Foundation-II Module — 3rd Year MBBS

AIM Concept Integration
3rd Year MBBS
Foundation Module

Foundations of Pharmacology, Drug Sources, Routes, Absorption and Bioavailability

Connect the core pharmacology concepts—from the identity and source of a drug to its route, absorption and eventual systemic availability—for rapid KMU-focused revision.

1. THE TOPIC IN ONE CONNECTED FLOW

A medicine begins as an active drug obtained from a natural, synthetic or biotechnology source. Its formulation and route determine how it enters the body. Membrane transport and physiological factors then determine absorption, while presystemic metabolism determines how much unchanged drug finally reaches the systemic circulation.

Drug Identity & Source

Drug / medicine
Natural, synthetic or recombinant source
Active principle + suitable excipients

→

Dosage Form & Route

Oral, sublingual, rectal, parenteral, inhalational, topical or transdermal

→ determines speed, convenience and site of delivery

→

Membrane Transport

Simple diffusion, facilitated diffusion, active transport, filtration, ion-pair transport or endocytosis

→

Absorption

Lipid solubility + ionization + surface area + blood flow + contact time + dissolution

→ determine entry into blood

→

Presystemic Handling

Oral absorption

→ portal circulation

→ intestinal/hepatic first-pass metabolism

→

Systemic Availability

Amount of unchanged drug reaching systemic blood

→ bioavailability

→ reflected by concentration-time curve and AUC

→

Persistence & Recycling

Biliary excretion

→ intestinal reabsorption

→ enterohepatic circulation

→ prolonged drug persistence

2. KEY CLINICAL CONNECTIONS

Route Selection & First-Pass Effect

Oral drug
→
portal liver passage
→
presystemic metabolism
→
reduced systemic availability

Sublingual or transdermal delivery
→
avoids initial portal passage
→
more unchanged drug reaches systemic blood

Ionization & Ion Trapping

Non-ionized drug
→
greater lipid solubility
→
easier membrane passage

pH change after membrane crossing
→
increased ionization
→
reduced return across membrane
→
ion trapping

Equivalent Products & Systemic Exposure

Same active drug + dosage form + strength
→
pharmaceutical equivalence

Similar rate and extent of availability
→
comparable concentration-time profiles
→
bioequivalence

3. AIM HIGH-YIELD INTEGRATION REVIEW

⭐ Drug source → active principle: Natural crude drugs contain biologically active constituents; isolation improves identification, purity and standardization.

Drug + excipients → medicine: The active pharmacological substance is combined with inactive formulation components to produce a usable medicinal preparation.

Route → rate and extent of delivery: IV delivery enters systemic blood directly, while enteral, intramuscular, subcutaneous and transdermal routes require absorption.

⭐ Membrane form → absorption: A non-ionized, lipid-soluble drug crosses lipid membranes more readily; ionization can restrict movement and produce trapping.

Absorptive conditions → drug entry: Surface area, blood flow, concentration gradient, contact time and dosage-form dissolution influence the amount and rate absorbed.

⭐ First-pass metabolism → lower oral bioavailability: Drug metabolized in the intestinal wall or liver before systemic entry contributes less unchanged drug to systemic circulation.

Concentration-time curve → systemic exposure: The area under the curve represents overall drug exposure and helps compare the extent of availability between preparations.

⭐ Biliary excretion → intestinal reabsorption: Enterohepatic circulation returns drug to the body and can prolong its persistence before final elimination.

AIM Exam Trap: Pharmaceutical equivalence means the same active ingredient, dosage form and strength; it does not by itself prove bioequivalence. Bioequivalence additionally requires sufficiently similar rate and extent of systemic availability.

Foundations of Pharmacology, Drug Sources, Routes, Absorption and Bioavailability

1. THE TOPIC IN ONE CONNECTED FLOW

2. KEY CLINICAL CONNECTIONS

3. AIM HIGH-YIELD INTEGRATION REVIEW

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