Pediatric Dosage Calculations

Pediatric Dosage Calculations Pediatric Dosage Calculations Most drugs in children are dosed according to body weight (mg/kg) or body surface area (BSA) (mg/m2). Care must be taken to properly convert body weight from pounds to kilograms (1 kg= 2.2 lb) before calculating doses based on body weight. Doses are often expressed as mg/kg/day or mg/kg/dose, therefore orders written "mg/kg/d" which is confusing, require further clarification from the prescriber. Chemotherapeutic drugs are commonly dosed according to body surface area which requires an extra verification step (BSA calculation) prior to dosing. Medications are available in multiple concentrations, therefore orders written in "mL" rather than "mg" are not acceptable and require further clarification. Dosing also varies by indication, therefore diagnostic information is helpful when calculating doses. The following examples are typically encountered when dosing medication in children. Example 1. Calculate the dose of amoxicillin suspension in mLs for otitis media for a 1-yr-old child weighing 22 lb. The dose required is 40 mg/kg/day divided BID and the suspension comes in a concentration of  400 mg/5 mL. Step 1. Convert pounds to kg:

22 lb × 1 kg/2.2 lb = 10 kg

Step 2. Calculate the dose in mg:

10 kg × 40 mg/kg/day = 400 mg/day

Step 3. Divide the dose by the frequency: 400 mg/day ÷ 2 (BID) = 200 mg/dose mg/dose BID Step 4. Convert the mg dose to mL:

200 mg/dose ÷ 400 mg/5 mL = 2.5 mL BID

Example 2. Calculate the dose of ceftriaxone in mLs for meningitis for a 5-yr-old weighing 18 kg. The dose required is 100 mg/kg/day given IV once daily and the drug comes pre-diluted in a concentration of 40 mg/mL. Step 1. Calculate the dose in mg:

18 kg × 100 mg/kg/day = 1800 mg/day

Step 2. Divide the dose by the frequency: 1800 mg/day mg/day ÷ 1 (daily) = 1800 mg/dose Step 3. Convert the mg dose to mL:

1800 mg/dose ÷ 40 mg/mL = 45 mL once daily

Example 3. Calculate the dose of vincristine in mLs for a 4-yr-old with leukemia weighing 37 lb and is 97 cm tall. The dose required in 2 mg/m2 and the drug comes in 1 mg/mL concentration. Step 1. Convert pounds to kg:

37 lb × 1 kg/2.2 lb = 16.8 kg

Step 2. Calculate BSA (see Body Surface Area Nomograms): Nomograms): 16.8 kg × 97 cm/3600 = 0.67 0.67 m2 Step 3. Calculate the dose in mg:

2 mg/m2 × 0.67 m2 = 1.34 mg

Step 4. Calculate the dose in mL:

1.34 mg ÷ 1 mg/mL = 1.34 mg

Indication : dis turbances of GI motility, nausea & vomiting of central & peripheral origin associated w/ surgery,metabolic diseases, infectious & drug induced diseases, facilitate small bowel intubation & radiological proceduresof GIT Action : sti mulates motility of upper GI tract, increases lower esophageal sphincter  to ne , an d blo ck s do pam ine receptors at the chemoreceptor trigger zone Adverse Reactions : extrapyramidal reactions, drowsiness, fa tigue & lassitude, anxiety, less frequently, insomnia,headache, dizziness, nausea, galactorrhea, gynecomastia, bowel disturbances. Nursing Measures :  Monitor BP carefully during IV administration.  Monitor for extrapyramidal reactions, and consult physician if they occur.  Monitor diabetic patients, arrange for alteration in insulin dose or timing if  diabetic control is compromised byalterations in timing of food absorption.  Keep diphenhydramine injection readily available in case extrapyramidal reactions occur (50 mg IM).  Have phentolamine readily available in case of hypertensive crisis (mo st likely to occur with undiagnosedpheochromocytoma). 20) MIDAZOLAM HYDROCHLORIDEBrand name : Dormicum Classification : hypnotics & sedatives Dosage : 5mg/5mL Indication : tab : disturbances of sleep rhythm, insomnia esp difficulty in falling asleep either initially or  af te r p r e m a t u r e a w a k e n i n g , t a b / i n j : s e d a t i o n i n p r e m e d b e f o r e s u r g i c a l or di ag no s ti c pr oc ed ur es , i nd uc ti on &maintenance of anesth. Action : may potentiate the effects of GABA, depress the CNS, and suppress the spread of seizure activity Adverse Reactions : rarely cardioresp adverse events, nausea, vomiting, headache, hiccoughs, laryngospasm,dyspnoea, hallucination, oversedation, drowsiness, ataxia, rash, paradoxical reactions, amnesic episodes. Nursing Measures :  Do not administer intra-arterially, which may produce arteriospasm or gangrene.  Do not use small veins (dorsum of hand or wrist) for IV injection.   Administer IM injections deep into muscle.  Monitor IV injection site fo r extravasation. 

 Arrange to reduce dose of midazolam if patient is also being given opioid analgesics; reduce dosage by at least50% and monitor patient closely.  Monitor level of consciousness prior to, during, and for at least 2±6 hr after administration of  midazolam.  Carefully monitor P, BP, and respirations carefully during administration.  Keep resuscitative facilities readily available; have flumazenil available as antidote if  overdose should occur.  Keep patients in bed for 3 hr; do not permit ambulatory patients to operate a vehicle following an injection.   Arrange to monitor liver and kidney function and CBC at intervals during long-term therapy.  Establish safety precautions if CNS changes occur (use side rails, accompany ambulating patient).  Provide comfort measures and reassurance for patients receiving diazepam for tetanus.   Arrange to taper dosage gradually after l ong-term therapy.  Provide patient with written information regarding recovery and f ollow-up car e. Mida zol am is a pot ent amn esi acand memory may be altered. 21) MORPHINE SULFATEBrand name : Morin

Classification : Analgesics (Opioid) Dosage : Adult 5-20 mg IM/SC 4 hrly. Severe or chronic painChildn 10 mg IM/SC 4 hrly, range: 5-20 mg; 6-12 yr 5-10 mg, 1-5 yr 2.5-5 mg, 1-12 mth 200 mcg/kg, <1 mth 150 mcg/kg 4 hrly. Max: 15 mg. Analgesic effect Ped 100-200 mcg/kg SC 4 hrly, max: 15 mg/dose; or 50-100 mcg/kg slow IV. Pre-op 50-100 mcg/kg IM, max: 10 mg/dose. Indication : R e l i e f o f m o d e r a t e t o s e v e r e painnot responsive to non-narcotic analgesics. Pr em ed . An al gesi cadjunct in general anesth esp in pain associated w/ cancer, MI & surgery. Alleviatesanxietyassociated w/ severepain. Hypnotic fo r pain-related sleeplessness. Action : alters perception and emotional response to pain Adverse Reactions : Lightheadedness, dizziness, sedation, nausea, vomiting, constipation & sweating. Nursing Measures :  Caution patient not to chew or crush controlled-release preparations.  Dilute and administer slowly IV to minimize likelihood of adverse effects.  Tell patient to lie down during IV administration.

 Keep opioid antagonist and facilities for assist ed or controlled r e s p i r a t i o n r e a d i l y a v a i l a b l e d u r i n g I V administration.  Use caution when injecti ng SC or IM into chilled areas or in patients with hy pot en sio n or in sho ck ; im pai re dperfusion may delay absorption; with repeated doses, an excessive amount may be absorbed when circulation isrestored.  Reassure patients that they are unlikely t o become addicted; most patients who rec eiv e opi oid s f or med ic alreasons do not develop dependence syndromes. 22) NICARDIPINE HYDROCHLORIDEBrand name : Cardepine Classification :Calcium Antagonists Dosage : IV infusion Dilute to 10-20 mg/100 mL (conc of 1.01-0.02%). Initial infusion rate: 5 mg/hr; titrate dose upto 15 mg/hr un til de sired therapeu tic re sponse is ac hieved (DBP <95 mmHg, SBP <140 mmHg). Maintenancerate: Can be tapered down to 10 mg/hr. IV bolus inj 2-7 mg w/out dilution given over 1-2 min. Indication : Hypertensive emergencies or urgencies, peri-op & post-op HTN, hypertensive states of  NPO patients. Action : a C alcium channel blocker that inhibits Calcium ion influx ac ross cardiac and sm oot h mu scl e ce ll s, al so dilates coronary arteries and arterioles Adverse Reactions : Peripheral edema, headache, tachycardia, palpitations, localized thro mbophlebitis &hypotension. Nursing Measures :  Patients with hepatic impairment should receive lower dose.  Monitor blood pressure.Allow atleast 3 da ys between dosage adjustment to achieve steady plasma levels.   Advise patient to report immediately if experiencing chest pain 23) NTG PATCHBrand name : Deponit, Minitran, Nitrek, Nitro-Dur, Nitrodisc, Transderm-Nitro Classification : Anti-Anginal Drugs Dosage : Starting dose: 0.2-0.4 mg/hr. Dosing s chedule: Daily patch-on period of 12-14 hr & daily patch-off periodof 10-12 hr. Indication : Prevention of angina pectorisdue to coronary artery disease Action : a nitrate that reduces cardiac oxygen demand by decreasing left ventricular end diastolic pressure and toa lesser extent, systemic v ascular resistance, also increases blood flow through collateral coronary vessels Adverse Reactions : Headache. Transient episodes of lightheadedness. Infrequently, hypotension. Syncope,crescendo angina, rebound HTN, allergic & anaphylactoid reactions. Rarely severe, application site irritation.

Nursing Measures :   Administer transdermal systems to skin site free of hair and not subject to much movement. Shave areas thathave a lot of hair. Do not apply to distal extremities. Change sites slightly to decrease the chance of local irritationand sensitization. Remove transdermal system before attempting defibrillation or cardioversion.  To use transdermal systems, you may need to s have an area for application. Apply to a slightly different area eachday. Use care if changing brands; each system has a different concentration. 24) PARACETAMOLBrand name : Aeknil Classification : Analgesics (Non-Opioid) & Antipyretics Dosage : Adult & childn 10 yr 2-3 mL, 10 yr 1-2 mL. Depending on severity of case, dose may be repeated 4hrly. In severe cases, dose may be administered by IV very slowly Indication :Pyrexia of unknown origin.Fever &painassociated w/ common childhood disorders,tonsillitis, upper resp tract infections post-immunization reactions, after tonsillectomy & other conditi ons. Preventi on of febri leconvulsion.Headache,cold,sinusitis,muscle pain,arthritis&toothache Action: produce analgesia by blocking pain impulses by inhibiting synthesis of prostaglandin in CNS, relieves fever  Adverse Reactions : Hematological, skin & other allergic reactions Nursing Measures :  Use liquid form for children and patients who have diffi culty swallowing.  In children, don¶t exceed five doses in 24 hours.   Advise patient that drug is only fo r short term use and to consult the physician if giving to children for longer than 5days or adults for longer than 10 days.   Advise patient or caregiver that many over the counter products contain ace tami nophe n; be aware of thi s whencalculating total dailydose.  Warn patient that high doses or unsupervised long term use can cause liver damage.