Pharmacology

1. OBJECTIVES
• Definition of terms
• Types of antihistamines and examples
• Mode of action
• Indication
• Pharmacokinetic
• Side effects and adverse effects
• Drug interaction
• Nursing implications
• Precautions/Contraindication

2. DEFINITIONS
• Histamines – are amine that are produced as part of a local immune
response inflammation. It also act as a chemical messenger that carries
signals from one nerve to another.
• Antihistamines – are groups of medicines used in the treatment of
allergic disorders. They compete with histamines for receptor site.

3. TYPES OF ANTIHISTAMINES
1.First generation
These are the ones that cause drowsiness in most people e.g.
chlorpheramine and promethazine.
2.Second generation
These cause less drowsiness e.g. betamethasone

4. MODE OF ACTION
• They inhibit the action of histamines by blocking the receptors(H1
and H2).when these receptors are stimulated they may produce allergic
reactions such as itching and rash

5. INDICATION
 Antihistamines are administered to relieve allergic symptoms
Food allergies
Seasonal allergies
Indoor allergies
 other histamine based reactions e.g used as an OTC treatment of
insomnia.

6. PHARMACOKINETICS
• Onset of action after oral administration is 20-60 minutes.it has a half
life of 20-24 hours.metabolized by the liver and excreted in urine.They
don’t cross the BBB (blood brain barrier)
• For instance, dosage of chloropheniramine is given 4mg nocte or 8
hourly po.

7. EXAMPLES
PRESCRIPTION OTC
Azelastine promethazine
Eye drops ceterizine
Nasal spray chlorpheniramine
Carbinoxamine clemastine
Emedastine
chlorpromazine

8. SIDE EFFECTS
COMMON UNCOMMON
Drowsiness .irritability
Nervousness . blurred vision
Constipation .dry mouth
dizziness

9. INTERACTIONS
• They interact with narcotics, antidepressants and alcohol

10. NURSING IMPLICATIONS
• Advise patients to report if confusion and sedation
• Caution patient to avoid driving and other hazardous activity if
drowsiness occurs
• Instruct patient to avoid alcohol

11. PRECAUTIONS/CONTRAINDICATIONS
• Hypersensitivity to antihistamines
• Obstractive prostatic hypertrophy
• Pregnant and nursing mothers
• Premature and new born infants within 14 days

12. SIGNS OF TOXICITY
• Delirium
• Seizures
• sedation

13. SUMMARY
• Antihistamines compete with histamines for receptor site
• Some antihistamines needs prescription while others can be purchased
from local pharmacies

14. REFERENCES
• Greenstein.& Gould D(2009),clinical pharmacology for nurses,18th
Edition. Churchill
• McKendry.,Tessier.,Hogan.,(2006) pharmacology in nursing , Edition
22. Mosby inc.St .Louis, Missouri.
• Rage,H.P.,et,el,(2012)pharmacology, international Edition . Seventh
Edition