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Development And Classification Of A Medicine

Development And Classification Of A Medicine. Niall Byrne Wednesday 30 th January 2012. Lecture plan. Development of a medicine: How can we categorise drugs? How do drugs cause their effects? Specific receptors: lock & key Non-specific effects Pharmacokinetics. Introduction.

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Development And Classification Of A Medicine

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  1. Development And Classification Of A Medicine Niall Byrne Wednesday 30th January 2012

  2. Lecture plan • Development of a medicine: • How can we categorise drugs? • How do drugs cause their effects? • Specific receptors: lock & key • Non-specific effects • Pharmacokinetics

  3. Introduction • What is a drug? • Any biologically active chemical that does not occur naturally in the human body that can affect living processes

  4. 16th century Egypt Ebers papyrus poppy juniper berries beer lead swine teeth goose grease lizard's blood donkey hooves crushed precious stones excreta from various animals A little light history

  5. Where do drugs come from now? • Plants: Digoxin (foxglove) Belladonna (deadly nightshade) Diamorphine (opium poppy) • Animal tissue: Insulin, growth hormone • Synthetic manufacture: Most modern medicines

  6. Development of a medicine • Drug discovery • Pre-clinical • Testing drug in a lab • Clinical Trials • Testing drug on humans

  7. Drug discovery • In 1928 Alexander Fleming returned from holiday to find his bacterial plates had been contaminated with a fungus. • Fungus had killed the bacteria on the plate • Realised the potential of the mould to kill bacteria • He called the agent penicillin • it was over a decade before someone else turned penicillin into the miracle drug for the 20th century. • Awarded the 1945 Nobel Prize in Physiology or Medicine

  8. Pre clinical testing • Identify a compound which has the desired effect on a cell (~ 20 - 50 out of several 1000) • Test on panel of cell lines (5 - 10 / 50) • Pharmacodynamics (What drug does to body) • Test in animals ( 1 - 3 / 10) • Pharmacodynamics • Pharmacokinetics (What body does to drug) • Drug metabolism and elimination mechanisms • Toxicity

  9. Schematic of possible outcomes

  10. Lecture plan • Development of a medicine: • Clinical trials • How can we categorise drugs? • How do drugs cause their effects? • Specific receptors: lock & key • Non-specific effects • Pharmacokinetics

  11. Clinical trials: What are they? • Research studies involving humans • Used to determine if drug treatments are safe and effective • Are the safest and quickest way to find treatments that work • Three stages: I II and III

  12. Clinical trial protocol • Strict scientific guidelines • Purpose of study • How many participants • Who is eligible • How study will be carried out • What information will be gathered • End points

  13. Clinical trials – phases Stage 2 Preclinical Stage 1 Drug Discovery Stage 3 Clinical trials Phase I 20-100 volunteers Phase III 1000-5000 volunteers 10,000 compounds 250 compounds 5 compounds 1 approved drug Phase II 100-500 volunteers 6.5 years 7 years 1.5 yrs Adapted from Pharmaceutical Research and Manufacturers of America.

  14. Phases I trials • Use healthy volunteers • How does the drug affect the human body? • Drug absorption, metabolism and excretion • Preferred method of administration • What dosage is safe?

  15. Phase II trials • Use target patient group representative of those likely to benefit from the drug. • No pregnant women • Does the drug have a beneficial effect on the disease? • Determine therapeutic dose range. • Usually placebo controlled • Conducted by experts in the disease field

  16. Phase III trials • Obtains all data for regulatory agencies • Often multi-centered, multinational • Long term safety evaluated • Is new drug better than standard?

  17. Randomised controlled trial (RCT) • Volunteers randomly assigned to new treatment or best existing treatment • Doctors have no say in who goes in which group to reduce bias

  18. What is a placebo? An inactive pill, identical in appearance to the treatment pill which is given to the control group. Used to control for the placebo effect Patient feels better due to belief in the treatment Test pill Placebo

  19. Clinical trials – the results • Endpoint used to test trials success • Ideally use a hard endpoint – cure from disease • Statisticians analyse results – is A better than B? • Only after analysis do you tell which is A and B.

  20. Drug Licensing • Application submitted to Medicines and Healthcare products Regulatory Agency (MHRA) • MHRA carry out pre-marketing assessment of safety, quality and efficacy, examining all research and results in detail.

  21. Medicines and Healthcare products Regulatory Agency • An executive agency of the Department of Health • Enhance and safeguard the health of the public by ensuring that medicines and medical devices work and are acceptably safe. No product is risk free. 

  22. European Medicines Evaluation Agency (EMEA) • The EMEA co-ordinate drug licence applications within the European Union (EU). • Committee for Proprietary Medicinal Products (CPMP)

  23. Product Launch • When a drug has marketing authorisation, it is not available straight away. The company first have to apply to market their product. In the UK, they will apply to the MHRA. When this is done, the product is ‘launched’, and doctors can prescribe it. • The time it takes from marketing authorisation to launch in the UK is one of the fastest in the world.

  24. Lecture plan • Development of a medicine: • How can we categorise drugs? • How do drugs cause their effects? • Specific receptors: lock & key • Non-specific effects • Pharmacokinetics

  25. Names of drugs • Chemical name: describes the chemical structure: acetyl-p-amino-phenol • Generic name: a name that can be used by anyone: paracetamol • Trade name: owned by the manufacturer: Calpol

  26. Other ways to categorise drugs • What kind of molecule is it? • What organ system (or what disease) is it for? e.g., cardiac, psychotropic • What parts of cells are affected?

  27. What is the drug used for? • To cure e.g., infections, cancer • To suppress diseases or symptoms without attaining a cure e.g., hypertension, diabetes, pain control • To prevent disease (prophylactic) e.g., immunisation

  28. How does the drug act? • Replace a deficiency, e.g., vitamins, minerals, hormones • Interfere with cell function, e.g., block enzyme action • Kill / prevent growth of viruses, bacteria, fungi, protozoa, cancer

  29. Categories of drug • Anti-inflammatory • Analgesic • Antipyretic • Vaccine • Antihypertensive • Vitamin supplement • Antitussive Anaesthetic Surfactant Laxative Antiviral Antifungal Antibiotic

  30. Content of today’s lecture • How can we categorise drugs? • How do drugs cause their effects? • Specific receptors: lock & key • Non-specific effects • Pharmacokinetics

  31. How do drugs work? • Pharmacodynamics: study of how chemicals exert their effects The practical importance of this is enabling the design of new and better drugs

  32. receptor Receptors • Receptors are proteins on the cell surface or inside the cell. • They bind the body’s own chemical messenger • Convert the binding event to a signal that the cell can recognize and respond to signal

  33. “Lock & Key” • Interaction between a receptor and its signal molecule (ligand) is like “lock & key”. • Perfect fit depends on exact 3D shape and size of both molecules.

  34. drug receptor Receptors • Drugs also bring information to cells by fitting into the same receptor molecules. • The drug picks the lock and triggers a response by the cell.

  35. Agonists and Antagonists • Agonist: a drug that fits into a receptor and activates a response e.g., morphine, nicotine • Antagonist: a drug that fits into a receptor but blocks the receptor and does not activate a response.

  36. Content of today’s lecture • How can we categorise drugs? • How do drugs cause their effects? • Specific receptors: lock & key • Non-specific effects • Pharmacokinetics

  37. Non-specific effects • Acidic or alkaline properties • Surfactant properties (amphotericin) • Osmotic properties (laxatives, diuretics) • Interactions with membrane lipids (anaesthetics)

  38. Side-effects and other effects • Not the “wanted” effect e.g. aspirin causes gastric ulcer • Diphenhydramine has a useful side-effect

  39. Side-effects and other effects • Hypersensitivity / allergy: exaggerated adverse reaction to drug • Toxic effects e.g., Thalidomide: teratogenic • Tolerance: increasing amounts are needed to produce the same effect

  40. Content of today’s lecture • How can we categorise drugs? • How do drugs cause their effects? • Specific receptors: lock & key • Non-specific effects • Pharmacokinetics

  41. Pharmacokinetics How the body deals with the drug We need to consider • Dose • Route of Administration • Absorption and distribution • Metabolism and excretion

  42. Doseamount of drug taken at any one time • Aim is to give the patient a dose of drug that achieves the desired effect without causing harmful side effects • Therapeutic Index(TI) is the ratio of the therapeutic dose to the toxic dose • Egs of drugs with low TI include digoxin lithium and methotrexate

  43. Administration • how easy it is to use for patient • how quickly a drug needs to reach site of action • where it has to work in the body Route of administration depends on

  44. Routes of Administration

  45. Oral Route • Medications taken by mouth • Formulated in either a solid or liquid form • Absorbed from the GI tract mainly in the small intestine which is specialised for absorption (large surface area due to villi and microvilli).

  46. Disadvantages • Onset of action is relatively slow • Absorption may be irregular • Some drugs destroyed by enzymes or other secretions found in GI tract • Because blood from GItract passes through live it is subject to hepatic metabolism before reaching systemic circulation

  47. Buccal Route Drug is formulated as a tablet or a spray and is absorbed from the buccal cavity • Sublingual absorption very fast onset of action but duration is short • Buccal absorption quick onset of action that is of longer duration than sublingual route

  48. Rectal Route Drugs formulated as liquids ,solid dosages and semi solids. The chosen preparation is inserted into the rectum where it is released to give local effect or absorbed to give a systemic effect

  49. Rectal & Vaginal Route Advantages • Can be used when oral route unsuitable • Useful when drug causes GI irritation • Can be used for local action Disadvantages • Absorption irregular and unpredictable • Less convenient than oral route • Low patient acceptability

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