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| Route of drug administration-Pharmacy concepts |
The interval between administration of a drug and development of response is called Biological lag.
The choice of appropriate route in a given situation depends both on drug as well as patient related factors. The most common factors are as follows,
> Physical and chemical properties of drug
> Site of desired action (local or general action)
> Rate and extent of absorption of drug
> Effect of digestive enzymes and first pass metabolism
> Rapidity of response desired
> Accuracy of dosage required
> Patient's condition
The routes of administration can be classified as :
(1) ORAL OR ENTERAL ROUTE
(2) PARENTERAL ROUTE :- (a) Injection
(b) Inhalation
(c) Transcutaneous
(d) Transmucosal
(e) Drug delivery systems
(3) LOCAL APPLICATION
*ORAL OR ENTERAL ROUTE :
It is the oldest and most commonly used route of administration.
Advantages :
1. It is a safe, convenient and economical route.
2. Self medication is possible.
3. Withdrawal of the drug is possible.
Disadvantages :
1. Onset of drug action is slow.
2. Drugs which are bitter in taste are hard to administer.
3. Drugs producing nausea and vomiting cannot be administered.
4. The drug may be inactivated by gastric enzymes.
5. This route is not possible in an unconscious patient.
*PARENTERAL ROUTE :
Routes of administration other than oral route are referred as parenteral.
Advantages:
1. Absorption is quick and rapid.
2. Accurate dose of drug can be administered.
3. The drug enters into systemic circulation in an active form.
4. It is greatly useful in case of emergency.
5. It is also useful in an unconscious patient.
Disadvantages :
1. Pain may be produced at the site of administration.
2. There is a chance for abscess and inflammation.
3. Sterile procedures are required for this route.
4. It is an expensive route.
5. Self medication is not possible.
(a) Injection :-
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Route of drug administration-Pharmacy concepts
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> Intradermal : The drug is injected in the layers of skin.
E.g. B.C.G. vaccine
> Subcutaneous : Non-irritant substances alone can be injected by this route. Only small volume can be administered subcutaneously.
> Intramuscular : The drug is injected deep into muscle tissue. Depot preparations (oily solutions, aqueous suspensions) can be injected by this route.
> Intravenous: A drug is directly injected into a vein. The drug reaches directly into the blood stream and effects are produced immediately.
Advantages of this route:
-The drug enters into circulation in an active form.
-Desired blood concentration can be obtained.
-Irritant drugs can be administered by this route.
-Quick and immediate effects can be produced.
-It is useful in case of emergency.
-It is useful in an unconscious patient.
Disadvantages :
-Only solution can be administered by this route.
-Drugs which precipitate blood constituents cannot be administered.
-Untoward effects, if occur are immediate.
-Withdrawal of drug is not possible.
> Intra-arterial : A drug is injected into an artery in this route. The effect of drug can be localized in a particular organ or tissue by choosing the appropriate artery. Anticancer drugs are sometimes administered by this route.
> Intraperitoneal : In this route, a drug is injected into the peritoneal cavity. By this route, fluids like glucose and saline can be given to children.
> Bone-Marrow : It is very similar to intravenous injection. This route is useful when veins are not available due to circulatory collapse or thrombosis. In adults, the sternum and in children, tibia or femur is chosen for injection.
(b) Inhalation :-
Gases, volatile liquids, aerosols or vapors can be administered by this route. E.g. General anesthetics.
Advantages:-
-Rapid onset of action.
-Immediate absorption of drug.
-Localization of the effect in diseases of the respiratory tract.
Disadvantages:-
-Administration process is difficult.
-Poor ability to regulate the dose.
-Local irritation of the respiratory tract may occur.
(c) Transcutaneous Route :-
Highly lipid soluble drugs can be applied over the skin for slow and prolonged absorption. In this route, absorption of the drug can be increased by rubbing the preparation, by using an oily base and by an occlusive dressing.
This route is further classified as Iontophoresis, Inunction, Jet injection, Adhesive units.
(d) Trans mucosal route :- This route is classified as Sublingual, Trans nasal and Trans rectal.
Sublingual route :-
In this route, the tablet of medicament is to be placed below the tongue and is allowed to dissolve in the mouth cavity. Thus, the active medicament gets absorbed through the buccal mucous membrane. The absorbed material is then directly passed into systemic circulation. E.g. Ephedrine Hydrochloride tablet is administered by this route for the treatment of asthma. Also, for the treatment of angina pectoris, the tablet of Nitroglycerine is administered sublingually.
Advantages :-
-Rapid onset of action.
-Termination of the effect by spitting the tablet.
-Inactivation of the drug in the stomach is avoided.
-The drug enters directly into systemic circulation without inactivation in the liver.
-It is useful in medicinal emergency cases such as angina pectoris.
Disadvantages :-
-The only disadvantage of this route is that the drugs having direct or toxic effects on heart should be cautiously administered by taking at most care to avoid any such effect.
Trans-nasal route :-
In this route, the drug is rapidly absorbed through the mucous membrane of nose. E.g. posterior pituitary powder. It is useful for drugs in the form of snuff or nasal spray. However, only certain drugs like GnRH agonists and desmopressin applied as a spray or nebulized solution have been used by this route.
Trans rectal route :-
Certain irritant or unpleasant drugs can be put into rectum as suppositories or retention enema for systemic effect. E.g. Aminophylline for bronchospasm, Diazepam for status epilepticus. This route can be used when the patient is having vomiting or is unconscious.
Advantages :-
-Gastric irritation is avoided.
-Useful route in old and terminally ill patients.
(e) New drug delivery system :- It contains,
-Occusert :- In this system, the drug is placed directly under the eyelid. E.g. Pilocarpine fro prolonged effect.
-Progestasert :- It is an intrauterine contraceptive device. It produces controlled release of progesterone within the uterus for a year.
-Prodrug :- It is an inactive drug which after administration is metabolized into an active drug. E.g. L-Dopa is an inactive compound but after administration, it is metabolized to the active drug Dopamine which is effective in parkinsonism.
* LOCAL APPIACATION :-
Drugs in the form of powder, paste, lotion, drops and ointment can be administered locally for action at the site of application. Drugs can be applied on mucous membrane of nose, conjunctiva, vagina, urethra and rectum.
E.g. Bougie for urethra, Pessary for vagina, Suppository for vagina and rectum, Enema for rectum are the preparations used for local application.
(b) Inhalation :-
Gases, volatile liquids, aerosols or vapors can be administered by this route. E.g. General anesthetics.
Advantages:-
-Rapid onset of action.
-Immediate absorption of drug.
-Localization of the effect in diseases of the respiratory tract.
Disadvantages:-
-Administration process is difficult.
-Poor ability to regulate the dose.
-Local irritation of the respiratory tract may occur.
(c) Transcutaneous Route :-
Highly lipid soluble drugs can be applied over the skin for slow and prolonged absorption. In this route, absorption of the drug can be increased by rubbing the preparation, by using an oily base and by an occlusive dressing.
This route is further classified as Iontophoresis, Inunction, Jet injection, Adhesive units.
(d) Trans mucosal route :- This route is classified as Sublingual, Trans nasal and Trans rectal.
Sublingual route :-
In this route, the tablet of medicament is to be placed below the tongue and is allowed to dissolve in the mouth cavity. Thus, the active medicament gets absorbed through the buccal mucous membrane. The absorbed material is then directly passed into systemic circulation. E.g. Ephedrine Hydrochloride tablet is administered by this route for the treatment of asthma. Also, for the treatment of angina pectoris, the tablet of Nitroglycerine is administered sublingually.
Advantages :-
-Rapid onset of action.
-Termination of the effect by spitting the tablet.
-Inactivation of the drug in the stomach is avoided.
-The drug enters directly into systemic circulation without inactivation in the liver.
-It is useful in medicinal emergency cases such as angina pectoris.
Disadvantages :-
-The only disadvantage of this route is that the drugs having direct or toxic effects on heart should be cautiously administered by taking at most care to avoid any such effect.
Trans-nasal route :-
In this route, the drug is rapidly absorbed through the mucous membrane of nose. E.g. posterior pituitary powder. It is useful for drugs in the form of snuff or nasal spray. However, only certain drugs like GnRH agonists and desmopressin applied as a spray or nebulized solution have been used by this route.
Trans rectal route :-
Certain irritant or unpleasant drugs can be put into rectum as suppositories or retention enema for systemic effect. E.g. Aminophylline for bronchospasm, Diazepam for status epilepticus. This route can be used when the patient is having vomiting or is unconscious.
Advantages :-
-Gastric irritation is avoided.
-Useful route in old and terminally ill patients.
(e) New drug delivery system :- It contains,
-Occusert :- In this system, the drug is placed directly under the eyelid. E.g. Pilocarpine fro prolonged effect.
-Progestasert :- It is an intrauterine contraceptive device. It produces controlled release of progesterone within the uterus for a year.
-Prodrug :- It is an inactive drug which after administration is metabolized into an active drug. E.g. L-Dopa is an inactive compound but after administration, it is metabolized to the active drug Dopamine which is effective in parkinsonism.
* LOCAL APPIACATION :-
Drugs in the form of powder, paste, lotion, drops and ointment can be administered locally for action at the site of application. Drugs can be applied on mucous membrane of nose, conjunctiva, vagina, urethra and rectum.
E.g. Bougie for urethra, Pessary for vagina, Suppository for vagina and rectum, Enema for rectum are the preparations used for local application.
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