Preclinical studies design

Question 1

Acute or single dose studies

Answer 1

24 hours one or multiple doses

used to determine ld50

define toxicity of the chemical

identify target organ

Question 2

New ICH guidelines for acute toxicity tests

Answer 2

Lethality should not be the end point

separate studies do not need to be performed

studies can be non glp if supported by glp studies after

in some cases (microdose) can be the primary support for human trials

Question 3

Repeat dose studies

Answer 3

Demonstrate adverse effects due to repeated daily dosing with a chemical

Pharmacokinetic profile of administering a small daily dose of a substance will be different to that after administering a single large dose

Question 4

What do you try to find in a repeat dose study ?

Answer 4

• Determine adverse effects following repeated exposure to a chemical
• Demonstrate whether there is a latency period for the development of toxicity
• Demonstrate if the toxic effects induced are reversible
• Identify organs most affected
• Determine dose levels at which each effect occurs

Repeat dose studies should be carried out in two mammalian species (one non- rodent)

Question 5

Duration of repeat dose study

Answer 5

Duration of repeat dose studies depend on the duration, therapeutic indication and scale of the proposed clinical trials.

Should be carried out for at least as long as the proposed clinical trial. Six month rodent and 9 month non-rodent generally support dosing for longer than 6 months in clinical trials.

Question 6

Design of acute and repeat dose studies

Answer 6

The first studies - preliminary studies, or dose range finding studies (DRF) are used to select doses for subsequent regulatory studies

explore adverse effects in rodent species prior to non-rodent species. Data from the initial rodent study can be used to help set the starting dose, or to allow for specific monitoring of adverse effects in non-rodents.

Toxicity may be identified in the rodent studies that prevents further development of the drug and therefore avoid further animal studies

Staged or staggered approaches to dosing minimises the number of animals at risk of suffering. E.g. the first time the drug is administered, it is good practice to dose one group of animals at a time. The observations are used to inform the next dose

The time between dosing each group is determined by a number of factors, such as knowledge of previous compounds in the class, the dose route and predicted pharmacokinetics.

Number of animals dosed at each level should be small in initial studies (e.g. 1 or 2 of each sex) Acute studies – rodents approx 5 of each sex per dose; non-rodents = 2-3 animals
Sub-chronic – 20-25 animals per sex per group in rodent study; non-rodent – 4/5 per sex per group

Question 7

Considerations for design of studies

Answer 7

1. Administration route
2. Vehicle for the drug
3. Consider formulation.
4. Choice of animal species
5. Dose levels
6. Consider a recovery period

Question 8

Drug administered by relevant route

Answer 8

Most common routes are: Oral
Intravenous
Inhalation

Other routes include:
Dermal, subcutaneous, intramuscular, intra-vaginal, intra- ocular etc Intravenous infusion (intermittent or continuous)

Question 9

Formulation

Answer 9

Ideal scenario is to use a common batch to supply both toxicology and Phase 1 clinical trials for ‘automatic’ qualification of any impurities but not mandatory or always possible

Question 10

Vehicle for drug

Answer 10

Give simillar vehicle to controls

Must consider appropriate solvent

Question 11

Choice of animal species

Answer 11

Generally two species – rodent and non-rodent

Rodent

Non-rodent

Rabbits

Question 12

Dose levels

Answer 12

Selecting a dose that is too high or selecting a dose that does not produce toxicity may risk repetition of the study thus requiring the use of additional animals.

Doses should be selected to establish a dose or exposure response to treatment. This can generally be achieved by the use of three groups of animals receiving the test drug, at low, intermediate and high doses, plus a control group which receives vehicle alone

Question 13

High Dose

Answer 13

High dose should be selected to enable identification of target organ toxicity, or other non-specific toxicity, or until limited by volume or limit dose.

There are five general criteria for defining the high dose:

1. Maximum tolerated dose (MTD)
2. Limit dose
3. Saturation of exposure
4. Maximum feasible dose
5. Doses providing a 50-fold margin of exposure

Question 14

Maximum tolerated dose (MTD)

Answer 14

The maximum tolerated dose (MTD) is based on the fact that the animal may not tolerate adverse effects that may occur at higher doses. MTD is usually determined by parameters such as clinical signs and reductions in body weight and food consumption

Depends on the duration of dosing e.g. MTD for single administration is likely to be higher than the MTD for 3 or more days of dosing

Question 15

Limit dose

Answer 15

Usually 1000mg/kg/day for rodents and non-rodents. This dose should give a mean exposure margin of 10-fold to the clinical exposure

Highest dose that should be used in the absence of a demonstrable MTD

Question 16

Top dose based on saturation of exposure

Answer 16

Saturation can be demonstrated when measurable levels of the drug in the blood, plasma or serum no longer increase with the increase in dose

Question 17

Maximum feasible/practical dose

Answer 17

e.g. the highest dose may be limited by what is technically feasible based upon the solubility of the formulation or the dose volume that can be administered

Question 18

Dose giving a mean exposure margin of 50x clinical dose

Question 19

Low dose

Answer 19

Low multiple of expected therapeutic dose(2-3x)
Should demonstrate the NOAEL level. This is the maximum dose level that doesn’t induce a sign of toxicity in the most susceptible and appropriate species of animal tested

NOAEL in each animal species can be converted to ‘human equivalent dose’ (HED) - Conversion usually based on body surface area (dose mg/m2). A safety factor of at least 10 is used

Question 20

Intermediate dose

Answer 20

Required to demonstrate a dose response relationship. Some evidence of toxicity should be seen
Addition of a second intermediate dose group in certain circumstances may be required e.g. if there is a large dose interval between the low dose and MTD

Question 21

PATHWAY OF DOSING TESTS

Answer 21

Question 22

need for a recovery period

Answer 22

maintain separate group of animals for a treatment free period

Can be very important in assessing delayed toxicity or reversibility of any effects seen during the dosing period

Required when severe toxicity observed in a non-clinical study with potential adverse clinical impact or when toxicity is only detectable at an advanced stage of pathophysiology

Demonstration of full reversibility not always essential
– Trend towards reversibility (e.g. reduced incidence / severity) and scientific assessment generally sufficient

Terminal non-dosing period generally not needed if toxicity:
– Can be monitored at an early stage
– Known to be irrelevant to humans
– Is only observed at high exposures which are not clinically relevant
– Is similar to that induced by related agents for which prior clinical experience indicates risk is manageable