1. PHARMACOLOGY
It is the study of interaction of drug with biological system. The pharmacology is broadly defined as the knowledge of the history, source, physical and chemical properties, compounding, biochemical and physiological effects, mechanism of action, absorption, distribution, biotransformation, elimination, therapeutics and other uses of drugs.
2. CLASSIFICATION OF PHARMACOLOGY
2.1. PHARMACOKINETICS
It is simply defined as “what the body does to the drug” i.e. absorption distribution, localization, biotransformation and elimination of drug.
2.2. PHARMACODYNAMICS
- Simply it is defined as “what the drug does to the body” i.e. the biochemical and
physiological effects of drugs and their mechanism of action on the body.
- It is the study how drugs alter the functions of living cells.
2.3. PHARMACY
It is the art of preparing, compounding and dispensing drug in a form which is suitable for human use.
2.4. PHARMACOTHERAPEUTICS
It is the knowledge concerned with the application of drugs for the treatment of diseases.
2.5. TOXICOLOGY
It is that branch of pharmacology that deals with adverse effects of drugs.
2.6. DRUGS
A drug can be defined as a chemical substance which shows biological activities.
2.7. PRODRUG
Prodrug is a precursor of drug. It is a compound that must undergo chemical conversion by metabolic processes to become an active pharmacological agent.
3. PHARMACOKONETICS
3.1. ROUTES OF ADMINISTRATION
There are 4 main routes of drug administration.
3.1.1. Enteral (involving gastrointestinal tract)
• Oral
• Sublingual
• Rectal.
3.1.2. Parenteral
• I/M ( intramuscular )
• I/V ( intravenous )
• S/C ( subcutaneous )
• Intrathecal
• Intraperitoneal
• Intracardial
• Intra-arterial
3.1.3. Topical
• Skin
• Mucous membrane
3.1.4. Pulmonary or inhalation
4. ENTERAL
4.1. ORAL ROUTE
4.1.1. Merits
- Easy administration.
- Cheapest and economical.
- Irritant drug which cannot be given by parenteral route can be given through it.
- Provides largest surface area for absorption.
- Larger quantity of drug can be given.
- Suitable for producing local action on GIT e.g. antacid.
4.1.2. Demerits
- Cannot be used in patient with emergency.
- Cannot be used in unconscious.
- Absorption may not be proper.
- Drugs which are poorly lipid soluble are not absorbed e.g. neostigmine.
- Drugs that are destroyed in GIT cannot be used e.g. insulin.
- Drugs undergo in enterophepatic circulation and some or major portion is metabolized by the liver, therefore amount of drug entering into the circulation (called bioavailability) is low.
- Any pathological condition in GIT can interfere with absorption e.g. peptic ulcer.
4.2. SUBLINGUAL ROUTE
4.2.1. Merits
- Drugs do not go in entero-hepatic circulation.
- Maximum therapeutic concentration can be achieved rapidly. Therefore, in emergency this route is used e.g. nitroglycerin is given sublingually in angina attacks.
4.2.2. Demerits
- Large doses cannot be given.
- Repeatedly use damages the oral mucosa.
4.3. RECTAL ROUTE
4.3.1. Merits
- Highly irritant drugs can be given by this route.
- Less entero-hepatic metabolism (about 50% drugs will bypass the liver).
- Can be used in unconscious patient or in vomiting.
4.3.2. Demerits
Absorption is incomplete and irregular. Cannot be used frequently.
5. PARENTERAL ROUTES
5.1. INTRAVENOUS ROUTE
5.1.1. Merits
- Drug enters directly into blood so it is rout of emergency.
- Max. therapeutic concentration can be achieved rapidly.
- Highly irritant drugs which cannot be given by mouth can be given through it but requires dilution.
- Larger doses can be given.
- Bioavailability is 100%.
5.1.2. Demerits
- Drug once administered can’t be recovered back.
- Highly irritant drugs can produce thrombophlebitis.
- Defective technique can lead to pain and inflammation.
- Requires lot of skill.
- There is increased risk of side effects.
- Not suitable for oily solutions and insoluble substances.
5.2. INTRAMUSCULAR ROUTE
5.2.1. Merits
- It is easier for administration than l/V.
- Absorption is quicker than subcutaneous route.
- Suitable for moderate volumes and oily drugs.
5.2.2. Demerits
- Highly irritant drugs cannot be given.
- Insoluble drugs cannot be given because they are not absorbed.
- Defective technique can result in damage to nerve or blood vessel.
5.3. SUBCUTANEOUS ROUTE
5.3.1. Merits
- Absorption is low so the duration of action is prolonged.
- Suitable for some insoluble suspensions.
5.3.2. Demerits
Irritant drugs can produce inflammation, necrosis, and pain.
5.4. INTRAPERITONEAL ROUTE
5.4.1. Merits
Surface area is larger. Used in cases of poisoning.
5.4.2. Demerits
Repeated administration results in peritonitis.
5.5. INTRATHECAL ROUTE
5.5.1. Merits
Uses in cases of severe brain infection when drug cannot pass CSF barrier.
5.5.2. Demerits
Defective technique may result in damage to nervous system.
5.6. INTRA-ARTERIAL ROUTE
Through this route drug is injected in particular artery to localize the effect of drug on an organ or tissue..
5.7. INTRA-ARTICULAR ROUTE
Steroids and antibiotics are injected into the inflamed joints to produce potent effect.
6.TOPICAL ADMINISTRATION
6.1. Skin
Solution, emulsion, ointments, powders and creams are applied for their local topical action on skin and mucous membrane.
6.2. Mucous membrane
Some drugs are applied to the mucus membrane of conjunctiva, nasopharynx, oropharynx, vagina, colon, urethra, and urinary bladder for local effects.
6.3. Eye
Ophthalmic drugs are used primarily for their local effects.
7. INHALATION ROUTE
This route is used to produce local effects on lung or bronchi as in case of asthma and it is also used in general anaesthesia.
8. PASSAGE OF DRUG ACROSS CELL MEMBRANES
The ability of drug to cross cell membrane will determine whether the drug
will be absorbed or not. Important characteristics of drugs that influence their passage across the membrane are their molecular size and shape, solubility at the site of absorption, degree of ionization and lipid solubility. The passage of drug across membrane takes places by any of the following processes:
- Passive Transport: involving
• Simple diffusion: In this transport drug will pass from one side of the cell membrane to other along its concentration gradient. This process depends upon lipid solubility and ionization. Greater the lipid solubility greater will be diffusion. Unionized drugs are more lipids soluble than ionized ones so there rate of diffusion are also greater than ionized drugs.
• Filtration: In this process passage of drugs occurs through porous membrane by means of their hydrostatic or osmotic pressure.
- Specialized Transport: involving
• Active transport: In this process the drug is transferred against a concentration or electrochemical gradient with the expenditure of energy. Absorption takes place by this transport in renal tubules, choroid plexus and neuronal membrane.
• Facilitated diffusion: In this process drugs are transported along their concentration gradient with the help of a carrier e.g. absorption of glucose and amino acids.
• Pinocytosis: This refers to the ability of the cells to engulf fluid material by local invagination of the cell membrane and subsequently formation of vesicle containing fluid or solute within the cell.
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