DRUG DOSAGE BASED ON AGE • Neonate have immature renal and hepatic functions, while elderly in addition to diminished organ function, they frequently have concomitant pathologies, so age must be taken in consideration when determining the drug dosage. • In the past There were different rules used to calculate child dose but today these rules are no longer in use because age alone cannot provide an accurate valid dose. • Currently age is conjugated with another factor, such as weight. to determine the dosage of a potent therapeutic agents. DRUG DOSAGE BASED ON BODY WEIGHT • The usual doses generally suitable to the majority of individuals. • Some times the dose is expressed as a specific quantity of drug per unit weight, (eg. mg/kg). Patient’s dose (mg) = patient’s weight (kg) x drug dose (mg) 1 (kg) DRUG DOSAGE BASED ON BODY WEIGHT • Example: the usual initial dose of chlorambucil is 150 mcg/kg of body weight. How many milligrams should be administered to a person weighing 154 lb? 150 mcg = 0.15 mg 154 lb = 70 kg Patient’s dose (mg) = 70 x 0.15 = 10.5 mg. DRUG DOSAGE BASED ON BODY SURFACE AREA • Calculating dose based on body surface area (BSA) widley used for pediatric patient and chemotherapy. • Dosing tables may be provided with certain drugs to determine the dose based on the patient’s body surface area. • To calculate BSA we use standard nomogram, which includes both weight and hight or the following equition can be used: 2 = . ℎℎ × . ℎ () 3600 DRUG DOSAGE BASED ON BODY SURFACE AREA To calculate the dose based on BSA we use the following equation: = ( ) × . () DRUG DOSAGE BASED ON BODY SURFACE AREA Example if the usual adult dose of a drug is 120 mg, what would be the dose based on BSA for a person measuring 6 ft tall and weighing 200 lb? BSA fro nomogram = 2.13 m2 2.13 m2/ 1.73m2 X 120 mg = 147.75 mg PRACTICE PROBLEMS 1. How many erythromycin capsules, each containing 250 mg of erythromycin, are needed to provide 25mg/k per day for 1 week for a person weighing 154 lb? 2. If adult dose of drug is 100 mg, what would be the dose for a child with a body surface area of 0.7 m2? 3. How many milliliters of an injection containing 1mg of drug per milliliters of injection should be administered to 6-month-old child weighing 16 lb. to achieve subcutaneous dose of 0.01 mg/kg? 4. If the dose of TAXOL in treatment of metastatic overain cancer is 135 mg/m2 , what would be the dose for a patient 155 cm tall and weighing 53 kg? PRACTICE PROBLEMS 5. Rx Erythromycin Ethylsuccinate 400mg/5mL Disp. 100 mL Sig. _______ tsp. q.i.d. untill all medication is taken. If the dose of Erythromycin Ethylsuccinate is given as 40 mg/kg/day. a) What would be the proper dose of the medication in the Signa if the prescription is for a 44-lb child? b) How many days will the prescription last? 6. If the pediatric dose of dictinomycin is 15mcg/kg/day for 5 days, how many micrograms should be administered to 40-lb child over the course of treatment? 7. Using the equation to calculate body surface area, determine the BSA in square meter for an adolescent patient measuring 4 ft. 2 in. and weighing 90 lb? PRACTICE PROBLEMS 8. The pediatric dose of cefadroxil is 30 mg/kg/day. If a child was given a daily dose of 2 teaspoonfuls of pediatric suspension containing 125 mg of cefadroxil per 5 mL, what was the weight in pounds, of the child? 9. Calculate the dose for a child 4 years of age, 39 in. in hieght, and weighing 32 lbs. for a drug with an adult dose of 100 mg using the BSA equation. 10. The dose of mitomycin injection is 20 mg/m2 per day. Determine the daily dose for a patient who weighs 144 lb. and measures 68 in. in hight? HOME WORK 1. If the recommended dose of tobramycin for premature infant is 6 mg/kg/day divided into three equal doses administered every 8 hrs, how many milligrams of the drug should be given every 8 hours to 2.2 lb infant. 2. The drug carboplatin for ovarian carcinoma is administered intravenously at dose 400 mg/m2 except in patient with impaired kidney function, in with case the dose is reduced by 30 %. How many milligrams of the drug should be administered to renally impaired patient measuring 5 ft. 2 in. and weighing 110 lb?