Lecture 3: Orientation to Pharmacy - Ain Shams University PDF

Lecture 3 Dr. Roxane Abdel Gawad department Pharmaceutics & Industrial Pharmacy Faculty of Pharmacy Ain Shams University  Drug dosage  Drug (medicament): ‫ العالج‬-‫الدواء‬ is a material intended for use in the diagnoses, treatment or prevention of...

Lecture 3 Dr. Roxane Abdel Gawad department Pharmaceutics & Industrial Pharmacy Faculty of Pharmacy Ain Shams University  Drug dosage  Drug (medicament): ‫ العالج‬-‫الدواء‬ is a material intended for use in the diagnoses, treatment or prevention of diseases  Dose: ‫الجرعه‬ The quantity of drug administered by a patient at a specific time to exert the desired therapeutic response e.g. (5 mL antibiotic)  Dose regimen (schedule of dosage): ‫نظام الجرعات‬ The frequency at which drug doses are administered by a patient e.g. (5 mL twice daily for 5 days)  Usual dosage range: (Therapeutic window) The range of drug amounts that may be prescribed → doses outside that range are under dosage or over dosage MEC < Drug Dose Range < MTC MEC: Minimum effective concentration MTC: Minimum toxic concentration  Drug dose varies from patient to another & for the same patient from occasion to another → that’s why there must be a dose range & not a single dose  There is an Adult range & Pediatric range  The drug amount within the dose range that produces the desired effect in the majority of patients is considered the usual drug dosage 3  Median effective dose (ED 50) Is the drug amount which produces the desired therapeutic effect in 50 % of the patients  Median toxic dose (TD 50) Is the drug amount which produces a toxic effect in 50 % of the patients  Therapeutic index (TI) Is the ratio between the median toxic dose and the median effective dose = TD 50 (small TI values in potent drugs) ED 50 4  Types of doses  Prophylactic dose → prevents illness The amount of drug administered to protect the patient from contracting a disease e.g. vaccines  Therapeutic dose → treats illness - Is the dose administered to a patient after exposure to the illness Initial dose (primary) (loading) Maintenance dose dose(s) required to subsequent single reach the desired daily dose used to drug conc. in the maintain the drug blood concentration in the blood e.g. digoxin 4 times/day followed by single daily dose5  Factors affecting drug dosage 1. Age 2. Body Weight 3. Body Surface Area 4. Gender 5. Pathological State 6. Tolerance 7. Concomitant Drug Therapy 8. Time Of Administration in relation to Meals 9. Route Of Drug Administration 6  1. Age It is important for: neonatal and geriatric patients Newborn infants ------> immature renal & hepatic functions Geriatrics ----------------> impaired renal & hepatic functions In both these populations: failure to detoxify certain drugs → drugs accumulate in the tissues to toxic levels Pediatric dose is calculated as fraction of adult dose: a. Young's Rule: Age (years) x Adult dose = Child dose Age + 12 b. Cowling's Rule: Age (years) x Adult dose = Child dose 24 c. Fried's Rule: (for infants) Age (in months) x Adult dose = Infant Dose 150  2- Body weight: Usual adult doses are suitable for average weight individuals 70 kg (150 pounds) The weight of the body influences drug concentration at its site of action → Dose adjustment is required for abnormally lean or obese patients Doses may be expressed in terms of mg/kg body weight The following rule can be used for calculation of child dose: Clark's Rule: 1kg = 2.2 lb Weight of child (lb) x Adult dose = Child dose 150 (lb) 8  3. Body surface area (BSA) A close correlation exists between physiological processes and BSA → so doses can be expressed in terms of mg/m2 Body surface area can be obtained from NOMOGRAM → relates body height, weight and surface area The child dose can be calculated according to the following rule: BSA of child x Adult dose = Child dose 1.73 m2 9 (average BSA of adults)  4. Gender In general, women are more sensitive to certain drugs than men (lower metabolism, weight & BSA) → so their dosage may be reduced Caution in drug administration is necessary in 2 women populations: a. Pregnant females drugs maybe transported transplacental from maternal to fetal circulation and cause toxicity of the fetus (E.g. alcohol, anesthetics, narcotics & analgesics) b. Lactating females (infant breast feeding by mother): these drugs may 12 be excreted in mother’s milk  5. Pathological state Some drugs may be affected by the pathological state of the patient (especially renal & hepatic disorders) → dose modification needed E.g. Tetracycline accumulates to a toxic level when used in case of renal impairment → usual dose should be reduced The terms “precautions”, “warning” and “contraindication” are used to alert the physician to certain restrictions in the use of drugs: Severity: Precaution < warning < contraindicated Prohibited drug use: Diabetics & Hypertensives - Asthmatics & morphine syrups & systemic - Drugs causing allergy 13 decongestants  6. Tolerance Tolerance: a drug becomes less effective in the body due to its continuous use → drug dosage must be increased to maintain the therapeutic response E.g. tolerance to antihistamines & narcotic analgesics & nasal decongestants Normal sensitivity may be regained by: 1. Advise the patient to avoid prolonged administration (< 5 days) OR 2. Discontinue drug administration for a period of 14 time and use an alternative 7. Concomitant drug therapy (drug-drug interaction)  Drug-drug interactions are due to: 1-Chemical or physical interaction between drugs 2-Drug alters the absorption, distribution, metabolism or excretion of the other drug  Drug-drug interactions may be either: 1. Beneficial Probenecid (uricosuric drug) prolongs the action of penicillin → penicillin dose & frequency of administration must be reduced → less side effects 2. Detrimental (harmful) Tetracyclin combines with certain metal ions (Ca, Mg, and Al) present in antacids, milk & cheese → forms complexes which are poorly absorbed → tetracycline becomes ineffective → so antacids & milk should be avoided during 15 its administration 8. Time of administration Taking medications by the oral route in relation to meals is very important regarding 2 aspects: 1. In general: When the stomach is empty (before meals) → absorption of drugs is more rapid → SO, an effective dose before meals may be ineffective when taken after eating 2. Exception: drugs irritating to the GIT (e.g. NSAIDs) are better tolerated by the patient if taken after meals due to dilution by food 16 9. Route of administration The dosage of a drug may vary according to the dosage form and route of administration Injectable drug doses are lower than oral doses WHY ?? After I.V. Administration all the dose is present in the blood (100% absorbed), while a drug administered orally is not fully absorbed due to e.g. interactions with gastric contents or first pass metabolism 17  Thank you for your time! Please, Read this lecture today. If you want more information, please feel free to contact me [email protected]