Histamine and antihistamine agents

Antihistamine:

• The drugs which abolish or diminish some of the action of histamine in the body are called antihistamines.

• These drugs don not prevent the formation of histamine.

An antihistamine may be biologically classified as

1. H1 blockers or H1 –Antagonist or classical antihistamine

2. H2 blockers or H2 Antagonist

• H1 antagonists are useful for palliative (for reducing and curing) treatment of allergic reactions like

       • Seasonal rhinitis

       • Sneezing

       • Nasal discharge

       • Itching of eyes, nose, and throats

       • Hay fever

• H2 antagonists are mainly useful in the therapy of peptic ulcers as they inhibit the local secretions and gastric secretions stimulated by gastrin.

Classical antihistamines (H1 blockers) can be chemically classified as follows

• Amino alkyl ethers: e.g. Diphenhydramine

• Ethylene diamine: Mepyramine

• Alkyl amines or propylamines

a) Saturated propylamines: e.g.  Pheniramine, Chloropheniramine.

b) Olefinic propylamines: e.g. Triprolidine

• Phenothizine derivatives: e.g. Promethazine.

• Piperazine derivatives: e.g. Meclozine

• Miscellaneous: e.g. Cyproheptadine

Histamine

Properties of Histamine:

• It is a phosphate ester that occurs as colorless,

• Long prismatic crystals

• It is odorless.

• It is freely soluble in water.

• It is slightly soluble in alcohol.

Stability and storage of Histamine:

• It is stable in air but affected by light.

• Hence it is stored in tightly closed light-resistant containers.

Uses of Histamine:

• To treat the functional capacity of gastric glands

• To dingoes pheochromocytoma

Dosage forms of Histamine: Histamine injections

Brand names of Histamine: Allergram, Cortanhist, Maridex

Diphenhydramine

Structure of Diphenhydramine:

Chemical name: 1-Dimethyl amino, 2-dimethyl methoxy ethane

Properties of Diphenhydramine:

• It is a hydrochloride salt that occurs as a white crystalline powder.

• It is odorless.

• It has a bitter taste followed by a sensation of numbness.

• It is freely soluble in water and chloroform.

• Very slightly soluble in ethers.

Stability and storage of Diphenhydramine:  

• It darkens slowly when exposed to light.

• Hence it is stored in well-closed light-resistant containers.

Uses of Diphenhydramine:

• Allergic skin reactions like urticaria, purities.

• Seasonal rhinitis

• Vasomotor rhinitis

• Motion sickness and post-operating vomiting

• Cardiac arrhythmia in combination with antazolin.

Dosage forms: Capsules, elixir

Brand names: Benadryl, caladryl, Copex-D

Pheniramine

Properties of Pheniramine:

• It is official as melate salt.

• It is white crystalline powder.

• It has faint odour.

• It is soluble in water and alcohol.

• Slightly soluble in alcohol.

Stability and storage of Pheniramine:

• It is affected by air and light,

• Hence it is stored in tightly closed light resistant containers.

Uses: as under Diphenhydramine

Dosage forms: Pheniramine tablet.

Brand names: Histol, Phenil, Diavil

Chlorpheniranine

Structure of Chlorpheniranine:

Chemical name: 3-(p-chlorophenyl),3-(pyrid -2-yl) ,N,N-dimethyl propanamine

Properties of Chlorpheniramine:

• It is maleate salt which is a white crystalline powder

• It is odorless

• It has a bitter taste

• It is freely soluble in water

• Very slightly soluble in ether.

Uses: as under pheniramine

Dosage forms: Elixir, Injection

Brand names: Corex, Zeet, Alergin, histacort

Mepyramine

Properties of Mepyramine:

• It is white or creamy, white crystalline powder.

• It has bitter taste

• It is very soluble in water.

• Freely soluble in alcohol.

Stability and storage: it is light sensitive and hence it is stored in well closed, light resistant containers

Uses of Mepyramine:

• It is used to treat allergic and anaphylactic condition including hey fever

• It has local anaesthetic and sedative action.

Dosage forms: Tablet, Injection, elixir

Brand names: Antihist, Kafal, Amthical

Promethazine

Properties of Promethazine:

• Its hydrochloride salt is a white or faintly yellowish crystalline powder.

• It is odorless.

• It has a bitter taste.

• It is very soluble in water.

• Freely soluble in alcohol.

Stability and storage of Promethazine: 

• Promethazine hydrochloride is slowly discolored when exposed to light.

• Hence it is stored in well-closed light-resistant containers.

Uses of Promethazine:

• To treat non-allergic skin conditions like insect bite, and urticaria.

• To treat insomnia.

• As a premedication where sedation is necessary.

• In motion sickness.

• In Parkinsonism 

Cyproheptadine

Properties of Cyproheptadine:

• It is official as hydrochloride salt.

• It is white slightly yellowish crystalline powder,

• It is odourless.

• It has slightly bitter taste.

• It is very slightly soluble in water.

• It is sparingly soluble in alcohol

• Soluble in chloroform.

Stability and storage: it is stored in tightly closed containers.

Uses of Cyproheptadine:

• To treat non allergic skin condition like insects bite, urticaria.

• As appetite stimulant

• To treat anorexia nervosa

• To treat crushing’s syndrome (pituitary dependant).

• To treat migraine.

• It has Anticholinergics, sedative and antialdosterone activity.

Pharmaceutical dosage forms: Cyproheptadine tablets, Cyproheptadine Elixir

Brand names: Cyprid, Peritol, Set up

UNIT-VI, Pharmacology, D. Pharm 2nd year pdf notes

In this Unit, we cover following Topic…..

HISTAMINE AND ANTI-HISTAMINE

1. Pharmacological actions
2. Pharmacokinetics
3. Classification
4. Adverse effects
5. Uses