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Topic 9

Part of the FMGE study roadmap. Botany topic pharma-009 of Botany.

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Antimicrobial and Anticancer Pharmacology

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Antimicrobial and Anticancer Pharmacology — Key Facts for FMGE Core concept: Antibiotics work by targeting bacterial-specific processes; chemotherapy agents target rapidly dividing cells with limited selectivity High-yield point: Know the key adverse effects of major antibiotic classes and chemotherapeutic agents ⚡ Exam tip: Vancomycin (nephrotoxicity, red man syndrome), aminoglycosides (ototoxicity, nephrotoxicity), and化疗 agents (myelosuppression) are frequently tested

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Antimicrobial and Anticancer Pharmacology — FMGE Study Guide

Antibiotics - Detailed

Beta-Lactams

Penicillins:

  • Benzylpenicillin (Penicillin G): Gram-positive cocci (Strep, Staph - but not MRSA), syphilis, meningitis, anaerobic infections; IV/IM; short half-life
  • Amoxicillin/Ampicillin: Extended spectrum; respiratory, urinary, H. influenzae, E. coli, Listeria; oral and IV
  • Piperacillin: Antipseudomonal; used with tazobactam (Zosyn)

Mechanism: β-lactam ring binds PBPs → inhibit cell wall synthesis → bactericidal

Side effects:

  • Hypersensitivity (most common - 1-10%): Urticaria, anaphylaxis (IgE-mediated), maculopapular rash, serum sickness
  • Cross-reactivity between penicillins (10% with cephalosporins)
  • Diarrhea (C. difficile)
  • Nephrotoxicity (interstitial nephritis)

Cephalosporins (generations differ in spectrum):

  • 1st gen (cefazolin, cephalexin): Gram-positive cocci (skin, soft tissue infections)
  • 2nd gen (cefuroxime, cefaclor): H. influenzae, M. catarrhalis, some gram-negatives
  • 3rd gen (ceftriaxone, cefotaxime, ceftazidime): Serious infections, meningitis, sepsis; ceftriaxone once-daily for serious infections; no nephrotoxicity
  • 4th gen (cefepime): Pseudomonas coverage + gram-positive
  • 5th gen (ceftaroline): MRSA coverage

Carbapenems (imipenem, meropenem, ertapenem):

  • Imipenem: Broadest spectrum; combined with cilastatin (prevents renal degradation)
  • Meropenem: Better for CNS (crosses BBB)
  • Ertapenem: Once daily; not effective against Pseudomonas/Enterococcus
  • Side effects: Seizures (imipenem > others), GI upset, hypersensitivity

Monobactams (aztreonam):

  • Only gram-negative coverage including Pseudomonas
  • Safe in penicillin-allergic patients (no cross-reactivity)
  • No CNS penetration

Glycopeptides

Vancomycin:

  • Mechanism: D-Ala-D-Ala binding (binds peptidoglycan precursor) → cell wall synthesis inhibition
  • Spectrum: MRSA, C. difficile (oral), serious gram-positive infections (Staph aureus, Enterococcus)
  • Side effects:
    • Red man syndrome: Infusion-related histamine release (histamine ↑ with rapid infusion); prevent by slowing infusion rate, antihistamines
    • Nephrotoxicity: Monitor levels, trough 10-15 μg/mL for serious infections
    • Ototoxicity
  • Monitor: Trough levels (efficacy and toxicity)
  • Dosing: Given as dose/mg per target levels

Teicoplanin: Similar to vancomycin; less infusion reactions

Aminoglycosides

Examples: Gentamicin, tobramycin, amikacin, streptomycin, neomycin

Mechanism: Bind 30S ribosome → mRNA misreading → bactericidal

Spectrum: Gram-negative aerobes (Pseudomonas, Klebsiella, E. coli, Proteus); given with β-lactams for synergy in serious infections

Administration: IV; very poor oral absorption; can be given IM

Side effects (concentration-dependent toxicity):

  • Nephrotoxicity (most important): Acute tubular necrosis; monitor peaks/troughs
  • Ototoxicity: Vestibular (gentamicin - ataxia, vertigo) and cochlear (damage → deafness)
  • Neuromuscular blockade: Can cause respiratory paralysis (rare, but dangerous in myasthenia gravis); reversed by calcium or neostigmine

Monitoring: Peak and trough levels (trough <2 μg/mL for gentamicin to avoid nephrotoxicity)

Synergy: Often combined with β-lactams for enhanced gram-positive coverage (Enterococcus, Staph) and gram-negative coverage

Macrolides

Examples: Erythromycin, azithromycin, clarithromycin

Mechanism: Bind 50S ribosome → block translocation → bacteriostatic

Spectrum: Gram-positive (Strep, Staph - but not MRSA), atypicals (Mycoplasma, Chlamydia, Legionella), pertussis

Azithromycin: Longer half-life; better tolerated; used for community-acquired pneumonia, chlamydia, MAC in AIDS

Side effects:

  • GI distress (erythromycin - motilin agonist → nausea, diarrhea, abdominal cramps)
  • Hepatotoxicity (azithromycin > clarithromycin)
  • QT prolongation (all - monitor with other QT-prolonging drugs)
  • CYP450 inhibition (erythromycin, clarithromycin > azithromycin) → many drug interactions

Fluoroquinolones

Examples: Ciprofloxacin, levofloxacin, moxifloxacin, ofloxacin

Mechanism: Inhibit DNA gyrase and topoisomerase IV → bactericidal

Spectrum: Gram-negative (including Pseudomonas - ciprofloxacin), some gram-positive (atypicals), anthrax, bone/joint infections, UTI, prostatitis

Contraindications: Children (cartilage damage - tendons), pregnancy, seizure disorder (CNS toxicity)

Side effects:

  • Tendon rupture/damage (Achilles tendon - black box warning; avoid in patients >60, transplant patients, on corticosteroids)
  • QT prolongation (moxifloxacin > levofloxacin > ciprofloxacin)
  • CNS effects: Headache, dizziness, confusion, seizures
  • Photosensitivity
  • Cartilage damage in immature animals - not used in children/pregnancy

Tetracyclines and Glycylcyclines

Tetracyclines (tetracycline, doxycycline, minocycline):

  • Mechanism: Bind 30S → block tRNA attachment → bacteriostatic
  • Spectrum: Atypicals, Rocky Mountain spotted fever, Lyme disease, cholera, acne
  • Doxycycline: Most commonly used; can be used for malaria prophylaxis
  • Side effects: Photosensitivity, GI distress, hepatotoxicity (in pregnancy), tooth discoloration in children, antianabolic effect (↑BUN)
  • Contraindications: Pregnancy (tooth discoloration, hepatotoxicity), children <8 years (teeth, bone)

Glycylcyclines (Tigecycline):

  • Mechanism: Overcomes tetracycline resistance (tetM determinant); binds 30S
  • Broad spectrum: MRSA, VRE, resistant gram-negatives (Acinetobacter); used for skin/soft tissue and intra-abdominal infections
  • Side effects: Nausea, vomiting, photosensitivity

Lincosamides

Clindamycin:

  • Mechanism: Binds 50S → bacteriostatic
  • Spectrum: Gram-positive cocci (not enterococcus), anaerobes (Bacteroides)
  • Uses: Skin/soft tissue, bone/joint, toxoplasmosis, PCP (with pyrimethamine)
  • Side effect: C. difficile colitis (highest risk among antibiotics - even higher than fluoroquinolones)
  • Also: Skin rash, neutropenia

Oxazolidinones

Linezolid:

  • Mechanism: Binds 23S rRNA (50S) → bacteriostatic
  • Spectrum: MRSA, VRE (drug of choice for VRE infections)
  • Uses: Skin/soft tissue infections, pneumonia
  • Side effects: Thrombocytopenia (myelosuppression - monitor plt), peripheral neuropathy (with prolonged use >2-4 weeks), serotonin syndrome (MAOI-like)
  • Note: Linezolid is a weak MAOI - avoid with serotonergic drugs (SSRI, meperidine)

Anti-TB Drugs (RIPE)

Rifampin:

  • Inhibits DNA-dependent RNA polymerase → bactericidal
  • Used in: TB (with other drugs), H. influenzae prophylaxis, Staph infections (prosthetic joints)
  • Side effects: Hepatotoxicity, orange body fluids (tears, sweat, urine), drug interactions (CYP450 inducer - decreases many drug levels)
  • Discoloration: Warn patients about orange discoloration of body fluids (contact lenses stained)

Isoniazid (INH):

  • Inhibits mycolic acid synthesis → bactericidal (active only in replicating TB)
  • Side effects: Peripheral neuropathy (give pyridoxine B6 to prevent), Hepatotoxicity (age >35 risk), drug-induced lupus, sideroblastic anemia
  • Metabolism: Acetylator status affects half-life (slow acetylators = higher risk of toxicity)

Pyrazinamide:

  • Mechanism unclear; works in acidic intracellular environment
  • Side effects: Hepatotoxicity, hyperuricemia (gout - inhibit uric acid excretion)

Ethambutol:

  • Inhibits arabinosyl transferase (cell wall)
  • Side effects: Optic neuritis (red-green color blindness - check visual acuity and color vision monthly)
  • Contraindicated: Children (<6 years - can’t report visual changes)

Streptomycin (injectable aminoglycoside):

  • Uses: Severe TB (especially meningeal - crosses BBB)
  • Side effects: Ototoxicity, nephrotoxicity (aminoglycoside class)

Anti-Malarial Drugs

Chloroquine: First-line for susceptible malaria; also for amebic liver abscess Artemisinin derivatives: First-line for P. falciparum (resistant strains); fast-acting Mefloquine: P. falciparum resistance areas; also prophylaxis Primaquine: Radical cure of P. vivax and ovale (eliminates hypnozoites in liver); causes hemolysis in G6PD deficiency (test before giving) Atovaquone-proguanil (Malarone): Prophylaxis and treatment; well tolerated

Anticancer Drugs

Alkylating Agents

Nitrogen mustards (cyclophosphamide, mechlorethamine):

  • Cross-link DNA at guanine N-7 position
  • Cyclophosphamide: Active in liver (phosphoramide mustard); hemorrhagic cystitis (acrolein - give mesna to prevent); myelosuppression, SIADH
  • Side effects: Myelosuppression, alopecia, nausea, immunosuppression

Platinum compounds (cisplatin, carboplatin, oxaliplatin):

  • Cisplatin: Testicular, ovarian, lung, bladder cancer; nephrotoxicity (prevent with aggressive hydration), ototoxicity (high-frequency hearing loss), peripheral neuropathy
  • Carboplatin: Less nephrotoxic, less neurotoxic; more myelosuppressive
  • Oxaliplatin: Colorectal cancer; neurotoxicity (acute neuropathy with cold sensitivity)

Alkyl sulfonates (busulfan): CML; pulmonary fibrosis, hyperpigmentation

Antimetabolites

Methotrexate:

  • Mechanism: Folate analog → inhibits dihydrofolate reductase → blocks DNA synthesis
  • Uses: Leukemia, lymphoma, solid tumors, ectopic pregnancy (medical abortion), autoimmune diseases (RA, psoriasis, IBD)
  • Side effects: Myelosuppression, mucositis, hepatotoxicity, nephrotoxicity (crystalluria in renal tubules), pulmonary fibrosis
  • Rescue: Leucovorin (folinic acid) “rescues” from toxicity (bypasses DHFR block); also given with high-dose MTX

5-Fluorouracil (5-FU):

  • Inhibits thymidylate synthase → ↓DNA synthesis
  • Side effects: Myelosuppression, mucositis, hand-foot syndrome (palmar-plantar erythrodysesthesia)

Cytarabine (Ara-C):

  • Incorporates into DNA and inhibits polymerase
  • Uses: AML (drug of choice), lymphoma
  • Side effects: Myelosuppression, cerebellar toxicity (at high doses)

6-Mercaptopurine (6-MP), 6-Thioguanine:

  • Purine analogs; used in ALL
  • Side effects: Myelosuppression, hepatotoxicity
  • Metabolism: Xanthine oxidase; allopurinol ↑toxicity (must reduce 6-MP dose by 50-75% if given with allopurinol)

Plant Alkaloids

Vinca alkaloids (vincristine, vinblastine):

  • Mechanism: Inhibit microtubule polymerization → arrest in metaphase
  • Vincristine: Lymphomas, leukemias, solid tumors; neurotoxicity (peripheral neuropathy - most limiting)
  • Vinblastine: Testicular cancer, Hodgkin lymphoma; less neurotoxic but more myelosuppressive
  • Side effects: Neurotoxicity, myelosuppression, alopecia

Taxanes (paclitaxel, docetaxel):

  • Mechanism: Stabilize microtubules → prevent depolymerization → arrest cell division
  • Uses: Breast, ovarian, lung cancer
  • Side effects: Myelosuppression, hypersensitivity reactions (paclitaxel - requires premedication with steroids and antihistamines), peripheral neuropathy, fluid retention (docetaxel)

Topoisomerase Inhibitors

Anthracyclines (doxorubicin, daunorubicin, epirubicin):

  • Mechanism: Inhibit topoisomerase II → DNA damage
  • Uses: Breast cancer, Hodgkin lymphoma (ABVD), leukemia, sarcoma
  • Side effects: Cardiotoxicity (cumulative, dose-related dilated cardiomyopathy - avoid >450 mg/m²); myelosuppression, alopecia, nausea
  • Cardiotoxicity prevention: Dexrazoxane (iron chelator)

Etoposide:

  • Inhibits topoisomerase II
  • Uses: Testicular cancer, small cell lung cancer, lymphoma
  • Side effects: Myelosuppression, alopecia, nausea, secondary leukemia

Other Chemotherapy Agents

Bleomycin:

  • Generates free radicals → DNA strand breaks
  • Uses: Hodgkin lymphoma (ABVD), testicular cancer, squamous cell cancers
  • Side effects: Pulmonary fibrosis (dose-limiting - especially in older patients or with high O2 exposure); skin toxicity, mucositis

Asparaginase:

  • Depletes asparagine → leukemic cell death (can’t synthesize asparagine)
  • Uses: ALL
  • Side effects: Pancreatitis, coagulopathy (↓synthetic function → bleeding/thrombosis), hypersensitivity, hyperglycemia

Common Toxicities of Chemotherapy

Myelosuppression (most common - dose-limiting for many agents):

  • Neutropenia → infection risk
  • Thrombocytopenia → bleeding risk
  • Anemia → fatigue, dyspnea

Nausea and vomiting (chemoreceptor trigger zone):

  • Acute (within 24h): 5-HT3 antagonists, steroids
  • Delayed: NK1 antagonists, steroids

Alopecia: Anthracyclines, cyclophosphamide, etoposide; cold caps may prevent (vasoconstriction to scalp)

Immunosuppression: Many agents

Secondary malignancies: Alkylating agents, etoposide (secondary AML)

Gonadal dysfunction: Many agents (especially alkylators) → infertility

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