Sticks are an easily transportable and convenient dosage form for administering
topical medications. They can be compounded in different sizes and shapes for
application to different areas of the body. They can be applied directly to
the affected site of the body for local activity. Or they can be applied to
different epidermal sites if systemic activity is desired. Epidermal penetration
enhancers can be added to the formulation to promote this later use. Local anesthetics,
sunscreens, oncology drugs, antivirals, and antibiotics have all be administered
by medication sticks.
Sticks get their consistency from a combination of waxes, polymers, resins,
and in some cases from drug solids fused into a firm mass. Waxes, polymers,
oils, and gels (or combinations of these) that will soften at body temperature
and allow the formulation to be evenly spread over the affected area are called
soft sticks. These sticks are either clear or opaque depending on the base used
in the formulation. When applied to the skin, they leave no visible residue.
Soft clear sticks contain sodium stearate, glycerin, and/or propylene glycol
in their base. Soft opaque stick bases may contain petrolatum, cocoa butter,
and polyethylene glycol (PEG).
Hard sticks are made of crystalline powders that are either fused together
by heat or held together with a binder. The stick must be moistened to be "activated."
When it is wetted, a concentrated solution of the drug forms on the wetted
part of the stick and the solution is transferred when the stick is touched to the affected area. The crystalline
powder in the stick may leave a white residue on the skin. The prime example
of a hard stick is a styptic pencil.
Soft stick consistency is determined by the blend of high and low melting
point ingredients used as the base. Some common substances used in base formulations
and their melting points are given in the table below. Sometimes additional
high melting point ingredients are added to "stiffen" (i.e., make more solid)
some bases. There are several "stiffening agents" that can be used for this
Melting Point (°C)
||81 - 86
||45 - 50
|Cetyl esters wax
||43 - 47
||147 - 150
||30 - 35
||69 - 70
||55 - 60
|White wax (Beeswax, white and yellow)
||62 - 65
||44 - 48
||54 - 58
58 - 63
Additional substances used in stick bases include paraffin, castor oil, corn
oil, cottonseed oil, oleic oil, peanut oil, soybean oil, and PEG 300 and 400.
Adding lubricants will minimize the coherence of the waxes and improve spreadability.
Vitamins A and E can be added to enhance emollient and skin care effects. Zinc
oxide and p-amino benzoic acid (PABA) could be added to the stick as sun blocks.
When combining materials that have a range of melting points, it is best to
melt the material with the highest melting point first, and then melt the material
with the second highest melting point second, and so forth. As each new ingredient
is added to the melt, the temperature can be reduced. This will prevent over
heating the lower melting point ingredients.