There are two major differences between acute and subchronic: Objective and Duration

Acute study is intended to test the effects after single administration (or multiple administration within 24 hr). As the effect of any chemical depends on the dose and the duration, in acute studies, you will have to test higher doses to see effects. The data helps to understand what can happen in human incases of accidental or deliberate overdose. This also helps to select dose levels for the repeated dose studies. In subacute studies, the objective is to determine what effects the compound may produce when given daily for up to 4 weeks in rodents (incase of subchronic, up to 13 weeks and chronic, for >6 months). In these studies lower dose levels are used to ensure that the animals tolerate the dose for the duration of the study. The main objective is to see what effects compound may produce on different organs in the body (target organ effects).

The dose response of a CNS active chemical depends on the target, and it is to be noted that some drugs show a reverse effects. For example, CNS stimulation at lower dose levels and CNS depression at higher dose levels (example: Ethyl alcohol)

hello Sebastian Joseph , thank you for your reply. it's quite clear.  Do u have any article realated to it? so that  I can learn their differences and gain knowledge about their pharmacokinetic action.

Acute toxicity study involves the adverse effects produced by the single or multiple administration of the substance in the experimental animals within a short period of time generally 24 h or within the 14 days of exposure. While subchronic toxicity/ long term toxicity involves a 90 days study with repeated administration of the substance. Upon completion of the toxicity study, whole clinical and histological evaluations should be recorded, including experimental observations and whole body and individual organ analysis.

Attached article link will be helpful for you

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3127354/

thanks amit