DRUG INCOMPATIBILITIES, CONTRAINDICATIONS, AND ADVERSE EFFECTS
Occasionally, the drugs we use to improve a person's condition may not work in the manner intended. The outcome may be contrary to that which was expected, and, indeed, could even cause harm to the patient. It is important to be aware of symptoms that may indicate a drug is not doing its job properly.
There are instances when a drug used simultaneously with another drug or substance does not perform as it was intended. These drugs or substances may be incompatible together and, therefore, should not be administered at the same time. A drug incompatibility can also occur when drugs are compounded together in the pharmacy. There are three classes of drug incompatibilities: therapeutic, physical, and chemical. In the following sections, each class of drug incompatibility is discussed.
THERAPEUTIC INCOMPATIBILITIES.- Therapeutic incompatibilities occur when agents
Figure 6-2.-Pharmaceutical instruments.
PHYSICAL INCOMPATIBILITIES.- Physical incompatibilities are often called pharma- ceutical incompatibilities and are evidenced by the failure of the drugs to combine properly. It is virtually impossible for uniform dosages of medicine to be given from such solutions or mixtures. Ingredients such as oil and water (which are physically repellant to each other) and substances that are insoluble in the prescribed vehicle are primary examples of physical incompatibilities.
CHEMICAL INCOMPATIBILITIES.- Chemical incompatibilities occur when prescribed agents react chemically upon combination to alter the composition of one or more of the ingredients (constituents).
MANIFESTATIONS OF INCOMPATIBI ITY.- The following list outlines the various ways incompatibility between or among drug agents may be manifested. The respective type of incompatibility is also noted.
· Insolubility of prescribed agent in vehicle (physical)
· Immiscibility of two or more liquids (physical)
· Cementation of insoluble ingredients in liquid mixtures (physical)
· Precipitation due to chemical reaction (chemical)
· Addition of an ingredient that does no alter the therapeutic value (such
as the addition of an ingredient to
alter solubility of an agent)
· Change of an ingredient (e.g., substitution of a soluble form of an
ingredient for an equivalent insoluble