Body surface area calculation

Body surface area calculation square root (height in cm x body weight in kg divided by 3600). High doses required in infants < 1 yr because of kinetic variability. 

For children who can swallow capsules and for whom the current capsule formulations allow appropriate weight or body surface area calculated dosing, additional options to replace LPV/r include SQV/r and IDV/r. 

If the drug dose is based on body surface area (m2) the same meHiod of calculation may be used. 

DOSAGE CALCULATION BASED ON BODY SURFACE AREA... 

The dose of drags for children as well as adults may be adjusted based on the body surface area. The normal adult body surface area is 1.73 m2. The body surface area may be calculated in many ways. The following equation provides a useful estimate of the surface area when the height (in cm) and weight (in kg) of the patient are known ... 

The dose modifications based on body surface area provide a better approximation of dose than the dose based on body weight. The general equation to calculate the child s dose by the surface area method is as follows ... 

Convert the NOAEL to the human equivalent dose (HED) using the data from Table 5.3 (calculations are based on body surface areas). 

When correction for differences in body size is based on body surface area, the power n in the allometric equation is 2/3, or 0.67, and the human dose Xhuman (expressed in mg) can be calculated as follows ... 

The surface area for different species can be calculated by empirically derived equations using a species-specific shape factor, which depends on the ration of weight to height (Voisin et al. 1990). According to Voisin et al. (1990), there are several limitations in the accuracy of conversions based on body surface area (1) the surface area appears to be difficult to estimate (2) some analyses have indicated that the exponent of 2/3 may be inaccurate (3) some physiological parameters are not so well related to body surface area (4) body surface area conversions are inaccurate when the mode of administration is different across species and (5) not aU types of toxicity correlate with body surface area, e.g., skin toxicity. 

Body surface area (m ) can be calculated with the following equation Take the square root of a patient s height in centimeters multiplied by the patient s weight in kilograms divided by 3,600. 

Therapy, to be effective, depends upon administration of an adequate number of platelets, generally 5 X 10 in a 70 kg man or a 60 kg woman given over 15 minutes - with suitable adjustment for body surface area in children. It is mandatory that the increment is calculated and the duration of response be documented at 24 hours. The optimum practice is to relate the number infused to changes achieved in the patient by means of the corrected count index. This step anticipates the emergence of resistance that limits the value of repeated transfusions. Occasional allergic reactions have to be blocked by premedication with an intravenous injection 100 mg of hydrocortisone, 12.5 mg of phenergan and 1 g of paracetamol... 

Dose can be calculated more accurately by body surface area (BSA). 

There are many circumstances in which a fixed drug dose is likely to be ineffective or toxic in a significant number of individuals, e.g. cytotoxic chemotherapy, aminoglycoside antibiotics. It is usual then to calculate the dose according to body weight. Adjustment according to body surface area is also used and may be more appropriate, for this... 

Children require and tolerate a larger mg/kg dose than adults and cannot be considered as small adults. For example, the doses of digoxin required to maintain mean plasma concentrations of about 1-1.5 ng/ml are 15-20 pg/kg per day for children 4 weeks to 2 years of age, 10-15 pg/kg per day for children 2-12 years of age, and 4-5pg/kg per day for adults. Reasonable estimates of the doses required in children are often obtained by calculating the child s dose on the basis of body surface relative to that of an adult. An estimate of body surface area may be made from Eq. (11). 

In 1990, urine samples from an accidental laboratory exposure to sulfur mustard were obtained (Jakubowski et al., 2000). The erythematous and vesication areas of the individual were estimated to be less than 5% and 1%, respectively, of the total body surface area. The assay measured both free and conjugated TDG using GC-MS (Jakubowski et al., 1990). The maximum TDG urinary excretion rate was 20 (pg/day on day 3. TDG concentrations of 10 ng/mL or greater were observed in some samples for up to a week after the exposure. A first-order elimination was calculated from days 4 through 10 and found to be 1.2 days. A great deal of intraday variability was noted for the TDG urine concentrations. Attempts were made to estimate the total amount of sulfur mustard on the skin of the patient. The estimate was based on two assumptions (1) that the assay for the free and conjugated TDG represents approximately 5% of the total amount of sulfur mustard related products in the blood, and (2) that the bioavailability factor from skin to blood is 10. A total of 0.243 mg of TDG was recovered over a 2 week period. This would represent 4.86 mg in the blood or 48.6 mg on the skin. 

Calvert formula for dose modifications Dose (mg) = target AUC x (CLcr -E 25) CIcr calculated using Cockcroft-Gault equation note that the calculated dose is total dose, not dose per m body surface area Bone marrow recovery may require 6-8 weeks postadministration not a vesicant vein irritation and facial flushing may be related to alcohol vehicle... 

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