Drug interactions,classification,examples. Pharmacokinetics, pharmacodynemics drug interactions. B. Pharm 7th sem as per PCI syllabus.

1. Drug interactions
Presented by : Mr. Gp Kashyap (Asst. Professor)
M.Pharm (QA)
SVITS, Bilaspur (C.G)

2. Definitions:
 A drug interaction is a reaction
between two (or more) drugs or
between a drug and a food, beverage,
or supplement. Taking a drug while
having certain medical conditions can
also cause a drug interaction. For
example, taking a nasal decongestant
if you have high blood pressure may
cause an unwanted reaction.

3. Classification of Drug
Interactions
I. Consequences wise-
Beneficial –
Its not reported frequntely but in certain
conditions they have been used to minimize
the risk of a particular drug therapy or to
improve its better pharmacological effect.
Ex. Combination of Sulphamethoxazole with
trimethoprim-Enhance the antibacterial or
therapeutic effect.
Adverse drug interactions-

4. II. Sitewise
External- There are many physical and
chemical incompatibilities when drugs are mixed
in infusion, vials, syringe, etc. inactivation or
precipitations may occurs.
Internal- In which interaction at body site or in
system or site of drug action.
Ex. Atropine competitively block the action of
pilocarpine at muscarinic receptors.

5. III. Mechanism wise-
Pharmacokinetic Drug Interaction.
a. Altered drug absorption.
Factors may causes are followings-
 Physiochemical-Chenge in gastric
pH by one drug
(Ranitidine,cimetidine) which aafects
the ionisation of another drug.

6. Cont…
 Altered GI motility:
It effect the rate of drug absorption.
Ex. Metclopropamaide inhance gastric
emptying and intestinal motility and
so cause rapid absorption of drug
from the upper small intestine.

7. Cont…
 Changes in bacterial flora:
Drug (colchicine) may damage the GI
mucosa or block active transport and
so alter the absorption rate of the
drug.
 Blood flow: The better supplly of
blood to an area where the drug
being absorbed-greater the
concentration gradient-faster
absorption rate.

8. Cont…
b. Altered Drug Distribution-
 Tissue/organ blood flow
 Passive diffusion across cell
membranes
 Plasma protein and tissue binding

9. Cont…
c. Altered Drug Metabolism.
 Inuction of hepatic microsomal
enzymes:
Drugs like barbiturates,alcohol,and some
anticonvulsants are potent inducers of
hepatic microsomal enzymes.
The simultaneous use of these drug with
any other drug-decreased the
therapeutic effect.

10. Cont…
Inhibition of microsomal enzymes
Several drugs, including fluconazole,
spironolactone, and metronidazole,
can inhibit cytochrome
P450 enzyme activity.
This inhibition reduces the
metabolism of potential substrates and
secondarily delays their elimination.

11. Cont…
d. Altered Drug elimination.
 Competition for active site
a competitive inhibition of the renal
tubular secretion of gemifloxacin by
probenecid as the most likely
mechanism of the interaction.

12. Cont…
Changes in urine pH
 The drug must be excreted rapidly
from the body, so one strategy is to
alter the urine pH to
increase excretion.
 In aspirin poisoning for example,
making the urine more alkaline with
sodium bicarbonate increases
ionisation of the salicylic acid (aspirin
metabolite) therefore increasing
its excretion from the body.

13. Cont…
Pharmacodynamics Drug Interaction
1. Drugs having similar Pharmacological
effect- Hypnotic drug depressed CNS
but it causes allergic reaction and
therefore a antihistamines are also
given to the patients but both the drug
(Hypnotic and antihistamines) produce
sever CNS depressant.

14. Cont…
II. Drug having opposite Pharmacogical
effect.
Pilocarpin (Cholenergic drug) used for
glaucoma and at the same same
time anticholenergic drug for
abdominal pain cause the
interoccular pressure may be
altered.

15. “Always laugh when you can, it is cheap
medicine.”
Thank you