3 Phases of drug action

3 Phases of drug action

1. Pharmaceutic Phase

2. Pharmacokinetic Phase

3. Pharmacodynamic Phase

disintegration

– breakdown of the tablet into smaller particles

dissolution

– dissolving of smaller particles into the GI

rate-limiting

the time it takes the drug to disintegrate and dissolve to become available for absorption

Pharmacokinetic Phase

is the process of drug movement to achieve its function

4 Processes of Pharmacokinetic Phase

1. absorption

2. distribution

3. metabolism(biotransformation)

4. excretion (elimination)

Absorption

the movement of particles from the GI to the body fluids

• passive

• active

• pinocytosis

types of absorption

Active

– requires a carrier (enzyme/protein) to move the drug against a concentration gradient

routes that do not pass through the GI

1. parenteral

2. respiratory inhalants

3. eyedrops

4. transdermal drugs

5. eardrops -

6. sublingual drugs

7. nasal sprays

Factors that affect absorption

1. blood flow

2. pain

3. stress

4. hunger

5. fasting

6. food

7. pH

FIRST-PASS EFFECT

• process in which the drug passes to the liver first

• ex: warfarin, morphine, lidocaine

BIOAVAILABILITY

• the percentage of drug dose that reaches the systemic circulation

• percentage bioavailability is always <100%

• drugs should be 2-5x larger than the IV drug

oral drugs

have a higher first-pass effect

Factors that affect bioavailability

1. Drug form

2. Route of administration

3. GI mucosa and motility

4. Food and other drugs

5. Changes in the liver metabolism

Distribution

process by which the drug becomes available to body fluids and tissues

Distribution is affected by?

1. Blood flow

2. Affinity of the drug

3. Protein-binding effect

4. Drug dose

active drug

• unbound drug

• free drug

• cause pharmacologic response

Metabolism

• also known as Biotransformation

• Liver – primary site of drug

effects of liver metabolism

• lipid-soluble drugs are metabolized into water-soluble drugs for renal excretion

• some drugs are converted into an inactive metabolite

• some drugs are converted into active metabolites →increased pharmacologic response

• liver diseases → dec. metabolism → drug accumulation → drug toxicity

Excretion

• also called as Elimination

• Kidneys – the main route of elimination

• protein-bound drugs cannot be excreted through the kidneys

HALF-LIFE

• the time it takes for one half of the drug concentration to be eliminated

• short half-life – 4-8 hours

• longer half-life – 24 hours or above