Lecture 2
Lethal dose for 50% of subjects (LD50)
Definitions
• Xeno biochemistry (in Greek: ‘Xeno’ means foreign): the study of the PK and PD of foreign
compounds or normal compounds at abnormal concentration in the
organism (human, animal, bird, reptile, fish, plant, insect, fungus, bacteria or virus)
• Pharmacokinetics (in Greek: ‘pharmacon’ meaning drug and ‘kinetikos’ meaning putting in
motion, the study of time dependency (dC/dt), sometimes abbreviated as ‘PK’): a branch of
pharmacology dedicated to the determination of the fate of substances (drugs or nutrients)
administered externally to a living organism
• Pharmacodynamics: the study of the biochemical and physiological effects of drugs on the
body or on microorganisms or parasites within or on the body and the mechanisms of drug
action and the relationship between drug concentration and effect
Aspirin
• Aspirin or acetylsalicylic acid, is a derivative of salicylic acid that is a mild, nonnarcotic
analgesic useful in the relief of headache and muscle and joint aches
• The drug works by inhibiting the production of prostaglandins, body chemicals that are
necessary for blood clotting and which also sensitize nerve endings to pain
• The father of modern medicine is Hippocrates, who lived sometime between 460 B.C and
377 B.C.
• Hippocrates has left historical records of pain relief treatments, including the use of powder
made from the bark and leaves of the willow tree to help heal headaches, pains and fevers
• By 1829, scientists discovered that it was the compound called salicin in willow plants which
gave you the pain relief
Understanding the first lecture on aspirin
• The Greek physician Hippocrates wrote in the 5th century BC about a bitter powder
extracted from willow bark that could ease aches and pains and reduce fevers
• This remedy was also mentioned in texts from ancient Sumer, Lebanon, and Assyria
• The Cherokee and other Native Americans used an infusion of the bark for fever and other
medicinal purposes for centuries
,• The medicinal part of the plant is the inner bark and was used as a pain reliever for a variety
of ailments
• The Reverend Edward (Edmund) Stone, a vicar from Chipping Norton, Oxfordshire, England,
noted in 1763 that the bark of the willow was effective in
reducing a fever
• The active extract of the bark, called salicin, after the Latin name for the white willow (Salix
alba), was isolated in crystalline form in 1828 by Henri Leroux, a French pharmacist, and
Raffaele Piria, an Italian chemist
• Piria was able to convert the substance into a sugar and a second component, which on
oxidation becomes salicylic acid
• Salicylic acid was also isolated from the herb meadowsweet (Filipendula ulmaria, formerly
classified as Spiraea ulmaria) by German researchers in 1839
• While their extract was somewhat effective, it also caused digestive problems such as
gastric irritation, bleeding, diarrhea, and even death when consumed
in high doses
• All structures (unless specifically excluded) and definitions are for tests and exams
• Tables of data will be provided in tests and exams, you need to be able to interpret the data
in the tables
(medicinal chemistry is the highest paying job in chemistry)
CH3
HO O O OH O O
OH O O OH
CH3
2-hydroxybenzoic acid 2-(acetyloxy)benzoic acid methyl 2-hydroxybenzoate
Salicylic acid Aspirin Methyl salicylate
Lead Winter green
compound CH3
Lipinski's rule of five the five criteria for an orally active drug
HO O
1. O Not more
OH than 5 hydrogen bond donors (nitrogen or oxygen atoms with one or more
hydrogenOatoms)
O OH
2. Not more than 10 hydrogen bond acceptors (nitrogen or oxygen atoms)
3. A molecular weight
CH3 under 500 g/mol
propyloxy...
ethyl... CH3
O OH CH3
S O
O O
HO O
,4. A partition coefficient log P less than 5
5. Not more than one of the above rules should be violated
(Note that all numbers are multiples of five, which is the origin of the rule's name)
Understanding the first lecture on aspirin attend lectures 2 to 8!
• Biotransformation of salicylate takes place in many tissues, but particularly in hepatic
endoplasmic reticulum and mitochondria
• The three chief metabolic products are salicyluric acid (the glycine conjugate), the ether or
phenolic glucuronide, and the ester or acyl glucuronide
• In addition, a small fraction is oxidized to gentisic acid (2,5-dihydroxybenzoic acid) and to
2,3-dihydroxybenzoic and 2,3,5-trihydroxybenzoic acids
• Wilson and associates (1978) found an additional metabolite of salicylic acid in man
gentisuric acid, the glycine conjugate of gentisic acid
• Salicylates are excreted mainly by the kidney
• Studies in man indicate that salicylate is excreted in the urine as free salicylic acid (10%),
salicyluric acid (75%), salicylic phenolic (10%) and acyl glucuronides (5%), and gentisic acid
(1%)
Paracelsus
• The father of toxicology is Paracelsus (1493-24 September 1541), born
Philippus Aureolus Theophrastus Bombastus von Hohenheim, was a Swiss physician,
alchemist and astrologer of the German Renaissance
• ‘All substances are poisons: there is none that is not a poison, the right dose differentiates a
poison and a remedy.’
• Apostolides ‘Show me a poison and I will show you a therapy.’
• Not for tests or exams!
ADME
• Absorption is the process of a substance entering the body
• Distribution is the dispersion or dissemination of substances throughout
the fluids and tissues of the body
• Metabolism is the irreversible transformation of parent compounds
into daughter metabolites
• Excretion is the elimination of the substances from the body
, • In rare cases, some drugs irreversibly accumulate in a tissue in the body
• LD50 dose
• (mg/kg body weight per day)
• That is lethal to 50% of the exposed subjects
• If the Standard man weighs 72 kg, how many mg of nicotine per person per day will be lethal
to 5 out of 10 people, if a person absorbs 1 mg nicotine per cigarette?
• 72 mg nicotine, or 72 cigarettes per day
• If the Standard man weighs 72 kg, how many grams of salt per person will be lethal to 5 out
of 10 people?
• 288 grams salt, or one teacup full per person.
LD50 (mg/kg body
Agents Species
weight/day)
Ethanol Mouse 10, 000
Sodium chloride Mouse 4, 000
Morphine sulfate Rat 900
Phenobarbital, sodium Rat 150
DDT Rat 100
Strychnine sulfate Rat 2
Nicotine Rat 1
Tetrodotoxin Rat 0.1
Dioxin (TCDD) Guinea pig 1 x 10-3
Botulinum toxin (Botox) Rat 1 x 10-5
Ricin Human 2 x 10-3
Abrin Human 1 x 10-6
The table of toxicity illustrates the importance of
• Source of the toxin (plant, micro-organism, insect, snake etc.)
• Species of animal (mouse, rat etc.)
