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Efficient Parenteral Medication Dosage Calculation Guide

Learn to calculate dosages of parenteral medications, including liquid forms and dry forms that require reconstitution. Discover how to prepare injections accurately and handle solutions properly. Detailed examples and warnings provided.

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Efficient Parenteral Medication Dosage Calculation Guide

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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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