Route Of Drug Administration Free Pharmacology Note – 2021

In this topic “Route of Drug Administration” we are going to discuss the different types of Routes from where we can administrate the drugs. There are many ways to administrate a drug like the Parenteral route, Oral route, Local route, systemic route, and many other routes. In this post, we will do a detailed discussion on these routes and the advantages, disadvantages of these routes.

Routes of Drug Administration
Routes of Drug Administration

What is Route of Drug Administration

Route of drug administrations refers to the starting point of the body from where the drug will be introduced to the body and will be reached the target organ or system to show its effects. Most of these drugs can be administrated via different routes and they also depend on different factors

Factors Affecting Route of Drug Administration

There are many routes of drug administration and it is depend on many factors also. The factors that effect on the route of drug administration are given below:

  • The physical and chemical properties of drug molecules affect the routes for drug administration.
  • The site for the desired action also affects the routes
  • The route for administration of the drug also depends upon the condition of the patient. The route can change for unconscious, vomiting, diarrhea patients.
  • The age of the patient is also an important factor.
  • The route also depends on the usage type of the drug. This can be changed on emergency usages or routine usages.
  • Effects of gastric pH, digestive enzymes, and first-pass metabolism also affect the route of drug administration.

Different Routes of Drug Administrations

There are different type of routes for drug administration. There are mainly two different routes 1. Local Route and 2. Systemic Route.

Different routes of drug administrations
Different routes of drug administrations

Oral Routes

Drugs absorption via oral administration can be quite variable. Dosage form design may also be used modify the rate of absorption.

Advantages of Oral Drug Administration

  • Drugs administrated via Oral routes are safe, cheap and easy to take.
  • Drug administration via oral routes are very convenient.
  • Variety of dosage forms are available for oral administration.

Disadvantages of Oral Drug Administration

  • Sometimes inefficient – high dose or low solubility drugs may suffer poor availability, only part of the dose may be absorbed. Griseofulvin was reformulated about 1970 to include the drug as a micronized powder. The recommended dose at that time was decreased by a factor of two because of the improved bioavailability.
  • First-pass effect – drugs absorbed orally are transported to the general circulation via the liver. Thus drugs that are extensively metabolized will be metabolized in the liver during absorption.
  • Food – Food and G-I motility can affect drug absorption. Often patient instructions include a direction to take with food or take on an empty stomach. Absorption is slower with food for tetracyclines and penicillins, etc. However, for propranolol bioavailability is higher after food, and for griseofulvin, absorption is higher after a fatty meal.
  • Local effect – Antibiotics may kill normal gut flora and allow overgrowth of fungal varieties. Thus, antifungal agents may be included with an antibiotic.
  • Unconscious patient – The patient must be able to swallow solid dosage forms. Liquids may be given by tube

Buccal and Sublingual

Some of the drugs are taken as smaller tablets that are held in the mouth or under the tongue. These are buccal or sublingual dosage forms. Buccal tablets are usually harder tablets [4 hour disintegration time], designed to dissolve slowly. Nitroglycerin, as a softer sublingual tablet [2 min disintegration time], may be used for the rapid relief of angina. This Route of Administration is also used for some steroids such as testosterone and oxytocin. Nicotine-containing chewing gum may be used for cigarette smoking replacement.

Advantages

  • First pass – In this route, the Liver is bypassed so there is no loss of drug by the first-pass effect like the Oral administration route for buccal or sublingual administration. Bioavailability is higher also.
  • Rapid absorption – Because of the good blood supply to the area of absorption is usually quite rapid, especially for drugs with good lipid solubility.
  • Drug stability – pH in mouth relatively neutral (cf. stomach – acidic). Thus the drug may be more stable.

Disadvantages

  • Holding the dose in the mouth is somewhat difficult. If any part of the dose is swallowed mistakenly then that portion must be treated as an oral dose and it will be then subject to first pass metabolism.
  • Usually Buccal and Sublingual routes more suitable for drugs with small doses.
  • Drug taste may need to be masked

Rectal

Drugs are given by the rectal route of drug administration are most commonly given as suppository or enema. Some of the drugs that are given by this route include aspirin, theophylline, chlorpromazine, and some barbiturates.

Advantages

  • By-pass liver – Some (but not all) of the veins draining the rectum lead directly to the general circulation thus bypassing the liver. Therefore there may be a reduced first-pass effect.
  • Useful – This route may be most useful for patients unable to take drugs orally or with younger children.

Disadvantages

  • Erratic absorption – Drug absorption from a suppository is often incomplete and erratic. However, for some drugs, it is quite useful. There is research being conducted to look at methods of improving the extent and variability of rectal administration. Absorption from solutions used as an enema may be more reliable.

Intravenous

Drugs that are given via Intravenous are usually given into a peripheral vein. Rapid injections are used to treat epileptic seizures, acute asthma, or cardiac arrhythmias.

Advantages

  • Rapid – A quick response is possible for the drugs that are given via the Intravenous route. Plasma concentration can be precisely controlled using IV infusion administration.
  • Total dose – The whole dose is delivered to the bloodstream that is given via the Intravenous route. That is the bioavailability is generally considered to 100% after IV administration.

Disadvantages

  • Finding Suitable vein – It may be difficult to find a suitable vein to give the drug via the Intravenous route. There may be also some tissue damage at the site of injection if it is not given carefully.
  • Maybe toxic – As the drugs administrated via the Intravenous show the rapid response, toxicity can be a problem with rapid drug administrations.
  • Requires trained personnel – Trained personnel are required to give intravenous injections.
  • Expensive – Sterility, pyrogen testing, and larger volume of solvent mean greater cost for preparation, transport, and storage.

Subcutaneous

By Subcutaneous method the drugs are given under the skin. Insulin Injection is given to the patients via this route of administration.

Advantages

  • Drugs of this route can be given by the patient.
  • Absorption can be fast from an aqueous solution but slower with depot formulations. Absorption is usually complete. Improved by massage or heat. Vasoconstrictor may be added to reduce the absorption of a local anesthetic agent, thereby prolonging its effect at the site of interest.

Disadvantages

  • Can be painful. Finding suitable sites for repeat injection can be a problem.
  • Irritant drugs can cause local tissue damage.
  • Maximum of 2 ml injection thus often small doses limit use.

Intramuscular

Advantages

  • A larger volume than Subcutaneous can be given by Intramuscular. They may be easier to administer than intravenous injections.
  • A depot or sustained release effect is possible with the intramuscular injections, e.g. procaine penicillin

Disadvantages

  • Trained personnel required to give injections via Intramuscular routes.
  • Absorption can be rapid from an aqueous solution. Absorption is sometimes erratic, especially for poorly soluble drugs,e.g. diazepam, phenytoin. The solvent may be absorbed faster than the drug causing precipitation of the drug at the site of injection.
  • Sometime this method can be painful

Inhalation

Inhalation may be used for local effects like bronchodilators. Inhalation can also be use for systemic effects like general anesthesia. Drugs taken via Inhalation shows rapid absorption as it by pass the liver.

Topical

  • Local effect – ear drops, eye drops or ointment, antiseptic creams and ointments, sunscreens, callous removal products, etc.
  • Systemic effect – e.g., nitroglycerin ointment
  • Generally, absorption is quite slow. Absorption through the skin especially via cuts and abrasions or from sites where the skin is quite thin can be quite marked. This can be a real problem in handling toxic materials in the laboratory or pharmacy. This can also be a serious problem with garden chemicals.

Effect of Route of Drug Administration on Initiation of Effect of Drugs

Route of administrationTime
Intravenous30 – 60 sec
Intraosseous30 – 60 sec
Endotracheal2 – 3 min
Inhalation2 – 3 min
Sublingual3 – 5 min
Intramuscular10 – 20 min
Subcutaneous15 – 30 min
Rectal5 – 3 min
Oral39 – 90 min
Transdermal or Topicalmins to hours

Conclusion

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