PHARMA101: INTRODUCTION ①

4 min readMay 25, 2022

Lecture-1: Pharmacology to boost your USMLE preparation. Written most simply and lucidly. LET’s START WITH DRUGS.

Pharmacology is the science of drugs. According to WHO, a drug is any substance or product that is used or is intended to be used to modify or explore physiological or pathological states for the benefit of the recipient.

DIVISIONS OF PHARMACOLOGY

DIFFERENT ASPECTS OF PHARMACOLOGY

PHARMACOTHERAPEUTICS- Integrating pharmacological information with disease knowledge to cure patients and prevent the disease
CLINICAL PHARMACOLOGY- Pharmacodynamics and pharmacokinetic investigation in healthy volunteer
CHEMOTHERAPY DRUGS- Have two components-

Pharmacodynamic Agents- Pharmacodynamic Effects in the Recipients
Chemotherapic Agents- Inhibit/kill pathogens or malignant cells

4. PHARMACY- Art of making usable drugs

5. TOXICITY- Art to deal with the poisonous effect of drugs. A drug may cause toxicity when taken in higher concentrations.

NATURE OF DRUGS

Most are Organic. Some may be inorganic e.g., FeSO₄, Li, Mg(OH)₂
They can be Acidic(e.g., Aspirin, Penicillin), Basic(e.g., Morphine, Chloroquine) or even non-electrolytes(e.g., Alcohol, Diethyl Ether)
Can be Solid(most), Liquid(ethanol, propofol, castor oil) or gaseous(Nitrous Oxide)
Most of them have a weight range between-100–1000 D. Some may have a weight range of <100 D like Li⁺ with only 7 D. Some may be very huge like Heparin(10–20 kD), Enzymes(>50 kD) and other proteins

DRUG SOURCES

PLANTS- Alkaloids, Glycosides and Oils
ANIMALS
MICROBES
MINERALS
SYNTHETIC CHEMISTRY- Maximum new drugs are made by this nowadays.
BIOTECHNOLOGY

So, drugs are of various kinds. Nothing could have been predicted about the nature of the drugs for sure.

ROUTES OF DRUG ADMINISTRATION

Answer a question- “How can you administrate a drug to a patient- the method of drug administration?”

⓵LOCAL

The drug is restricted to a particular area of infection and does not spread to the whole body. It includes-

Topical- e.g., Skin Lotion
Intraocular- e.g., Eye Drops

⓶SYSTEMIC

The drug will act in the blood. Think of the possible ways by which a drug can reach the systemic circulation of the patient.

Enteral- It stands for towards the intestine. How can you reach the intestine? I think either from the mouth(oral) or anus(Rectal) routes. Oral and rectal drug administrated routes are preferred over pricking the patient.
Parenteral- It stands for away from the intestine. How can reach blood without an oral route or anal administration? You may have thought injection but there is more also-

Injection- 🎉You were right! The injection can be used for the systemic administration of drugs.

Injections are having some types also-
a) Intravenous- Always used by diluting/titrating. 25° angle is taken with the body surface.
b) Intramuscular- Used by Z-Track Technique. 90° angle
c) Subcutaneous- 45° angle; even self-administration is possible 
d) Intradermal- ≤15° angle. Used to test allergy before systemic drug administration and BCG vaccine is given through it.

Non-Injection- Sublingual method(place it below tongue and drug will be absorbed), Intranasal, Transdermal, Inhalation

Q1 Sublingual Drug Administration Benefits?
Ans. Fast, No first-pass metabolism, termination is so easy; just spit the tablet and self-administration is possibleQ2 Drugs Given Intranasal?
Ans. Desmopressin, Calcitonin, Esketamine,...Q3 A Drug given by Inhalation?
Ans. Salbutamol

PHARMACOKINETICS- ABSORPTION

Drugs are absorbed through various membranes. There is only a single rule for the crossing of the drug-

Drugs will cross the medium when both of them are of the same nature.
♋︎ Acidic Drug- Acidic Medium- Non-ionic Drug- CROSS
♋︎Basic Drug- Basic medium- Non-ionic Drug- CROSS

Why?

The drug has to cross the plasma membrane that is non-ionic. The drug has to be non-ionic. An acidic drug will be non-ionic in an acidic medium and a basic drug will be non-ionic in a basic medium.

Q Where will the acidic drug will be absorbed more- stomach or small intestine?
Ans. Small Intestine; Despite the basic medium, a dynamic relationship for a longer time and larger surface area leads to more absorption through the small intestine.

BIOAVAILABILITY

% of Drugs reached the systemic circulation
Helped in Determining the dose.

But we can’t measure the exact no. of molecules entering the systemic circulation. So, here is another approach-

Plot the plasma concentration vs time graph and then the Bioavailability will be-

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Read part 2:-

② PHARMA101: PHARMACOKINETICS➚

Task:- What are Bioequivalent drugs?
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