Background and Importance Topical minoxidil solution is a safe and effective treatment for alopecia. However, some patients present pruritus and scalping. Patients suffering from allergic contact dermatitis may benefit from patch testing to determine the causative allergen. In the few reported cases of suspected hypersensitivity to topical minoxidil, propyleneglycol triggered the allergic response in the majority of cases.

Aim and Objectives Describe the design, preparation and results of patch tests and prick tests for minoxidil.

Material and Methods The allergology department requested to perform minoxidil patch tests and prick tests for a patient with suspected type IV hypersensitivity.

The pharmacy department proposed carrying out a battery of epicutaneous tests, both for minoxidil and the excipients present in the commercial drug the patient used.

For patch tests two different vehicles were used in the compounding: Vaseline (usual excipient for patch tests) and dimethyl sulfoxide (DMSO) since it has been described for its involvement in increasing the skin penetration of the accompanying active ingredient.

Results As the commercial drug the patient used had alcohol and propyleneglycol as excipients, the following battery of epicutaneous syringe tests for minoxidil patch test was designed:

• Minoxidil 2 and 5% in liquid Vaseline (compounded as 20 mg and 50 mg in 1 mL).

• Minoxidil 2 and 5% in DMSO (compounded as 20 mg and 50 mg in 1 mL).

• 1 mL of liquid Vaseline.

• 1 mL of DMSO.

• 1 mL of propyleneglycol 10, 50 and 100%.

• 1 mL 70° alcohol.

Additionally, the pharmacy prepared the following syringes for prick tests:

• Sterile minoxidil 2 and 5% in sodium chloride 0.9% (compounded as 20 mg and 50 mg in 1 mL).

• Propyleneglycol prick test was obtained commercially.

The compounding was prepared ready to use.

Results after exposure were negative in the immediate readings, as well as at 48 and 96 hours, ruling out this drug and its excipients as causing the hypersensitivity.

Conclusion and Relevance The design and preparation of patch tests and prick tests are key when it comes to dismiss hypersensitivity to a specific drug. Excipients must be taken into account to rule out their involvement.

Conflict of Interest No conflict of interest.