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.
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)