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Back to the Future with Toxicological Sciences:
Impact on the Art of Pharmacy
Ho Han KiatBSc (Pharmacy, Hons, NUS),
PhD (Medicinal Chemistry, U. of Washington)
Understanding The Audience
• I like to know more about toxicology• I want to learn more about pursuing a
higher degree overseas• What else is out there beyond pharmacy
as a profession?• I came because I was asked to• I came for the refreshment
Talk outline
• How I ended up doing what I am doing• PhD education system in US• What are toxicological sciences• Relevance of toxicology to pharmacy
practice• Opportunities in toxicology
University of Washington- Medicinal Chemistry
University of Washington Seattle, Washington, USA
How I ended up doing what I am doing?
•Most commonly used drug in the world•Most common cause of acute liver failure
How I ended up doing what I am doing?
N
O
OH
N
O
OSO3H
N
O
O-Glucuronide
O
O
NN
O
OH
SG
N
O
OH
S-Hepatic protein
Sulfation Glucuronidation
Paracetamol
P450oxidation
Glutathione
Conjugation Conjugation
Protein
Glutathione depletion
DetoxificationOxidative
stressLiver injury
Prof Sidney D. Nelson
• Dean, School of Pharmacy, University of Washington
• APha Academy of Student Pharmacists Outstanding Dean of the Year 2007
• ISI List of Most Highly Cited Scientists
Chemical Structure Can Predict Toxicity
SO
CH3
H
OOH
Suprofen (Nephrotoxic)
S
CH3
H
OOH
O
Tiaprofenic acid (Interstitial cystitis)
CH3
H
OOH
OKetoprofen (Non-toxic)
PhD Education System In US
• Admission requirements:– 4-year undergraduate education– GRE– TOEFL– Recommendation letters– Essay of intent
• Typically 5 years• Lab rotations in first year• Coursework for 1-2 years• General/qualifying exams• Final exams- thesis defense
What do I wish I’d known before starting PhD
• With a BSc (Pharmacy), you can pursue a PhD in ANY field in biomedical sciences!
• The name of the department tells you nothing about the work they engage in
• Don’t have to wait till you complete your undergraduate to start applying
• A masters is helpful but not necessary• Scholarships are available, you just need to
know where to find them
What is Toxicology?
“Poison is in everything, and nothing is without poison. The dosage makes it either a poison or a remedy.” Paracelsus (1493-1541)
“It is impossible to differentiate between therapeutic herbs and poisons” Da Chang Jin (around 1494-1544)
Approximate LD50 Of Some Chemical Agents
Agent LD50 (mg/kg)Ethyl alcohol 10000Sodium chloride 4000Ferrous sulphate 1500Morphine sulphate 900Phenobarbital sodium 150Picrotoxin 5Strychnine sulphate 2Nicotine 1D-Tubocurarine 0.5Hemicholinium 0.2Tetrodotoxin 0.1Dioxin (TCDD) 0.001Botulinum toxin 0.00001
Casarett & Doull’s Essentials of Toxicology, 2003
Drug?
Poison?
Definitions• Toxicology is the science that deals with the study of
adverse effects (toxicities) of chemical, biological or physical agents that may produce in living organisms under specific conditions.
• Who: Who is at risk? • What: Direct? Idiosyncratic?• Where: Which organ is targeted?• When: Immediate or delayed?• Why: Oxidative stress, binding to macromolecules?• How: What molecular mechanism(s) are invoked?
Toxicology: An Integral Part Of Drug Development
Reasons for failure in clinical development. (Data for 198 development compounds*)Reasons for failure PercentagePharmacokinetics 39Lack of efficacy 30ToxicologyToxicology 1111Adverse effects in manAdverse effects in man 1010Commercial considerations 5Others 5Note: Of 198 compounds, 77 were anti-infective drugs; if these are excluded, lack of efficacy was the main cause (49%) and PK failures were less common (7%). * Kennedy T, Drug Discovery Today 1997, 2, 436-444.
Why Should We Care About Toxicology?
Iatrogenic causes are the 3rd leading cause of death
Iatrogenic Causes No. of deaths per year
Unnecessary surgeries 12,000
Medication errors 7,000
Other errors in hospital 20,000
Nosocomial infections 80,000
Adverse drug reactions 106,000Total 225,000
Cost of ADR: 136 Billion USD annually!!!
Drug Toxicity- The Major Cause For Drug Withdrawal
Drug Toxicity- The Major Cause For Drug Withdrawal
Drug Toxicity- The Major Cause For Drug Withdrawal
Notable Withdrawal From Market In The Last 10 Years
• Fenfluramine (1997)- Cardiotoxicity• Mibefradil (1998)- Dangerous interaction• Bromfenac (1998)- Hepatotoxicity• Terfenadine (1998)- Cardiac arrythmias• Cisapride (2000)- Cardiac arrythmias• Troglitazone (2001)- Hepatotoxicity• Cerivastatin (2001)- Rhabdomyolysis• Rofecoxib (2004)- Myocardial infarction• Valdecoxib (2005)- Myocardial infarction• Pemoline (2005)- Hepatotoxicity• Tageserod (2007)- Myocardial infarction
Toxicology Whose job is it anyway?
Not me! I can’t diagnose
I don’t make drugs.I know no chemistry
I just synthesize
what I was told
It better not haveanything to do
with me
The Multi-disciplinary Nature Of Toxicological Sciences
Toxicology
Biology Pathology
Pharmacology
Physiology
Molecular biology
Immunology
Chemistry
Epidemiology
Statistics
Genetics
How is Toxicology Relevant to Pharmacists and Pharmacy Practice?
• Broad-based education in medical, pharmaceutical, biological and chemical sciences allows us to appreciate toxicology
• As the “master of drugs”, we have the moral and professional responsibility to advocate the safe use of drugs
• We are to educate other healthcare professionals about drug toxicities
The Use Of Toxicological Knowledge- 3 Examples
• Restore public confidence on previously failed drugs. E.g. Thalidomide
• Clarify misintepretation. E.g.Sulphur drugs• Dispense the right information about non-
pharmaceutical toxicities. E.g. TEFLON
Thalidomide
• Introduced in 1956 as a mild sedative and against morning sickness
• Severe teratogenic effects with malformation of limbs• Withdrawn in 1961• US FDA issued the first guidelines for reproductive
toxicology testing in preclinical drug development
Thalidomide- Mechanism Of Toxicity
Intercalate DNAGuanine-rich region
Thalidomide- Stereochemistry Affecting Toxicity
GC-rich regions of DNAParticularly promoters of FGF2 and IGF1
Google image
Thalidomide- Mechanism of Toxicity
• Promoters of genes encoding integrin subunits and growth factors: IGF-1 and FGF-2 are guanine-rich
• Highly abundant in cells involved in limb bud development and angiogenesis
Stephens TD, 2000
Sulfa drugs- Hypersensitivity
Stevens Johnson Syndrome
Are Sulphur Drugs-induced Hypersensitivities Due To Sulphur?
NH2 SO
ONH
ONNH2 S
O
ONH
O
Sulfamethoxazole Sulfacetamide
NH2 SO
ONH2
Dapsone
NN
SO
ONH2
CF3
Celecoxib
No hypersensitivity
Haptenization of Sulfamethoxazole
NH2 SO
ONH
ONNH
SO
ONH
ONOH
N SO
ONH
ONO
SulfamethoxazoleProtein binding
(Hapten formation)
Hypersensitivityreaction
Toxicology: An Environmental Issue
TEFLON coating: A polymer of tetrafluoroethylene
Metabolism of TFEC
Job Opportunities
• Industrial/pharmaceutical toxicologists• Clinical toxicologists• Forensic toxicologists• Ecotoxicologists• Regulatory toxicologists
Industrial/pharmaceutical Toxicologists
• Safety testing of new products• Check for contamination of industrial
processes• Work opportunities:
– Pharmaceuticals– Petrochemicals– Cosmetics– Food and beverages– Medical diagnostics
Clinical Toxicologists
• Clinical assessment of adverse drug reactions
• Treatment of poisoning events• Work opportunities:
– Hospitals– Universities
Forensic Toxicologists
• Establish and explain circumstances of legal cases where drugs and chemicals are implicated
• Analytical testing of biological samples• Work opportunties:
– Forensic departments
Ecotoxicologists
• Study the toxic effects of chemicals on the environment and populations
• Tracing movement of pollutants through the ecosystem
• Work opportunities:– Environment and public health agencies– Water treatment plants
Regulatory Toxicologists
• Assessment of toxicological data- do they satisfy legal requirements for licensing
• Work opportunities:– Government agencies
Conclusion
Back to the Future with Toxicological Sciences: Impact on the Art of Pharmacy
Closing Words
“You too, can be a toxicologist in two easy lessons, each of ten years”
Prof Arnold Lehman (1900-1979)