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

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

Disposable syringes or cartridges

Calculate doseMay need to discard remainder to prepare dose

E.g. diazepam 5 mg IM Available 2 ml disposable syringe

labeled 5 mg/ml

Parenteral drugs in single or multi-dose ampules and vials

Calculate dose if different from labelDetermine amt to be administeredWithdraw desired amt from ampule or vialE.g. chlorpromazine 12.5 mg IM Available chlorpromazine 25 mg/ml in

1 ml ampule

Note

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

example

Chlorpromazine 10 mg IMAvailable 25 mg/ml

Answer is 2/5 X 15 minims = 6 minims (also 0.4 cc)

WARNING

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

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!

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 amtsAmt of IV may involve 50 ml or more

Add to label when reconstituted

Amt of diluent addedConcentration of dose of drug in ml e.g 500 mg/ml Date of reconstitutionExp date.

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 lightAntibioticssteroids

example

cephalothin (Keflin) 500 mg q6h IMAvailable multi-dose vial containing 3 g of powder.Prepare to 500 mg = 1 mlConvert g to mgSet up ratio:proportion or D/A

Give cephalosporin 200 mg/1 ml

Available: 1 g vial powderAmt of diluent to add?Add enough diluent so sode ordered may be given in no more than 0.5 to 1 ml

problems

See handouts

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)

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.

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

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 insulinDraw up 30 units NPH insulin to equal 50 U in syringe.

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

calculation

D= 80 U 64A = 100 U X 16 = 5 = 12.8

minims

NOTE: You MUST use 16 – not 15- minims/ml for very accurate calculations.

Intravenous infusions

Drug ordered to add to an intravenous IV fluidAmt of fluid to be adm over a specific period of time: E.g. 125 ml / h

Determine IV flow rate: drop factor

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: