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Development And Classification Of A Medicine Niall Byrne Wednesday 30th 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 • What is a drug? • Any biologically active chemical that does not occur naturally in the human body that can affect living processes A little light history 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 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 Development of a medicine • Drug discovery • Pre-clinical ▫ Testing drug in a lab • Clinical Trials ▫ Testing drug on humans 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 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 Schematic of possible outcomes •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 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 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 Clinical•Stage trials – phases 2 •Stage 1 •Drug Discovery •Preclinical •Stage 3 •Clinical trials •Phase I •20-100 volunteers •10,000 •compounds •250 compounds •Phase III •1000-5000 volunteers •5 compounds •Phase II •100-500 volunteers •6.5 years •7 years •1 approved drug •1.5 yrs Adapted from Pharmaceutical Research and Manufacturers of America . 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? 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 Phase III trials • • • • Obtains all data for regulatory agencies Often multi-centered, multinational Long term safety evaluated Is new drug better than standard? 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 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 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. 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. 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. European Medicines Evaluation Agency (EMEA) • The EMEA co-ordinate drug licence applications within the European Union (EU). • Committee for Proprietary Medicinal Products (CPMP) 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. 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 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 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? 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 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 Categories of drug • • • • • • • Anti-inflammatory Analgesic Antipyretic Vaccine Antihypertensive Vitamin supplement Antitussive • Anaesthetic • Antiviral • Surfactant • Antifungal • Laxative • Antibiotic Content of today’s lecture • • • • • How can we categorise drugs? How do drugs cause their effects? Specific receptors: lock & key Non-specific effects Pharmacokinetics 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 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 receptor “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. 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. drug receptor 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. Content of today’s lecture • • • • • How can we categorise drugs? How do drugs cause their effects? Specific receptors: lock & key Non-specific effects Pharmacokinetics Non-specific effects • Acidic or alkaline properties • Surfactant properties (amphotericin) • Osmotic properties (laxatives, diuretics) • Interactions with membrane lipids (anaesthetics) Side-effects and other effects • Not the “wanted” effect e.g. aspirin causes gastric ulcer • Diphenhydramine has a useful side-effect 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 Content of today’s lecture • • • • • How can we categorise drugs? How do drugs cause their effects? Specific receptors: lock & key Non-specific effects Pharmacokinetics Pharmacokinetics How the body deals with the drug We need to consider • Dose • Route of Administration • Absorption and distribution • Metabolism and excretion Dose amount 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 Administration Route of administration depends on 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 Routes of Administration 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). 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 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 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 Rectal & Vaginal Route Advantages Disadvantages • Can be used when oral route • Absorption irregular and unsuitable • Useful when drug causes GI irritation • Can be used for local action unpredictable • Less convenient than oral route • Low patient acceptability Inhalation Route • Advantages • Drugs inhaled through the nose or mouth to produce local or systemic effects • Drug dose required to produce desired effect is much smaller than oral route therefore reduction in side effects • Used predominately in the treatment of asthma • Drugs delivered directly to their site of action ie lungs Topical Route • Skin used as site of administration • Lotions creams ointments powders • Skin has natural barrier function but specialised dosage forms have been developed that when applied they allow the drug to pass through and produce systemic effect Parenteral Route (drugs that are given by injection) • IV route -drugs injected directly into the systemic circulation (fast onset of action) • Subcutaneous route -drugs injected into the s/c layer of the skin (easiest and least painful) • Intramuscular route –drugs injected into muscle layers Examples in each category local action inhaled oral across rectal the skin injected into skin or muscle Intravenous Vick’s Vaporub antacid cold sore foam cream enema Novocaine (the dentist’s choice!) Local thrombolytic therapy systemic cigarette Nurofen action tablets Nicotene Panadol contrapatch suppos- ceptive itory adrenalin ADME • Absorption: the mechanism by which a drug enters the body • Distribution: the drug is transported throughout the body • Metabolism: the drug interacts with, and is processed by, the body • Elimination: the drug is removed from the body Absorption • Disintegration • Dissolution • Direct absorption at site of action, e.g., in the gut Steps in distribution Drug must spread throughout blood volume Drug must get out of the bloodstream between or through endothelial cells • Drug must cross the cell membrane into cells • • Factors affecting distribution 1. Binding to plasma proteins: if a drug is bound to large plasma proteins, it will be unable to get out as the proteins are too large. Arggh! I can’t fit through! Factors affecting distribution 2. Extent of blood supply. If a tissue is well perfused with blood, drugs will get there faster. Adipose tissue has low blood perfusion so drugs reach it slowly. Factors affecting distribution 3. pH. A drug will pass through membranes better if it is not ionised 4. Binding of drugs to other tissue components Drug Concentration Metabolism: what happens to a drug Lethal Dose Injected Dose Therapeutic Range Oral Dose SubTherapeutic Time First pass effect • All nutrients and drugs absorbed from the gut travel in the blood directly to the liver. The liver breaks down many drugs so they are inactivated before they ever enter the systemic circulation! • This can decrease drug delivery to target tissues • But some drugs are activated by the first pass effect Elimination • Mainly in the kidney. Also bile, gut, lung, breast milk. • Elimination of a drug is usually linked to renal function. Individual variation • Each person is unique how they respond to a drug • Age and sex (hormonal differences) • Weight: some drugs are stored in fat so less effective and longer lasting in obese people • Allergy • Kidney & liver function: how will they affect elimination? And finally… • Pharmacodynamics is… • What the drug does to the body • Pharmacokinetics is… • What the body does to the drug • Receptor is like… • Lock • Ligand or drug is like a… • Key • First pass occurs in… • Liver • Many drugs are excreted by… • Kidney