Drug Preparation & Calculation PDF

DRUG PREPARATION & CALCULATION Converting from One System of Measurement to Another  IMPORTANT TERMS Household System (English System): – designed so that dosage can be measured at home using ordinary containers. E.g. cups, teaspoon, tablespoon, feet, pound and pint...

DRUG PREPARATION & CALCULATION Converting from One System of Measurement to Another  IMPORTANT TERMS Household System (English System): – designed so that dosage can be measured at home using ordinary containers. E.g. cups, teaspoon, tablespoon, feet, pound and pint Metric System (SI): – easiest to use of all systems of measurement, also known International System of Units. E.g. cm, kg, ml, L Approximate Equivalent Between Metric and Household Units  Metric Conversions Weight: – From heavier units to small units multiplied by 1,000 Kg g mg mcg Kg to g = 1kg x 1000 = 1000 g G to mg = 1 g x 1000 = 1000 mg Mg to mcg = 1 mg x 1000 = 1000 mcg – From smaller units to heavier units divide by 1000  Metric Conversions Volume – Liters (L) milliliters (ml) 1L = 1000 ml – From heavier units to smaller units multiplied by 1000 – From smaller units to heavier units divide by 1000  Exercises 1: 1.) ____ ml = 2 teaspoon 2.) ____ tablespoon = ____ ml = 3 teaspoon 3.) ____ ounce = ____ teaspoon = 2 tablespoon 4.) _____ cup = _____ tablespoon = 8 ounce 5.) _____ pint = _____ ounce = 2 cups 6.) 250 lbs = _____ kg 7.) 1,200 mcg = ______ gram 8.) 2.5 kg = _____ gram = _____ mcg  Adam is 6 feet 3 inches tall. What is his height in centimeters? 6 ft 3 in means 6ft + 3in 1 ft= 12in = 6 X12 = 72in So, 72+3= 75 in 2.5 cm = 1 in = 2.5 X 75 = 187.5 cm  A medication cup contains 22.5 ml of solution. How many tablespoons are in the medication cup? 1 Tablespoon = 15 ml 22.5÷ 15 = 1.5 T Answer is 1.5 T  An obese patient weighs 355 pounds (Ibs) will receive medications base on his weight in kilograms. Find his weight in kg. Answer is 161.36 kg Because 1kg= 2.2 Lb 335 ÷ 2.2 = 161.36 kg  Oral Medications Forms: Solid form (mg) - tablets, capsules Liquid form (ml) - syrup  Very Important Formulas What you want X Quantity it comes in What you have Required Dose X Stock volume Available Dose  Example A doctor prescribed for Zoloft 50 mg PO bid. The tablet available is in 25 mg. Determine how many tablets you will give to the patient? Answer is 2 tablets Because 1 tab = 25mg  Example The physician orders Furosemide oral solution 50 mg. Available concentration is 10mg per ml. Determine the dosage in ml? required dose X stock volume available dose 50 X 1 = 5 ml 10  Example Doctor ordered 1 gram Adol (Paracetamol) tablet to the patient. Available dose is 500 mg. per tab. How many tablets will you give to the patient? Answer is 2 tablets  The doctor ordered Cemetidine (Tagamet) 0.2 g PO q.i.d. Available form is in 400mg each tablet. How many tablets should you give to the patient? Answer ½ tablet Change g to mg-------- 0.2X1000=200mg Required dose= required dose X stock volume stock dose =200 X 1 = 0.5 400  Strength of Solutions as Ratios, Fractions and Percent Example: Epinephrine – 1:1 (ratio) Enfamil – ½ strength (fraction) – Strength = Solute/Solution IV – 0.9% NaCl (percentage)  Example Fill in the missing strength The solution contains: The Strength of a Solution is Ratio Fraction Percent 1 part solute in 2 parts solution 1:2 1/2 50% 1:4 1/5 3% 5% 2/5 1 part solute in 1,000 parts solution  Example 1. There are 70g of a drug dissolved in 140ml of a solution. What is the strength of this solution expressed as fraction, ratio and a percent? 2. Suppose 40mL of an iodine solution contains 10mL pure iodine. Express the strength of this solution as a ratio, a fraction and a percentage. 3. Verify if two strengths 2mg/mL (.2%) is equal. 4. How many grams of sodium chloride are contained in 2L of a 4% sodium chloride solution?  IV infusions Two Types of Infusion Rate Calculations: 1. drops/min: – when infusions are given under gravity as with fluid replacement. 2. mL/hour: – when infusions have to be given accurately or in small volumes using infusion or syringe pumps – particularly if drugs have to be given as infusions  Giving sets There are two giving sets: The standard or macrodrops set (SGS) has a drip rate of 20 drops per mL for clear fluids (i.e. sodium chloride, glucose) and 15 drops per mL for blood. The micro-drop set or burette has a drip rate of 60 drops per mL. In all drip rate calculations, always remember that it is simply converting a volume to drops (or vice versa) and hours to minutes. Infusion Set  Infusion Sets Macro-drop Set Micro-drop Set Infusion Pump Syringe Pump  Flow Rates Flow rate = Volume Time Example: Normal saline 1000ml continuous IV for 24 hour. Find the pump setting in ml per hr. Flow rate= volume = 1000 = 41.67 ml/h time 24 42ml/hr  Finding the Volume Infused Lactated Ringer’s at 167 ml/h IV for 6 h. How much milliliters will the patient receive in 6 hours. Flow rate = volume time 167ml/hr = volume (?) 6hr Volume = 167 x 6 = 1002 ml  Finding Duration of an Infusion Order: ½ NS 500 ml IV at 125ml/h. How long will this infusion take? Flow rate = volume time 125 = 500 time (?) Time = 500 ml = 4 hr 125ml/hr  Exercise: 800 ml of dextrose Saline is to be administered IV. The fluid is running at 70 ml/hour for the first 5 hours. And then the rate reduced to 60 ml/hour. Calculate the total duration of the infusion.  Solution: Volume infused in the first 5 hours = 5X 70= 350 ml Remaining fluid= 800- 350 = 450 ml Flow rate = volume time 60 ml/hr = 450 ml time Time = 450 ml = 7.5 hours 60ml/hr Total time of infusion = 5+ 7.5 = 12.5 hours