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Summary BGZ2026 - Basic Principles of Pharmacology
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BGZ2026 – Basics of PharmacologyCases
Case 1 – Paracetamol & Alcohol
How does alcohol affect people differently? What is the difference between the dose
effectives? What is the effect of an overdose?
1) What is pharmacokinetics?
Pharmacokinetics is described as what the body does to a drug. It is the movement of drug
into, through and out of the body:
- Input, distribution and elimination
Absorption, Distribution, Metabolism, Excretion
- Absorption in the body (uptake in the circulation)
o Process by which toxicants cross body membranes and enter the
bloodstream. Main sites of absorption are:
⇒ GI tract
⇒ Lungs
⇒ Skin
⇒ Other sites (subcutis,
peritoneum, muscle)
▪ Passive diffusion directly
through the lipid (mostly in
intestine)
▪ Diffusing through aqeous pores
formed by special proteins
(aquaporins)
▪ Pinocytosis
▪ Active transport by a carrier (SLC) or other membrane transporter
(few drugs)
▪ Size, lipophilicity, charge, nature of membrane, medium on either
size (pH) 🡪 know basically
,The velocity and rate of absorption are distinguished. A specific amount of lipophilicity Is
necessary to pass the intestinal wall.
▪ Side effects can be due to a bigger absorption velocity because of a
quick increase in the plasma
concentration
▪ Also, the sort of administration
(oral/liquid) is very important
for the progression of the time-
concentration curve
▪ Bioavailability = part that
reaches the blood
▪ Low lipid solubility is generally
poorly absorbed from the gut. Absorption from the gut depends on
many factors:
● Gastrointestinal motility
● Gastrointestinal pH
● Particle size
● Chemical interaction with gut content
▪ Size + lipophilicity + charge 🡪 determine absorption
🡪 Biological availability (F) = indication how much of the administrated effective substance
eventually achieves the general circulation and will be available for operation compared to
intravenous administration
- F variates from 0 (no effective substance available) to 1 (all of the effective substance
available)
- It can differ a lot between the same person
(intra-individuality) and between persons
(inter-individuality)
- Paracetamol mostly like 80%
- Membrane = fat-soluble
🡪 The first pass effect = after oral administration a part
of the absorbed substance will be metabolized by
enzymes in the intestinal wall cells, intestine flora or
liver before entering the general circulation
MW high is unable to cross intestinal membranes
Atenolol MW 246 = oral, can cross membrane (hydrolyzed in stomach, degradation in gut +
transport = loss of medicine)
Oxytocin MW 1007 = nasal, cannot cross membrane
Calcitonin 3432 MW = intravenously, does not cross any membrane
,High MW = strong molecule, big molecule 🡪 No diffusion
- Distribution
o After entering the blood by absorption/intravenous administration, a toxicant
is distributed to tissues throughout the body, this occurs rapidly. The rate of
distributions to organs or tissues is determined primarily by blood flow and
rate of distribution out of the capillary bed into the cells. Final distribution
depends largely on the affinity of a xenobiotic for various tissues
▪ Distribution in the blood
▪ Binding to albumin, glycoproteins or erythrocytes
▪ Diffusion to tissues outside the bloodstream
▪ Binding to cell components the drugs have affinity to
▪ Volume of distribution = amount of drug in the body / plasma drug
concentration
🡪 All depends on the physicochemical properties of the drug
o Organ blood flow
o Drugs physicochemical properties
o Organ size
o Binding of drug in tissues
o Movement across membranes
● First/initial phase = dominated by blood flow
● Eventual distribution = determinate largely by affinity
Major compartments are:
o Plasma (5% of body weight)
o Interstitial fluid (16%)
o Intracellular fluid (35%)
o Transcellular fluid (2%)
o Fat (20%)
Volume of distribution = volume in which the amount of drug would need to be uniformly
dissolved in order to produce the observed blood concentration
- Lipid insoluble drugs = mainly confined to plasma and interstitial fluids, most don’t
enter the brain
- Lipid soluble drugs = reach all compartments and may accumulate in fat
- Metabolism
, o Happens mostly in the liver to make lipophilic compounds hydrophilic so that
the kidneys can excrete them
o Drug elimination = irreversible loss of drug from the body, which occurs by:
▪ Metabolism and excretion
o Drugs are eliminated from the body either unchanged through the kidneys
and bile/they may undergo chemical changes that allow them to be more
easily excreted = biotransformation/metabolism
o Anything absorbed through the GI tract goes directly into the portal
circulation that feeds into the liver 🡪 Liver is adapted to clear toxins from the
body and is the major site for drug metabolism, but specific drugs may
undergo biotransformation in other tissue
o Most drugs leave the body in the urine, unchanged or as polar metabolites
▪ Some drugs are secreted into bile via the liver, but most of these are
then reabsorbed from the intestine
o Lipophilic substances are not eliminated efficiently by the kidney
▪ Most are metabolized to more polar products, which are excreted in
the urine
o Drug metabolism occurs predominantly in the liver, by the cytochrome p450
o Factors that affect metabolism:
▪ Age
▪ Genetics
There are 2 phases:
1) These are catabolic (oxidation, reduction or hydrolysis) and the products are often
more chemically reactive and hence sometimes more toxic or carcinogenic than the
parent drug.
a. It mainly takes place in the liver
b. Drugs who are made more polar through oxidation-reduction reactions or
hydrolysis. In the enzyme-catalyzed reactions, the rate of the reaction is
accelerated by the presence of enzymes. A limited amount of enzyme is
present at any given time in the liver. Once enzymes become saturated,
blood levels increase exponentially toward toxicity
c. Hydroxylation, deamination, dehalogenation, dessulfuration, epoxidation,
peroxygenation, reduction
d. Catalyzed by CYP-450 enzymes
🡪 Phase 1 reaction CYP P450 (monooxygenase = catalyzed reaction)
o RH + O2 + NADPH + H+ 🡪 R-OH + H2O + NADP
2) Synthetic reactions and involve conjugation (attachment of a substituent group)
which usually results in inactive procedures. Conjugation reactions can occur
independently or can follow phase 1 (hydroxylation) reaction.
a. Conjugation reactions = drug undergoing change is joined with another
substance. The result of conjugation is more water-soluble compound that is
easier for the kidneys to excrete
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