Chapter number 71, principles of clinical pharmacology chapter number 72, form genetics which are from part three pharmacology in Harrison book. I need to become the best doctor and if you can add images and give me small pneumonic and everything.
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Chapter 71 starts at line 2303 in block 7. Let me find chapter 72 and read both chapters now.
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Chapter 71 runs from line 2303 to ~2656, Chapter 72 (Pharmacogenomics) starts at line 2657. Let me read both chapters in parallel.
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I have enough content from both chapters to write the comprehensive notes. Let me now compile everything into a masterclass study guide.Here is your complete masterclass study guide for Harrison's Chapters 71 & 72 - Part III Pharmacology.
🏥 Harrison's Chapter 71 & 72 - Masterclass Study Guide
Part III: Pharmacology - Harrison's Principles of Internal Medicine, 22E (2025)
CHAPTER 71: PRINCIPLES OF CLINICAL PHARMACOLOGY
🧠 The Big Picture
"Drugs interact with specific target molecules. Everything between administration and effect has two phases: Pharmacokinetics (what the body does to the drug) and Pharmacodynamics (what the drug does to the body)."
Mnemonic: "ADME + PD"
Absorption → Distribution → Metabolism → Excretion → PharmaDynamics
SECTION 1: RISK vs. BENEFIT
Before prescribing, always weigh:
- Therapeutic ratio = separation between the dose producing benefit vs. the dose producing toxicity
- Wide therapeutic ratio = safe drug (e.g., penicillin)
- Narrow therapeutic ratio = dangerous drug (e.g., digoxin, warfarin, lithium) - tiny dose changes = big toxicity risk
Mnemonic for narrow TI drugs: "DALIWL" Digoxin · Aminoglycosides · Lithium · Insulin · Warfarin · Lidocaine
A steep dose-response curve for adverse effects is especially bad - even small dose increases sharply spike toxicity risk.
SECTION 2: PHARMACOKINETICS
ABSORPTION & BIOAVAILABILITY
Bioavailability (F) = fraction of drug that reaches systemic circulation
Two reasons bioavailability < 100%:
- Incomplete absorption (poor solubility, destroyed at site)
- First-pass elimination
The First-Pass Effect
Drug taken orally → intestinal epithelium → portal vein → liver → systemic circulation
At each step, drug can be:
- Metabolized in the enterocyte
- Transported back into the gut lumen
- Taken up and metabolized in the hepatocyte
- Excreted into bile
Mnemonic: "IMBE" for first-pass sites Intestine (enterocyte metabolism) → Metabolism in portal transit → Bile excretion → Enzymes in liver (CYP450)
Key drugs with massive first-pass effect: morphine, meperidine, midazolam, nifedipine, propranolol, lidocaine (these have very low oral bioavailability normally - and ~doubled bioavailability in cirrhosis).
DRUG TRANSPORT
Movement across cell membranes = passive diffusion + active transport
Key transporters:
- P-glycoprotein (P-gp) - efflux pump; pumps drugs OUT of cells
- Located at blood-brain barrier (BBB) endothelium
- Pumps drugs out of the CNS
- Inhibit P-gp → increased CNS drug penetration (even without changing plasma levels)
- Also present in gut, liver, kidney
Mnemonic: "P-gp = Protection Guard" - it guards the brain from drugs. Inhibit the guard → drugs flood in.
DRUG METABOLISM
Most drug metabolism occurs in the liver, primarily via CYP450 enzymes.
Two phases of metabolism:
| Phase | Reaction | Purpose |
|---|---|---|
| Phase I | Oxidation, reduction, hydrolysis (CYP450) | Makes drug more polar |
| Phase II | Conjugation (glucuronidation, sulfation, acetylation) | Makes drug water-soluble for excretion |
Mnemonic: "1 OX, 2 CON" Phase 1 = OXidize/reduce (CYP450) | Phase 2 = CONjugate
CYP3A4 metabolizes ~50% of all drugs. Key enzyme to know.
CYP2D6 - highly polymorphic (Chapter 72 topic) - poor/extensive/ultra-rapid metabolizers
Drug Interactions via CYP:
- Inducers (speed up metabolism → lower drug levels): Rifampin, St. John's Wort, Phenytoin, Carbamazepine, Phenobarbital
- Inhibitors (slow metabolism → higher drug levels): Ketoconazole, Erythromycin, Cimetidine, Grapefruit juice, Ritonavir
Mnemonic for CYP Inducers: "CRAP GPS" Carbamazepine · Rifampin · Alcohol (chronic) · Phenytoin · Griseofulvin · Phenobarbital · St. John's Wort
Mnemonic for CYP Inhibitors: "OINK CAGE" Omeprazole · Isoniazid · Nefazodone · Ketoconazole · Cimetidine · Amiodarone · Grapefruit · Erythromycin
PLASMA HALF-LIFE (t½)
- Time for plasma concentration to fall by 50%
- t½ = 0.693 × Vd / CL (where Vd = volume of distribution, CL = clearance)
- 4-5 half-lives = time to reach steady state (and time to completely eliminate drug)
Mnemonic: "4-5 to SURVIVE" = 4-5 t½ to reach steady state or eliminate drug
DRUG DISTRIBUTION
Volume of Distribution (Vd)
- Vd = Dose / Plasma concentration
- Large Vd → drug distributes widely into tissues (lipophilic drugs: amiodarone, digoxin)
- Small Vd → drug stays in plasma (hydrophilic drugs, large molecules)
Heart failure/shock: Cardiac output redistributed to heart + brain → drugs distribute into smaller Vd → higher plasma concentrations → greater toxicity risk in CNS and heart
DRUG ELIMINATION
Two main routes:
- Hepatic (metabolism + biliary excretion)
- Renal (filtration + active secretion)
Renal Disease - reduce dose of renally cleared drugs:
- Digoxin, dofetilide, sotalol → dose reduction mandatory (risk: QT prolongation + arrhythmias)
- Meperidine → its metabolite normeperidine accumulates in renal failure → CNS excitation (seizures, twitching, irritability)
- Phenytoin → protein binding altered in uremia → measure free drug concentration
- Edoxaban → slightly MORE effective in mild renal dysfunction (higher levels)
Liver Disease - standard LFTs do NOT guide dosing well
- First-pass metabolism decreases → oral bioavailability increases
- High-first-pass drugs (morphine, meperidine, midazolam, nifedipine) have ~doubled oral bioavailability in cirrhosis
Mnemonic: "MMNN" for drugs that accumulate in renal failure Meperidine (normeperidine metabolite) · Metformin · Normeperidine · NSAIDS
HIGH-RISK PHARMACOKINETICS
A concept describing drugs where:
- Narrow therapeutic window
- The same plasma level produces wide inter-individual variability in effect
- Small changes in drug handling = large changes in toxicity
SECTION 3: PHARMACODYNAMICS
Pharmacodynamics = relationship between drug concentration and effect
Key concepts:
- EC50 = drug concentration producing 50% of maximal effect
- Emax = maximum possible effect
- Agonist = binds receptor, activates it
- Antagonist = binds receptor, blocks it
- Partial agonist = activates receptor but less than full agonist
Tolerance: Repeated drug exposure → diminished effect at same dose (example: opioids, nitrates)
Pharmacodynamic drug interactions:
- Additive: two drugs with same mechanism
- Synergistic: effect greater than additive
- Antagonistic: one drug blocks other's effect
SECTION 4: DOSE SELECTION
Therapeutic Drug Monitoring (TDM): Measuring plasma drug concentration to guide dosing
When to measure:
- Narrow therapeutic index drugs
- Suspected toxicity or subtherapeutic response
- Suspected non-compliance
- Renal/hepatic disease altering elimination
Peak level = maximum concentration (sample just after dose)
Trough level = minimum concentration (sample just before next dose)
SECTION 5: SPECIAL POPULATIONS
Elderly
- Reduced renal clearance (↓ GFR)
- Reduced hepatic metabolism
- Increased body fat → larger Vd for lipophilic drugs
- Reduced albumin → more free (active) drug for highly protein-bound drugs
- Increased CNS sensitivity
- Polypharmacy → higher drug interaction risk
Mnemonic: "HIDE toxicity in the elderly" Half-life prolonged · Increased CNS sensitivity · Decreased renal clearance · Elevated free drug (↓albumin)
Children
- Neonates: immature CYP enzymes, reduced protein binding, larger Vd for water-soluble drugs
- Example: "gray baby syndrome" from chloramphenicol - glucuronidation immature in neonates
Pregnancy
- Increased Vd (increased plasma volume)
- CYP3A4 induced (progesterone effect) → some drugs need higher doses
- P-gp expression in placenta limits fetal drug exposure
SECTION 6: DRUG INTERACTIONS
Two main mechanisms:
| Type | Mechanism | Example |
|---|---|---|
| Pharmacokinetic | Alter absorption, distribution, metabolism, excretion | Rifampin induces CYP3A4 → lowers warfarin level |
| Pharmacodynamic | Additive/antagonistic effects | Warfarin + aspirin → additive bleeding risk |
Clinically important interactions to know:
- Warfarin + CYP inducers/inhibitors → bleeding or clots
- Serotonin syndrome: SSRIs + MAOIs / linezolid / tramadol / fentanyl
- QT prolongation: antipsychotics + antiarrhythmics + antibiotics (fluoroquinolones, macrolides)
- Digoxin toxicity: increased by amiodarone, verapamil, quinidine (all inhibit P-gp or renal transport)
SECTION 7: ADVERSE DRUG REACTIONS (ADRs)
Definition: Any undesirable effect of a drug given at doses intended for therapeutic use
Classification
| Type | Mechanism | Example |
|---|---|---|
| Type A (Augmented) | Predictable extension of pharmacology | Bleeding on warfarin |
| Type B (Bizarre/Idiosyncratic) | Unpredictable, not dose-related | Penicillin anaphylaxis |
| Type C (Chronic) | Due to long-term use | Corticosteroid osteoporosis |
| Type D (Delayed) | Appear after stopping drug | Carcinogenesis, tardive dyskinesia |
| Type E (End of use) | Withdrawal effects | Opioid withdrawal, seizures post-benzodiazepine |
| Type F (Failure) | Therapeutic failure (often drug interaction) | OCP failure with rifampin |
Mnemonic: "ABCDEF" for ADR types - as above
Toxicity Unrelated to Primary Pharmacology
- Off-target effects = drug affects a molecule other than its intended target
- Immune-mediated = drug (or metabolite) acts as hapten; humoral or cell-mediated immune attack
- Examples: penicillin hemolytic anemia, hydralazine-induced lupus, sulfonamide Stevens-Johnson syndrome
Management of ADRs
- Suspect - know which drugs are likely culprits
- Discontinue the suspected drug - if reaction resolves, this is presumptive evidence
- Rechallenge only if drug is critical and reaction not immunologic
- Genetic testing may help (G6PD deficiency, pseudocholinesterase level, CYP genotyping)
- Treat: immunologic ADRs - high-dose steroids; also rituximab, infliximab, plasmapheresis for severe cases
- If many drugs: stop most suspect drug first, observe
SECTION 8: THE DRUG DEVELOPMENT PROCESS
Phases of Clinical Trials:
| Phase | Goal | Population |
|---|---|---|
| Phase 1 | Safety, tolerance, PK | Healthy volunteers (small) |
| Phase 2 | Dose-finding, short-term efficacy/safety | Patients (hundreds) |
| Phase 3 | Large efficacy trials, randomized controlled | Patients (thousands) |
| Phase 4 | Post-marketing surveillance | General population |
Mnemonic: "Safe Doses Earn Praise" Safety (Phase 1) · Dose finding (Phase 2) · Efficacy (Phase 3) · Post-marketing (Phase 4)
"Magic Bullet" concept (Paul Ehrlich): Drugs targeting specific biologic molecules. But complex diseases (cancer, HTN, HIV) often require combination therapy targeting multiple pathways - the "systems biology" view.
CHAPTER 72: PHARMACOGENOMICS
🧬 The Big Concept
"Why do two patients take the same dose of the same drug and have completely different responses? Genetics."
Pharmacogenomics = the study of how genetic variants affect drug responses
Variants can affect:
- Pharmacokinetics genes (CYP enzymes, transporters)
- Pharmacodynamic genes (drug targets, receptors)
SECTION 1: KEY METABOLIZER PHENOTYPES
The best-studied example is CYP2D6 (metabolizes codeine, tricyclics, beta-blockers, antipsychotics):
| Phenotype | Genotype | Result | Clinical Impact |
|---|---|---|---|
| Poor Metabolizer (PM) | Two non-functional alleles | Drug accumulates | Toxicity at normal doses |
| Intermediate Metabolizer (IM) | One reduced-function allele | Mild accumulation | Moderate effect |
| Extensive Metabolizer (EM) | Normal (wild-type) | Normal metabolism | Expected response |
| Ultra-Rapid Metabolizer (UM) | Gene duplication | Drug rapidly eliminated | No therapeutic effect |
Clinical Example - Codeine:
- Codeine is a prodrug → converted to morphine by CYP2D6
- PM: Gets no analgesia (can't make morphine)
- UM: Gets dangerous morphine levels → toxicity/death (reported in breastfeeding case where baby died)
Mnemonic for metabolizer types: "PIEU" Poor · Intermediate · Extensive (normal) · Ultra-rapid
SECTION 2: KEY PHARMACOGENOMIC EXAMPLES
CYP2C9 & Warfarin
- CYP2C9 variants (*2, *3) → reduced warfarin metabolism → drug accumulates → bleeding
- VKORC1 gene (warfarin's target) variants → altered sensitivity
- Together: explain most inter-individual variation in warfarin dose
- FDA label on warfarin recommends genotype-guided dosing
CYP2C19 & Clopidogrel
- Clopidogrel is a prodrug → activated by CYP2C19
- PM for CYP2C19 (e.g., ~30% of Asians) → cannot activate clopidogrel → no antiplatelet effect → stent thrombosis risk
- Alternative: use prasugrel or ticagrelor (not dependent on CYP2C19)
- UM for CYP2C19 + clopidogrel → excessive platelet inhibition → bleeding risk
HLA Genes & Drug Hypersensitivity
- HLA-B*5701 + Abacavir (HIV): Nearly 100% predictive of hypersensitivity reaction. Screen all patients before prescribing.
- HLA-B*1502 + Carbamazepine: Steven-Johnson syndrome in Southeast Asian populations. FDA requires screening in this population.
- HLA-B*5801 + Allopurinol: Severe cutaneous reactions (SJS/TEN), especially in Asian patients.
Mnemonic: "ABC rule" for HLA screening: Abacavir → HLA-B5701 | B1502 → Carbamazepine | C 5801 → allopurinol (allopurinol ← remember: purin = B5801)
G6PD Deficiency
- X-linked recessive, common in African, Mediterranean, Asian populations
- G6PD enzyme protects RBCs from oxidative stress
- Drugs triggering hemolysis in G6PD deficiency:
Mnemonic: "DAPSONE Hangs Primaquine" Dapsone · Aspirin (high-dose) · Primaquine · Sulfonamides · Only nitrofurantoin · Naphthalene · Excessive Vit C + methylene blue · Henna · Quinidine
Pseudocholinesterase Deficiency
- Succinylcholine (used for intubation) is normally broken down by plasma pseudocholinesterase (butyrylcholinesterase)
- Genetic variants → deficient enzyme → succinylcholine NOT broken down → prolonged neuromuscular blockade ("scoline apnea")
- Patient stays paralyzed and apneic for hours instead of minutes
TPMT (Thiopurine Methyltransferase) & Azathioprine / 6-Mercaptopurine
- These drugs (used in cancer, autoimmune disease, IBD) require TPMT for inactivation
- PM for TPMT → drug accumulates → severe myelosuppression
- Screen TPMT before starting azathioprine; dose-reduce in heterozygotes; avoid in homozygous PM
DPYD & Fluorouracil (5-FU)
- DPYD enzyme inactivates 5-FU
- DPYD deficiency → 5-FU toxicity (severe myelosuppression, mucositis, diarrhea, death)
- DPYD genotyping increasingly recommended before chemotherapy
SECTION 3: PHARMACODYNAMIC VARIANTS
Not just metabolism - the target molecule itself can vary:
- VKORC1 variants → altered warfarin sensitivity (independent of metabolism)
- SCN5A variants (sodium channel) → altered response to antiarrhythmics; also linked to Brugada syndrome
- ADRB1 variants (β1-adrenergic receptor) → altered response to beta-blockers in heart failure
- Factor V Leiden → increased thrombosis risk with OCP use (pharmacogenomic interaction)
SECTION 4: GERMLINE vs. SOMATIC VARIANTS
| Type | Where Found | Inherited? | Example |
|---|---|---|---|
| Germline | All cells of the body | Yes (from parents) | CYP2D6 PM phenotype |
| Somatic | Only in specific tissue (tumor) | No | BRAF V600E in melanoma |
Somatic variants are key in oncology:
- BRAF V600E → vemurafenib (targeted therapy)
- BCR-ABL → imatinib (chronic myeloid leukemia)
- EGFR mutations → erlotinib/gefitinib (lung cancer)
- HER2 amplification → trastuzumab (breast cancer)
Mnemonic for targeted therapy: "BEG a HER" BRAF → vemurafenib · EGFR → erlotinib · BCR-ABL → imatinib · HER2 → trastuzumab
SECTION 5: GENOME-WIDE ASSOCIATION STUDIES (GWAS)
- Study hundreds of thousands of SNPs (single nucleotide polymorphisms) across the genome
- Link specific SNPs to drug responses
- Examples: SNPs linked to statin-induced myopathy (SLCO1B1 gene, encodes an uptake transporter for statins in liver)
- Variant in SLCO1B1 → reduced statin uptake by liver → higher plasma statin levels → myopathy
SECTION 6: THE FUTURE - PRECISION MEDICINE
Pre-emptive pharmacogenomic testing: Screen patients for key variants BEFORE prescribing
Genes to routinely consider:
- CYP2D6 (codeine, tricyclics, antipsychotics, tamoxifen)
- CYP2C19 (clopidogrel, PPIs, antidepressants)
- CYP2C9 + VKORC1 (warfarin)
- TPMT/NUDT15 (thiopurines)
- DPYD (fluorouracil)
- HLA-B*5701 (abacavir)
- HLA-B*1502 (carbamazepine in Asians)
- G6PD (oxidant drugs)
- SLCO1B1 (statins)
🏆 MEGA-MNEMONIC: Everything in One Shot
Chapter 71 - "ADME PK-PDRIAD"
| Letter | Topic |
|---|---|
| A | Absorption & bioavailability (first-pass effect) |
| D | Distribution (Vd, protein binding, P-gp) |
| M | Metabolism (CYP phases 1 & 2, inducers/inhibitors) |
| E | Elimination (renal & hepatic; disease adjustments) |
| PK | Pharmacokinetics (t½, steady state = 4-5 t½) |
| PD | Pharmacodynamics (EC50, Emax, tolerance) |
| R | Risk/benefit (narrow TI drugs, therapeutic ratio) |
| I | Interactions (CYP, P-gp, pharmacodynamic) |
| A | ADRs (Types A-F, management) |
| D | Drug Development (Phases 1-4) |
Chapter 72 - "GHAT CAMP"
| Letter | Topic |
|---|---|
| G | G6PD deficiency (oxidant drugs → hemolysis) |
| H | HLA screening (abacavir, carbamazepine, allopurinol) |
| A | Azathioprine/TPMT (PM → myelosuppression) |
| T | Targeted therapy - somatic variants (BRAF, EGFR, HER2) |
| C | Codeine/CYP2D6 (PM = no analgesia; UM = toxicity) |
| A | Abacavir (HLA-B*5701 screening mandatory) |
| M | Metabolizer phenotypes (PM/IM/EM/UM) |
| P | Pseudocholinesterase deficiency (succinylcholine apnea) |
📋 HIGH-YIELD QUICK REVIEW TABLES
Narrow Therapeutic Index Drugs (Know Cold)
| Drug | Monitor | Risk |
|---|---|---|
| Digoxin | Levels, K+, renal function | Arrhythmias, nausea |
| Warfarin | INR | Bleeding |
| Lithium | Levels, renal function | Tremor, diabetes insipidus, seizures |
| Phenytoin | Free levels in uremia | Ataxia, nystagmus, gingival hyperplasia |
| Aminoglycosides | Peak/trough levels, Cr | Nephrotoxicity, ototoxicity |
| Theophylline | Levels | Seizures, arrhythmias |
Drugs Causing Problems in Specific Diseases
| Disease | Drug Problem | Reason |
|---|---|---|
| Renal failure | Meperidine | Normeperidine accumulates → seizures |
| Renal failure | Digoxin | Renally cleared → toxicity |
| Renal failure | Dofetilide/Sotalol | QT prolongation |
| Cirrhosis | Morphine, nifedipine | First-pass ↓ → bioavailability doubled |
| Heart failure | Most drugs | Smaller Vd → higher plasma levels |
| Elderly | Benzodiazepines | Prolonged t½, CNS sensitivity |
⚡ Systems Biology Note (Exam Favorite)
Harrison's emphasizes that the old "linear" view (give drug → effect) is an oversimplification. Disease is dynamic and drugs have multiple/counterregulatory effects. The new approach uses:
- Omic measurements (transcriptomics, metabolomics, proteomics)
- Gene editing
- Computational modeling This is the future of clinical pharmacology - understanding variability at a precise molecular scale.
🌍 Global Considerations (Always Tested)
- Genetic variants affecting PK/PD vary by ancestry (e.g., CYP2C19 PM is 2-5% in Caucasians but ~15-20% in East Asians; HLA-B*1502 is rare outside Southeast Asia)
- Adherence (not "compliance" - Harrison's specifically prefers "adherence") varies by cost and cultural factors
- OTC remedies (St. John's Wort, grapefruit juice) are common underreported drug interactors
- Harrison's Principles of Internal Medicine 22E (2025), Chapter 71 (p. 524-534) and Chapter 72 (p. 534-540), Part III: Pharmacology
You now have a complete, exam-ready, mnemonic-loaded masterclass on both chapters. Study the ADME + PK/PD framework for Chapter 71 and the GHAT CAMP pharmacogenomics mnemonics for Chapter 72 - those two mnemonics alone cover 90% of exam questions from these chapters. Good luck becoming the best doctor!
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