By: Dr. Sara Khalid Memon, 3rd year MBBS !

1. Dr. Sara Khalid Memon
10 LM 283

2. Definition:
“Effect or Response caused by a drug on the BODY
or/and any another DRUG”
This interaction can be PHARMACOKINETIC,
PHARMACODYNAMIC OR PHARMACEUTICAL !!

3. Drug interactions can b mainly classified into;
Drug – Drug interactions
Drug – Receptor interactions
>> This is just for the sake of understanding !!

5. Pharmacokinetic interactions can be discussed
under;
a) Ingestion
b) Absorption
c) Distribution
d) Metabolism(biotransformation)
e) Excretion
It is actually the effect of the body over the drug
.. !

6. Pharmocokinetics

7. Pharmacodynamics interactions can be discussed
under the headings of DRUG RECEPTOR
interactions .. !
It can be
> Ion channels linked interaction
> G coupled linked interaction
> Enzyme receptor linked interaction
> Intracellular receptor linked interactions
> Other misc. interactions
It is the effect of the drug on the body .. !

9. Pharmacodynamics includes the concepts of AFFINITY of the
drug for receptor, INTRINSIC ACTIVITY caused by that drug
..
On the basis of intrinsic activity , a drug can be an AGONIST or
ANTAGONIST .. !
Agonism can be complete or partial .. This is when a drug has
affinity and shows complete intrinsic activity at its therapeutic
dose then it is complete agonism .. Where as on maximum
therapeutic dose, if an agonist is unable to show complete
intrinsic activity then we call it as partial agonist .. !
Examples: Bethanicol (on M receptors), Pilocarpine, etc.

10. Antagonism can be CHEMICAL, PHYSIOLOGICAL and
PHARMACOLOGICAL
>* Chemical is when receptor is not involved .. 2 or more drugs
combine 2gether to inactivate each other.
e.g: Protamine inactivates heparin
>* Physiological is when opposite effects are produced by
acting on different receptors. e.g: insulin and glucagon,
norepinephrine and acetylcholine
>* Pharmacological is when one drug binds with the same
receptor of the agonist and prevents it response
e.g: atropine at muscuranic receptors, propranolol at beta
receptors..

11. Other interactions between the drugs can be
>* Addition : 1+1 = 2
e.g: combined therapy of ephedrine and aminophylline in
asthma
>* Synergism : 1+1 =>2
e.g: Sulphonamides with trimethoprim used as antibacterial
drugs ..
>* Potentiation : 0+1=>1
e.g: Carbidopa and levodopa in treatment of Parkinsonism ,, !

13. Pharmaceutical interactions include
interactions between the drugs ..
It is mainly the interaction before the drugs have systemic
effect,
for example 2 incompatible drugs when given intravenously ..
(it may show precipitation or not)
e.g: Promethazine hydrochloride 50 mg/2 mL is incompatible
when given with dexamethasone sodium phosphate,
frusemide, morphine, phenytoin, sodium bicarbonate in
syringe !

14. Adverse Drug Reactions !!!
Drugs, which are used together to treat multiple problems , can
cause more adverse drugs reactions, for example;
> Antihistamines (e.g benadryl, actifid,etc) used for treating
allergy can adversely cause Sedation !
> NSAIDs (e.g Aspirin, Ibrufen, Mefenamic acid, etc) used as
analgesics and anti- pyretics can adversely cause irritation of GIT
leading to dyspepsia, diarrhea, ulceration, etc ..
> Opoids (e.g Morphine, paracetamol, etc) used as painkillers can
adversely cause nausea, vomiting, drowsiness, constipation, etc !

15. The End ..
Thankyou* =)