This document discusses antihistamines and their classification, mechanisms of action, and effects. It describes first and second generation antihistamines. First generation drugs like dimenhydrinate are highly sedating and act as H1 receptor antagonists to reduce allergic reactions. Second generation drugs like astemizole have less sedation and do not cross the blood brain barrier. Antihistamines are used to treat allergic conditions by blocking the effects of histamine at receptor sites and providing relief from symptoms.

4. Histamine receptors :
Receptors Function
H1 Itching , Systemic
vacuolization , Bronco
construction
H2 Speed up sinus rhythm ,
stimulation of gastric acid
secretion
H3 Pre synaptic auto receptor
H4 Mediate mast cell
chemotaxis

6. Introduction
Anti – histamine inhibit the effect of
histamine at H1 receptors . Anti-histamine
have a number of clinical indication
including allergic condition like rhinitis ,
dermatoses , conjunctivitis . They also
control pruritus in skin disorder such as
eczema

7. Definition :
Anti – histamine are drug that blocks the
action of histamine (a compound
released in allergic inflammatory
reaction) at the H1 receptor site
responsible for immediate
hypersensitivity reaction such as
sneezing and itching .

8. Classification :
 First generation
 Second generation

9. Moderative
sedative
Mild sedative
Highly
sedative
First generation drug

10. Highly sedative :-
a) Dimenhydrinate
b) Hydroxyzine
Moderative sedative :-
a) Cyproheptadine
b) Pheniramine
Mild sedative :-
a) Triprolidine
b) Betahistine

11. Second generation drug
2nd
generation
cetiriazine
astemizole
hizolastiv

13. 1. Dimenhydrinate:
It acts as
competitive
antagonist of H1
receptor in brain . It
control
anticholinergic
action it block the
extrapyramidal

14. Route :
1. Orally
2. intramuscular

15. Dosage:
Usual adult dose: IM,50mg every 4
hours injected
Pediatric dose :IM,1.25mg/kg injected
IM 4 times a day

16. Oral:
Age 2 to 5 :
12.5to 25 mg
orally 6 to 8
hours
maximum
dose 75 mg in
24 hours

17. Pharmacokinetics :
• Absorption : the conventional H1 anti-
histaminie are well absorbed from oral
and parenteral route
• Distribution : well distribute through
out the body and cross the placental
barrier
• Metabolism : in the liver
• Excretion : metabolized and excreted
in urine

18. Pharmacodynamics :
Dimenhydrinate directly inhibit the
stimulation of certain nerves in the brain
and inner ear to suppress nausea and
vomiting

19. Mechanism of action :
Dimenhydrinate diminish vestibular
stimulation and depress labyrinthine
function. An action on medullary
chemoreceptive trigger zone may also
be involved in the antiemetic effect
which is widely distributed in human
being

20. Indication :
Use along with other
anti-emetic in
nausea and
vomiting . Also use
in post operative
emesis and
prevention of motion
sickness

21. Contra-indication :
Hypertension or porphyria

22. Side effects:
• Hypertension
• Nausea
• Insomnia
• Wheezing
• rashes

23. Nursing intervention :
 Caution the patient to
avoid use of alcohol and
other CNS depressants
.
 Patient on anti-allergic
medicine may be
protected from fall an
injury .
 Monitor , BP , pulse
,and respiratory rate will
be check .

24. 2. Cyproheptadine
It increase appetite
and has been
recommendated in
children and poor
eater to promote
weight gain . An
action growth
hormone secretion
has also been
suggested for this .

25. Route :
• Orally
Dose :
• Adult :- 4-8 mg TDS
• Pediatric :- 4mg BD, TDS

26. Pharmacokinetics :
Absorption : readily absorbed from GI tract
duration: 6 to 9 hours
Distribution : breast milk not known
Metabolism: in liver
Elimination : in urine

27. Pharmacodynamics
This drug also antagonize serotin receptor
. This action makes cyproheptadine useful
in condition such as headache and
anorexia . It does not prevent the realize of
histamine but with free histamine for
binding at H1 receptor sites .

28. Mechanism of action :
The cyproheptadine inhibit PRL release at
the pituitary level by blocking of ca2+ influx
at the cell membrane. without affecting the
movement of ca2+ between the
intracellular compartment

29. Side effects:
1.Vomiting
2.Diarrhea
3.Nervousness
4’Hallucination
5’Dry eyes

30. Indication :
Appetite stimulation
also useful to treat
acute allergic
dermatitis with
pruritus

31. Contraindication :
Not recommended
in pregnancy
lactation and very
young children.

32. Nursing intervention
 maintain
sufficient fluid
intake to help to
relive dry mouth
and also reduce
risk of
cholestasis
jaundice.
 Do not breast
feed while taking
this drugs.

33. 3.Triprolindine
Triprolindine is a
quick acting drug
that can clear the
congestion and
stop runny noses
in 15-30 minutes

34. Route
 Orally

35. Dosage
 Adult dose :
tablet -60mg
syrub-10ml
 Pediatric dose:
tablet – ½ tablet 6 to 12 years
1 tablet 13 or older

36. Cond….
syrup- 5ml orally 6 to 12 years
10ml orally 13 years or older

37. Pharmacokinetics
o Absorption : triprolidine are well
absorbed from oral route
o Distribution: widely in the body and
enter brain
o Metabolism: in liver
o Excretion : in urine

38. Pharmacodynamics
In allergic reaction and allergen interacts
with and cross link surface IgG
antibodies on mast cell antibody-antigen
complex is formed . A complex series of
event occurs that eventually lead to cell
degranulation and release of histamine
from mast cell or basophils

39. Mechanism of action
Triprolidine binds to the histamine H1
receptor . This blocks the action of
endogenous histamine , which
subsequently leads to temporary relief of
the negative symptoms brought on by
histamine

40. Indication
 Allergic rhinitis
 Urticaria
 Dermatoses
 Pruritius

41. Contraindication
• Severe
hypertension
• Severe coronary
artery disease

42. Side effect :
 Dry mouth
 Anorexia
 Vomiting
 Headache
 dizziness

43. Nursing intervention
 Patient should be instructed to avoid
driving or operating machinery
 To be used with caution in patient with
urinary retention

45. a) Astemizole :
A second generation anti-histamine which
does not cross blood brain barrier and so
has minimum CNS effect and sedative

46. Route
 orally

47. Dosage :
 Adult
10mg OD before meal
 Children
1ml/kg body weight(2 to 6
years)
5mg OD (6 to 12 years)

48. Pharmacokinetics
Astiemizole when given orally has a slow
onset of action ( 2-4 hours ). It highly
plasma protein bound it has plasma half
life 20 hours. This drug is mainly excreted
feces

49. Pharmacodynamics
Astemizole is a second generation H1
receptor antagonist . It's does not
significantly cross the BBB therefore does
not cause drowsiness or CNS depression

50. Mechanism of action
Astemizole competes with histamine for
binding at H1 receptor sites in GI tract ,
large blood vessels. This reversible binding
of astemizole to H1 receptor suppress the
formation of edema, flare and pruritus
resulting from histamine activity

51. Indication
 Rhinitis
 Chronic and Delayed allergic
 Conjunctivitis

52. Contraindication :
 Hypersensitivity
 porphyria

53. Side effect :
o Dry mouth
o Headache
o Nausea
o Dizziness
o Cardiac arrest

54. Nursing intervention:
 The drug should be given empty
stomach
 The patient should be told not to drive or
operate machinery