depending on the half-life of your compound and the physicochemical properties it has, the least problematic repeated chronic administrations would be:

Oral gavage

Intraperitoneal IP injections 

Subcutaneous SC injections

in case the compound is not suitable(liable to proteolysis for oral, poor compartmental biodistribution from IP and SC) then 

Intravenous but not as frequent as the other routes above, or,

alternatively if the animal is somewhat constrained and you can do it, a permanent venous cannulation for IV infusions ad hoc

Dear Mr. Sakthivel Govindaraj!

In order to get an unambiguous answer, you should specify what drug you are going to administer.

In the case of water soluble drugs, you  may use classical intravenous administration with dose recalculation of course. You can also use the methods for activity prolonging.

In the case of water-insoluble drugs, try to use of alternative delivery methods.

In any case, I guess you should read books on classical methods of drug delivery, for example:

see the attached files

Regards

It varies from drug to drug. However, in theoretically ideal situation:

1) First try oral or intra peritoneal administration as those two routes are the most preferred ones to see effect of first pass metabolism as well as easiest way to administer.

2) Depending on the pharmacokinetics of drug and it hydrophilicity/lipophilicity, you may try sub cutaneous dose (lipophilic) or intravenous dose (hydrophilic compounds.

In majority of situation first method is preferred over all others due to clinical convenience perspective

Oral route is best if suitable

second choice can be intraperitoneal injection

Dear Andriy,

           It is a water soluble compound.

For water soluble compounds; try oral, then intraperitoneal

if either of them have some issue then last option would be IV

If I understand correctly you want to have an administration route that gives you good brain coverage for up to 25 days. What is your cmpd supposed to do and what do you want to evaluate? Most administration procedures for such prolonged period of time will induce stress to your rats.. If the compound is not toxic and it is suppose to act directly (i.e. not after being metabolized), then an additional option is to implant an  intra-ventricular cannula, that will allow to apply daily you compound at relatively high concentrations. Depending on its ability or not to cross the BBB you may end up with no brain penetration is you apply it systemically....

Hello Tiziana,

            What I am going to use is not a toxic compound, Which is a marine extract.

           and also i am using pregnant rats for my studies. so which will be the best route

I think intraperitoneal route will be best in your scenario 

Hello Zahid,

             It won't be harmful any of the way to pups know?

Ip and oral

For long-term drug administration in rats, the choice of the route of administration depends on various factors, including the nature of the drug, the desired effect, the duration of the study, and the welfare of the animal. Here are some commonly used routes and their considerations:

The "best" route will depend on the specific requirements of the study, the drug's pharmacokinetics, the potential impact on the animal's well-being, and the feasibility of maintaining the administration schedule over the desired timeframe. In all cases, it is important to balance the scientific needs of the study with the ethical considerations of animal welfare.

l This protocol list might provide further insights to address this issue.