Safe Drug Preparation

Two ways to calculate doses Basic Calculation & Ratio and Proportion Basic Calculation 1st Desired dose x quantity of on-hand dose on hand dose In short: D _____ X Q OH

Example 1 The physician orders aspirin gr 10 q4h PRN for fever over 101. On hand aspirin gr 5 tabs. Step one: check to see if all measures are in the same system. No conversion is necessary. Both measures are in grains Step two: use the formula 10 gr ___ x 1 tab = 10 divided by 5 = 2 5 gr 2 x 1 = 2 tabs

Example 2 Ampicillin 0.5g. The unit dose packet reads 250mg/cap Check to see if all measures are in the same system 1g = 1000mg 0.5g = 0.5 x 1000 = 500mg Then use the formula D 500mg ____ X Q or ____ X 1 cap = OH 250 Reduce fraction 500/250 = 50 divided by 25 = 2 2 X 1 = 2 caps

Example 3 Order: Versed 3 mg IM preoperatively. On hand are vials labled 5mg per ML Check to see if all measures are in the same system Use formula: 3mg _____ X 1ML = 3 divided by 5 = 0.6 5mg 0.6 X 1ml = 0.6 ml

Ratio Ratio describes a relationship between two numbers. Example: 1g : 15gr

Proportion A proportion consists of two ratios that are equal Example: 1g : 15gr = 2g : 30gr

Solving problems using ratio and proportion Known unit of measure : known equivalent = desired unit of measure : unknown equivalent Example: 1000 mg : 1 g = 500 mg : xg 1000 x = 500 = 500 divided by 1000 = 0.5 X = 0.5g

Example 1 using ratio and proportion Ordered: Demerol 60mg IM on call. The narcotics draw contains labled Demerol 100mg/2ml Verify measures are in same system Set up problem: Dose on hand : know quantity = dose desired : unknown quantity 100mg : 2ml = 60mg : X ml 100X = 120 = 120 divided by 100 = 1.2 X = 1.2ml

Pediatric and Infant doses Remember that 1lb = 2.2 kg (always divide # of lbs by 2.2) 33lbs = ? kg 24lbs = ? kg 66 lbs = ? kg Most orders for peds will read: give xmg/kg/24h

Peds example Give Demerol 6mg/kg/24h for pain in divided doses every six hours prn. Demerol is available 50mg/ml. How much Demerol would be appropriae for a 33lb child every 6 hours? 1st convert weight = 33 divided by 2.2 = 15kg Next get your daily dose 6mg x 15kg = 90mg in 24 hours Next calculate ml needed in 24 hours = Dose on hand : know quantity = dose desired : unknown quantity 50 mg : 1 ml = 90mg : X ml 50X = 90 = 90 divided by 50 = 1.8 X = 1.8ml in 24 hours Then calculate the ml per dose (every 6 hours) 24h : 1.8ml = 6h : xml 24X = 10.8 = 10.80 divided by 24 = 0.45 You will give 0.45ml every 6 hours