Side Effects - Pharmacology

A drug can have a side effect in addition to its pharmaceutical response. A side effect is a physiologic effect other than the desired effect. Sometimes side effects are predictable and other times they are not and may be unrelated to the dosage. Some side effects are desirable and others are undesirable.

A severe undesirable side effect is referred to as an adverse reaction that occurs unintentionally when a normal dose of the drug is given to a patient. For example, an adverse reaction might be anaphylaxis (cardiovascular collapse) Some adverse reactions are predictable by age and weight of the patient. Young children and the elderly are highly responsive to medications because of an immature or decline in hepatic and renal function. Body mass also influences the distribution and concentration of a drug. The dosage must be adjusted in proportion to body weight or body surface area.

Drug effects can also be related to other factors. These include:

Gender. Women typically are smaller than men and have a different proportion of fat and water which affects absorption and distribution of the drug.

Environment.Cold, heat, sensory deprivation or overload, and oxygen deprivation in high altitude create environmental factors that might interact with a drug.

Time of administration. A drug might be influenced by the presence or absence of food in the patient’s gastrointestinal tract or by the patient’s cortiocosteroid secretion rhythm. In addition, circadian cycle, urinary excretion pattern, fluid intake, and drug metabolizing enzyme rhythms all might influence a drug’s effect.

Pathologic state. A drug can react differently if the patient is experiencing pain, anxiety, circulatory distress, or hepatic and/or renal dysfunction.

Idiosyncracy. This is an abnormal response that is unpredictable and unexplainable that could result from the patient over responding or under responding to the drug or the drug having an effect that is different from what is expected.

Tolerance. The patient has a decreased physiologic response after repeated administration of the drug. This is common with tobacco, opium alkaloids, nitrites, and ethyl alcohol. The dosage must be increased to achieve the pharmaceutical response.

Drug dependence. This can be either a physical or psychological dependency. With a physical dependency, the patient experiences an intense physical disturbance when the drug is withdrawn. With psychological dependency, the patient develops an emotional reliance on the drug.

Drug interaction. The administration of one drug increases or decreases the pharmaceutical response of a previously administered drug.

Synergism.more desirable pharmaceutical response is achieved through the interaction of two drugs that are administered.

Potentiation. Concurrent administration of two drugs increases the pharmaceutical response of one of those drugs.

Toxic effect. This occurs when the administered drug exceeds the therapeutic range through an overdose or by the drug accumulating in the patient.

Tachyphylaxis. The patient builds a tolerance to the drug due to the frequency in which the drug is administered. This occurs with narcotics, barbiturates, laxatives, and psychotropic agents. The patient may eventually need more of the drug to reach the desired effect.

Placebo effect. The patient receives a psychological benefit from receiving a compound that has no pharmaceutical response. A third of patients taking a placebo experience the placebo effect.

Pharmacogenetic effect. A drug varies from a predicted response because of the influence of a patient’s genetic factors. Genetic factors can alter the metabolism of the drug and results in an enhanced or diminished pharmaceutical response.

Allergic reactions. If the patient was previously sensitized to the drug, a drug might trigger the patient’s immunologic mechanism that results in allergic symptoms.Antibodies are produced the first time the drug is introduced to the patient creating a sensitivity to the drug. The next time the drug is given to the patient, the drug reacts with the antibodies and results in the production of histamine. Histamine causes allergic symptoms to occur. The patient should not take any drug that causes the patient to have an allergic reaction.

There are four types of allergic reactions. These are:

  • Anaphylactic. This is an immediate allergic reaction that can be fatal.
  • Cytotoxic reaction. This is an autoimmune response that results in hemolytic anemia, thrombocytopenia, or lupus erythematosus (blood disorders). In some cases, it takes months for the reaction to dissipate.
  • Immune complex reaction. This is referred to as serum sickness and results in angioedema, arthralgia (sore joints), fever, swollen lymph nodes, and splenomegaly (large spleen). The immune complex reaction can appear up to three weeks after the drug is administered.
  • Cell mediated. This is an inflammatory skin reaction that is also known as delayed hypersensitivity.

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Pharmacology Topics