Introduction to Pharmacology/High School (Nurse)

Pharmacology deals with:

• pharmacodynamics − the mechanisms and effects of drugs → what a drug does to an organism,
• pharmacokinetics − the fate of drugs in the body (absorption, distribution, metabolism, excretion).

For didactic reasons, we divide pharmacology into:

• general pharmacology
• special pharmacology

General pharmacology

Defines, on the basis of experiments, the generally valid laws manifested in the interaction between the organism and the pharmaceutical. Its knowledge is a prerequisite for understanding special pharmacology.

Special pharmacology

Classifies drugs in terms of pharmacodynamics. It studies the properties of drugs in their specific form. Examines and determines their pharmacokinetics.

Recipes

A set of basic provisions that must be followed when handling and creating a prescription.

Medicinal forms

• more about on Medicinal forms

Drug Elimination

• more about on Elimination of drugs
• Determined by the chemical properties of the substance of interest.

→ water-soluble substances can be eliminated relatively quickly by the kidneys (PNC)

→ fat-soluble drugs are poorly excreted in urine → require transport binding to proteins (e.g. plasma albumin) that are not present in urine → lipophilic drugs require conversion to more hydrophilic metabolites, i.e. are biotransformed

Biotransformation - metabolism

• Processes occurring predominantly in the liver that are mediated by a number of enzymes.
• Two phases:

Phase I reactions → change in drug structure (oxidation, reduction, hydrolysis).

• Enzymes of the cytochrome P450 family. A metabolite often retains some liposolubility.

Phase II reactions → conjugation reactions, such as binding to glucuronic acid, sulfuric acid, or glycine → metabolites with larger molecules and good water solubility to allow hepatic and renal elimination.

Excretion

• I.e. the removal of a substance from the internal environment of the body.
• It takes place mainly in the liver and kidneys, less significantly in the lungs, intestine, salivary and sweat glands, etc.
• Binding during excretion by the liver is substrate specific, therefore drug-drug interactions may occur when multiple drugs are administered simultaneously.

Distribution

• Means the penetration of the drug from the systemic circulation into the tissues.
• The process of distribution is strongly influenced by the properties of the administered substance.

• For example, highly lipophilic drugs rapidly penetrate barriers and therefore tend to rapidly escape from the circulation and concentrate in tissues.
• Hydrophilic drugs are unable to penetrate barriers and remain predominantly in the blood or extracellular fluid (see below).

Volume of distribution - Vd

• This quantity relates the dose administered to the concentration achieved:
• more about on Mathematical description of pharmacokinetic processes

Receptors

• Receptor mechanisms → the substance acts through a receptor, i.e. protein macromolecules with which it reacts and thereby induces a cellular response,

→ when endogenous or exogenous regulatory substances interact, they trigger a series of events that manifest themselves as a phamacological effect.

• Affinity - characterizes the ability of a substance to bind at a given concentration to a given receptor.
• Intrinsic activity - the ability of an attractant to elicit an effect.
• Agonist - binds to a receptor and produces an effect by interacting with it. (Full agonist = 100% effect)¨¨

• Partial agonist - has little agonist effect when acting alone, competitively antagonizes their effect when acting with stronger agonists.

• Antagonist - inhibits the effect of agonists but has no effect on its own.

• Reversibly interacting antagonists are referred to as competitive antagonists (they have relatively high affinity but very low intrinsic activity).
• Non-competitive antagonists either bind irreversibly to the receptor while having very low intrinsic activity or inhibit the signal transduction induced by the agonist.

Non-receptor mechanisms

• Influenced by the chemical properties of substances or their interaction with other protein molecules, e.g. in body fluids.
• These include:

• Increase in substrate supply (e.g., used to treat Parkinson's disease),
• administration of a false precursor (e.g., α-methylnoradrenaline instead of NA is formed at the terminals),
• Blockade of bioactive substance degradation (e.g., inhibition of a Physostigmine leading to acetylcholine accumulation; also e.g., inhibition of MAO),
• affecting DNA function (cytostatics),
• action of antibiotics and chemotherapeutics (affecting metabolism and function of the micro-organism).

Doses

• more about on Relationship between dose, plasma level and effect

Changes with repeated administration

• more about on Tachyphylaxis
• more about on Tolerance
• After repeated administration, allergy may occur on immunological grounds.

Drug interactions

• more about on Drug interactions

Links

External links

• Recipe basis in czech

Sources

• MUDR. PETR VOJTÍŠEK, . Základy farmakologie [lecture for subject Modul Algeziologie, specialization Sestra pro intenzivní péči – postgraduální studium, Vyšší odborná škola zdravotnická škola Střední a vyšší zdravotnická škola Ústí nad Labem]. Ústí nad Labem. 11.11. 2011.