unit 1 Pharmacokinetics

Absorption vs Filtration

1. Absorption

What it means: The drug enters the bloodstream.

💡 Easy memory: Absorption = Drug gets into the blood.

Example: You swallow a pill → the drug is absorbed from your stomach/intestines into your blood.

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2. Filtration

What it means: Solids and fluids are separated through a filter.

💡 Easy memory: Filtration = Straining things apart.

Example: Your kidneys filter waste from your blood.

Think of it like using a coffee filter—liquid passes through, but larger particles stay behind.

3. Passive Transport (Diffusion)

vs

4. Osmosis

Passive Transport (Diffusion)

What it means: Drugs move from an area where there is more drugs to an area where there is less drugs.

💡 Easy memory: High → Low = No energy needed.

Example: If a room is full of perfume, the smell spreads throughout the room on its own.

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4. Osmosis

What it means: Water moves across a semipermeable membrane from one side to another.

💡 Easy memory: Osmosis = Water movement.

Example: A raisin placed in water swells because water moves into it.

👉 Diffusion = movement of particles/drugs
👉 Osmosis = movement of water

Active Transport

What it means: Drugs or substances move using energy (ATP) .

💡 Easy memory: Active = Requires energy.

Example: Moving something uphill takes work. Cells use energy to move substances where they need them.

Side by side chart

drugs going in

Term	Easy Meaning	Energy Needed?
Absorption	Drug enters bloodstream	No
Filtration	Separates solids and fluids	No
Diffusion (Passive Transport)	Moves from high → low concentration	No
Osmosis	Water moves across a membrane	No
Active Transport	Moves substances using energy	Yes

• Absorption = Into the blood 🩸

• Filtration = Filter it ☕

• Diffusion = High → Low ⬇

• Osmosis = Water moves 💧

• Active Transport = Uses energy 🔋

Factors Affecting Drug Absorption (Easy Version)

Absorption = how a drug gets into the bloodstream.

Think of it as "How fast can the drug enter the body and start working?"

• Factors Affecting the Rate of Absorption
  
  1. Solubility of the Drug

Simple meaning: How easily the drug can pass through cell membranes.

💡 Cell membranes are mostly made of fat (lipids).

• More lipid (fat) soluble = absorbed faster

• Less lipid soluble = slower absorbed

Easy Memory Trick:

🧈 "Fat likes fat."

Since cell membranes are fatty, drugs that dissolve in fat pass through more easily.

Example:

• Drug A is very fat-soluble → enters cells quickly → works faster.

• Drug B is not fat-soluble → enters cells slowly → works slower.

the more lipid soluble the drug, the faster it passes through the cell membrane

• Factors Affecting the Rate of Absorption
  
  2. Route of Administration / Drug Formulation

Simple meaning: How the drug is given.

Different routes absorb at different speeds.

Fastest → Slowest

1. IV (intravenous) 💉 → immediate (already in bloodstream)

2. Liquid medicine 🥤 → absorbed quickly

3. Tablets/Capsules 💊 → absorbed slower because they must dissolve first

Easy Memory Trick:

🏃 "The fewer steps, the faster the drug."

• IV = no steps → fastest

• Liquid = one step → fast

• Tablet = must dissolve first → slower

• liquids absorb more quickly than solids, faster rate for IV drugs vs tablets

Factors Affecting the Rate of Absorption
3. Ionization of Drugs

Simple meaning: Whether the drug has an electrical charge.

For a drug to cross a cell membrane easily:

✅ Un-ionized = no charge = absorbed better

❌ Ionized = has a charge = absorbed poorly

Easy Memory Trick:

🚪 "No charge, no problem."

• Un-ionized drug = slips through the membrane door easily.

• Ionized drug = has trouble getting through.

• Must be un-ionized (no charge) for absorption

• Factors Affecting the Rate of Absorption

• side by side absorption

Factor	Faster Absorption
Solubility	More lipid (fat) soluble
Route	IV > Liquid > Tablet
Ionization	Un-ionized (no charge)

"Fat, Fast Route, No Charge."

• Fat-soluble drugs absorb faster.

• Fast routes (IV, liquids) absorb faster.

• No charge (un-ionized) absorbs faster.

Distribution

the drug traveling through the bloodstream to different tissues and organs.

💡 Think of distribution as a delivery service .

• Absorption = drug enters the bloodstream.

• Distribution = bloodstream delivers the drug around the body.

1. Plasma Proteins

Distribution

Simple meaning: Some drugs stick to proteins in the blood.

Think of plasma proteins as parking spots 🚗.

• Bound drug = parked on a protein → can't work yet

• Free (unbound) drug = not parked → can leave the blood and work

Easy Memory Trick:

🔓 "Free drug = active drug."

Only the free (unbound) drug can:

• Leave the bloodstream

• Reach tissues

• Produce an effect

Example:

100 mg of drug enters the blood:

• 80 mg binds to proteins ❌

• 20 mg stays free ✅

Only the 20 mg free drug can work.

many drugs are attracted to plasma proteins, only unbound/free drugs can give a pharmacological effect

2. Blood Flow

Distribution

Simple meaning: The more blood that reaches an organ, the more drug reaches it.

Think of blood as a delivery truck 🚚.

More trucks = more drug deliveries.

Organs with Lots of Blood Flow:

❤ Heart
🧠 Brain
🫁 Lungs
🩺 Kidneys
🫀 Liver

These organs receive drugs quickly.

Easy Memory Trick:

🚚 "More blood = more drugs."

• the greater blood flow, the greater the amount of drug

3. Blood-Brain Barrier (BBB)

Distribution

Simple meaning: The brain has a special protective wall.

The BBB protects the brain from harmful substances.

🧠Think of it as a security gate .

Most drugs cannot get through easily.

Which drugs can pass?

✅ Lipid-soluble (fat-soluble) drugs

❌ Water-soluble drugs

Because the BBB is made mostly of fats (lipids).

Easy Memory Trick:

🧈 "Fat gets through the brain gate."

• lipid barrier protects brain, drugs must be lipid soluble to pass into brain (most drugs are primarily water soluble)

Distribution side by side. chart

Factor	Easy Meaning
Plasma Proteins	Only free (unbound) drugs can work
Blood Flow	More blood = more drug delivered
Blood-Brain Barrier	Fat-soluble drugs enter the brain easier

"Free drugs work, blood delivers, fat enters the brain."

• 🔓 Free drug = active drug

• 🚚 More blood = more drugs

• 🧠🧈 Fat-soluble drugs cross the BBB

Metabolism

the body changing a drug into a form that can be removed.

💡 Think of metabolism as the body's drug-processing factory .

🏭 Drug goes into the factory → gets changed → leaves the body.

• chemical alteration of drug (biotransformation)

Liver

Main Metabolism Organ

The liver is the body's main drug-processing factory.

🩺 Liver enzymes break down drugs so the body can get rid of them.

Easy Memory Trick:

🏭 Liver = Drug Factory

DMMS (Drug Microsomal Metabolizing System)

This is a group of liver enzymes that metabolize drugs.

What does it do?

Many drugs are lipid-soluble (fat-soluble) .

The kidneys cannot easily remove fat-soluble drugs.

So the DMMS:

➡ Changes fat-soluble drugs
➡ Into water-soluble drugs
➡ So the kidneys can remove them in urine

Easy Memory Trick:

🧈 ➡ 💧 ➡ 🚽

Fat → Water → Pee

take lipid soluble drugs and alter them to become water soluble so they may be excreted by the kidneys and not repeatedly absorbed

Enzyme Induction

MORE liver enzymes are made.

More enzymes = drugs are broken down faster.

What's happening?

🏭🏭🏭 More workers in the factory

• The drug is metabolized faster

• The drug leaves the body faster.

• The drug doesn't last as long

Result:

⬇ Duration of action decreases/ drug works shorter

⬇ Drug effect may decrease

• increase in the amount of liver enzymes, faster metabolism of drugs, duration of action is decreased

Easy Memory Trick:

🚀 Induction = Increased enzymes = Increased metabolism

Common Enzyme Inducers

• 🚬 Smoking

• 🍺 Chronic alcohol use (long-term drinking)

• Phenobarbital

• Phenytoin

• Carbamazepine

Enzyme Inhibition

liver enzymes are blocked or slowed down.

inhibit liver enzymes

What's happening?

🏭 Fewer workers in the factory

• The drug is metabolized slower

• Drug stays in body longer

• Drug effect becomes stronger

Result:

⬆ Duration of action increases/ drug stays in longer

⬆ Intensity of action increases/ drug effect becomes stronger

Easy Memory Trick:

🐢 … = Slow metabolism = Stronger/Longer drug effect

Common Enzyme Inhibitors

• Grapefruit juice 🍊

• Cimetidine (Tagamet)

• Erythromycin

• Allopurinol

• Calcium Channel Blockers

• Fluoxetine

• Short-term alcohol use 🍺

Enzyme Induction vs Enzyme Inhibition

Enzyme Induction	Enzyme Inhibition
More enzymes	Fewer/blocked enzymes
Faster metabolism	Slower metabolism
Drug removed faster	Drug stays longer
Weaker effect	Stronger effect
Shorter duration	Longer duration

Imagine the liver is a drug factory 🏭.

Enzyme Induction

The factory hires more workers.

👷👷👷👷👷

The drugs get processed very quickly.

➡Drug leaves quickly.
➡ Effect doesn't last long.

Enzyme Inhibition

The factory loses workers.

👷

The drug is processed slowly.

➡ Drug stays longer.
➡ Effect is stronger and lasts longer.

Enzyme Induction

FAST metabolism = LESS drug effect

🚀

enzyme Inhibition

SLOW metabolism = MORE drug effect

🐢

DMMS

Fat → Water → Pee

🧈 ➡ 💧 ➡ 🚽

First-Pass Effect

Metabolism = the body (mostly the liver) changes a drug so it can be removed.

The first-pass effect happens when an oral (PO) drug is swallowed and goes through the liver before reaching the bloodstream.

The liver breaks down some of the drug right away.

As a result:

➡ Less drug reaches the bloodstream

➡Less drugs are available to work

Easy Way to Think About It

Imagine you have 100 mg of a drug .

💊 Swallow the pill

➡ Drug goes to the liver

➡ Liver breaks down 30 mg

➡Only 70 mg reaches the bloodstream

The liver got the "first pass" to the drug before the rest of the body did.

First–Pass effect

Why Does It Matter?

Because some of the drug is destroyed before it can work.

Result:

⬇ Less drug reaches circulation (bloodstream)

⬇ Drug effect may be reduced

• when drugs are transported through the liver and become metabolized before being distributed

• reduces the amount of drug reaching circulation/bloodstream

Which Routes Have a First-Pass Effect?

Oral (PO) ✅

• Swallowed pills

• Capsules

• Liquid medicines

These go through the liver first.

Which Routes Avoid the First-Pass Effect?

IV (Intravenous) 💉

Drug goes directly into the bloodstream.

IM (Intramuscular) 💪

Drug is injected into a muscle and enters the blood.

Inhalation 😮‍💨

Drug is breathed into the lungs and enters the blood quickly.

These routes bypass the liver at first , so more drug reaches the bloodstream.

Easy Memory Trick

🚪 First-Pass Effect

The liver takes the first bite of the drug.

🍪💊

If you start with 100 mg:

• Liver takes some first 🍪

• Less drugs are left for the body

First-Pass Effect
= Oral drug goes through the liver first.

What's happening?

• Liver metabolizes part of the drug.

• Less drugs reach the bloodstream.

Routes that avoid it:

• 💉 IV

• 💪 IM

• 😮‍💨 Inhalation

One-Line Memory Trick

"PO goes through the liver first, so less drug reaches the blood." 💊➡🏭➡🩸

What is excretion?

getting rid of a drug from the body.

💡 Think of it as taking out the trash.

After a drug has done its job, the body needs to remove it.

1. Kidneys 🩸➡🚽

vs 2. GI Tract 🚽

excretion

The kidneys are the main way drugs leave the body.

They remove drugs through urine (pee).

The kidneys remove drugs best when they are:

✅ Water-soluble

✅ Ionized (charged)

Easy Memory Trick:

💧 Water-soluble drugs leave in urine.

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2. GI Tract 🚽

Some drugs leave through the digestive system and come out in stool (feces/poop).

Easy Memory Trick:

🍔➡💩

GI tract = drugs leave in stool

• Excretion

Lungs 🫁 vs 4. Sweat 😓

Lungs 🫁

Some drugs are breathed out.

This mainly happens with anesthetic gases used during surgery.

Example:

A patient receives anesthesia

🫁 The lungs help remove the gas when the surgery is over.

Easy Memory Trick:

😮‍💨 Lungs = breathe drugs out.

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4. Sweat 😓

Small amounts of some drugs can leave through sweat.

😓 Sweat can carry drugs out of the body.

• Excretion

milk vs saliva

5. Milk (Lactation) 🍼

Some drugs can pass into a mother's breast milk.

A nursing baby may be exposed to the drug.

That's why healthcare providers check if medications are safe during breastfeeding.

Easy Memory Trick:

👩‍🍼 Mom takes drug → some may enter breast milk → baby may receive it.

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6. Saliva 👄

Small amounts of drugs can leave through saliva.

Easy Memory Trick:

👄 Some drugs leave in spit (saliva).

• Excretion side by side chart

Organ/System	How Drug Leaves
Kidneys	Urine (pee) 🚽
GI Tract	Stool (poop) 💩
Lungs	Exhaled air 😮‍💨
Sweat Glands	Sweat 😓
Breast Milk	Milk 🍼
Salivary Glands	Saliva 👄

"Pee, Poop, Breathe, Sweat, Milk, and Saliva."

🚽 💩 😮‍💨 😓 🍼 👄

These are the main ways the body excretes (eliminates) drugs.

1. Bioavailability 🩸

how much of the drug actually gets into the bloodstream.

Example:

You take a 100 mg pill 💊

But your body only absorbs 80 mg .

That means:

🩸 80 mg reached the blood

❌ 20 mg was lost

Bioavailability = 80%

Easy Memory Trick: how much it gets in.

💊➡🩸

❓"How much drug got INTO the blood?"

Example:
100 mg given → 80 mg reaches blood

"How much of the drug does it make into the blood?"\

• percentage of the drug that is actually absorbed

• affected by drug form and route of administration

2. Half-Life ⏰

how long it takes for HALF of the drug to leave the body.

Example:

Start with 100 mg

After one half-life:

100 mg ➡ 50 mg

After another half-life:

50 mg ➡ 25 mg

After another half-life:

25 mg ➡ 12.5 mg

The amount keeps getting cut in half.

Easy Memory Trick:

✂ Half-Life = Half Left\

Every half-life, half of the drug is gone.

❓"How long does it take for HALF the drug to LEAVE the body?"

how fast it leaves.

Example:
100 mg → 50 mg → 25 mg → 12.5 mg

3. Reconstitution

mixing a powdered drug with a liquid to make a liquid medication.

Think of making chocolate milk.

🥄 Powder + 💧 Liquid = Ready to use

Example:
A medication comes as a powder in a vial.
You add sterile water.
The powder dissolves and becomes a liquid that can be given to the patient.

Easy Memory Trick:
🧪 ,… = "Powder + Liquid = Medication Ready"

Mixing powder with liquid. 🧪💧

1. Loading Dose

a larger first dose given to make the drug work quickly.

What's happening?

The body needs a certain amount of drug before it can work well.

Instead of waiting a long time, the healthcare provider gives a bigger first dose .

Easy Example:

💊 First dose = 100 mg

This quickly gets the drug level up to the therapeutic range (where the drug works).

Easy Memory Trick:

🚀 … Dose = Launch Dose

A big first dose to get things started fast.

2. Maintenance Dose

smaller doses given after the loading dose to keep the drug working.

What's happening?

Once the drug level is where it should be, you don't need another big dose.

You just give smaller doses to keep the level steady.

Easy Example:

After the 100 mg loading dose:

💊 25 mg every day

This keeps the drug in the therapeutic range.

Easy Memory Trick:

🔧 … Dose = Maintenance = Keep it going

Loading Dose vs Maintenance Dose

Loading Dose	Maintenance Dose
Large first dose	Smaller ongoing doses
Gets drug level up quickly	Keeps drug level steady
Given at the beginning	Given after the loading dose

• Loading dose = Turn the faucet on full blast to fill the tub quickly. 🚿

• Maintenance dose = Use a small amount of water to keep the tub at the same level. 💧

🚀 Loading Dose = Get there fast.

🔧 Maintenance Dose = Keep it there.

1. Incompatibility ❌

two drugs cannot be mixed together.

When mixed, something physically changes.

What's happening?

• Clumps form

• Color changes

• Precipitate (particles) form

• cannot mix together, physical alterations occur when mixed

Easy Memory Trick:

❌ … = Can't Mix

Think: oil and water don't mix.

2. Additive Effects ➕➕

Two drugs work the same way (same MOA) and their effects add together.

Formula:

1 + 1 = 2

What's happening?

Drug A = effect of 1

Drug B = effect of 1

Together = effect of 2

two drugs combined, same effect, same MOA, is equal to the sum of their individual effects

• 1+1=2 same MOA

Easy Memory Trick:

👯 Same way + same effect = Additive

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3. Summation ➕➕

Two drugs produce the same effect but work in different ways (different MOA).

Formula:

1 + 1 = 2

What's happening?

Drug A works one way.

Drug B works in a different way.

But both produce the same result.

Together = effect of 2.

• combined effect of two drugs, producing same effect by different MOA, is equal to the sum of their individual effects

• 1+1=2 different MOA
  

Easy Memory Trick:

🛣🛣 Different roads, same destination.

Difference Between Additive and Summation

Additive

Same effect

✅ Same MOA

1 + 1 = 2

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Summation

Same effect

✅ Different MOA

1 + 1 = 2

4. Synergism 🚀

The combined effect is GREATER than expected.

Formula:

1 + 1 > 2

What's happening?

Drug A = effect of 1

Drug B = effect of 1

Together = effect of 3 or more

• combined effect of two drugs is greater than the sum of their individual effects

• 1+1>2

Easy Memory Trick:

🚀 … = Super Strong Together

The drugs help each other work better.

5. Antagonism 🛑

One drug reduces or blocks the effect of another drug.

Formula:

1 + 1 < 2

What's happening?

Drug A = effect of 1

Drug B = effect of 1

Together = less than 2 because one drug interferes with the other.

• combined effect of two drugs is less than the sum of their individual effects 

• 1+1<2

Easy Memory Trick:

🛑 …. = Against

One drug fights the other.

Common Drug Interactions side by side chart

Term	Meaning	Formula
Incompatibility	Cannot be mixed	❌
Additive	Same effect, same MOA	1+1=2
Summation	Same effect, different MOA	1+1=2
Synergism	Greater effect together	1+1>2
Antagonism	One drug blocks another	1+1<2

❌ Incompatible = Can't mix

👯 Additive = Same way, same effect

🛣 Summation = Different way, same effect

🚀 Synergism = Stronger together

🛑 Antagonism = One blocks the other

Factors That Affect How a Drug Works

1-2

1. Age 👶👴

Age affects how the body handles drugs.

• Babies have immature organs.

• Older adults may have slower liver and kidney function.

Easy Memory Trick:

👶👴 Very young and very old people process drugs differently.

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2. Nutritional Status 🍎

What a person eats affects drug action.

• Poor nutrition can change how drugs are absorbed and used.

• Some foods can interact with drugs.

Easy Memory Trick:

🍎 Good nutrition helps the body handle drugs better.

Factors That Affect How a Drug Works

3-4

3. Weight ⚖

Body weight affects how much drug may be needed.

• Larger people may need higher doses.

• Smaller people may need lower doses.

Easy Memory Trick:

⚖ Bigger body = may need more drugs.

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4. Sex and Body Fat % 🚹🚺

Men and women have different body compositions.

Some drugs are stored in fat.

Easy Memory Trick:

🧈 More body fat can affect where drugs are stored and how long they stay in the body.

Factors That Affect How a Drug Works

5-6

5. Genes 🧬

Genes can affect how fast or slow a person metabolizes drugs.

Easy Memory Trick:

🧬 Different genes = different drug responses.

The same drug may work differently in different people.

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6. Emotional State 😊😟

Feelings and stress can affect how a person responds to a drug.

Easy Memory Trick:

🧠 Mind and body are connected.

Factors That Affect How a Drug Works

7-8

7. Placebo Effect 💊

A person feels better because they believe the treatment will work, even if it contains no medicine.

Example:

A sugar pill is given.

The patient thinks it is medicine and feels better.

Easy Memory Trick:

💭 Belief can affect how a person feels.

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8. Other Disease Conditions 🤒

Having other illnesses can change how drugs work.

Example:

Kidney disease may slow drug removal.

Liver disease may slow drug metabolism.

Easy Memory Trick:

🤒 Other diseases can change drug effects.

Factors That Affect How a Drug Works

9. Patient Compliance ✅

Compliance = taking the medication as prescribed.

Good Compliance:

• Takes the right dose

• Takes it at the right time

Poor Compliance:

• Skips doses

• Stops taking the medication

Easy Memory Trick:

✅ The drug can't work if you don't take it correctly.

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10. Polypharmacy 💊💊💊

Polypharmacy = taking many medications at the same time.

The more drugs a person takes, the greater the chance of drug interactions.

Easy Memory Trick: 💊💊💊 More drugs = more chances for problems or interactions.

Factors That Affect How a Drug Works

side by side chart

Factor	Easy Meaning
Age	Young and old process drugs differently
Nutrition	Food affects drug action
Weight	Body size affects dose
Sex/Body Fat	Fat affects drug storage
Genes	People respond differently
Emotional State	Feelings can affect response
Placebo Effect	Feeling better because you believe it works
Disease Conditions	Other illnesses affect drugs
Compliance	Taking meds correctly
Polypharmacy	Taking many drugs at once

👶 Age • 🍎 Nutrition • ⚖ Weight • 🧈 Fat • 🧬 Genes • 😊 Emotions • 💭 Placebo • 🤒 Disease • ✅ Compliance • 💊💊💊 Polypharmacy

These all affect how a drug works in the body.