Focus on PHARMACOLOGY ESSENTIALS FOR HEALTH PROFESSIONALS CHAPTER

Focus on PHARMACOLOGY ESSENTIALS FOR HEALTH PROFESSIONALS CHAPTER 7 Adult and Pediatric Dosage Calculations

Accuracy in Drug Calculations • Accurately calculating drug dosages is an essential skill in health care. • Serious harm to a patient may occur from a mathematical error during dosage calculation. • Health-care professionals who administer drugs must follow medical orders precisely and efficiently. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Background • Dose: amount of drug taken by patient for intended therapeutic effect • Dosage regimen: schedule of taking drug dose • Most drug doses are measured in units of weight (e. g. , 500 mg). • Many drug doses are general, not patient specific. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Dosage Calculation Terms • Desired dose: amount to be administered at one time • Amount to administer: volume containing desired dose • Dosage ordered: total amount of ordered drug and its frequency of administration Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Dosage Calculation Terms • Dosage unit: volume of medication containing quantity of drug as listed on drug label • Dose on hand: amount of drug in dosage unit • Dosage strength: dose on hand per dosage unit Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Calculating Dosages • First step: make sure the strength of drug ordered and the strength of drug available are in same unit of measure • If necessary, convert to a single unit. • Then, use formula: D/H × Q = X, which can also be expressed as D × Q/H = X Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Using the Formula • D/H × Q = X – Divide D (desired dosage) by H (dose on hand or dosage of drug available). – Then multiply by Q (number of tablets, milliliters, etc. , that contains available dosage). – Equals X (amount to be administered) Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Ratio Formula of Dosage Calculation • Example: Amoxil 500 mg is ordered. It is supplied as 250 mg/5 m. L liquid. – 250 mg ÷ 5 m. L = 500 mg ÷ X – In this example, X = 10 m. L (the dose ordered) Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Oral Dosages • Oral medications are either liquid or solid. • Tablets are most common solid oral medications. • Oral medications may be chewable, administered sublingually or buccally, swallowed, or dissolved in water. Check the label before administering. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Solid Medications • Scored (notched) tablets can be broken only along the line of scoring. • Unscored tablets must not be broken. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Calculating Solid Doses • Dose on hand (H) divided by dosage unit (Q) equals desired dose (D) divided by amount to administer (X). • H/Q = DX or D × Q/H = X, which can also be expressed as D/H × Q = X. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Zocor Calculations • Ordered: Zocor 40 mg bid • On hand: Zocor 20 mg tablets – D × Q/H = X – 40 × 1 tablet/20 mg = X – X = 2 tablets Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

(For educational purposes only) Figure 7 -1 Drug label for doxazosin mesylate. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Cardura Calculations 2 tablets = X Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

(For educational purposes only) Figure 7 -2 Drug label for amlodipine besylate. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Norvasc Calculations Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Liquid Medications • Liquid medications can be measured in small units of volume. • Examples of liquid drugs are: – Syrups – Spirits – Elixirs – Suspensions Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Measuring Liquid Doses • Liquids can be measured by: – Measuring cup: calibrated in fluidounces, fluidrams, milliliters, teaspoons, or tablespoons – Medicine dropper or oral syringe: calibrated in milliliters, minims, or drops – Calibrated spoon: calibrated in teaspoons and milliliters Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Calculating Liquid Doses • The physician orders 400 mg of the antibiotic cefdinir (Omnicef). How many milliliters will you administer? Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

(For educational purposes only) Figure 7 -3 Drug label for cefdinir. . Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Calculating Liquid Doses • Label on bottle indicates that 5 m. L contains 125 mg of cefdinir. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

(For educational purposes only) Figure 7 -4 Drug label for erythromycin ethylsuccinate. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Administering Medicine to Pediatric Patients • Dosage cups: for children who know how to drink from a cup • Syringes: for infants who cannot drink from a cup; can be squirted into back of mouth • Droppers: safe for infants; measure at eye level • Cylindrical dosing spoons: easily used by small children Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Smart Bottles for Elderly Patients • Bottles that release correct amount of medication dosages • Self-locking feature to prevent accidental overdose • System alerts pharmacist when medication supply is low Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Parenteral Medications • Injectable mixtures that contain drug dissolved in appropriate liquid • Prescribed in grams, milligrams, micrograms, grains, or units • Can be packaged as premixed solutions, or in powdered form that requires mixing with a solution Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Intradermal Injection • Usually used for skin testing to diagnose an allergy or for tuberculin test • Tuberculin syringe with a 25 -gauge needle • Site of injection: inner portion of forearm or upper back • A reddened or raised area within 48 to 72 hours indicates a positive reaction Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Subcutaneous Injection • Drugs that must be absorbed slowly are usually injected subcutaneously • Tuberculin syringe or a 3 -m. L syringe is used • Heparin is a drug commonly administered subcutaneously Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Insulin Injection • Injection sites usually rotated • May be administered subcutaneously, IV, or with insulin pump • Four types of insulin: – Quick-onset, short-duration – Intermediate-acting – Long-acting – Ultra-long-acting Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -5 Mixing regular and NPH (Neutral Protamine Hagedorn) insulins in one syringe. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -6 Insulin syringes: 100 unit (A), 50 unit (B), and 30 unit (C). Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -7 Tuberculin syringe. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -8 100 -unit insulin syringe. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -9 50 -Unit insulin syringe. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -10 30 -unit insulin syringe. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -11 A partially filled 50 -unit insulin syringe. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -12 A partially filled 100 -unit insulin syringe. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Preparing Insulin Injections • Use 30 -unit insulin syringe for insulin doses less than 30 units. • Use 50 -unit insulin syringe for insulin doses less than 50 units if standard 100 -unit syringe is not available. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Preparing Insulin Injections • To remove insulin from vial, first inject same quantity of air as ordered insulin volume • Then withdraw appropriate insulin • Two types of insulins can be combined in one syringe; draw up shorter-acting insulin first. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Safe Insulin Practices • Avoid keeping insulin on top of medication carts or counters because it can be confused with heparin. • If insulin concentration is not 100 units/m. L, apply bold warning labels. • Order insulin cartridges for outpatients to help ensure correct dispensing. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Heparin Calculation • Heparin is an anticoagulant that is measured in USP (United States Pharmacopeia) units. • It can be administered IV or subcutaneously. • The term units should always be written out, and the abbreviation U avoided. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Heparin Calculation • With a premixed parenteral solution of heparin, you have to convert the physician’s order to the volume of solution that contains the amount of heparin ordered. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Heparin Calculation • Ordered: heparin 5, 000 units subcutaneously q 8 h • On hand: heparin 10, 000 units/m. L • Convert units to milliliters: If 10, 000 units equal 1 m. L, then 5, 000 units equal 0. 5 m. L • 0. 5 m. L should be administered Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Intravenous Drugs • IV fluid therapy: to administer fluids containing water, dextrose, vitamins, electrolytes, and drugs • Medications for IV administration are usually available in small-volume vials. • Amount of drug can be listed in terms of concentration (5 mg/5 m. L) or as amount of drug in vial (80 mg in a 2 m. L vial). Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Dosage Calculation in Pediatrics • Dosages for infants and children are usually less than adult dosages for same medication. • Dosage calculations for pediatric patients must be precise. • The most accurate methods of determining appropriate pediatric doses are by weight and body area. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Drug Dosage Calculation by Body Surface Area • Body surface area (BSA) is determined by using a nomogram (a numerical relationship chart) and the child’s height and weight. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Figure 7 -13 Pediatric nomogram used for determining body surface area. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Calculating Drug Dose by BSA • First determine BSA using nomogram. Then use formula calculation: Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Calculating Ampicillin Dose • Child’s BSA is 0. 4 m 2; adult dose of ampicillin is 250 mg. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Pediatric Doses in Package Inserts • Drug data for pediatric doses are usually supplied in the drug’s package insert. • Pediatric dosages are often based on mg/kg, mcg/kg, or units/kg. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Finding Safe Pediatric Dosage • Ordered: amoxicillin 60 mg PO tid • On hand: 125 mg/5 m. L • Child weighs 12. 5 lb. First determine child’s weight in kilograms: – 12. 5 2. 2 = 5. 7 kg • Safe pediatric dosage is 20– 40 mg/kg/day in 3 equal doses. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Finding Safe Pediatric Dose • Find a range of lowest to highest safe dosages: – 20 mg × 5. 7 kg =114 mg/day; 40 mg × 5. 7 kg =228 mg/day • 60 mg PO tid = 180 mg/day, which falls in the safe range of 114 mg to 228 mg per day. • Ordered dose is safe for this child. Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Clark’s Rule • Clark’s rule: based on weight of child, which is much more accurate than either Young’s or Fried’s rules Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Young’s Rule • Young’s rule: for children older than 1 year Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini

Fried’s Rule • Fried’s rule: for infants younger than 1 year: Focus on Pharmacology: Essentials for Health Professionals , Second Edition Jahangir Moini