general principles and regulation

Question 1

how are the toxic effects of pre-clinical drugs assessed

Answer 1

in vitro: high throughput screening can identify toxicological effects

in vivo:
animal tests: low dose and high dose toxicity studies carried out (mice most frequent, dogs/cats most frequent from non-rodent species, non-human primates are also used)
human volunteer (phase 1) : establish safe first human dose

Question 2

define hazard, risk, LD50, ED50, TD50, TI and MOS.

Answer 2

1. hazard: a compounds potential to cause harm
2. risk: the likelihood that a harmful effect from hazard will occur
3. LD50: lethal dose that cause death in 50% of animals tested (nowadays an estimate of LD50 values are sufficient (extrapolation from when toxicity is observed)) measured in mg/kg. death can be produced within 14 days but often occurs in 24 hrs.
4. ED50: dose where 50% of subjects exhibited a desired effect
5. TD50: dose where 50% of subjects exhibit a toxic effect
6. TI: TD50/ED50 ratio of dose producing toxic effect to dose required for desired effect. if compound doesnt have therapeutic effects can be divided by NOAEL instead. is an expression of safety.
7. MOS expression of safety where TD1% and ED99% is used

Question 3

define biomarker in regards to toxicological studies

Answer 3

-biochemical or physiological endpoint that indicates toxicity.

Question 4

what does the ICH aim to do

Answer 4

international committee on harmonization seeks to establish a uniform approach to toxicity testing around the world

Question 5

define NOAEL, LOAEL, MTD, FIH AND LDLo

Answer 5

1. no observable adverse effects level. highest conc where there are no observable adverse effects
2. lowest observable adverse effects level; lowest conc. where toxicity is observed.
3. maximum tolerated dose: largest conc. of agent which produces desired effect with an acceptable level of toxicity.
4. First in human dose (NOAEL used to determine ex: 1/100 of NOAEL)
5. lowest dose where a lethality is detected

Question 6

give examples of drugs administered via the intrathecal route and why this route could pose toxic risks.

Answer 6

ziconotide: analgesic calcium channel blocker very potent. administered via this route to bypass systematic side effects.
chemo agents: methotrexate, cytarabine for cancer in the CNS
hydrocortisone (for inflammation)

chemo vincristine was mistaken for cytarabine and administered intrathecally. it normally doesn’t cross BBB and is neurotoxic.

Question 7

define the toxicity categories

Answer 7

toxic: LD50 < 300mg/kg (oral) (skull)
-category 1: oral: <5mg/kg (fatal if swallowed)
-category 2: oral: <50mg/kg (fatal if swallowed)
-category 3: oral: <300mg/kg (toxic if swallowed)

health hazard: 300mg/kg<LD50<2000mg/kg (exclamation)
-category 4 (harmful if swallowed)

serious health hazard: man symbol, indicates long term toxic effects such as causing allergies or carcinogenic.

Question 8

differentiate toxicity determination methods related to exposure time (acute, chronic, sub-acute)

Answer 8

acute toxicity: single administration. determined via LD50

sub-acute toxicity: repeated exposure less than a month. used to identify MTD and NOAEL. tests 3-4 doses

sub chronic: repeated exposure for 1-3 months. establishes NOAEL and LOAEL. also reports what toxic effects are observed. establishes justification for first in human dose.

chronic: repeated exposure from 3 months to (2) years. tests at least 3 doses. tests a list of endpoints including: carcinogenicity, genotoxicity, neurotoxicity, reproductive toxicity, eye/skin irritation, immunotoxicology, environmental impact (worms), pk, photosafety.

Question 9

what factors determine toxicity (give an example of each)

Answer 9

1. route

ex: vincristine intrathecal neurotoxicity
ex: tubocurarine: muscle relaxant (nicotinic neuromuscular junction antagonist)
oral LD50= 150mg/kg (has time to be broken down before peritoneal cavity is reached) Intraperitoneal LD50: 0.42mg/kg. 350 times more toxic

2. Species differences
   - due to receptor expression and affinity differences
   -also different immune reactions between species.
   ex: cats poor at sulfating require taurine in diet
   humans highly susceptible to digoxin (LD50 28mg/kg in rat 75ug/kg in humans)
   coumarin selectively toxic to rats as 7-hydroxylation route is poor (leads to more toxic hydroxyphenyl acetic acid production)
   rodents cant vomit
3. metabolic pathways
   -due to kinetic factors like half life and distribution, metabolic inactivation/activation and enzyme inductions

ex: cytarabine (cytosine arabinoside) for cancer inhibits DNA pol. but has half life of 15 min. (deaminated by cytidine deaminase to inert uracil arabinoside).
rat oral LD50 is 5000mg/kg (similar to salt)
cultured cell IC50 is 0.018ug/ml
ex: paracetamol liver toxicity can occur at lower dose if cyp450 induced via ethanol (paracetamol sulfated or glucoronidated. via cyp it can be n-hydroxylated into NAPQI which is toxic.)

4. accumulation
   ex: lead accumulates in bone (mimics Ca and modifies vit d3 action)
   DDT insecticide accumulates in adipose.
   cadmium half-life of 5-10 years. forms metallothionine complex and accumulates in kidney
   asbestos in lungs for decades.
5. modified kinetics in distinct populations