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INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS

An introduction to clinical pharmacology for medical students.

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INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS

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  1. INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS Dr. Kenneth Orimma B.Sc., M.Sc., M.B.B.S, D.I.R, D.M Psychiatry Sample Footer Text

  2. INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS • Clinical pharmacology is the science of medicine discovery, development, regulation and use in the context of the effects of drugs on humans • Sound knowledge of clinical pharmacology is essential for all professionals involved in the treatment of patients with medicines. • We live in an era of intensive research which drives new discoveries and maintains the field of therapeutics in a state of constant evolution • keeping this knowledge up to date can be challenging but essential our day-to-day practice both as clinicians and as pharmacists. Sample Footer Text

  3. INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS General principles for Studying Drugs as a pharmacist or clinician is to Compartmentalize Everything • Focus on Drug Groups/Families first not individual drugs • Learn The Primary Uses – Selected Clinical Applications & Implications • Learn Key Side-Effects – (Most side-effects are due to mechanism of action, except idiosyncratic side-effects) Sample Footer Text

  4. INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS Learn the Mechanism of Action of each drug Group/Family: o @ The Cellular Level – Ie: Target on the cell & Effects on the cell o @ The Physiology Level – Ie: How the Cellular Effects change the Body’s Physiology Sample Footer Text

  5. INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS Assimilate individual drug names into each Drug Group: • o Eg: Benzodiazepine Family includes Diazepam, Lorazepam, Clonazepam, Midazolam, etc • o Eg: Opioid Family includes Codeine, Morphine, Buprenorphine, Oxycodone, Methadone, etc Focus on General Therapeutic Principles for treating certain diseases (Rather than specific drugs): o Eg: Heart Failure is treated with ACE-Inhibitors, Beta-Blockers, and Diuretics o Eg: Asthma is treated with Bronchodilators (Adrenergic & Anti-cholinergic), Corticosteroids (inhaled) Sample Footer Text

  6. Definitions for Keywords Drug: • A Chemical substance of known structure, other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect Chemical Name: • Describes the chemical structure (Eg: N-(4-hydroxyphenyl)acetamide = Acetaminophen Aka: Paracetamol ) Generic Name: • The generally-agreed upon official name for a drug (Eg: Acetaminophen / Paracetamol) Trade/Brand Name: • The brand name/registered trademark (Eg: Tylenol / Panadol) Sample Footer Text

  7. Definitions for Keywords Pharmacodynamics: • o Describes the drug’s effect on the body at the receptor level, including efficacy, potency, agonism and antagonism Pharmacokinetics: • The relationship between drug administration, time-course/rate of absorption & distribution, concentration changes in the body, and the drug’s removal from the body Selective Toxicity: • A useful feature of Chemotherapy & Antibiotic drugs – Ie: Drugs that are ‘Selectively Toxic’ to Microbes/Tumours, while having minimal effects on the host • Selective Toxicity depends on the ability to exploit Biochemical differences between Microbes/Tumours & the Host Sample Footer Text

  8. Definitions for Keywords Agonist: • A drug capable of binding and activating a receptor, leading to a pharmacological response that may mimic that of a naturally occurring substance. Can be classified as full, partial or inverse Antagonist: • Does not produce a biological response on binding to a receptor but instead blocks or reduces the effect of an agonist. It may be competitive or non-competitive. Allosteric modulator: • A drug that binds to a receptor at a site distinct from the active site. A conformational change is induced in the receptor, altering the affinity of the receptor for the endogenous ligand. Desensitization • A loss of responsiveness which may be due to the continued presence of an agonist at a receptor or repeated presentation of the agonist Sample Footer Text

  9. Definitions for Keywords Efficacy • Used to describe agonist responses in relation to receptor occupation. High efficacy agonists can produce a maximal response whilst occupying a relatively low proportion of receptors. Half-life (t.) • The metabolic half-life of a drug in vivo is the time taken for its concentration in plasma to decline to half its original level • Clearance and distribution of a drug from the plasma are important parameters for half-life determination Potency: • Measure of the effective concentration of a drug. • It is a vague term, and it is advisable to further categorise the measurement Sample Footer Text

  10. Definitions for Keywords Occupancy • The proportion of receptors to which a drug is bound Sample Footer Text

  11. Quality Use of Medicines – Ie: Choosing Between Drug Therapies: Beneficial Effects: • Where does the drug sit on the wide spectrum of benefits?: ß Low-level relief, but ↑Quality of Life → Prevent/Control Serious Symptoms → Prevent Death → Harmful Effects: • Where does the drug sit on the wide spectrum of drawbacks?: ß Low-level harm, but tolerable → Serious/Severe Effects → Potentially Fatal→ Sample Footer Text

  12. Quality Use of Medicines – Ie: Choosing Between Drug Therapies: Cost-Benefit Analysis – Important Considerations for Therapeutics: o Risk of Treatment Vs Risks associated with Non-Treatment o Financial cost of treatment vs Opportunity cost of that money elsewhere (eg: Public health) o Personal toll of side effects Vs Personal benefit of treatment Sample Footer Text

  13. Quality Use of Medicines – Ie: Choosing Between Drug Therapies: Reducing Risk – How?: o Get a better Understanding of the Disease: § Gives insight into potential Drug Targets § Helps explain to patient Why Drug is Useful/Necessary → ↑Patient Compliance § Understand How the Drugs Work (Major Effects/Side-Effects) o Improve the Pharmacokinetics – Eg: Deliver drug Specifically to the Site of Action o Improve the Pharmacodynamics – Eg: Use drugs that are more Selective (to receptor subtypes) o Ensure Informed, Careful & Responsible Prescription Sample Footer Text

  14. Screening Physician prescriptions: 4 Qualities of A Good Prescription: 1: Judicious use of Medicines: o Consideration of non-medical alternatives (Eg: Exercise to ↓BP rather than Anti-hypertensives) 2: Appropriate Use: • o Is the medicine chosen The Most Appropriate, given all clinical factors? (Eg: A K+ wasting diuretic in someone with an existing arrhythmia) 3: Safe Use: o Minimize Misuse – Ie: Make sure the patient knows how/when to use the drug (Eg: Diabetic taking too much insulin → DKA) 4: Efficacious Use: o Drug MUST deliver beneficial outcomes that are GREATER than adverse outcomes Sample Footer Text

  15. Patient’s perspectives in choice of Drug Therapies: Traditional” Medicine Vs Western Medicine: Generally, Western Medicine is objectively more effective because: o Purity of the active compound o Accurate Dosage & Concentration o Knowledge of Toxicity Sample Footer Text

  16. Patient’s perspectives in choice of Drug Therapies Why some patients prefer Traditional Medicine: o Some people believe that “Natural” = “Safer” = Good for you … (Although not necessarily the case; all of the most potent toxins and venoms are ‘natural’) o May be ‘cheaper’ than prescription medicines … (Although not necessarily the case when taking into account the Cost:Efficacy ratio) o May be easier to purchase OTC (Over the counter) o Common Eg: St John’s Wort – a crude OTC ‘antidepressant’ (Weak NA/5HT Uptake Inhibitor – similar mechanism to SSRIs) – Risk of Serious Drug Interactions Sample Footer Text

  17. Drug Administration Goals of drug administration: 1: Get it into the Circulation – So it can access its target tissue 2: Make sure it is a “Free-Drug” by the time it reaches its target – So it can exert its effect Sample Footer Text

  18. Drug Administration Routes of Administration: o There are numerous routes of Administration (eg: IV/Oral/Suppository/Mucosal-Absorption) • o Choice depends on drug properties, desired onset, duration of action, pH of entry environment, & bioactivation requirements (eg: Prodrugs) Sample Footer Text

  19. Drug Administration Tissue Reservoirs: o After absorption, some of the Free-Drug is lost to Tissue Reservoirs/Blood Proteins o Often bound drugs are released from tissues/proteins as the Concentration Of Free Drug dwindles (Bound Drug ↔ Free Drug → Used/Metabolized) Target of Action: o Where are the target Receptors/Enzymes/Cells/Tissues? o Will Free-Drug in the blood be able to access its target? Sample Footer Text

  20. Drug metabolism Biotransformation: o The Liver plays an important role in: § Bio-Activation: Drug Precursor → Active Drug Metabolites § Bio-Inactivation: Active Drug → Water-Soluble, Inactive Drug Metabolites § Detox: Toxic Substance → Water-Soluble, Non-toxic Metabolites § Conjugating: Ie: Making H2O-Soluble → Aids Renal Excretion o Q: Does the drug pass through the liver before its target? (Eg: Yes- if oral; No- if IV) Sample Footer Text

  21. Drug metabolism Excretion: o Typically via the Kidney o Substance must be H2O-Soluble Sample Footer Text

  22. PHARMACOKINETICS: What is Pharmacokinetics? – “What the Body Does to the Drug”: • The relationship between drug administration, time-course/rate of absorption & distribution, concentration changes in the body, and the drug’s removal from the body Sample Footer Text

  23. PHARMACOKINETICS: What Determines a Drug’s Pharmacokinetics?: 1.Characteristics of Biological Membranes (across which ALL drugs must pass): o Bi-phospholipid layer o Hydrophilic Exterior o Lipophilic Interior o Selectively Permeable – allows passage of some, but not all drugs Sample Footer Text

  24. PHARMACOKINETICS: 2.Properties of the Drug (Physical/Chemical): o Lipid Solubility (High Solubility = High Permeability) o Degree of Ionisation (Ionised/Charged molecules = Impermeable) § Determined by pKa (The pH where the drug is 50% Ionised) o Molecular Size (Smaller = More Permeable) Sample Footer Text

  25. PHARMACOKINETICS: 3.Concentration Gradient (Simple Diffusion): o Most drugs cross membranes via Simple Diffusion o ‘Diffusion-Controlled Distribution’ = Drugs will move down Concentration Gradients until Concentrations of the drugs are equal in all parts of the body Sample Footer Text

  26. PHARMACOKINETICS: Why Pharmacokinetics is Important: • A Drug must reach its site of action to exert its pharmacological effect • 4 Things that determine the Concentration Of the drug at its site of action: 1: Absorption 2: Distribution 3: Metabolism 4: Elimination Sample Footer Text

  27. PHARMACOKINETICS:ABSORPTION Definition: o The movement of the drug from site of administration into the plasma o The Rate of Absorption determines the Intensity and Duration of drug action o Eg: IV drugs bypass the problem of absorption because they’re instantly available in plasma Sample Footer Text

  28. PHARMACOKINETICS:ABSORPTION MECHANISMS OF ABSORPTION Most drugs are absorbed by Simple Diffusion → Therefore the Rate depends on: § Solubility (Influenced by pH & drug’s pKa) § Tissue Permeability § Surface Area § Blood Supply • o Other mechanisms include active transport, facilitated diffusion, etc Sample Footer Text

  29. PHARMACOKINETICS:ABSORPTION Bioavailability: (‘F’) o The amount of active drug that reaches the systemic circulation o Is expressed as a percentage of the dose (Eg: IV dose has 100% bioavailability) o Low ‘F’-values for Bioavailability occur with: 1: Poorly Absorbed drugs 2: Drugs that undergo extensive ‘First Pass Metabolism’ in the liver o High ‘F’-Values for Bioavailability occur with IV dosing Sample Footer Text

  30. PHARMACOKINETICS:ABSORPTION The ‘First-Pass’ Effect: o Where a drug is metabolised by the liver before it reaches systemic circulation o Results in reduced Bioavailability (F) o Eg: An Orally-administered drug is: 1: Absorbed in the GIT 2: Transported via the Portal Vein → Liver 3: Liver metabolises drug (first pass metabolism) 4: Then releases metabolites into the systemic circulation o Eg: Lignocaine – local anaesthetic & treat arrhythmias § If administered Subcutaneously, it is instantly at the site of action § If orally administered, all is absorbed, but none is available because it passes through the liver before reaching the site of action Sample Footer Text

  31. PHARMACOKINETICS:DISTRIBUTION Definition: • Movement of drugs between different body compartments and to the site of action • (Ie: Once the drug is in the circulation, How Well & How Much gets to the site of action) Major Body Fluid Compartments: • Plasma • Interstitial Fluid • Intracellular Fluid • Transcellular Fluid (eg: CSF, Peritoneal Fluid, Pleural Fluid) • Fat • Brain Sample Footer Text

  32. PHARMACOKINETICS:DISTRIBUTION Distribution depends on Drug’s Ability to Cross Membranes: • Lipid Solubility: § Lipophilic drugs readily cross membranes § Hydrophilic drugs don’t cross membranes • Blood pH & Drug pKa: § Charged drugs don’t cross membranes • Protein Binding: § Limits amount of drug that is free to cross membranes § Note: Generally, only unbound drug can be distributed across membranes § Most acidic drugs (Including All antibiotics) bind to albumin • Regional Blood Flow: § Determines the amount of drug that is ‘available’ to that tissue in a given time period Sample Footer Text

  33. PHARMACOKINETICS:BIOTRANSFORMATION Definition: • Chemical transformation of a drug within the body as a result of ‘Biotransformation’ Sites of Biotransformation: • Mainly Liver • GI Tract • Lung • Plasma • Kidney Sample Footer Text

  34. PHARMACOKINETICS:BIOTRANSFORMATION Biotransformation may result in: • Pro-Drug Activation: § Pro-drug → Active (for some drugs the active form of the drug is unsuitable for absorption/distribution, and hence has to be administered in an inactive form that gets metabolised by the liver into an active form) • Drug may be Changed to another Active Metabolite § Eg: Diazepam to Oxazepam § Eg: Codeine to Norcodeine & Morphine • Drug may be Changed to a Toxic Metabolite § Eg: Meperidine to Normeperidine • Drug may be Inactivated: § Active Drug → Inactive form Sample Footer Text

  35. PHARMACOKINETICS:BIOTRANSFORMATION Factors Influencing Biotransformation: • Interactions Between Drugs: § Drug-induced alterations of liver-enzymes: (includes herbal medicines & natural remedies) § Competition for metabolic pathways • Enzyme Inhibition: § Enzyme inhibition may lead to increased concentration/bioavailability of another drug § Eg: Erythromycin (a CYP3A4 inhibitor) can increase risk of simvastatin toxicity (which ismetabolised by CYP3A4) • Enzyme Induction: § Some drugs can enhance gene transcription, increasing the activity of a metabolizing enzyme § Eg: Phenobarbital can induce the metabolism of oral contraceptives via the CYP system Sample Footer Text

  36. PHARMACOKINETICS:BIOTRANSFORMATION Genetics: § Some people vary in their expression of the Cytochrome-P450-Enzymes § May alter the effectiveness of a drug (may have no effect/may overdose) • Eg: CYP2D6 is absent in 7% of Caucasians → no response • CYP2D6 is hyperactive in 30% of East Africans → same dose = toxic Disease Status: § Compromised organs: • Liver • Kidney • Heart • Vasculature § Viral infections can alter enzyme activity § Bacterial infections can produce toxins → alter drug activity/metabolism Sample Footer Text

  37. PHARMACOKINETICS:BIOTRANSFORMATION Hormone Status: § Oestrogen can affect metabolic enzyme activity Age/Gender: § Enzyme expression & activity changes with age § Gender differences related to hormonal status Diet: § Enzyme activity is affected by certain foods, vitamins & alcohol Sample Footer Text

  38. INRODUCTION TO CLINICAL PHARMACOLOGY & THERAPEUTICS THE END THANK YOU Sample Footer Text

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