Chemistry of Pharma
World D — Polymers & Biomolecules
50.A — DRUG MECHANISMS & TARGETS
R50.01 Receptors as Targets
- Proteins embedded in the cell membrane.
- They receive chemical messengers from outside the cell.
- Drugs are designed to fit perfectly into the active site of specific receptors.
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R50.02 Agonists vs Antagonists
- Agonists: Mimic the natural messenger, turning the receptor "ON".
- Antagonists: Bind to the receptor and block the natural messenger, turning it "OFF".
R50.03 Allosteric Inhibition
- Some drugs don't bind to the active site.
- They bind to an alternate (allosteric) site.
- This changes the shape of the enzyme/receptor, rendering the active site useless.
EFFECTIVE ↔ TOXIC
R50.04 Therapeutic Index
- The ratio between the toxic dose and the effective dose of a drug.
- High Index: Safe drug (e.g., Penicillin).
- Low Index: Dangerous, requires careful dosing (e.g., Chemotherapy drugs).
50.B — THERAPEUTIC CLASSES
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R50.05 Analgesics (Painkillers)
- Non-narcotic: Aspirin, Paracetamol. Work by inhibiting prostaglandins (chemicals causing inflammation/pain).
- Narcotic: Morphine, Heroin. Bind directly to opioid receptors in the CNS. Habit-forming.
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R50.06 Antibiotics
- Bactericidal: Kill bacteria outright (e.g., Penicillin destroys cell walls).
- Bacteriostatic: Inhibit bacterial growth/reproduction (e.g., Erythromycin).
- Spectrum: Broad (kills many types) vs Narrow (targets specific strains).
R50.07 Antacids
- Overproduction of HCl in stomach causes ulcers.
- Old treatment: Neutralize acid with weak bases ($NaHCO_3$, $Mg(OH)_2$).
- Modern treatment: Cimetidine/Ranitidine prevent histamine from triggering acid release.
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R50.08 Tranquilizers & Neurologics
- Drugs affecting the Central Nervous System.
- Treat stress, anxiety, and severe mental diseases.
- Examples: Barbiturates (sleep agents), Equanil, Valium, Serotonin modulators.
50.C — ANTIMICROBIALS & EVERYDAY CHEM
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R50.09 Antihistamines
- Histamine is a potent vasodilator causing allergy symptoms (sneezing, congestion).
- Antihistamines (Brompheniramine, Terfenadine) block histamine receptors.
- Do not cure allergies, only suppress symptoms.
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R50.10 Antiseptics vs Disinfectants
- Antiseptics: Safe for living tissue (wounds/cuts). E.g., Dettol (chloroxylenol + terpineol), Tincture of Iodine.
- Disinfectants: Only for inanimate objects (floors/instruments). Toxic to tissue. E.g., 1% Phenol solution.
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R50.11 Artificial Sweeteners
- Provide sweetness without calories (excreted unchanged in urine).
- Saccharin: 550x sweeter than cane sugar.
- Aspartame: 100x sweeter (unstable at cooking temps).
- Sucralose: 600x sweeter (stable at cooking temps).
R50.12 The Beta-Lactam Ring
- The core structural feature of Penicillin and cephalosporins.
- It binds to and irreversibly inhibits the enzyme bacteria use to build their cell walls.
- Without a wall, the bacterial cell bursts due to osmotic pressure.