Drug interactions occur when two or more substances administered together alter their effects on the body. There are two main types of drug interactions - pharmacodynamic interactions, which involve drugs acting on the same receptors or tissues, and pharmacokinetic interactions, which alter a drug's absorption, distribution, metabolism, or excretion. Common examples of drug-drug interactions include aspirin increasing the effects of anticoagulants like warfarin and antibiotics affecting blood thinners. Food and disease can also interact with drugs. It is important for pharmacists to monitor for potential interactions and advise patients.

1. Drug interactions their types, examples
and role of hospital pharmacist to avoid
drug interactions
By
Yousra Ashraf
(PHM –D)

2. Introduction
 A drug interaction is a situation in which a substance affects the activity
of a drug when both are administered together. This action can be
synergistic (when the drug's effect is increased) or antagonistic (when
the drug's effect is decreased) or a new effect can be produced that
neither produces on its own.
 Drug interactions may be the result of various processes. These
processes may include alterations in the pharmacokinetics of the drug,
such as alterations in the absorption, distribution, metabolism, and
excretion of a drug. Alternatively, drug interactions may be the result of
the pharmacodynamic properties of the drug, e.g. the co-administration
of a receptor antagonist and an agonist for the same receptor

3. Definition
 It is defined as “an alternation in the duration or magnitude of
pharmacological effects of one drug produced by another drug, food, or
any other substance”.

4. Types
 Typically, interactions between drugs come to mind (drug-drug
interaction). However, interactions may also exist between drugs and
foods (drug-food interactions), as well as drugs and medicinal plants or
herbs (drug-plant interactions) and also (drug-disease interactions). But
there are essentially two types of drug interactions
 Pharmacodynamic
 Pharmacokinetic

5. Pharmacodynamic
 Pharmacodynamic interactions are those in which the effect of one drug is
changed by the presence of another drug acting at the same biochemical or
molecular site (e.g., drug receptor or second messenger system), on the
same target organ, or on a different target but one that is associated with a
common physiological process essentially when one drug modulates the
pharmacologic effect of another by producing additive, synergistic or
antagonistic effects.

6. Conti…..
 Additive effect
An effect in which two substances or actions used in
Combination produce total affect the same as the
sum of the individual effects.
 synergistic effect
Interaction between two or more drug agents, entities, factors,
or substances that produces an effect greater than the sum of
their individual effects.
 Antagonistic effect
Interaction of two or more drug substances such that the
action of any one of them on living cells or tissues is lessened or
diminished

7. Pharmacokinetics
 Pharmacokinetic interactions are those in which one drug results in an
alteration (increase or decrease) of the concentration of another drug in the
system. Different parameters can be affected by pharmacokinetic
interactions, including a drug’s bioavailability, volume of distribution,
peak level, clearance and half-life. Such changes can lead to changes in
drug plasma concentrations and ultimately increase the risk of side effects
or diminish the efficacy of one or more drugs. Pharmacokinetic
interactions are more complicated and difficult to predict because the
interacting drugs often have unrelated actions.

8. Conti……
 Bioavailability
Bioavailability is a measurement of the rate and extent to which a
drug reaches the systemic circulation.
 Peak level
The highest level of drug that can be obtained in
the blood usually following multiple doses
 Half life
This is the period of time required for the concentration or amount
of drug in the body to be reduced by one half.

9. Examples
 Drug-Drug interaction
 Drug-Food interaction
 Drug-Disease interaction

10. Drug-Drug interactions
 Drug-drug interactions occur when a drug interacts, or interferes, with
another drug. This can alter the way one or both of the drugs act in the
body, or cause unexpected side effects.
1. Aspirin+ Warfarin Synergism (excessive bleeding)
2. Antibiotic+ Blood thinner Antagonism (less effect)
3. Decongestants+ Antihypertensive Potentation (high blood pressure)
4. Codeine+ Paracetamol Addition ( increased analgesic effect)
5. Clavulanic acid+ Amoxicillin Synergism (increased antibiotic effect)
6. NSAID+ Cox 2 inhibitors Synergism (increased bleeding)
7. SSRI’S+ Vitamin K Synergism (increased bleeding)
8. Ant emetics+ Tranquilizers Unknown effect (breathing
problems)
9. H2 blockers+ PPI’S Alteration (increase ph of stomach)
10. Phenobarbital + Warfarin Antagonism (less effect)
11. Erythromycin + Warfarin Synergism ( increased bleeding)

11. Drug-Food interactions
 A drug-food interaction happens when the food you eat affects the
ingredients in a medicine you are taking so the medicine cannot work the
way it should.
1. Bisphosphonates+ Any drug Reduced effectiveness of drug`
2. Benzodiazepines + grapefruit Inhabit enzymes involved in drug
metabolism
3. Digoxin + Oatmeal Decreased adsorption of drug
4. Aspirin + Milk Upset stomach
5. Acetaminophen + Alcohol Liver damage
6. MAO Inhibitors + food(tyramine) Severe headache
7. Tetracycline’s + calcium food Reduced absorption of drug
8. Warfarin + Vitamin K Reduced effect of drug
9. Celecoxib + Milk Upset stomach
10. Naproxen + fatty food Upset stomach
11. Oxycodon + Alcohol Coma , asthma
12. Caffeine + food Rapid heart beat

12. Drug-Disease interactions
1. Drug-condition interactions occur when a drug worsens or exacerbates an
existing medical condition
2. Nasal decongestants+ Hypertension Increased blood pressure
3. NSAID’S+ Asthmatic patients Air way obstruction
4. Minoxidil+ Heart failure Fluid rentation
5. Calcium channel blocker + Heart failure Negative inotropic activity
6. Nicotine + high blood pressure Increased heart rate
7. Beta blockers+ Heart failure Worsen asthma
8. Metformin + Heart failure Increased lactate level

13. Role of pharmacist in avoiding drug
interactions
 Pharmacists in every practice setting need to be vigilant in monitoring for
potential drug interactions and advising patients regarding drugs proper
use, foods or beverages to avoid when taking certain medications and
about disease conditions. It is imperative for pharmacists to keep up-to-
date on potential drug-food interactions of medications, especially today’s
new drugs, so that they may counsel properly to the patient.

14. References
 Pharmacology & toxicology by Mrs. S.R Kale pg 18 (2008)
 British National Formulary. 46thedition, British medical association,
London;( 2003)
 ASHP. ASHP guidelines on pharmacist-conducted patient education and
counseling.
 Remington the science of practice of pharmacy by David. B (2006)