Drug Dosage Calculation PDF

# Drug Dosage Calculation ## Terms & Terminology * **FLOW RATE:** is the volume per unit time usually expressed as ml/hr. Can be ml/min or ml/sec * **DRIP RATE:** is the number of drops per unit time usually expressed as drops/min(dpm) * **DOSE:** amount of drug per unit time given to the patient...

# Drug Dosage Calculation ## Terms & Terminology * **FLOW RATE:** is the volume per unit time usually expressed as ml/hr. Can be ml/min or ml/sec * **DRIP RATE:** is the number of drops per unit time usually expressed as drops/min(dpm) * **DOSE:** amount of drug per unit time given to the patient expressed as mg/min, g/hr or IU/min * **CONCENTRATION:** amount of the drug in a given volume usually expressed as mg/ml, g/l or mIU/ml * **DROP FACTOR:** is the number of drops per unit volume. Expressed as drops/ml * **TITRATION:** adjustment of the IV medication dosage within prescribed parameters to achieve a desired effect. ## Key Considerations * **Nurses must know generic and trade names of drugs to be administered, classification, average dose, route of administration, use, side and adverse effects, contraindications, and nursing implications in administration.** * **Essential parts of Medication order.** * **Abbreviations and symbols used in writing medication order as per hospital policies.** * **Preparation of solutions and fractional doses** * **Storing of medicines** * **Factors of safety in the administration of medicines** * **Rules for the administration of medicines** * **Ethical and legal aspects** * **Nurse's role in the administration of medicines.** ## Side and Adverse Effects **Side effects are non-therapeutic reactions to a drug.** * **Unintended secondary effects a medication predictably will cause** * **May be harmless or serious** * **If side effects are serious enough to negate the beneficial effect of meds therapeutic action, it may be discontinued** * **People may stop taking medications because of the side effects (An example of side effect is Drowsiness, which occurs with antihistamines)** * **Adverse Drug Reaction:** Any reaction to a drug that is undesirable, unexpected, and occurs at doses normally used for the prevention, diagnosis, or treatment of disease. * **All adverse medication reactions or suspected medication reactions are reported to the Physician, Nurse Manager/Charge Nurse and Pharmacist. An adverse reaction is reported to the Pharmacy by filling out the Adverse Drug Reaction Notification Form.** ## Pregnancy Category | Category | Description | |---|---| | Category A | Studies indicate no risk to the human fetus. | | Category B | Studies indicate no risk to animal fetus; information in humans is not available. | | Category C | Adverse effects reported in animal fetus; information in humans is not available. | | Category D | Possible fetal risk in humans reported; however, considering potential benefit vs. risk may, in selected cases, warrant the use of these drugs in pregnant women. | | Category X | Fetal abnormalities reported and positive evidence of fetal risk in humans is available from animal and/or human studies. These drugs should not be used in pregnant women. | ## Medication Safety Guidelines * **Medications are not given without physician's written orders.** * **Do not administer a drug about which any doubt exists, check further with the physician.** * **Labels must be clear if not return to pharmacy.** * **A nurse not to pour medication to one bottle to another, not to put a medicine back into bottle, Nurses are not authorized to re-label medication bottles, Medication which loses its label or which lacks a legible label shall be return to the pharmacy.** * **Nurse who administer the medications are responsible for their own action. Question any order that you considered incorrect (may be unclear or inappropriate)** * **Be knowledgeable about the medication that you administer** * **Keep the Narcotics in locked place.** * **Use only medications that are in clearly labeled containers.** * **Return liquid that are cloudy in color to the pharmacy** * **Before administering medication, identify the client correctly** * **The nurse who prepares the drug administers it. Only the nurse prepares the drug knows what the drug is. Do not accept endorsement of medication.** * **If the client vomits after taking the medication, report this to the nurse in-charge or physician.** * **Preoperative medications are usually discontinued during the postoperative period unless ordered to be continued.** * **When a medication is omitted for any reason, record the fact together with the reason.** * **When the medication error is made, report it immediately to the nurse in-charge or physician. To implement necessary measures immediately. This may prevent any adverse effects of the drug.** * **Each nurse should know the common dose, maximum dose, how to compute dosage if necessary.** * **Do not leave the medication at the bedside. Stay with the client until he takes the medications.** * **Prepare medications for one patient at a time.** * **Do not label the medicine by patient room number or bed number.** ## Patient & Family Education * **Name dose and action of the drug.** * **Time of administration** * **Special storage and preparation of the drug** * **Specific OTC drugs and alternate** * **Special comfort and safety reasons** * **Specific points about drug toxicity** * **Specific warning about drug discontinuation.** ## Unit Conversion **Mass:** * mcg → mg → g→ kg (÷by 1,000) * mcg ← mgg kg (x by 1,000) * lb → kg (+ by 2.2) * lb + kg (x by 2.2) **Volume:** * mcL → ML → L → KL (÷by 1,000) * mcL + ML + L + KL (x by 1,000) **Time:** * min → hr (÷by 60) * min ← hr (x by 60) **Example 1:** Convert 5,000 mcg to mg. mcg → mg → g→ kg (÷by 1,000) 5,000 mcg ÷ 1,000 = 5 mg **Example 2:** Convert 44 lb to kg. lb → kg (÷by 2.2) 44 lb + 2.2 = 20 kg **Example 3:** Convert 0.003 L to mcL. mcL ← mL + L + KL (x by 1,000) 0.003 L x 1,000 = 3 mL 3 mL x 1,000 = 3,000 mcL **Example 4:** Convert 5 hours to minutes. min - hr (x by 60) 5 hr x 60 = 300 min ## Dosage Calculation Conversions * 1 mg = 1000 mcg * 1 gm (g) = 1000 mg * 1 L = 1000 mL * 1 mL = 1 cc * 5 mL = 1 Tsp * 3 Tsp = 1 Tbsp * 15 mL = 1 Tbsp * 30 mL = 1 oz * 1 oz = 2 Tbsp * 8 oz = 1 cup * 1 kg = 1000 gm (g) * 1 kg = 2.2 lbs ## Calculation Methods * **Various methods are used for solving medication calculation** * **The most common methods are:** * Formula, * Proportion * Dimensional Analysis * **No one method is best for solving every type of problem. Several good approaches are available, however and one of the best is dimensional analysis** * **Rule #1 in drug calculations - STICK TO ONE METHOD!** ## Recommended Volume for Administration Per Sites: * **Intradermal = 0.1 - 0.5 ml (allergy testing)** * **Subcutaneous injection = 0.5 - 1.0 ml per site** * **Intramuscular injection = 2.5 - 3.0 ml per site (1 ml in the deltoid)** * **IV injection (IV push) = 1 – 60 ml** ## Universal Formula for Drug Dosage Calculation (Toney-Butler, 2021) In the universal formula (or “desired over have method"), the desired amount (D) is the dose prescribed and the amount on hand (H) or the amount you "have" is the available dose or concentration. The quantity (Q) is the form and amount in which the drug is supplied (i.e. tablet, capsule, liquid). To calculate the dose, take the desired amount and divide it by the amount on hand, then multiply it by the quantity, like this: **UNIVERSAL FORMULA** D (desired amount) x Q (quantity) = Dose H (amount on hand) ## Calculating Tablet Dosages * In calculating tablet dosages, the following formula is useful Desired dosage Number of tablets = stock strength **Example:** Orders 1,500 mg of calcium carbonate for the patient. The drug is available in 250 mg tablets. How many tablets should be given to the patient? Number of tablets = 1500 mg 250 mg = 6 tablets ## Calculating Mixtures And Solutions The following formula is useful in calculating mixtures and solutions: Amount of solution to be given= Desired dosage stock strength 2 X Stock volume **The orders 375 mg of cefuroxime for the patient. The drug is available in 750 mg vial. You plan to dilute it in 10 mL of sterile water. How much should you give to your patient?** Amount of solution to be given = 375 mg 750 mg x 10 ml = 0.5 mg x 10 ml = 5 ml ## Calculate IV Rate - mL per hour and minute * It is easy to calculate the running rate of IV fluids in terms of mL per hour or mL per minute: * ML per hour or minute = Total IV Volume Time (Hour or Minute) * Start venoclysis with D5 0.9 NaCl 1 L to be infused for 16 hours. How many mL of the IV fluid should you infuse per hour? * 1 L ÷ 16 hours = mL per hour [1 L x 1,000] = 62.5 mL per hour 16 hours ## Calculate IV Rate - drops per minute * Calculating for drops per minute is simple with the following formula: - Drops Per Minute = _Total IV Volume_ x Drop Factor Time (Minute) **Example:** * The physician orders to start venoclysis with D5 0.3 NaCl 1 L solution. The IV fluid will be infused for 14 hours and the drop factor of the macrodrip used is 20. It should be regulated to how many drops per minute? - Drops Per Minute = [1 L x 1,000] [14 hours x 60] X 20 - [1,000 mL ÷ 840 minutes] x 20 = drops per minute - 1.19 x 20 = 23 to 24 drops per minute ## Fried's Rule Fried's rule: for infants younger than 1 year: Upto 2 years of Age Child's age (in months) Average adult weight (150 lb) x adult dose **Example:** Calculate the child dose for a 2-year-old baby, where the adult dose of the medicine is 500 mg. Given: Age of child(months) = 24 (2 years baby) Average adult dose = 500 mg TO find; child's dose Solution: Using with the formula we get Child's dose = age of child (months) x _average adult dose 150 24 -×500 mg = 80 mg 150 ## Young's Rule Young's rule: for children older than 1 year Child's age (in years) Child's age (years) + 12 x adult dose **Example:** A 10-year-old girl was prescribed paracetamol( 500 mg as average adult dose). Calculate the child dose Given: Age of child = 10 years, Avg adult dose: 500 mg To find; child dose Solution: child dose = Age of child x Average adult dose Age of child + 12 10 x 500 mg 10+12 10 X 500 mg = (0.45) x 500 mg = 225 mg 22 ## Clark's Rule Clark's rule: based on weight of child, which is much more accurate than either Young's or Fried's rules Child's weight (lb) Average adult's weight (150 lb) × adult dose **CLARK'S RULE USE WEIGHT IN POUNDS, NEVER IN KILOGRAMS** **Example:** Consider a 10-year-old girl/ 60 lb (pounds) prescribed Amoxicillin 500 mg adult dose. Calculate child dose Given: Weight of the child = 60 lbs, Adult dose = 500 mg To find; child dose Solution: Child dose = weight of child (lbs) x Adult dose Avg adult weight (150 lbs) 60 x 500 mg = 200 mg 150 ## Drug Calculation When Dose is Known to Find Amount in Milliliters **For vial:** what we want Amount = X No. of divisions in syringe what we have **Example:** A 5-year-old pre-schooler was prescribed 20 mg of Pantoprazole. Calculate the amount to be administered from the vial. Solution: What we want = 20 mg What we have = 40 mg Dilution = 40 mg Pantoprazole in 5 ml of sterile water Calculate the amount to be taken in ml to administer to child 20 x 5 40 = 0.5 x 5 = 2.5 ml **For syrup:** A 3-year-old toddler is prescribed 200 mg of paracetamol syrup. Calculate the dose on ML What we want = 200 mg What we have = 250 mg (available in bottle) Dilution = 250 mg in 5 ml 200 = x 5 250 = 0.8 x 5 = 4 ml ## When Amount is Prescribed and Dose to be Found Out Dose available in bottle Dose per 1 ml = x dose to be administered Rate of dilution **Example:** A 3-year-old toddler is prescribed to be administered 2 ml of Paracetamol syrup. Calculate the dose in milligrams. Solution: What we want = 2 ml What we have =m 5 ml contains 250 mg in a bottle Dose == 250 x 2 5 = 50 mg x 2 = 100 mg ## Calculating Pediatric IV Solutions No. of drops/ min = Amount of fluid in (ml) x drop factor to be given in 24 Hrs No. Of hours x 60 Drop factor = 60 (micro drip) and 15 (macro drip) **Example** Normal saline (500 ml) in 4 Hours 500 x 60 4 x 60 = 125 drops / min