FACTORS AFFECTING DRUG ACTION
In drug administration, many factors affect the action of the medication. These factors also affect the dose to be administered. The usual adult dose of medication as listed in standard references, is based on the assumption that the adult weighs 150 pounds, but since the following variables influence the action of the medication, they also may alter the quantity of the drug necessary to produce the desired results
a. Weight. Heavy, burly clients require larger doses than weak, emaciated ones. The doses of many drugs are calculated on a weight basis; a specified number of grams or milligrams are administered per pound or kilogram of body weight. b. Age. As a rule, the very young and the very old require less than the normal adult dose. As you recall from lesson 1, several formulas are available for estimating a child's dose when the average adult dose is known. c. Sex. Females usually require smaller doses than males. Iron preparations and other hematinics are exceptions to this rule because of the blood lost by women during menstruation. In males the metabolism could be faster (testosterone is a CYP3A inductor), LD50 values may be higher–this is not always true d. Race. Race can be a factor affecting drug action, since enzyme systems, body chemistry, and stature may vary. e. Temperament. The high-strung, nervous, always-busy type of individual requires smaller amounts of stimulants but larger amounts of sedatives than the phlegmatic (dull, apathetic) individual. f. Climate. Cathartics seem to be effective in smaller doses in warm climates than in cold. g. Occupation. Men who work outdoors and who engage in strenuous, physical activity usually require larger doses than those who are engaged in sedentary or indoor work. h. Disease. Certain disease conditions also modify certain ,drug response e.g., hepatitis prolongs anaesthesia-with the ultra short acting barbiturates because the liver normally metabolizes these drugs. Some pathological conditions require changes in dosage. People in extreme pain need more analgesic and sedative drugs than those suffering only mild pain. The extremely weak or debilitated client may require smaller doses of some medications. i. Tolerance. The therapeutic effects of some medications are lessened in individuals after prolonged use. Thus, a person who has used such a drug for a long time needs larger doses than he did when he first began to take it in order to realize the same therapeutic effects from it. This is called tolerance. Users of opium, morphine, cocaine, amphetamines, and barbiturates fall into this category. Cross-tolerance develops when the use of one drug causes a tolerance to another. Alcoholics, barbiturate habitues, and narcotic addicts develop a cross-tolerance to sedatives and anesthetics. These individuals require very large amounts of anesthetics before surgical anesthesia can be attained. j. Mode of Administration. Generally, drugs given parenterally are used in smaller quantities and those given rectally are used in greater quantities than the usual oral dose. k. Frequency of Administration. Drugs given at frequent intervals are administered in smaller doses than those given at wide intervals. l. Time of Administration. Some drugs given by the oral route are absorbed more rapidly before a meal (on an empty stomach) than they would be if they were administered immediately after a meal. m. The Drug. Many factors of the drug itself can influence its action. They may alter its potency, making some preparations weaker and others stronger. The form of a drug, that is, solution, powder, or suspension, may alter the amount of the drug necessary and the effects derived from it. n. Additive Effect. If two drugs exhibit the same overt effect and their combined effects are equal to the sum of their individual effects, they are additive o. Synergism. Synergism is the joint action of two or more drugs such that their combined effects are greater...
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