An Overview of Drugs
Definition of drug
Drug means 'dry herb'
WHO scientific groups definition
Any substance or product that's used or shall be wont to modify or explore or physiological systems or pathological states for the advantage of the recipient is named drug.
Source of drug
(A) Natural source
1) Plant
- Digitalis
- Morphine
- Atropine
- Reserpine
2) Animal
- Insulin
- Heparin
- Gonadotrophin
3) Microorganism
- Penicillin
- Chloramphenicol
- Bacitracin
- Tetracyclin
4) Minerals
- Magnesium sulfate
- Ferrous sulfate
- Liquid paraffin
(B) Synthetic source
- Aspirin
- Anti-malarial drugs
- Sulphonamides
- Paracetamol
(C) Semisynthetic source
- Ampicillin
- Tetracycline
(D) Recombinant DNA technology
- Human insulin
The dosage form of drug
A drug may be designed either solid, semisolid, liquid, or gaseous form. Each form is suitable for a particular route of administration.
The product designated for administration into the body is called the dosage form of the drug.
Available dosage forms are:
(A) Solid Preparation:
- Tablet form
- Capsule form
- Pill form
- Suppository form
- Powder form
- Granules
(B) Semisolid preparation
- Ointment
- Cream
- Paste
- Gel
(C) Liquid preparation
- Solution
- Suspension
- Emulsion
- Elixir
- Injection
- Drop
- Mixture
(D) Gaseous preparation
- Gas in cylinder
- Aerosol
- Volatile liquid
Routes of drug administration
The main routes of drug administration are:-
1) Systemic route
(A) Enternal or alimentary routes
- Sublingual
- Oral
- Rectal
(B) Parenteral routes
- Subcutaneous
- Intracutaneous
- Intraarterial
- Intravenous
- Intramuscular
- Intraarticular
- Intraperitonial
- Intraventricular
- Intracardiac
- Intrapleural
- Intramedullary
(ii) Inhalation
- As a gas:
e.g. Volatile anesthetic; N2O, Chloroform
- As an aerosol:
e.g. Salbutamol (Bronchodilator)
- As a powder:
e.g. Sodium cromoglycate
2) Local routes
Applied to the localised area and action is confined to that particular area.
- Topical application: Ointment, paste, drops, powder, lotion, etc.
- Skin inunction
- To eye and ear
- To mucous membrane of nose, urethra, rectum, anal canal, and vagina.
- Iontophoresis: In this process, the drug is applied to the particular area of skin and Galvanic current is used to increase absorption through the skin.
Advantage of Oral Route
- The oral route is a cheap, safe, and painless route.
- It is a convenient route because the drug can be given in the form of a tablet or capsule form which contains an exact dose.
- Self-medication is possible.
- Prolong action can be obtained due to delayed absorption.
- drugs need not sterile and highly purified.
- Free from fear and anxiety for pricking needle and associated with pain.
- This route has a psychological effect on the patient that he has taken medicine.
- It is easy and the patient can take the drug without interrupting his activity.
- Hypersensitivity reaction in many cases is less.
The disadvantage of Oral Route
- The onset of action is slow due to delayed absorption. So not suitable for emergency cases.
- Irritant. unpleasant, and hypertrophic drugs can not be administered.
- This route may not be useful in the presence of vomiting or diarrhea.
- This route can not be employed in an unconscious or non-cooperative patient.
- Drugs that are destroyed by digestive juice are not administered orally. e.g. Insulin, Heparin.
- Drugs having high first-pass metabolism are not given orally. e.g. Testosterone.
- The absorption of certain drugs is irregular and negligible. e.g. Streptomycin, Neomycin.
Advantage of I/V route
- I/V route is used in emergency cases to obtained immediate effect.
- Large volume. An unpleasant and irritant solution can be given.
- Suitable for unconscious and non-co operative patients.
- Drugs can be given through the I/V route in cases of Diarohhea, vomiting, or where the patient is unable to swallow.
- This route avoids drug modification by the digestive juice or hepatic enzymes. e.g. Oxytocin
- Rapid action and accuracy of dose are ensured.
The disadvantage of I/V route
- It is an invasive painful procedure.
- Self-medication is difficult.
- Strict aseptic measures, special techniques are essential.
- There may be a risk of infection, hypersensitivity, reaction, pyrogenic reaction, local venous thrombosis, and hemolysis may occur.
- Leakage of the drug outside the vein can produce severe irritants.
- Overdose may have effects so immediate that it is impossible to reverse them.
- There may be a chance of injury to surrounding nerves and vessels.
- Drugs must be water-soluble.
- The short duration of action, as the excretion is rapid.
- Expensive.
Advantage of I/M route
- Absorption of drugs is more rapid and uniform than subcutaneous injection due to rich blood supply to the muscle.
- Slightly irritant drugs can be given that are too irritant for the subcutaneous route.
- The moderately large volume can be given (but not above 5 ml)
- Depot preparation can be administered.
The rate of absorption is slower for females because of more subcutaneous fat.
The disadvantage of I/M route
- It is the invasive and painful route
- Self-medication is difficult
- The large volume of the drug can not be given.
- There may be a chance of local inflammation, infection,, abscess formation, paresis, and even paralysis of the muscle.
- Tissue binding or precipitate from solution may delay the appearance of drugs in the systemic circulation, e.g. Diazepam.
