This presentation aimed to cover the Drug interaction topic which is a part of academic syllabus. it may help to the B.Pharm Students

1. Drug Interactions
Mr. P. N. Amale
Assistant Professor in Pharmacology
Priyadarshini J. L. College of Pharmacy,
Hingna Road, Nagpur

2. • Drug Interaction (DI)
• DI is a situation in which the effect of one drug is
altered by prior or concomitant administration of
another drug.
DI my be harmful and some time beneficial also.
Now a day DI is increasing and development of the
medical field and awareness helping in reducing this.
Drug is a foreign moiety in body so it can interact with
any of the following :
Food, beverages, disease condition, environmental
contaminants, laboratory tests and other drug when
taken prior or concurrently.

3. Mechanism of DI:
Understanding mechanism of DI is helpful in anticipating
and dealing with such situations (DI’s).
Mechanism of DI is classified into two types:
1.Pharmacokinetic DI’s
2.Pharmacodynamic DI’s
Pharmacokinetic DI’s:
Interactions occurring at the pharmacokinetic process like
absorption, distribution, metabolism and excretion.
Different types of PK interactions are…

4. • 1. Alteration of the gastrointestinal absorption
a. Alteration of pH: pH of GI influences the absorption
of drug. The non ionised form absorb faster than the
ionised.
• Acidic drug remain unionised in stomach and easily
absorb. If antacid administered with such drug it will
inhibits absorption.
• Ex. Bisodyl-Antacid
b. Complexation and adsorption
Ex. Tetracycline and metal
Tetracycline can combine with metals like Ca, Mg, Fe,
Al and form complex which is difficult to absorb hence
milk product, metal ion preparation and antacid are
avoided with tetracycline

5. c. Alteration of GI motility:
• Cathartic increases the GI motility so drug taken with
cathartic stay less time in GIT and drug which require
long time for absorption get less absorb.
• Ex. Metaclopramide increases GI motility and
influences absorption of drug taken together
d. Presence of food:
• Presence of food reduces absorption of many drug as
food may change pH of stomach or may interfer with
dissolution and stability of drug.
• Ex. Acidic drugs.

6. e. Inhibition of GI Enzymes:
Absorption of some drug depends on their metabolism by
enzymes. If these enzymes inhibited then absorption of
drug also decreases.
Folic acid conjugase enzyme Folic acid
Polyglutamate Monoglutamate
Poor absorption Readily absorb
2. Alteration of distribution:
When the protein binding site for two drug is same they
compete with each other. Drug having greater affinity
binds faster and easily than those with less affinity
toward protein.
Ex.Phenylbutasone, valproic acid and Methotrexate are
highly protein bound drug.

7. 3. Alteration of metabolism:
Many drug posses power of stimulating and inhibiting
metabolism of other drug.
a. Stimulation of metabolism ( Enzyme Induction):
One drug stimulates the synthesis of enzymes which
metabolise other drug
Ex. Pentobarbital increase metabolism of warfarin
Rifampicin induces itself and oral contraceptives.
b. Inhibition of Metabolism:
Isoniazid and cemetidine inhibits metabolism of the
phenytoin and diazepam respectively.

8. 4. Alteration of Excretion:
One drug may block renal excretion of other by
competing for the same tubular transport system or
may increase excretion by ionisation.
a. Inhibition of renal excretion:
Quinidine and verapamil both increase serum digoxin
level by inhibiting tubular secretion, renal excretion
and non renal clearance.
Probencid inhibits excretion of penicillin by competing
for renal secretion.
b. Increase in renal excretion:
Antacid NaHCo3 makes urine alkaline and enhances
ionisation of weakly acidic drugs like asprin,
barbiturates and leads to their rapid excretion.

9. Pharmacodynamic Interactions:
1. Drug having opposing p’cological effect:
Common with two drug having opposite effect.
Diuretics-Anti-diabetic drugs.
2. Drug having similar pharmacological effects:
Drug acting on same site or influencing the same
physiological system causes synergistic effect.
Ex. Alcohol with CNS depressant drug causes excessive
CNS depression.
3. Alteration of electrolyte level:
Some drug have ability to alter the electrolytes such as
Na+ and Ca++.
Thiazide diuretic causes excessive loss of K+

10. 4. Interaction at receptor sites:
Agonist and antagonist shows opposite effect on same
receptors.
Ex. Ach and Atropine.
5. Alteration of Gastric flora:
Ex. Anticoagulant and antibiotics
6. Antibiotic combination:
Tetracycline and chloramphenicol with penicillin.

11. Types of DI
1. Drug-Drug interaction
a) Prescription drugs
b) OTC drugs
2. Drug-Food Interaction
Ex. -Presence of food delays absorption of acidic drugs,
antibiotics, while increases absorption of riboflavin,
-Milk product, banana, cheese, chocolate with MAOs
3. Drug-laboratory test interaction:
Ex. Diuretics and anti- diabetic drug

12. 4. Drug Disease Interaction:
- Paracetamol if given to the patient suffering from liver
cirrhosis leads to worsening of condition
- Sulphonamide given to nephritis patient leads to renal
impairment.
5. Drug-Alcohol interactions:
CNS depressant drug causes excessive CNS
depression in Alcoholics.
6. Drug-Environmental contaminants:
Ex. Exposure with pesticide like DDT stimulates GI
enzymes and increase metabolism of the cortisol in
human.
7. Drug-Smoking interaction: smoking increases
metabolism of diazepam and chlordiazepoxide

13. Reasons for increasing number of DI’s:
1. Drug potency: Potent drugs having same final
outcome when administered together causes serious
effects.
Ex. Anticholinergics, NSAIDS
2. Patient consult several physicians:
An ophthalmologist prescribe pilocarpine eye drop to
patient who is previously taking propantheline given
by other Dr. for GI problems.
3. Concurrent use of prescription and non-
prescription drugs:
OTC drugs like asprin, antacid, paracetamol, and
prescription drugs my interact.

14. 4. Patient non-compliance: due to lack of information,
confusion.
5. Drug abuse and misuse:
Psychiatric patient continue to take drugs like
barbiturates narcotics and amphetamine, if such
patient receives antipsycotics or analgesic drug
produces harmful effect.

15. Factors causing DI:
1. Age:
Increased no. of DI is seen in paediatric and geriatric.
2. Sex and genetic:
Females have fluctuating hormone level than male so
number of drugs shows variable effect in either sex.
3. Disease state:
1. Impaired renal function: Aminoglycoside,
sulphonamides in patient having renal problem.
2. Impaired hepatic function:
Barbiturates, paracetamol, isoniazid etc. affect
metabolism in hepatic patient.

16. Role of pharmacist in minimising DI
• Literature evaluation
• Identify the patient risk factor
• Take a detail medical history
• P’cological knowledge of drug
• Consideration of therapeutic alternatives
• Avoid complex therapeutic regime wherever possible
• Patient education
• Monitoring of therapy
• Individual therapy
• Enthusiasm and guidance
• Awareness in society
• Patient record and data storage

17. Thank you