Hospital Pharmacy: Lecture Three

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Hospital Pharmacy Calculations

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Hospital Pharmacy: Lecture Three

  1. 1. Anas Bahnnassi PhD RPhHospital Calculations‫ الحسابات الصيدالنية‬Calculations Related to ‫ في المستشفيات‬Common Hospital Formulations ‫الدكتور أنس البهنسي‬ 1
  2. 2. Lecture Objectives Understand the prescription components. Ability to read Latin signa. The use of the metric system and understand the apothecary and Anas Bahnnassi PhD RPh avoirdupois systems with the ability to make conversions. Solve proportional calculations. The ability to render a solution isotonic using NaCl or Boric Acid. Apply skills to produce new concentrations out of a different concentration with a specific volume. Solve calculations related to injectable medications, including reconstitution, milliequivalent concentrations, and dose calculations. 2
  3. 3. Components of Prescription Prescriber Name, Address and PhoneSuperscription Patient Name Address Age Date Inscription: Name of Anas Bahnnassi PhD RPh Medicationand number of Paracetamol 500mg units #30 Subscription Directions to the dispenser like: Dissolve tablets in 3 oz of simple syrup Usually in Latin Take 1-2 tablets qid PRNTranscription Refills: Signa DAW Signature 3
  4. 4. Anas Bahnnassi PhD RPh 4Common Latin Abbreviation
  5. 5. Example Anas Bahnnassi PhD RPh• A prescription reads: – Trandate 300mg po BID F7D. – You only have Trandate 150mg in stock – How many tablets do you dispense???? 5
  6. 6. The Metric System• A measurement system based on subdivisions and multiples of 10; made up of Anas Bahnnassi PhD RPh three basic units: meter, gram, and liter – Temperature – Distance – Volume – Weight 6
  7. 7. 7 Anas Bahnnassi PhD RPh
  8. 8. Common Metric Units8 Anas Bahnnassi PhD RPh
  9. 9. Apothecary Measures9 Anas Bahnnassi PhD RPh
  10. 10. Anas Bahnnassi PhD RPhAvoirdupois Measures 10
  11. 11. Household Measures11 Anas Bahnnassi PhD RPh
  12. 12. Temperature• Conversions °F = (1.8 x °C) + 32° Anas Bahnnassi PhD RPh °C = (°F - 32°) ÷ 1.8 © Paradigm Publishing, Inc. 12
  13. 13. IV Room CalculationsIV Room Lingo:• Stock solution: the most concentrated form of Anas Bahnnassi PhD RPh a drug that you can put your hands on.• Bag: flexible, soft plastic container filled with a sterile fluid.• Standard Concentration: a set volume and concentration of a commonly-made medication 13
  14. 14. A List of Standard Concentrations forA Hospital Anas Bahnnassi PhD RPh 14
  15. 15. Proportional Calculations: ������ ������ = ������ ������ Anas Bahnnassi PhD RPh ������������ ������ = ������Only true if you make sure all units cancel out, leaving the ones you want (Dimensional Analysis) 15
  16. 16. • You need to mix a syringes filled with 1g of Cefazolin in 20ml Example diluent. Your stock Anas Bahnnassi PhD RPh solution contains 200mg/ml Cefazolin.• How many mls of the • Solution: stock solution you need to draw and put in the ������������������������������������ ������������������������������ – = ������ ������������ ������ ������������ 20ml syringes then add the diluent. ������������������������������������ – ������ = = ������������������ ������������������ 16
  17. 17. Osmolarity and Tonicity• Very important when mixing solutions for instillation into the body fluids. Anas Bahnnassi PhD RPh• The term is used to describe the number of milliosmoles in a given amount of solution(1L).• Blood osmolarity is around 300mOsmol/L.• Infusion of solutions with different osmolarity with the bloodstream will result in shifting of the fluids between blood cells and the serum. 17
  18. 18. Osmolarity and Tonicity• Tonicity is the term used for osmolarity when it is used in the context of body fluids. Anas Bahnnassi PhD RPh• Accordingly solutions can be: – Hypotonic – Isotonic – Hypertonic 18
  19. 19. • Step 1: Write your units ������������������������������������ ������• Step 2: Line up available data: Example Anas Bahnnassi PhD RPh 5������ ������������������������������������������������ – D5W= ������������ 180������������ ������������������������������������������������ – ������������: ������������������������������ ������������������������������������ – Osmolarity: ������������������������������• Step 3: Perform calculations: ������������������������������������ ������������������������������������������������������ – =27.8mOsmol/dL ������������������������������������������������ = ������������������������������ ������ – Isotonic 19
  20. 20. Osmolarity and Tonicity• To ensure isotonicity we need to equate everything administered to NaCl solution. Anas Bahnnassi PhD RPh• Considerations: – Amount of drug in solution – NaCl equivalent of the drug (E). – NaCl concentration nearest to blood concentration: Normal Saline 0.9%NaCl. 20
  21. 21. How to determine (E)?• The best way to examine the difference between the freezing point of the drug and NaCl. (both are driven by the number of particles) Anas Bahnnassi PhD RPh• We do not have the equipment or the time to calculate.• Use Remington’s: The Science and Practice of Pharmacy ������������.������ ������.������ • ������ = ������������ ������ 21
  22. 22. 22 Anas Bahnnassi PhD RPh
  23. 23. Example Anas Bahnnassi PhD RPh = 0.34 which means that:1 g of Silver Nitrate is equal to 0.34g of NaCl 23
  24. 24. Once you know the amount of drug, its E-value, the volume you need to make,1. Calculate total amount of NaCl needed for the product. (multiply NS concentration by the desired volume) Anas Bahnnassi PhD RPh2. Multiply total drug amount in g by (E).3. Subtract 2 from 1. to determine the amount of NaCl to be added.4. Complete calculations to determine the amount of other drugs ingredients that needed to be added. 24
  25. 25. Example• Find the quantity of NaCl required to be added to the following compounded prescription Anas Bahnnassi PhD RPh• NaCl equivalent of Chlorbutanol is 0.18 Amount of NaCl to render the total ������.������ volume isotonic: × ������������ =0.45g ������������������ Amount of NaCl represented by Chlorbutanol: 0.5 X 0.18= 0.09g Amount need to be added of NaCl to render it isotonic: 0.45-0.09=0.36g 25
  26. 26. Example• E values: – Chlorbutanol: 0.18 – Zinc Sulfate: 0.15 Anas Bahnnassi PhD RPh – Boric Acid: 0.52• Solution: – Amount of NaCl to render the total volume isotonic: 0.9 × 30 = 0.27������ 100 – Chlorbutanol: 0.1×0.18= 0.018������ – Zinc Sulfate: 0.05×0.15 = 0.0075������ – Amount of NaCl to be added: 0.27-(0.018+0.0075)=0.245������ – Amount of Boric Acid: ������ = 0.47������ 26
  27. 27. Homework • The prescriber orders tobramycin 1% ophthalmic solution, 10ml. • You have sterile preservative free tobramycin stock Anas Bahnnassi PhD RPh solution with a concentration of 40mg/ml, as well as NaCl in crystalline form. • Tobramycin MW=468 • E=0.07 • What is the amount of NaCl need to be added to turn the solution isotonic • What is the amount of tobramycin stock solution needed to be added.Answers need to be submitted by email or paper no longer than next week 27
  28. 28. Diluting and Concentration• The algebraic method: – CL: Concentration of the initial commercial Anas Bahnnassi PhD RPh product (the product with the smallest concentration). – VF: The desired final volume of the product. – CH: Concentration of stock solution. – X: Volume of stock solution that is needed to be added. – CF: Concentration of the final desired pharmaceutical preparation. 28
  29. 29. Diluting and Concentration• The algebraic method: – We need to start with initial concentration CL, Anas Bahnnassi PhD RPh remove part of it VF-X, replace the removed part with the same amount of the stock solution CHX, then we will have the correct volume VF of the desired final concentration CF. (������������ − ������������ ) ������ = ������������ (������������ − ������������ ) 29
  30. 30. This equation will work for all situations where you desireExample to dilute or concentrate a product and end up with the same amount or volume at which you started.• A prescription for Hyrdrocortisone2% Anas Bahnnassi PhD RPh cream 30g.• In the pharmacy we have a tube of (������������ − ������������ ) ������ = ������������ Hydrocortisone1% (������������ − ������������ ) cream 30g, and a tube (1% − 2%) of Hydrocortisone2.5% ������ = 30 = 20g (1% − 2.5%) cream 30g. 20g of H-sone 2.5% +10g of H-sone 1% We have 30g of Hydrocortisone2% 30
  31. 31. Homework • Solve the previous problem if the prescriber is asking for a total quantity of 50g: Anas Bahnnassi PhD RPhAnswers need to be submitted by email or paper no longer than next week 31
  32. 32. Reconstitution Calculations Assuming that the dry powder volume does not contribute to the final volume, how many mls of the reconstituted Anas Bahnnassi PhD RPh solution must be used to obtain the 600,000IU of Penicillin G Na from original concentration of 1,000,000IU/5ml 1 × 106 6 × 105 = 5������������ ������ ������������ ������ = 3������������ 32
  33. 33. Milliequivalent Calculations Anas Bahnnassi PhD RPh 33
  34. 34. How many milliequivalents of Ca Example Anas Bahnnassi PhD RPh ions are in a solutioncontaining 40mg/100mL 34
  35. 35. Injectable Medicines• Intravenous infusion flow rate: – Drop factor: drops per milliliter. Anas Bahnnassi PhD RPh – Number of drops per minute can be calculated: ������������������ ������������ ������ℎ������ ������������������������������������������������ ������������ ������������ ������������������������������������������ ������ ������������������������ ������������������������������������ – gtt/min = ℎ������������������������ ������������ ������������������������������������������������������������������������������������ ������ 60 min(1ℎ������) – The above formula can be simplified to: ������������ R= rate of iv infusion (gtt/min) ������ = V= Total volume to be infused (ml) ������ D= drop factor (gtt/ml) T= total time of infusion (min) 35
  36. 36. Example• iv solution (1000ml) was Solution: started 8:00AM was scheduled to run for Anas Bahnnassi PhD RPh 12hrs. • Fluid remaining= 800ml• At 3:00PM it was found • Time remaining= 5hrs or that 800ml remained. 5X60 = 300 mins• At what rate should the remaining fluid be • Number of drops per regulated to complete min= the administration in the ������������������������������������ = ������������������������������/������������������ scheduled time. ������������������������• The iv settings is set to deliver 15 drops/ml. 36
  37. 37. Example• If 800ml are infused • If 15 drops are in 300min? contained in 1ml Anas Bahnnassi PhD RPh how many drops are contained in 2.67ml? ������������������������������ ������ ������������ = ������������ ������������������ ������ ������������������ ������������������������������������ ������ ������������������ = ������ ������������ ������. ������������ ������������ → ������ = ������. ������������������������ → ������ = ������������ ������������������ 37
  38. 38. Insulin DosageTypes of Insulin Syringes Anas Bahnnassi PhD RPhThe strength of insulin is measured by units of activity/mlSyringes are calibrated according to the strength of insulin used 38
  39. 39. Example:• A patient is required to Solution: take 10 units of U-40 • U-40 insulin contains isophane insulin and 100 40 units /ml. Anas Bahnnassi PhD RPh units of U-100 protamine • U-100 insulin contains zinc insulin. 100 units/ml.• What volume (ml) of each type of insulin is  ������������ ������������������������������ = ������������ ������������������������������ needed to provide the ������ ������������ ������ ������������ required dose? ������������−������������ = ������. ������������������������ ������������ ������ − ������������ ������������������ ������������������������������  ������ ������������ ������������−������������������ = ������������������ ������������ ������ − ������������������ 39
  40. 40. Heparin Dosage• The normal adult heparinizing dose is 20,000 to 40,000 units in 24 hrs. Anas Bahnnassi PhD RPh• Heparin is usually ordered in units per hour.• It can also be ordered to be infused at specific infusion rate of ml per hr. 40
  41. 41. Example• A heparin dose of • Solution: 120units/hr/kg is ������������������ ������������������������������ ������ ������������������������������ • = Anas Bahnnassi PhD RPh ordered for a patient ������.������ ������������ ������������������ ������������ undergoing surgery.• How many mls of an ������ = ������������, ������������������ ������������������������������ injection containing ������������������������ ������������������������������ ������������,������������������ ������������������������������ • = 5,000units/ml should ������ ������������ ������ ������������ be administered to the 220lb patient? ������ = ������. ������������������ 41
  42. 42. Hospital PharmacyAnas Bahnassi PhD RPh Anas Bahnnassi PhD RPh abahnassi@gmail.com http://www.linkedin.com/in/abahnassi http://www.slideshare.net/abahnassi http://bahnassi.coursesites.com http://twitter.com/abahnassi attribution – non-commercial – share alike

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