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Flashcards in Preclinical studies design Deck (22):

Acute or single dose studies 

24 hours one or multiple doses 

used to determine ld50

define toxicity of the chemical 

identify target organ 


New ICH guidelines for acute toxicity tests

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


Repeat dose studies 

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


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

• 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)


Duration of repeat dose study 

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.


Design of acute and repeat dose studies 

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


Considerations for design of studies 

1. Administration route 

2. Vehicle for the drug 

3. Consider formulation. 

4. Choice of animal species 

5.  Dose levels 

6. Consider a recovery period 


 Drug administered by relevant route

Most common routes are: Oral

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



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


Vehicle for drug 

Give simillar vehicle to controls 

Must consider appropriate solvent 


Choice of animal species

Generally two species – rodent and non-rodent





Dose levels 

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


High Dose

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


Maximum tolerated dose (MTD)

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


Limit dose

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


Top dose based on saturation of exposure

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


Maximum feasible/practical dose

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


Dose giving a mean exposure margin of 50x clinical dose


Low dose

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


Intermediate dose

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



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need for a recovery period

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