Ketoconazole is a synthetic antifungal drug used to prevent and treat fungal skin infections, especially in immunocompromised patients such as those with AIDS or those on chemotherapy. Ketoconazole is sold commercially as an anti-dandruff shampoo, topical cream, and oral tablet.

Function:

Ketoconazole is usually prescribed for fungal infections of the skin and mucous membranes, such as athlete's foot, ringworm, candidiasis (yeast infection or thrush), jock itch, and tinea versicolor.

Topical ketoconazole is also used as a treatment for dandruff (seborrheic dermatitis of the scalp) and for seborrheic dermatitis on other areas of the body, perhaps acting in these conditions by suppressing levels of the fungus Malassezia furfur on the skin.

Application:

Ketoconazole shampoo in conjunction with an oral 5α-reductase inhibitor has been used off label to treat and rogenic alopecia. 
The antifungal properties of ketoconazole reduce scalp microflora and consequently may reduce follicular inflammation that contributes to alopecia.Limited clinical studies suggest ketoconazole shampoo used either alone or in combination with other treatments may be useful in reducing hair loss. At least one study has been performed showing that ketoconazole may be useful in temporarily reducing erectile function in postoperative penile surgery patients.
 
Veterinary use
Ketoconazole is also sometimes prescribed by veterinarians for use on pets, often as unflavored tablets that may need to be cut to smaller size for correct dosage.