Erectile dysfunction in Minoxidil Users: What's the Naranjo Score?

Erectile dysfunction in minoxidil users

Anyone who reads online will see that there are reported links between topical minoxidil use and erectile dysfunction. But is it accurate ?  My opinion is that it's not impossible - but very unlikely for most users. Let's take a look at the data. 

One one study to date supports an association

To date, there are no really good clinical studies that support an associated between topical minoxidil use an worsening erectile dysfunction.  The original studies from the 1980s did not raise this issue. However a recent study did suggest that topical minoxidil was the cause of erectile dysfunction. 

MINOXIDIL ASSOCIATED WITH ERECTILE DYSFUNCTION

Blood pressure medications can cause impotence

Minoxidil is a blood pressure medication and was used orally in the 1980s as Loneten. It's certainly not out of the question for blood pressure medications to cause erectile dysfunction. Drugs like beta-blockers and diuretics like hydrochlorothiazide can sometimes cause erectile dysfunction. Blood pressure medications like ACE inhibitors, Angiotensin receptor blockers are less likely.  Minoxidil was FDA approved in 1979 as an oral medication to treat blood pressure problems. Topical minoxidil however, does not impact blood pressure to any significant degree in most users. Erectile dysfunction is not a side effect that has been raised in clinical trials to date.

The Naranjo Adverse Drug Reaction Probability Scale

When a patient asks me whether their minoxidil could be causing sexual dysfunction, my answer is first that it is possible and that we really need to consider something know as the Naranjo Adverse Drug Reaction Probability Score.

Anything applied to the skin or taken by mouth has the potential to cause a side effect. Some medications rarely cause side effects and others tend to cause frequent side effects. Occasionally a patient will report a side effect that perhaps has never been reported before. The question then becomes - is this a real side effect from the drug or is it happening from something else?

 

A Closer Look at the Naranjo Adverse Drug Probability Scale

The Naranjo Scale was created nearly 40 years ago to help standardize how clinicians to about assessing whether or not a drug could be implicated in an adverse drug reaction. It is used in controlled clinical trials. The scale is quite easy to use - and involves asking the patient 10 questions. Answers to the question are recorded as "yes", "no" or "don't know" and different points are assigned to each answer (-1, 0, +1, +2). 

Typical Questions in the Naranjo Scale (using minoxidil associated erectile dysfunction ("ED") as an example)

1. Are there previous "conclusive" reports of minoxidil causing ED? (yes) 
2. Did the ED (or worsening ED) appear after the drug was given or were their such issues before the patient started minoxidil?
3. Did the ED improve when the drug was discontinued or a specific antagonist was given?
4. Did the ED reappear upon readministering the minoxidil?
5. Were there other possible causes for the ED that were explored by the family doctor?
6. Did the ED occur again with administration of placebo?
7. Was the minoxidil detected in the blood or other fluids in toxic concentrations?
8. Was the ED worsened upon increasing the dose of minoxidil (from once to twice daily)? Or, was the reaction lessened upon decreasing the dose? (ie. does going to once daily minoxidil make sexual performance better?)
9. Did the patient have a similar reaction to  minoxidil or a related  blood pressure drug in the past?
10. Was the ED confirmed by any other objective evidence?

 

Determining the Naranjo Score

Scores can range from -4 to + 13. A score of 0 or less means the likelihood of the drug causing the side effect is doubtful, a score 1 to 4 indicates it is 'possible', a score 5 to 8 means it is 'probable' and a score 9 to 13 means it is 'definite'

 

Reference

Tanglertsampan C. Efficacy and safety of 3% minoxidil versus combined 3% minoxidil / 0.1% finasteride in male pattern hair loss: a randomized, double-blind, comparative study. J Med Assoc Thai. 2012.

Cecchi M, et al. Vacuum constriction device and topical minoxidil for management of impotence. Arch Esp Urol. 1995.

Radomski SB, et al. Topical minoxidil in the treatment of male erectile dysfunction. J Urol. 1994