AIM • Step 10
3rd Year MBBS
Pharmacology
3rd Year MBBS
Pharmacology
Student Memory Support
Drug Interactions, Altered Drug Response, Adverse Reactions and Drug Development
High-yield memory reinforcement and rapid revision for KMU 3rd Year MBBS.
1. High-Yield Flashcards
Tap each question to reveal the answer.
What is a drug interaction?
Modification of the effect of one drug by another drug, food or other factor.
How does a pharmacokinetic interaction alter drug response?
By altering absorption, distribution, metabolism or excretion of a drug.
What is a pharmacodynamic drug interaction?
An interaction in which one drug modifies another drug’s effect at the site or system of action without necessarily changing its concentration.
How do summation, synergism and potentiation differ?
Summation gives an additive effect; synergism gives more than the expected sum; potentiation occurs when one substance enhances another drug’s effect.
What is tolerance?
Reduced response to a drug after repeated use, so a larger dose may be required for the previous effect.
What is cross-tolerance?
Tolerance to one drug that produces reduced responsiveness to another related drug.
What is reverse tolerance or sensitization?
An increased response to a drug after repeated exposure.
What is tachyphylaxis?
A rapidly developing decrease in response when repeated doses are given at short intervals.
What mechanisms can produce tolerance or tachyphylaxis?
Increased metabolism, receptor adaptation or desensitization, and depletion of endogenous mediators.
What is drug intolerance?
An unusually exaggerated response to an ordinary or small dose of a drug.
Which adverse drug reactions are predictable and dose-related?
Type A reactions.
Which adverse drug reactions include allergic and idiosyncratic reactions?
Type B reactions.
Which ADR categories correspond to chronic, delayed and withdrawal reactions?
Type C = chronic, Type D = delayed, and Type E = end-of-use or withdrawal.
What is a lead compound?
A promising compound selected for further development after drug screening.
What does an ADME study assess?
Absorption, distribution, metabolism and excretion of a drug.
What are the main purposes of Phase I and Phase II clinical trials?
Phase I mainly evaluates initial human safety and pharmacokinetics; Phase II evaluates therapeutic efficacy and continued safety in patients.
What are the main purposes of Phase III and Phase IV?
Phase III confirms efficacy and safety in larger trials; Phase IV monitors the drug after marketing.
Why is post-marketing surveillance important?
It helps detect rare, delayed or previously unrecognized adverse effects during widespread clinical use.
What is the difference between a placebo response and a nocebo response?
Placebo response is perceived or actual benefit without the specific active treatment effect; nocebo response is an adverse response related to negative expectation.
How do IND and NDA differ?
IND permits investigation of a new drug in humans; NDA seeks approval to market the drug after adequate clinical evidence.
2. Mnemonics
Mnemonic Title: Pharmacokinetic Processes
ADME
Meaning: Absorption → Distribution → Metabolism → Excretion.
Mnemonic Title: ADR Types A–E
A-B-C-D-E
Meaning: Augmented → Bizarre → Chronic → Delayed → End-of-use.
Mnemonic Title: Clinical Trial Progression
S-E-C-M
Meaning: Phase I = Safety → Phase II = Efficacy → Phase III = Confirmation → Phase IV = Monitoring.
3. Memory Tables
Pharmacokinetic vs Pharmacodynamic Interaction
| Feature | Pharmacokinetic | Pharmacodynamic |
|---|---|---|
| Main change | Drug concentration | Drug effect |
| Basis | Altered ADME | Interaction at physiological or target level |
| Result | Higher or lower exposure | Enhanced or opposed response |
Clinical Trial Phases
| Phase | Core Memory Target | Timing |
|---|---|---|
| I | Initial safety, tolerability, pharmacokinetics | First human studies |
| II | Therapeutic efficacy and continued safety | Patients with target disease |
| III | Confirm efficacy and characterize safety | Large pre-marketing trials |
| IV | Rare and delayed adverse effects | After marketing |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Drug interactions may be pharmacokinetic, pharmacodynamic, drug–food or drug–disease interactions.
- Enzyme induction can reduce the effect of a susceptible drug by increasing its metabolism.
- Enzyme inhibition can increase drug exposure and the risk of toxicity.
- Tolerance develops progressively; tachyphylaxis develops rapidly after closely repeated doses.
- Type A ADRs are predictable and dose-related; Type B reactions are unusual and non-dose-related.
- Type C = chronic, Type D = delayed, and Type E = withdrawal/end-of-use reactions.
- Aminoglycosides are important nephrotoxic drugs; doxorubicin is an important cardiotoxic drug.
- Isotretinoin is an important drug associated with serious adverse effects on fetal development.
- ADME studies assess absorption, distribution, metabolism and excretion.
- Phase I → safety; Phase II → efficacy; Phase III → confirmation; Phase IV → post-marketing surveillance.
- IND precedes human investigation, whereas NDA seeks marketing approval.
KMU Exam Trap: Do not confuse Phase III with Phase IV. Phase III is the large confirmatory pre-marketing stage; Phase IV begins after marketing.
5. Clinical Memory Hooks
Stable drug effect falls after enzyme induction
→ increased metabolism → reduced plasma concentration → therapeutic failure
→ increased metabolism → reduced plasma concentration → therapeutic failure
Repeated doses at very short intervals produce progressively smaller effects
→ tachyphylaxis → rapid desensitization or mediator depletion
→ tachyphylaxis → rapid desensitization or mediator depletion
Unusual genetically determined response at a therapeutic dose
→ idiosyncratic reaction → Type B ADR
→ idiosyncratic reaction → Type B ADR
New drug is first administered to humans
→ Phase I → initial safety, tolerability and pharmacokinetic assessment
→ Phase I → initial safety, tolerability and pharmacokinetic assessment
Rare adverse effects appear only after widespread use
→ Phase IV → post-marketing surveillance
→ Phase IV → post-marketing surveillance
6. Starred High-Yield Exam Points
- ⭐ Pharmacokinetic interaction: altered ADME changes drug concentration and therefore clinical response.
- ⭐ Tachyphylaxis: rapid loss of response after closely repeated doses.
- ⭐ Type A vs Type B: Type A is predictable and dose-related; Type B includes bizarre, allergic or idiosyncratic reactions.
- ⭐ Isotretinoin: major prototype drug associated with serious fetal adverse effects.
- ⭐ Phase I → II → III → IV: safety → efficacy → confirmation → post-marketing monitoring.
- ⭐ Post-marketing surveillance: detects rare, delayed and previously unrecognized adverse effects after widespread use.
- ⭐ IND vs NDA: IND permits clinical investigation; NDA seeks authorization for marketing.