence on a drug or other psychoactive substance.

Example

Heroin addiction.

DependenceA state in which there is a compulsive or chronic need.

Physical

Substance dependence in which there is evidence of tolerance, withdrawal or both.

Example

Nicotine dependence in smokers.

Psychical

Substance dependence in which the drug is used to obtain relief from tension or emotionaldiscomfort, rather than being associated with tolerance or withdrawal.

Example

Alcoholism

References

Katzung B. Basic Pharmacology. Lange.

Dorlands 31st

Illustrated Medical Dictionary. Elsevier.

Ament PW, Roth JD, and Fox CJ (1994) Famotidine-induced mixed hepatocellular jaundice.Ann

Pharmacotherapy28: 4042.

Denervation Supersensitivity:

denervation supersensitivity occurs in autonomic effector tissues after administration of drugs

that deplete transmitter stores and prevent activation of the postsynaptic receptors for a sufficient

period of time. For example, administration of large doses of reserpine, a norepinephrine

depleter, can cause increased sensitivity of the smooth muscle and cardiac muscle effector cells

served by the depleted sympathetic fibers