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- 1. Posology &Dosage Calculations
- 2. DEFINITIONS • Posology – the pharmacological study of drug dosage. – The study of dosage quantity and prescription.
- 3. Usual Recommended dose – the amount of drug that will ordinarily produce the effect for what is intended.
- 4. •Minimum dose - the smallest dose of drug that produces therapeutic effect. •Maximum dose -the largest dose that can safely administered. Ex. Acetaminophen 10 to 15 mg/kg/dose
- 5. Toxic dose •amount of drug that cause harmful effect. Lethal dose •amount of substance that will cause death.
- 6. Single dose - to be taken at one time.Daily dose - amount to be taken in 24 hour period.
- 7. Maintenance dose - amount to be taken to maintain the therapeutic effective dose.Loading dose - first dose given to achieve maintenance drug level quickly.
- 8. System of Measurement1. Metric system2. Apothecary system3. Household system
- 9. System of Measurement1. Metric System – Most widely used system of measurement – A decimal system based on the power of ten – Units: • Gram (weight) • Liter (volume) • Meter (length)
- 10. System of Measurement2. Apothecary System – Uses Roman numerals to express quantity – Old system of measurement – Uses: • minim = liquid • Grains = solid
- 11. System of Measurement3. Household System – Not as accurate as metric system due to lack of standardization of spoons, cups and glasses – Teaspoon (tsp) = liquid – Pound (lb) = solid
- 12. System of Measurement ml- millilitercc- cubic centimetergm- grammg- milligramgr- grainmEq- milliequivalentmcg- microgram
- 13. GENERAL METHODS FOR DRUG CALCULATION1. BASIC FORMULA2. RATIO& PROPORTION3. FRACTIONAL EQUATION4. BODY WEIGHT5. BODY SURFACE AREA
- 14. 1. Basic Formula: DxV=AHD- desired dose (drug dose ordered by health care provider)H- on-hand (stock on hand/on label of container)V- vehicle ( Q- quantity/drug form in which drug comes)A- Amount calculated to be given to client
- 15. Examples:1. Order:Avandia 2mg OD. How much tablet will you give? DxV=A HSolution: 2mg x 1 tablet 4mg = .5 tablet
- 16. Paracemol 500mg. Q 4 hour Round the Clock (RTC) p.o. The stock on hand is 250mg/5ml in 60ml bottle. How many ml should be administered? DxV=A H 500 mg x 5 ml = 250 mg 10 ml
- 17. 2. Dilute Terramycin to 50ml of sterile water. Give 5000mg po Q12.
- 18. 3. Banophen 50mg. TID p.o. a. How many tablet will you give in 1 dose? b. How many tablets will you give in a day?
- 19. 2. Ratio and Proportion H : V = D : xWhere: H = drug on hand (available) V = vehicle/drug form (capsule/tablet/liquid) D = desired dose (as ordered) x = unknown amount to give
- 20. ExampleOrder: Cefdinir (3rd gen cephalosporin) 100 mg PO q.i.d *How many mL should the client receive?
- 21. Order: Cefdinir (3rd gen cephalosporin) 100 mg PO q.i.d *How many mL should the client receive?Solution: H : V = D : X 250mg : 5mL = 100mg : xmL
- 22. • Your drug order is for morphine sulfate 5 mg, IV, q3h, PRN. The drug is available as morphine sulfate 10 mg/mL. Your instructions are: infuse morphine sulfate 5 mg; not to exceed 10 mg/4mins – How many mL equal morphine sulfate 5 mg? – What is the number of minutes to administer morphine sulfate?Solution:• a. 0.5 ml• b. 2 min
- 23. 3. Fractional Equation• Same as R & P except it is written as a fraction. H = D V X
- 24. ExampleOrder:Ciprofloxacin 500 mg PO q12h*how many tablets should the client receive? H = D V X
- 25. Order:Ciprofloxacin 500 mg PO q12h*how many tablets should the client receive?Solution: H=D 750mg = 500mg V X 1 tablet x 750(x) = 500 x = 0.67 tablets
- 26. 4. Body Weight (BW)• Allows individualization of the drug dose• Involves 3 steps:1. Convert pounds to kg – 1 Kg = 2.2 lbs2. Determine drug dose per BW – Drug dose x body weight = clients dose per day3. Follow basic formula, R & P
- 27. ExampleOrder:Fluorouracil (5-FU), 12 mg/kg/day IV, not to exceed 800 mg/day. The adult weighs 132 lb.1. Convert pounds to Kg : 132/2.2 = 60kg2. mg x kg = client’s dose: 12 x 60 = 720 mg/kg/dayAnswer: fluorouracil 720 mg/kg/day
- 28. 5. Body Surface Area (BSA)• Most accurate to calculate drug dose for: – Infants – Children – Older adults – clients who are on antineoplastic agents – low body weight• In m2, determined by where the person’s height and weight intersect the nomogram scale.• To calculate the drug dosage using the method, multiply the drug dose by # of square meters.
- 29. ExampleOrder:Cyclophosphamide (Cytoxan) 100 mg/m2/day, IV; available dosage is 200mg; client’s height is 70 inches, weight is 160 lbs.1. 70 inches and 160 lbs intersect the nomogram scale at 1.97 m2 (BSA).2. 100 mg x 1.97 = 197mgAnswer:Administer cyclophosphamide 197 mg/day
- 30. ExampleThe doctor has ordered an antibiotic whose average adult dose is 250 mg per day. What would the dosage for this medication be on a child who has a length of 120 cm and weight of 40 kg?Determine the BSA.
- 31. The doctor has ordered an antibiotic whose average adult dose is 250 mg per day. What would the dosage for this medication be on a child who has a length of 120 cm and weight of 40 kg?Child dose : surface area in sq m (m2) x ave adult dose (mg) 1.73Solution: 1.2 m2 x 250 mg 1.73 = 173 mg of medication would be given.
- 32. Pediatric considerationsFried’s rule – applies to the child younger than 1 year of age.Child’s dose: infant age (months) X adult average dose 150 months
- 33. Pediatric considerationsYoung’s Rule- applies to children 1-12 y.oChild’s dose: child’s age (years) X adult average dose child’s age (yrs) +12
- 34. Pediatric considerationsClark’s Rule – Uses the child’s weight to calculate the appropriate dose and assumes that the adult dose is base on 150 lb person.Child’s dose: child’s weight (pounds) X adult average dose 150 lbs (pounds)
- 35. Calculation of Intravenous Fluid – 3 different methods – gtt/minMETHOD I: Three-StepMETHOD II: Two-StepMETHOD III: One-Step
- 36. Calculation of Intravenous Fluid• METHOD I: Three-Step Step 1: Amt of soln = mL/hr hrs o administer Step 2: mL per hr = ml/min 60 minutes Step 3: Ml/min x gtt/ml = gtt/min
- 37. Calculation of Intravenous Fluid• METHOD II: Two-Step Step 1: Amnt of fluid = ml/hr Hrs to administer Step 2: mL per hr x drops per mL = gtt/min 60 mins
- 38. Calculation of Intravenous Fluid• METHOD III: One-Step Amnt fluid x gtt/mL = gtt/min Hrs to admin x min/hr
- 39. Drop factors:Macro drip – 15/60Micro drip – 60/60No. of drops/min= no. of fluids (cc) X drop factor no. of hours X 60No of hours= no. of fluids (cc) X drop factor no. of drops/min X 60
- 40. • Your drug order is for 1000mL of D5/0.5NSS to run for 8 hours. – Would you used macrodrip or microdrip IV set? – Calculate the drops per minute (gtt/min) using the 2-step method
- 41. Example:No. of drops/min= no. of fluids (cc) X drop factor no. of hours X 601. D5LR 1L for 12 hours. The drop factor is 15gtts/ml. Compute for the no. of drops/min.gtts/min= 1000cc X 15 12 hour X 6020gtts/min.
- 42. 2.No. of HourNo of hours= no. of fluids (cc) X drop factor no.of drops/min X 60D5LR 1L at 2ogtts/min. The IV set delivers at 15gtts/ml. Compute for the no. of hours consumed.No. of hour= 1000cc X 15 20gtts/min X 6012 hours = answer
- 43. Fahrenheit And Centigrade conversionsC= F- 32 x 5 9F= C X 9 +32 5
- 44. Reference Information:Conversion Factors And Equivalents:• 1cc = 1ml• 1gm = 1000mg.• 1mg = 1000mcg.• 1kg = 1000gm• 1000cc = 1 liter = 1 quart• 1 oz = 30 cc• 1 teaspoon = 5 ml• 1 tablespoon = 15 ml• 1kg. = 2.2 lbs.• 1 grain = 60mg.• ½ grain = 30mg
- 45. Route:• p.o = per orem• I.M. = intramuscular ( 90 degree)• S.Q/ S.C = subcutaneous ( 45 degree)• I.V= intravenous• I.D = intradermal• Direct I.V• Nebulization• Intrathecal = spinal• p.c. =post cebum (after meal)• a.c = ante-cebum ( before meal )• O.D = oculo-dexter (right eye)• O.S = oculo-sinester ( Left eye)• O.U = oculo-urique (Both eyes )• E.T = endotracheal• Per rectum- anus/anal• Intra-vaginal- vagina• I.J = Intra-jugular• S.L = Sublingual
- 46. Frequency• OD = once a day • PRN = as needed• BID = twice a day • H.S = hour of Sleep• TID = Thrice a day • STAT = immediately• QID = Four times a day • ASAP = as soon as possible• Q4hr = every 4 hours • QD = everyday• Q6hr = Every 6 hours • QOD = every other day• Q8hr – Every 8 hours • D• Q12hr = every 12 hour

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