Questions on Dosage Calculations

The administration of safe and effective drug therapies depends on dosage calculations. Each person has a unique chemistry that affects the way a drug works. Factors that pharmacologists take into consideration for dosage calculations include the patient's age, body mass, overall health, possible drug interactions and tolerance.

Age and Metabolism

• The body considers a drug to be a foreign substance. Children and patients with impaired health require smaller amounts of prescription medications because their livers cannot effectively metabolize higher quantities of medicine. If a patient has poor liver function, he will not be able to process a drug effectively, which can cause toxic levels of the drug to accumulate within the system.

Body Mass

• Dosage calculations also take into account a patient's weight and body fat. Hospitals rely on standard calculations to determine the dosage of IV medications according to a patient's weight in kilograms. Generally, overweight patients require higher doses of drugs to adequately treat them because the drugs need to be absorbed in higher quantities to produce the desired effects. Women generally carry more body fat than men and may require higher amounts of a medication.

Drug Interactions

• Pharmaceutical research involves the use of hundreds of calculations to determine drug dosages.

  If a patient is taking several different medications, her physician takes into account the side effects that each drug has and possible synergistic effects. When a patient takes drugs with synergistic effects, more than the normal amount of one drug may become available to the body. Other drug pairs have an antagonistic effect, which means that the presence of one or more drugs causes a decline in the amount of another drug.

Tolerance

• The longer a patient takes a particular drug, the more likely he is to build up tolerance to it, leading to the need for a larger dosage to obtain the desired effect. A patient who develops cross-tolerance no longer responds to any drugs in a class because of tolerance for one drug within the group. For example, a person who gains a tolerance for alcohol may require higher doses of drugs in the same class of sedatives including anxiolytics, barbiturates and certain pain medications.