Drug Administration: Routes, Pharmacokinetics, and More
Routes of Administration
The three primary routes of administration for frequently reported drugs are:
- Parenteral and cigarette use with heroin.
- Nasally, in the case of cocaine and stimulants.
- Smoked: Like hashish.
- Ingested by mouth: Alcohol and synthetic drugs.
- Aspirated: Such as cocaine and speed.
- Inhaled: As adhesives.
- Injected: Sometimes as heroin.
Classification (Rang HP, Dale MM…)
Routes of drug administration can be classified into four groups according to the place of drug deposition:
- Enteral: Via the digestive tract.
- Parenteral: Outside the digestive tract.
- Inhalation: Using the respiratory tract.
- Topical: Using the external body surface of the patient.
Subclassification:
- The enteral route is subdivided in three ways: oral, sublingual, rectal.
- Parenteral: subcutaneous, intramuscular, intravenous, intrathecal, epidural, intraventricular, intraarterial, intraperitoneal.
- The topical route: via topical mucous membranes, skin topically, via topical eye cornea.
Pharmacokinetics
The study of the processes by which the body absorbs, metabolizes, and eliminates drugs.
Absorption
Absorption is the access of the drug into the bloodstream. Passive diffusion is the most important mechanism of this process. Absorption depends on:
- Route of administration
- Solubility of the drug
- Local conditions
- Point of administration
- pH
- Concentration of the drug dose
- Existence of enteric coating on oral drugs
Distribution
Distribution is the transfer of the drug to the sites of action, metabolism, and excretion. It depends on:
- Places with a good blood supply
- Binding to plasma proteins (drugs bound to plasma proteins are maintained for longer in the body fluids)
- Circulatory problems (can slow distribution)
Biotransformation
Drugs are metabolized in the liver, where they are converted into products which are generally less active and more easily excreted. Metabolism is usually performed by the enzyme systems of the body. Factors that suppress these enzymes decrease metabolism, and the drugs can accumulate to toxic levels.
Excretion
Excretion is the clearance of metabolized and non-metabolized drugs through different routes. Gaseous substances are excreted from the lungs. Most drugs and their derivatives are excreted by the kidneys and eliminated in the urine.
Routes of Administration
Oral
The oral ingestion of drugs is common in self-medication and drug use, as well as with hallucinogens.
Sublingual
Absorption through the oral mucosa is important for certain drugs, even though the area available for absorption is small. Drugs administered via this route must have a high potency, so that only a few molecules are required to produce the desired pharmacological effects. Since venous drainage of the mouth is to the superior vena cava, the drug does not undergo first-pass metabolism and is therefore completely absorbed into the systemic circulation.
Topical
Via these pathways, drugs are administered on the external surface of the patient, generally seeking a local pharmacological effect.
Subcutaneous
This route is especially useful for insoluble suspensions and for the introduction of solid pellets, which produce a sustained effect for weeks or months. This pathway is not limited to drugs that irritate the tissues. The subcutaneous tissue blood flow is lower than in muscular tissue, so absorption is slower than intramuscularly, but faster than orally.