Posology, Intro To Chem PDF

Kwame Nkrumah University of Science & Technology, Kumasi, Ghana Pharm 161 Posology( Calculation of Doses) FREDERICK W.A. OWUSU, PhD Department of Pharmaceutics  Outline/Course Objectives Introduce students to posolgy and the concept of dose selection and calculation...

Kwame Nkrumah University of Science & Technology, Kumasi, Ghana Pharm 161 Posology( Calculation of Doses) FREDERICK W.A. OWUSU, PhD Department of Pharmaceutics  Outline/Course Objectives Introduce students to posolgy and the concept of dose selection and calculation of doses in infants and children www.knust.edu.gh www.knust.edu.gh  Learning Outcomes It is expected that at the end of this section students should be able to; Define Posology Explain factors affecting dose selection Calculate doses for Infants and Children www.knust.edu.gh www.knust.edu.gh  Posology Derived from the Greek words posos and logos Posos how much Logos science Posology is the branch of medicine that deals with doses www.knust.edu.gh www.knust.edu.gh  Posology What is a dose? A quantity of medicine prescribed to be taken at one time www.knust.edu.gh www.knust.edu.gh  Posology Factors that influence doses; Genetic Makeup Acquired Tolerance Idiosyncrasy Route of Administration Rate of Elimination Drug Interactions Formulation www.knust.edu.gh www.knust.edu.gh  Posology Genetic makeup; Variations in response of different individuals to the same dose of a drug may be due to differences in genetic makeup. www.knust.edu.gh www.knust.edu.gh  Posology Acquired Tolerance; A common illustration can be found with drug addicts. They have over a long period acquired the ability to take, with comparative safety, large doses of certain drugs which in normal persons would produce harmful or fatal effects. Examples of drugs for which tolerance can be acquired : morphine, heroin and cocaine. Can you name some more???????? www.knust.edu.gh www.knust.edu.gh  Posology Idiosyncrasy; This indicates exceptional and individual intolerance towards certain drugs. Examples: Aspirin causes asthma in some people Penicillin produces an irritating rash Barbiturates give rise to skin eruption that resembles measles. www.knust.edu.gh www.knust.edu.gh  Posology Route of Administration; The rate and degree of absorption of a drug and the rapidity with which its effect is produced vary according to the method of administration In general, absorption of drugs is more rapid and complete via the parenteral route (injection) than the oral route. As a result, oral doses of most medicaments are greater than the parenteral doses. www.knust.edu.gh www.knust.edu.gh  Posology Rate of Elimination; This affects the duration of activity of medicines. The duration of activity may be prolonged or the activity may be greater and this may cause toxic reactions. Factors that affect rate of elimination include Age and disease conditions. Age or disease can impair the liver function and the breakdown of drugs may be delayed. Reduction in kidney activity will lead to incomplete excretion of drugs. www.knust.edu.gh www.knust.edu.gh  Posology Drug Interactions; Simultaneous administration of two drugs may result in a synergistic effect and necessitate reduction of the dose of one or both. When certain drugs are given concurrently, dangerous reactions can occur. Lists of important drug interactions may be found in official books such as British National Formulary (BNF), British Pharmaceutical Codex (BPC) and others. www.knust.edu.gh www.knust.edu.gh  Posology Formulation; The rate and degree of absorption of a drug and its dose may be influenced by the form in which it is prepared for administration. What are the various forms in which drugs may be formulated?????? www.knust.edu.gh www.knust.edu.gh  Posology Dose Frequency: This may be stated in a number of ways The average range of quantities suitable for adults, stated for the different routes of administration. For example; oral, subcutaneous or intravenous. The amount suitable for administration over 24 hours; Where appropriate, a statement that it must be given in divided doses. E.g. Griseofulvin 1 g daily in divided doses. www.knust.edu.gh www.knust.edu.gh  Posology The amount suitable for administration over 24 hours; When this is not stated, the quantities mentioned are usually suitable for administration on one occasion. E.g. Sodium bicarbonate 5 g ** there is sometimes difficulty in deciding whether the above mentioned can be administered more than once a day. Consult reference compendia such as Extra Pharmacopoeia Consult the prescriber www.knust.edu.gh www.knust.edu.gh  Posology Official doses are not binding on a prescriber Doses in excess of the official maxima are sometimes required in specific cases Can you name some cases????? In such cases, these doses are usually underlined, circled or initialled by the prescriber It is the duty of the Pharmacist to ensure that an overdose has not been prescribed www.knust.edu.gh www.knust.edu.gh  Posology A Pharmacist should check each dose before dispensing a prescription A pharmacist should look out for changes in dosing, new research findings etc. (BNF,…..) www.knust.edu.gh www.knust.edu.gh  Posology Paediatric Dosage: Doses proportionate to Age Doses proportionate to Body weight Doses proportionate to Surface Area www.knust.edu.gh www.knust.edu.gh  Posology Doses Proportionate to Age: Many methods have been used to relate doses for children to their ages The 2 most commonly known are Young’s Rule Dilling’s Rule www.knust.edu.gh www.knust.edu.gh  Posology Young’s Rule Age in years = proportion of adult dose Age in years + 12 E.g. For a child of 6 years Calculate the proportion of adult dose to be given www.knust.edu.gh www.knust.edu.gh  Posology Dilling’s Rule Age in years = proportion of adult dose 20 E.g. For a child of 6 years Calculate the proportion of adult dose to be given www.knust.edu.gh www.knust.edu.gh  Posology Doses proportionate to Body Weight The doses of many drugs in the Pharmacopoeias and Formularies are based on the body weight of the patient This is based on the theory that the concentration of a drug at its site of action will often be influenced by the size of the patient This implies that heavily-built individual should receive a larger dose than someone of normal weight www.knust.edu.gh www.knust.edu.gh  Posology Doses proportionate to Body Weight Examples and calculations Artesunate and Amodiaquine for the treatment of uncomplicated malaria have the following dosage regimen; Artesunate : 4 mg/ kg Amodiaquine : 10 mg/kg What is the dose for a child who weighs 22 kg? This medication is taken twice daily for 3 days. Calculate the total amount of each medication required by the above mentioned patient. www.knust.edu.gh www.knust.edu.gh  Posology Doses Proportionate to Surface Area Reasons for using this method include: The dose to be given depends on factors such as ; metabolic rate, lean body mass and extracellular fluid volume These factors are more closely related to surface area than to age or weight. This method is however not as simple as the methods based on age and weight. Surface area of child X 100 = percentage of adult dose Surface area of adult www.knust.edu.gh www.knust.edu.gh  Tutorial Kindly refer to your British National Formulary (BNF) for more posology practice. www.knust.edu.gh www.knust.edu.gh  Thank you Any questions??? www.knust.edu.gh www.knust.edu.gh