Lab No 2: Introduction To Experimental Pharmacology PDF

Lab N0 2 Introduction to experimental pharmacology LAB NO 2: Introduction to experimental pharmacology The aim from this lab is: A- To identify action and mechanisms (Qualitative activity) screening. Looking for specific pharmacological...

Lab N0 2 Introduction to experimental pharmacology LAB NO 2: Introduction to experimental pharmacology The aim from this lab is: A- To identify action and mechanisms (Qualitative activity) screening. Looking for specific pharmacological activity of test drug in order to: 1. Identify the action. 2. Know how it acts (mechanisms). B-To calculate concentration and potency (Quantitative activity) bioassay. Quantitative estimation of the active principle in a drug preparation or biological material by measuring its activity on suitable biological preparation : 1. It is a comparative method for estimation of potency of drugs. 2. It gives the relative potency , which indicates how many times that test drug is more or less potent than standard drug 1 Lab N0 2 Introduction to experimental pharmacology (has known concentration) i.e., it gives the relative value and not absolute value. 3. It used to determine concentration and potency of drug. Types of laboratory biological objects The substance should be tested in biological object, it may be: 1-whole animal: A. Small animals: mice, rat, frog, guinea pig (G.P) B. Intermediate : rabbit, guinea pig C. Large: dog , cat, monkey. 2- Isolated organ: rabbit heart , frog heart (langerdroff,s preparation) 3-isolated tissues: A. Smooth muscle: guinea pig ileum, rat aortic strip, guinea pig tracheal chain. B. Skeletal muscle : frog rectus abdominis, diaphragm, tibialis anterior, dorsal muscle of the leech. C. Cardiac muscle: piece of atria. There are some differences between the experiments that are performed on whole animal and those performed on isolated preparations : 2 Lab N0 2 Introduction to experimental pharmacology 1. The effects of drug in whole animal are complicated by the possibility that what is observed is the consequence of the drug acting at many sites at once , e.g; effect of drug on the blood pressure. 2. Also complicated by how the drug is administered. 3. Pharmacokinetics (rate of excretion and metabolism). However , intact preparations indicate the likely clinical effects of a drug much better than isolated preparations but they may be more difficult to know how the drug is acting. Biological response: It is a measurable response, which is produced by drug in a living organs or tissue. e.g. blood pressure, contraction, relaxation. Types of responses: 1. Graded response 2. Quantal response 1- Graded response: is a response which increases with increasing the dose , until a maximum response is obtained. Application: Determination of potency and efficacy. Potency: ability to produce higher response at low dose. 3 Lab N0 2 Introduction to experimental pharmacology Efficacy: ability to produce maximum response Drug a&c have the same efficacy. Drug a more potent than drug b. Drug b more potent than c & drug c more efficient than drug b. Dose-Response Relationship: As the dose of a toxicant increases, so does the response. 4 RESPONSE 0-1 NOAEL 2-3 Linear Range 3 4 Maximum Response 2 0 1 DOSE DOSE DETERMINES THE BIOLOGICAL RESPONSE 2- Quantal response (all or none response) A response when all or none effect is observed i.e. specific dose may or may not produce a response. e.g; Analgesia , death and convulsions. #aspirin given to 100 patients: 4 Lab N0 2 Introduction to experimental pharmacology DOSE %RESPONDERS % NONE 300 MG 10 % 90 % 400 MG 30 % 70 % 500 MG 80 % 20 % 600 MG 100 % 0% Applications: Calculation of ED 50% Calculation of LD 50% Therapeutic index (therapeutic ratio) (TI=LD50% / ED50%) Example: Animals were injected with varying doses of sedative-hypnotic , and the responses were determined and plotted. The calculation of TI is an indication of how selective a drug in producing its desired effects relative to its toxicity. 5 Lab N0 2 Introduction to experimental pharmacology How we can give the drug? Drug is given in a solution form and rarely in suspension form. - Whole animal in normal saline as mg/kg. - Isolated preparation in physiological solution in organ bath as µg/ml, ng/ml, pg/ml. Molar solution =molecular weight /liter of water Mole = m.wt. in gram Example 1M solution of NaCl is prepared by dissolving 58.5 gram of NaCl in 1 liter of water. 3.5M NaCl dissolve 204.75 grams NaCl in 1 liter water. (Na=23, Cl=35.5) Dose calculation: Miga 1000 kilo 1000 gram 1000 miligram 1000 Microgram 1000 nanogram 1000 pictogram 1 L=1000 ML 1L= 1DM3 1ML =1 CM3 1DM3 = 1000 CM3 6 Lab N0 2 Introduction to experimental pharmacology How we can prepare drug solution? Ex: Dose of drug 20mg/kg 20mg/1000g 2mg/100g Rat wt = 200gm Constant: 0.1ml drug /100gm of body weight So, 2mg/0.1ml 20mg/ml is prepered Volume of injection 0.1ml 100gm x 200gm x=0.2ml Problem 1: Dose = 10mg/kg volume = 0.1ml body weight = 100g conc = ? 10mg 1000gm X 100gm X = 10*100/1000 = 1mg 1mg 0.1ml X 100ml 7 Lab N0 2 Introduction to experimental pharmacology X = 1*100/0.1 = 1000 mg = 1gm Conc = 1% Problem 2: Dose = 20mg/kg volume =0.1ml Concentration = 2% Body weight = ??? Problem 3: Animal weight = 300gm Dose = 150mg/kg Volume of injection = ??? Concentration = ??? 8