PHARAMACLOGY Flashcards
(21 cards)
WHAT IS PHARMACOLOGY
- science that examines the composition, effects and use of drugs
- drugs made from plants from 20th century
- chemicals are syntehsised in lab used in medicine
NMC CODE
must have enough knowledge of the person’s health and you are satisfied that the medicines serve their health needs. The medicines must be compatible with any other care or treatment they are receiving.
You should ensure that the medicines are stored securely and appropriately.
PRINCIPLES OF ADMINISTRATION OF MEDICINES
- therapeutic uses of meds to be administered, normal dosage, side effects, precautions
- considering the dosage, method of administration in context in the condition of patietn & co-exsiting therapies
CHARACTERISTICS WOULD MEAN PERFECT DRUGS
> Safety
Effectiveness
Selectivity – only the response > needed. But all drugs have side effects.
Additional properties of an ideal drug
> Reversible action
> Predictable
> Easy to administer
> Low cost
> Chemically stable
PHARMACOKINETICS
Absorption: movement of a drug from its site of administration to the bloodstream
Distribution: movement of a drug from the blood to the cells in different parts of the body.
Metabolism: the chemical alteration of drug structure.
Excretion: removal of drugs from the body
ROUTE OF DRUG ADMINISTRATIOIN
PHARMACOKINETICS: ABSORPTION
- Some of the oral drug is absorbed through the stomach lining into the blood.
- oral drugs are absorbed in the small intestines, then to the liver, where first-pass metabolism happens.
- Blood leaving the stomach and small intestines goes to the liver via the hepatic portal vein.
- Then to the general (systemic) circulation. Blood leaves the liver by the hepatic vein. See picture on next slide.
SOME DRUGS NOT SUITABLE FOR ORAL ADMINISTRATION?
Glyceryl trinitrate is given sub-lingually. If swallowed, it would almost entirely be broken down by the liver by fist-pass metabolism.
Sub-lingually administered drugs avoid first-pass metabolism, as the drug is directly absorbed in the systemic circulation
Pharmacokinetics: distribution
Process of dispersion or dissemination of drugs throughout the fluids and tissues of the body.
Fat-soluble drugs concentrate in adipose tissue.
Water-soluble drugs concentrate in body water.
The blood-brain barrier separates the nervous tissue of the brain from its blood supply
Pharmacokinetics: distribution circulation in the bloodstream
Some of the drug binds to proteins in the plasma (bound), but some remains free (unbound) in the plasma.
The free part of the drug can pass through the capillary walls and enter the tissue fluid surrounding body cells, where it exerts its effect.
The bound part of the drug is inactive, as the protein-drug complex is too large to leave the blood capillaries.
Older adults may have lower blood albumin.
Albumin is a protein in the blood that some drugs bind to. The result is more free drug available and a lower dose might be needed for the same effect.
If a person is prescribed sodium valproate and warfarin at the same time, this could result in more bleeding and bruising. The sodium valproate displaces the warfarin that is bound to plasma proteins, resulting in more free warfarin and an increased anticoagulant effect.
Pharmacokinetics: metabolism
Happens mainly in the liver. It is not just breaking down drugs. Metabolism can also reduce activity or create other metabolites. It can also activate drugs.
The main purpose of metabolism is to make the drug more water soluble for easy excretion by the kidneys.
The liver is the main site for drug metabolism, but they can be metabolised in the GI tract, plasma and lungs
- which is a pro-drug, which means it is metabolised in the liver to morphine, which can cause respiratory depression in children.
Morphine is metabolised mainly in the liver, but also in the mucosal cells of the small intestine.
Pharmacokinetics: Excretion
Water-soluble drugs and metabolites and excreted via the kidney.
Drugs may also be excreted in bile, tears, sweat and breath. Any bodily fluid can contain drugs and their metabolites.
PHARMACODYNAMICS
Pharmacodynamics is the study of the biochemical and physiological effects of drugs on the body.
It is the study of what drugs do to the body and how they do it.
It includes the mechanism of drug action and side effects.
drug act on the body
There are binding sites in the body. Most of these binding sites are proteins.
Proteins are large molecules that fold into different 3D shapes.
Common binding sites for drugs are:
Receptors
Enzymes
Carrier Molecules (transporters)
it must first come into contact with and bind to, the cells of the body it is acting upon.
Different drug molecules have different shapes and will only bind to certain proteins in the body.
CELL MEMBRANE
The plasma membrane, like all cellular membranes, is made of lipids and proteins, with a phospholipid bilayer forming a stable barrier between the inside and outside of the cell. The bilayer’s hydrophilic heads face water on both sides, while the hydrophobic tails face inward, making the membrane selectively permeable and effectively “waterproof.”
Proteins in the membrane perform key roles such as transporting molecules, recognizing other cells, and receiving chemical signals like hormones. Some proteins form channels or pumps to move substances that can’t pass through the lipid layer directly.
Carbohydrates on the membrane’s outer surface give the cell its immune identity.
Importantly, the membrane is fluid and flexible, not rigid like a wall. A good analogy is a football crowd—tightly packed, but able to part and reform. This explains how cells can be pierced by a fine needle without bursting; the membrane parts around the needle and reseals afterward.
DRUGS ACTING AT RECEPTORS
Most drug receptors are protein molecules on cell surfaces.
When a chemical (drug) binds to receptors, there is a response.
Drugs that activate a receptor to produce a response, are agonists.
Drugs that bind to a receptor and produce no response, are antagonists.
Agonist and antagonist
A drug that acts on receptors
Beta2 adrenoreceptors on the bronchial muscle are cell-membrane receptors on bronchial muscle. These receptors bind with bronchodilators to relax the bronchi, but increase heart rate.
So this highlights the effects on body systems, including a side-effect.
DRUGS ACTING ON ENZYME
- Enzymes (usually proteins) speed up chemical reactions and maintain cell functions.
- Some drugs are enzyme inhibitors – they bind to the enzyme and decrease its activity.
- Ibuprofen is a non-steroidal anti-inflammatory drug that binds to and inhibits cyclo-oxygenase (COX).
- COX is needed to make prostaglandins, which are inflammatory molecules.
Prostaglandins cause pain and pyrexia.
DRUGS ACTING ON TRANSPORTERS
Transporter proteins are found in the cell membrane. They transport substances across the cell membrane.
Some anti-depressants e.g. citalopram need a transporter. Citalopram is a selective serotonin reuptake inhibitor (SSRI).
DRUGS ACTING ON TRANSPORTERS
