In the process of preparing some pharmaceutical preparations, you may need to use specialized instruments. To acquaint you with some of the more commonly used pharmaceutical instruments, the following sections will give you a description of each instrument and explain its purpose. See figure 6-2 for an illustration of each instrument discussed.

Pharmaceutical Balances

Two types of pharmaceutical balances are in common use in the Navy: torsion balances (shown in figure 6-2) and electronic balances (not shown). These balances are classified as either “Class A” or “Class B.” Class A balances are used for weighing loads from 120 mg to 120 g. All dispensing pharmacies are required to have at least one Class A balance on hand at all times. Class B balances weigh loads of more than 648 mg, and they must be conspicuously marked“Class B.” Class B balances are optional equipment in the pharmacy.

Ribbed Funnel

Ribbed funnels are utensils used in the filtering process. They are most commonly made of glass, but other substances (tin, copper, rubber) are occasionally used. The funnel is shaped so that the inside surface tapers at a 600 angle, ending in a tapered delivery spout. The inside surface is “ribbed” to allow air to escape from between the glass and the filtering medium (improving the filtration process).

Erlenmeyer Flask

The Erlenmeyer flask is a glass container with metric measurements inscribed on it. It is used for mixing and measuring various medicinal ingredients.

Mortar and Pestle

These two items always go together, one being useless without the other. The mortar is basically a heavy bowl, with one distinct property: the inside concavity is geometrically hemispheric. The accompanying pestle is primarily a hand tool that has a tip made of identical material as the mortar, and its convexity forms a perfect hemisphere. The reason for the two opposing hemispheres is to provide an even grinding surface. Mortars and pestles are made of glass, metal, or unglazed pottery called wedgewood. Glass is used when triturating (reducing substances to fine particles or powder by rubbing or grinding) very pure products (such as eye ointments), and when the preparations contain stains.


Metal mortars and pestles should never be used when the drugs are likely to react with the metals.


The spatula is a knifelike utensil with a rounded, flexible, smoothly ground blade, available in various sizes. The spatula is used to “work” powders, ointments, and creams in the process of levigation (the rubbing, grinding, or reduction to a fine powder with or without the addition of a liquid) and trituration. It is also used to transfer quantities of drugs from their containers to the prescription balance. Spatulas should not be used to pry open cans or as knives for opening boxes. Once the surface is scratched or the edges bent, the spatula is ruined, and it becomes useless for pharmacy work.

Figure 6-2.—Pharmaceutical instruments.


Graduates are conical or cylindrical clear glass containers, graduated in specified quantities and used to measure liquids volumetrically. Measuring should always be done at eye level.


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.


LEARNING OBJECTIVE: Identify the three classifications of drug incompatibility, and recall what causes these drug incompatibilities to occur.

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 that are antagonistic to one another are prescribed together. Such circumstances seldom occur, but when they do, the Hospital Corpsman should bring the perceived incompatibility to the attention of the physician. The pharmaceutical agents may have been used together for one agent to modify the activity of the other. The physician will verify the prescription as necessary.

PHYSICAL INCOMPATIBILITIES.— Physical incompatibilities are often called pharma­ceutical 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 INCOMPATIBILITY.— The following list outlines the various ways incompatibility between or among drug agents may be manifested. The respective type of incompatibility is also noted.

Although it is, of course, impossible to eliminate all drug-agent incompatibilities, some combinations may respond to one of the following corrective measures.

· Addition of an ingredient that does not alter the therapeutic value (such as the addition of an ingredient to alter solubility of an agent)

· Omission of an agent that has no therapeutic value or that may be dispensed separately

· Change of an ingredient (e.g., substitution of a soluble form of an ingredient for an equivalent insoluble form)

· Change of a solvent

· Utilization of special techniques in com­pounding