This document discusses different types of drug interactions. It defines drug interaction as when the pharmacological activity of one drug is altered by another concomitantly used drug or substance. The main types of interactions discussed are: drug-drug, drug-food, chemical-drug, drug-laboratory test, and drug-disease. The mechanisms of interactions are pharmaceutical, pharmacokinetic, and pharmacodynamic. Pharmacokinetic interactions alter absorption, distribution, metabolism, or excretion of a drug. Pharmacodynamic interactions change a drug's effects through direct or indirect means like antagonism, addition, or synergism. Factors like multiple drug therapy, diseases, and age can contribute to interactions.

1. NAME-GOURAV SINGH
DEPARTMENT OF PHARMACOLOGY
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2. Drug Interaction
 Drug interaction is defined as the Pharmacological Activity of one
drug is altered by the concominant use of another drug or by the
presence of some other substance
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3. Types of Drug Interaction
1) Drug- Drug Interaction
2) Drug-Food Interaction
3) Chemical-Drug Interaction
4) Drug-Laboratory Test Interaction
5) Drug-Disease Interaction
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4. Factor Contributing to Drug
Interaction
1) Multiple drug therapy
2) Multiple Prescribers
3) Multiple pharmacological of drug
4) Multiple disease/predispasing illness
5) Poor patient Compliance
6) Advancing age of patient
7) Drug related factors
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5. Mechanism of Drug Interaction
 The three mechanism by which an interaction can develop are;
1) Pharmaceutical Interaction
2) Pharmacokinetics Interaction
3) Pharmacodynamics Interactions
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6. 1. Pharmaceutical Interaction
 Pharmaceutical Interaction also called as incompatibility.
 It is a physicochemical interaction that occur when drugs are mixed
in IV (Intravenous).
 Infusion causing precipitation or inactivation of actives principles.
 Examples- Ampicillin, chlorpromazine and Barbiturates interact with
dextran in solution and are broken down or from chemical
compounds.
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7. 2. Pharmacokinetics Interaction
 These interaction are those in which ADME properties of the object
drug is altered by the precipitant and hence such interaction are
also called as ADME interaction.
 The resultant effect is altered plasma concentration of the object
drugs.
 These are classified as:-
1. Absorption Interaction
2. Distribution Interaction
3. Metabolism Interaction
4. Excretion Interaction
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8. a. Absorption Interaction
 Absorption Interaction are those where the absorption of the object
drug is altered.
 The net effect of such an interaction is-
i. Faster or Slower drug absorption
ii. More or Less complete drug absorption
1.Complexation and absorption 4.Malabsorption syndrome
2.Alteration in GIT pH 5.Alteration in Gut motility
3.Inhibition of GIT Enzymes 6.Alteration & inhibition in
microflora
Major mechanism of absorption interaction are:-
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9. a. Absorption Interaction
Object Drugs Precipitant Drugs Influence of object Drugs
Ciprofloxacin pencillamine Antacid, Food and Mineral
Supplements containing Al,
Mg, Fe, Zn and Ca ions.
Formation of poorly soluble
and unabsorbel complex
with such Heavy metal ions.
Sulphonamides
Aspirin Ferrous Sulphate
Antacid, Sodium
Bicarbonate, Calcium
carbonate
Enhanced Dissolution and
Absorption rates
Decrease Dissolution and
hence Absorption
1) Complexation and Absorption
2) Alteration in GI pH
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10. a. Absorption Interaction
Object Drugs Precipitant Drugs Influence of object Drugs
Aspirin Diazepam
levodopa, Mexiletine
Metaclopramide Rapid Gastric Emptying
Increased rate of
absorption
Levodopa Lithium
Carbonate Mexiletine
Anticholinergics Delayed gastric
emptying, Decrease rate
of Absorption
Digoxin Antibiotics Increased Bioavalibility
3) Alteration in GIT motility
4) Inhibition of GastroIntestinal Enzyme
5) Alteration of GastroIntestinal Microflora
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11. a. Absorption Interaction
Object Drugs Precipitant Drugs Influence of object Drugs
Vitamin A, B12, Digoxin Neomycin Inhibition of Absorption
Due to mal absorption
6) Mal Absorption Syndrome
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12. b. Distribution Interaction
 Distribution interaction are those where the distribution pattern of
the object drug is altered.
 The major mechanism for distribution interaction is alteration in
protein drug binding.
 Competitive displacement Interaction
Object Drugs Precipitant Drugs Influence of object Drugs
Anti-coagulant Phenylbutazone, chloral
hydrate
Increased clotting time,
Increased risk of
Hemorrhage
Tolbutamide Sulphonamides Increased hyperglycemic
effect
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13. c. Metabolism Interaction
 Metabolism Interaction are those where the metabolism of the
object drug is altered.
 Mechanism of Metabolism Interaction Include:
1) Enzyme Induction – Increased rate of metabolism.
2) Enzyme Inhibition – Decreased rate of metabolism.
 It is most significant interaction in comparison to other interaction
and can be total.
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14. c. Metabolism Interaction
Object Drugs Precipitant Drugs Influence of object Drugs
Carticosteriod, oral
contraceptives,
coumarins, Phenytain.
Barditurates Decrease plasma level,
Decreas efficacy of
object drugs.
Oral contraceptive
Oral Hydrogulcaemics
Rifamicin Decrease plasma level.
1) Enzyme Induction
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15. Object Drugs Precipitant Drugs Influence of object Drugs
Tyramine Rich Food Mao inhibitor Enhanced absorption of
an metabolized Tyramine
Caumarins Metranidazole phenyl
butazone
Increase Anticoagulant
Activity
Alcohol Disulbhiram metronidazole Increases in plasma
acetaldehyde levels
c. Metabolism Interaction
1) Enzyme Inhibition
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16. d. Excretion Inhibition
 Excretion interaction are these where the excretion pattern of the
object drug is altered.
 Major mechanism of excretion interaction are:
1) Alteration in renal blood flow
2) Alteration in urine pH
3) Competition for active secretion.
4) Forced diuresis.
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17. d. Excretion Inhibition
Object Drugs Precipitant Drugs Influence of object Drugs
Penicillin cephalosp orins,
Nalidixic Acid.
probenicid Elevated plasma levels of
acidic drugs.
Amphetamine Antacids, Thiazidesa
cetazolamide
Increased Passive
Reabsorption of basic drugs
increased risk of toxicity.
Lithium Bicarbonates NSAIDS Decreased Renal
Clearance of lithium risk of
toxicity.
1) Change in active tubular secretion
2) Changes in urine pH
3) Changes in renal blood flow
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18. 3. Pharmacodynamics Interaction
 Pharmacodynamics Interaction are those in which the activity of
the object drug at its site of action is altered by the precipitant.
 Such interaction may be direct or indirect.
 These are of two types:-
1) Direct pharmacodynamics Interactions
2) Indirect pharmacodynamics Interactions
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19. a. Direct pharmacodynamics
Interactions
 In which drug having similar or opposing pharmacological effect
are used concurrently.
 The three consequence of direct interaction are
1. Antagonism
2. Addition or summation
3. Synergism or Protonation
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20. a. Direct pharmacodynamics
Interactions
1. Antagonism:- The interacting drug have opposing action
e.g Acetylcholine and noradrenaline have opposing effect on
heart rate.
2. Addition or summation:- The interacting drug have similar action
and resultant effect is the some of individual drug response.
e.g CNS depressants like sedative and hypnotics etc.
3. Synergism or Potentiation:- it is an enhancement of action of one
drug by another
e.g alcohols enhance the analgesics activity of aspirin.
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21.  In which both the object and the precipitant drug have unrelated
effect but the latter in some ways alert the effect but latter in some
ways alert the effect of the farmer.
Example:- Salicylates decrease the ability of the platelets to
aggregates thus impairing the homeostasis if warfarin induced
bleeding occurs.
b. Indirect pharmacodynamics
Interactions
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