Why can a second drug that competes for plasma protein binding make warfarin dangerous?

The second drug displaces warfarin from the proteins, raising the amount of free, active warfarin. The patient's blood may then clot too slowly, risking bleeding.

How can binding to tissue components affect where a drug goes and how long it lasts?

Fat-soluble drugs such as some anaesthetics collect in fat and are released slowly, prolonging their effect. Tetracycline antibiotics bind to calcium in growing bones and teeth, so they are avoided in young children.

How does pH affect the absorption and distribution of a weak acid such as aspirin?

Aspirin stays mostly un-ionised in the acidic stomach, so it crosses cell membranes easily. Ionised molecules are charged and cannot pass through the lipid bilayer, so pH controls where a drug can go.

CCEA A-Level Life and Health Sciences 0008

Experimental Techniques

Topic overview Standard solutions, titrations and qualitative tests Rates of reaction and organic preparations Physics measurements: oscillations, resistivity, lenses and critical angle Biological tests, colorimetry, chromatography and osmosis

Human Body Systems

Topic overview Blood vessels, the heart and cardiac output Heart sounds, ECG traces, pulse and blood pressure Body fluids, haemoglobin and the Bohr effect The respiratory system, gas exchange and lung disease Monitoring breathing and lung volumes Cellular respiration and ATP Homeostasis, blood glucose and thyroxine Sodium, blood pH and oxygen saturation A balanced diet and nutritional needs through life Cholesterol, minerals, vitamins, alcohol and exercise

Physical Chemistry in Industrial Processes

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Brain ScienceDouble Award

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Material ScienceDouble Award

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Medicine, Drugs and Clinical TrialsDouble Award

Topic overview Categories of medicine and routes to drug discovery Medicines from natural sources, drug names and the ATC system Drug development, preclinical testing and the therapeutic index Phases of clinical trials and trial design Licensing, UK regulators, Yellow Card and trial ethics Formulations, routes of administration and drug absorption Distribution, metabolism, elimination and sites of drug action Quantitative analysis of medicines and antibacterial bioassays

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Organic Chemistry

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Topic overview Transverse and longitudinal waves and wave graphs Phase difference and the electromagnetic spectrum Outer, middle and inner ear Sound intensity and the decibel scale Standing waves, harmonics and resonance tubes Hearing response, phons and equal loudness curves Structure of the eye, rods and cones Accommodation, lens power and correcting long sight Total internal reflection and fibre-optic communication Dipole antennas, wireless networks and radar Attenuation of radio waves and the Doppler effect

Genetics, Stem Cell Research and CloningA2 option

Topic overview DNA structure and the evidence for the double helix RNA, genes and the triplet code Genotype, phenotype and monohybrid inheritance Dihybrid crosses, epistasis and the chi-squared test DNA replication and the Meselson–Stahl experiment Meiosis and genetic variation Insulin, factor VIII and chymosin from genetically modified microbes Recombinant DNA technology and gene cloning Genetic engineering, food supply and ethics Gene therapy and cystic fibrosis Genetic disease, screening and counselling Genetic fingerprinting and gel electrophoresis Stem cells, therapeutic cloning and their ethics

MicrobiologyDouble Award

Topic overview Bacteria, fungi and protozoa Viruses, viroids and prions Classifying bacteria, fungi and viruses Light and electron microscopy Laboratory safety, biocontainment and quality assurance Aseptic technique, growth media and inoculation Counting and measuring microbial growth Growth requirements and growth inhibition Antibiotics, PCR, gene therapy and pharmaceutical microbiology The gut microbiome in health and disease

Oral Health and DentistryDouble Award

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Histology and PathologyDouble Award

Topic overview Specimen processing, data protection and safety law Clinical biochemistry tests and electrophoresis Blood smears and identifying blood cells Blood grouping, cross-matching and transfusion Diagnostic and surveillance work in hospital microbiology Preparing and staining tissue sections Recognising tissues, atheroma and emphysema on slides

Analytical Chemistry TechniquesDouble Award

Topic overview Volumetric analysis in industry and healthcare Applied titrations of vinegar, indigestion tablets and bleach Redox titration of iron tablets and evaluating titrations Principles of colorimetry Colorimetric analysis of copper ore, aspirin and iron Thin-layer chromatography and its uses Visualising chromatograms and identifying painkillers and pigments Calorimetry and combustion Molar enthalpy and bond energy calculations Qualitative tests for cations and gases

Enabling TechnologyDouble Award

Topic overview ECG and EEG machines in patient monitoring Ultrasound and IVF equipment in fertility treatment Prosthetic limbs, hearing aids and cochlear implants Workflow and equipment in a medical laboratory Ongoing monitoring of a long-term condition Health data collection, databases and data protection

Medicine, Drugs and Clinical Trials

Distribution, metabolism, elimination and sites of drug action

3 things to know
AS 6

Overview

Pharmacodynamics and pharmacokinetics, distribution and protein binding, pH and levodopa, metabolism and prodrugs, elimination and half-life, agonists and antagonists, and how aspirin acts.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is the difference between pharmacodynamics and pharmacokinetics?

Key term

How is a drug distributed around the body after absorption?

Key term

How does binding to plasma proteins affect the distribution of a drug such as warfarin?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the difference between pharmacodynamics and pharmacokinetics?
Model answer
Pharmacodynamics is the study of what a drug does to the body and how it produces its effects. Pharmacokinetics is the study of what the body does to a drug: absorption, distribution, metabolism and elimination.
2
How is a drug distributed around the body after absorption?
Model answer
The drug is carried in the blood plasma and leaves the capillaries into tissue fluid and cells. Organs with a rich blood supply, such as the heart, liver and kidneys, receive the drug first.
3
How does binding to plasma proteins affect the distribution of a drug such as warfarin?
Model answer
About 99% of warfarin in the blood is bound to plasma proteins such as albumin. Bound drug cannot leave the blood or act, so only the small unbound fraction reaches tissues.
4
Why can a second drug that competes for plasma protein binding make warfarin dangerous?
Model answer
The second drug displaces warfarin from the proteins, raising the amount of free, active warfarin. The patient's blood may then clot too slowly, risking bleeding.
5
How can binding to tissue components affect where a drug goes and how long it lasts?
Model answer
Fat-soluble drugs such as some anaesthetics collect in fat and are released slowly, prolonging their effect. Tetracycline antibiotics bind to calcium in growing bones and teeth, so they are avoided in young children.
6
How does pH affect the absorption and distribution of a weak acid such as aspirin?
Model answer
Aspirin stays mostly un-ionised in the acidic stomach, so it crosses cell membranes easily. Ionised molecules are charged and cannot pass through the lipid bilayer, so pH controls where a drug can go.

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