How safe is prescribing oral minoxidil in patients allergic to topical minoxidil?

Abstract

To the Editor: We present 9 female patients (Table I) who became allergic to topical minoxidil and were able to tolerate low-dose oral minoxidil without adverse effects.Table IList of patientsPatientAge, y∗Mean age of 47.2 years (range, 22-72 years).SexTopical minoxidil use, yAdverse effects from topical minoxidilOral minoxidil use, 0.25 mg twice daily, mo†All patients currently on treatment.Adverse effects from oral minoxidil148Female8Scalp pruritus15None247Female12Scalp pruritus, scaling20None372Female14Scalp pruritus, scaling33Mild hypertrichosis on temples449Female3Scalp pruritus, eczematous rash on ears10None554Female1.5Scalp pruritus7None655Female0Scalp pruritus18None731Female0Scalp pruritus, eczematous rash on ears8None847Female4Scalp pruritus, scaling24Mild hypertrichosis on cheeks922Female1Scalp pruritus, eczematous rash on ears18None∗ Mean age of 47.2 years (range, 22-72 years).† All patients currently on treatment. Open table in a new tab Topical minoxidil is the only approved treatment for female pattern hair loss.1Friedman E.S. Friedman P.M. Cohen D.E. Washenik K. Allergic contact dermatitis to topical minoxidil solution: etiology and treatment.J Am Acad Dermatol. 2002; 46: 309-312Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar It has a safe profile, and the most common adverse effects include irritant and allergic contact dermatitis and hypertrichosis. Contact dermatitis to commercial minoxidil is often caused by propylene glycol that is present in the 2% and 5% solutions. Patients with contact allergy or irritation to propylene glycol can use the 5% minoxidil foam, which is free of this ingredient. Contact allergy to minoxidil itself is uncommon and requires discontinuation. Our patients had been using topical minoxidil for an average of 4.8 years (range, 1-14 years) (Table I) when an acute contact dermatitis developed. All were patch tested with propylene glycol 30% in water (Chemotechnique Diagnostics, Vellinge, Sweden), 5% commercial minoxidil solution, and 5% commercial minoxidil foam. Patches were removed after 48 hours and the reading was performed at 72 and 96 hours. All 9 patients had a positive patch test result to the 5% minoxidil solution and the foam and a negative patch test result to propylene glycol, indicating that the cause of contact dermatitis was minoxidil itself (Fig 1). Oral minoxidil has been used in the last few years as an off-label treatment both in male and in female pattern hair loss with good clinical efficacy.2Jimenez-Cauhe J. Saceda-Corralo D. Rodrigues-Barata R. et al.Effectiveness and safety of low-dose oral minoxidil in male androgenetic alopecia.J Am Acad Dermatol. 2019; 81: 648-649Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar,3Sinclair R.D. Female pattern hair loss: a pilot study investigating combination therapy with low-dose oral minoxidil and spironolactone.Int J Dermatol. 2018; 57: 104-109Crossref PubMed Scopus (58) Google Scholar Proposed doses are different in men than in women, with a range from 0.25 to 1 mg daily.4Ramos P.M. Sinclair R.D. Kasprzak M. Miot H.A. Minoxidil 1 mg oral versus minoxidil 5% topical solution for the treatment of female-pattern hair loss: a randomized clinical trial.J Am Acad Dermatol. 2020; 82: 252-253Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar Lower doses are used in women because hypertrichosis is a common adverse effect.3Sinclair R.D. Female pattern hair loss: a pilot study investigating combination therapy with low-dose oral minoxidil and spironolactone.Int J Dermatol. 2018; 57: 104-109Crossref PubMed Scopus (58) Google Scholar Our experience with more than 200 patients on oral minoxidil indicates that 0.5 mg daily is effective and very well tolerated. The possibility that patients with contact allergy to topical minoxidil could safely tolerate oral minoxidil was suggested by the fact that systemic skin reactions to topical or oral minoxidil have never been described. Systemic contact dermatitis refers to a rare diffuse reaction that individuals sensitized to a contact allergen might develop after exposure to the same allergen via a different route. The exact pathophysiology is unknown; however, it appears to be mediated by a type 4 and possibly type 3 hypersensitivity reaction. Cases of systemic contact dermatitis have been reported for propylene glycol5McGowan M.A. Scheman A. Jacob S.E. Propylene glycol in contact dermatitis: a systematic review.Dermatitis. 2018; 29: 6-12Crossref PubMed Scopus (32) Google Scholar but not for minoxidil, so treatment with oral minoxidil was started at the dose of 0.25 mg twice daily. The 0.25-mg capsules were compounded by pharmacies. All of our patients have been using the same dose to date, for an average of 17 months (range, 7-33 months) without any adverse effects. All of them were satisfied with results of treatment. Cardiac adverse effects of oral minoxidil, such as edema, pericarditis, or pericardial effusion, are dose-dependent and have never been reported with low doses. Our experience therefore suggests that oral minoxidil is reasonably safe in patients allergic to topical minoxidil, even if it is advisable to warn patients to stop the medications in case of cutaneous adverse effects.