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Calculation of parenteral dosages of medication

Calculation of parenteral dosages of medication. Parenteral doses must be in liquid form for injection. Parenteral available as:. Liquids in prefilled disposable cartridges or disposable syringes with specific amt of drug in specific volume. Meperidine 50 mg/ml or 100 mg

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Calculation of parenteral dosages of medication

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  1. Calculation of parenteral dosages of medication Parenteral doses must be in liquid form for injection

  2. Parenteral available as: • Liquids in prefilled disposable cartridges or disposable syringes with specific amt of drug in specific volume. • Meperidine 50 mg/ml or 100 mg • Single/ multi dose ampules or vials containing specific amt of liquid form of drug in specific volume • Epinephrine [Adrenalin] 1:1000 in 0.1 ml • Ampules or vials containing powder or crystals which must be reconstituted

  3. Disposable syringes or cartridges • Calculate dose • May need to discard remainder to prepare dose • E.g. diazepam 5 mg IM • Available 2 ml disposable syringe labeled 5 mg/ml

  4. Parenteral drugs in single or multi-dose ampules and vials • Calculate dose if different from label • Determine amt to be administered • Withdraw desired amt from ampule or vial • E.g. chlorpromazine 12.5 mg IM • Available chlorpromazine 25 mg/ml in 1 ml ampule

  5. Note • Amt in any multidose vial is not entered into the equation • Enter as the quantity Q the amt available contained in a specific volume • When dose is less than 1 ml, may need to convert to answer to minims using 15 or 16 minims/ml.

  6. example • Chlorpromazine 10 mg IM • Available 25 mg/ml • Answer is 2/5 X 15 minims = 6 minims • (also 0.4 cc)

  7. WARNING • Always check drug labels carefully. • Some may be labeled differently from others of same medication. • Narcan • Epinephrine • 2 ml amp labeled 0.25 mg/2 ml • 2 ml amp labeled 5 mg/1 ml

  8. Parenteral drugs in dry form • Available in dry or crystal form and must reconstitute or make into liquid form to be removed and administered. • Usual directions: • Name of solution to be used (sterile water or normal saline for injection) • Amt of diluent • ALWAYS check label carefully for instructions!

  9. Methicillin sodium: • Reconstitute 1 g vial add 1.5 ml of sterile water for injection of sodium chloride for injection. Each reconstituted ml contains approx 500 mg of methicillin. • Amt for IM, ID or SC involve very sm amts • Amt of IV may involve 50 ml or more

  10. Add to label when reconstituted • Amt of diluent added • Concentration of dose of drug in ml e.g 500 mg/ml • Date of reconstitution • Exp date.

  11. Handling solutions: • Chemicals may be fragile: • Affected by heat, light and time • Change or deteriorate • Reason why manufactured as powder • Reconstitute and use within few hrs and protect from light • Antibiotics • steroids

  12. example • cephalothin (Keflin) 500 mg q6h IM • Available multi-dose vial containing 3 g of powder. • Prepare to 500 mg = 1 ml • Convert g to mg • Set up ratio:proportion or D/A

  13. Give cephalosporin 200 mg/1 ml • Available: 1 g vial powder • Amt of diluent to add? • Add enough diluent so sode ordered may be given in no more than 0.5 to 1 ml

  14. problems • See handouts

  15. Insulin • Parenteral medication replacing insulin not produced by pt. • Calculating and preparing insulin dosage unique: 1. Standardized measure: unit • Available in 10 ml vials in two strengths (concentrations): • U-100 = 100 units per 1 ml solution • U-500 = 500 units per 1 ml solution (rarely used)

  16. Insulin • 2. Should be drawn up in special insulin syringe calibrated in units. • If insulin syringe not available may use TB syringe calibrated in minims • 3. Insulin order, insulin bottle, insulin drawn up should ALWAYS be rechecked by another nurse for accuracy.

  17. Insulin • When two different types of insulin ordered, give both at same time in same syringe. • Short-acting (regular) • Intermediate or longer-acting (NPH or zinc) • Dray up regular insulin first, then longer acting type. • Give both in same syringe

  18. Insulin example • Order: 20 units regular (Iletin) insulin U-100 and 30 u NPH U-100 before breakfast. • Prepare: use a U-100 syringe for total of 50 units. • Draw up 20 units regular insulin • Draw up 30 units NPH insulin to equal 50 U in syringe.

  19. To use a TB syringe for insulin • Calculate number of minims: Insulin desired insulin available X 16 minims= number of minims to administer E.g. 80 U regular U-100 insulin

  20. calculation D= 80 U64 A = 100 U X 16 = 5 = 12.8 minims NOTE: You MUST use 16 – not 15- minims/ml for very accurate calculations.

  21. Intravenous infusions • Drug ordered to add to an intravenous IV fluid • Amt of fluid to be adm over a specific period of time: • E.g. 125 ml / h • Determine IV flow rate: drop factor

  22. Drop factor • Drop factor ( number of drops/ml) given on pkg containing drip chamber and IV tubing • Use one of three methods for determining IV infusion rate:

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