When treating a patient, or just taking a medication by yourself, we always need to wonder what is the exact dose of the drug we choose. And the truth is that we dose (or should dose) nearly everything in our life, from cooking dinner to taking medications! However, regarding drugs, there are certain different kinds of dosing that depend on the specific drug and/or the patient. 1. One dosage Drugs with one fix dosage are the easiest to use; you just take it and forget about it (e.g., vaccines). You don't need to use any dosage calculation formulas! 2. Different, fixed dosages The dosage of these drugs is usually set by the doctor according to the patient's needs or age (e.g., hypotensive drugs). In this case, you also don't have to worry about medical dosage calculations! 3. Different, variable dosages In this case, the doctor usually suggests the patient a sample dosage; the patient then modifies it according to his/her needs and the situation (e.g., insulin). 4. Blood concentration-dependent dosages This is a relatively small group of drugs. The doses are different depending on the concentration of the drug's active compound in the serum (e.g., vitamin K antagonists, lithium, etc.). 5. The dosage of the drug depends on the patient's body weight The dose of the drug depends on the weight of the patient. It means that two patients with the same disease may receive a different amount of the same drug! Our dosage calculator will help you calculate appropriate doses of this kind of drugs! General 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.
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 prediluted in a concentration of 40 mg/mL.
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 is 2 mg/m2 and the drug comes in 1 mg/mL concentration.
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