There are a variety of reasons that a given drug administration route is taken, among which are:

• Physical and chemical properties of the drug. The physical properties being solid, liquid, and gas. The chemical properties primarily being solubility, stability, pH, irritancy, etc.
• Site of desired action: the action may be localised and approachable or generalised and not approachable.
• Rate of extent of absorption of the drug from different routes.
• Effect of digestive juices and the first phase of metabolism.
• Condition of the patient.

There are other factors too--often a drug can be given in multiple forms, and then it can come down to cost or patient comfort (for example, someone may prefer a daily pill to going in for an injection daily). The other factor in how a drug is commercialized is the form in which it was tested in animals. You will have a harder time getting a pill approved if all your in vivo tests are with tail vein injections, for example. But if your in vivo experiments involved an ingested oral dose, getting a pill approved is easier.

There are a variety of reasons that a given drug administration route is taken, among which are:

• Physical and chemical properties of the drug. The physical properties being solid, liquid, and gas. The chemical properties primarily being solubility, stability, pH, irritancy, etc.
• Site of desired action: the action may be localised and approachable or generalised and not approachable.
• Rate of extent of absorption of the drug from different routes.
• Effect of digestive juices and the first phase of metabolism.
• Condition of the patient.

There are other factors too--often a drug can be given in multiple forms, and then it can come down to cost or patient comfort (for example, someone may prefer a daily pill to going in for an injection daily). The other factor in how a drug is commercialized is the form in which it was tested in animals. You will have a harder time getting a pill approved if all your in vivo tests are with tail vein injections, for example. But if your in vivo experiments involved an ingested oral dose, getting a pill approved is easier.

The best method often comes down to the least costly method.

It depended on the drug and how quick you want the effect of drug in the body.

The drug insertion methods to be choosen as a trial for newely invented drug could be a traditional. Aforementioned methods of injection, eaten, inhale, drink, touch, pills, radiations, etc would not create a chaotic behavior. Keeping in view the adoption of the chemical, the insertion method would be changed.

It depends on the types of drug and where the part of body that becomes the object. The properties of drug and how quick the effect of the drug have to be considered.

Apart from all the answers that are correct, recently researchers are working on a new drug delivery platform by the name of "organ-on-a-chip" which is a device using human living cells in an environment similar to their native environment inside the body. https://www.nature.com/articles/s41578-018-0034-7

It depends upon drug molecule whether you need quick action or delayed but i always prefer transdermal drug delivery for prolong and delayed action

it depend on drug formulation, acute or chronic treatment, drug use for animal or human, what we need from this experiment.

It all depends on the onset and duration of action of the drug under investigation. Moreover one needs to keep in mind its ADME profile when deciding its route of administration.

Dear researcher,

There are several reasons to choose best drug insertion to body. These cases are type of disease, patient and disease condition, drug uptake rout, physico-chemical properties of drug, and etc. However, the intravenous administration rout is generally applied to evaluate the invented drugs.

It depends on several variables, we can discuss about the routes and the points of each of them in-depth critique, if you want, send me a message.

To give examples, injectables are preferred for rapid onset of action and systemic delivery.

Oral route may be used for systemic delivery for which rapid onset is not critical.

Suppositories are used for localized action in the lower genitourinary and gastrointestinal region

This may be obvious but creams and ointments, are preferred for skin diseases while drops are preferred for ocular and nasal treatment.

Physicochemical characteristics of the drug and its absorption window defines the route of administration. Set your objectives on the basis of desired pharmacokinetics, and keeping physicochemical characteristics in mind select a dosage form, which is safe for drug and can provide better pharmacokinetics

It depends on the physiochemical properties of the drug and body system of the patient.If thee dose need immediately so it should be given into IV or if it is decomposed due to the gastric juice so the route should be avoided. For the more bioavailability of the drug IV or IM is more prepare as well as 100% bioavailability of the dose.

If the effects are in the GI system so the drug should be taken into the Oral.

Fir the rapid effects some time rectal rout is to be choosen.

I thought these 2 articles would help you.

Article Mitragotri, S, Burke, PA and Langer, R. Overcoming the chall...

Article Drug delivery across length scales

you have many criteria to consider in choosing the desired dosage form. such as aim of treatment, site of action, physico-chemical properties of drug, dosage schedule, type of disease etc

I agree with Mr or Mrs Bhupesh Vaidya, who used the correct term in the answer: "ADME" is what counts for your delivery route. The other answers are correct, too, and you should read them carefully. Generally, best method depends from lipophilic or hydrophilic active substance and especially, if you go/want/wishes an immediate action (intravenous) and perhaps short acting activity (limited to surgery time for example) or along-lasting delivery effect over several hours (e.g. blood pressure , diabetes , Rheumatoid arthrites etc).