If you have used of any of the antibiotics below in his past, then the flora that produces biotin may have been killed back or competing poorly with the other microbes.  Unfortunately, no one has ever quantified how much biotin we get from our flora, but we know we get some, and it may be that we get a lot more than we get from diet under normal circumstances.

Biotin is apparently stored, so when some of our body is deficient, our bodies may overutlize the biotin that is stored.  One of those places that might get depleted is the basal ganglia in the brain.  I found some studies that suggested that depletion may happen before the carboxylases whose tracks show up in urine begin to show weaknesses.

The following information on which drugs hurt the biotin chemistry are from the following university medical school website:

http://www.umm.edu/altmed/ConsSupplements/Depletions/VitaminHBiotincs.html

I don't think this list is complete, in that there are many more sulfa drugs, including sulfasalazine!

Susan

Drugs that Deplete: Vitamin H (Biotin)
Antibiotic Medications
 Antibiotic Combination: Sulfa Drugs

 Co-Trimoxazole
 Trimethoprim
 Trimethoprim-Sulfamethoxazole
 Cephalosporins
 Cefprozil
 Cefuroxime
 Loracarbef

 Macrolides
 Azithromycin
 Clarithromycin
 Erythromycin, systemic
 Penicillin Derivatives
 Amoxicillin
 Amoxicillin and Clavulanate
 Penicillin V Potassium

 Quinolones
 Cinoxacin
 Ciprofloxacin
 Enoxacin
 Gatifloxacin
 Levofloxacin
 Lomefloxacin
 Moxifloxacin
 Nalidixic Acid
 Norfloxacin
 Ofloxacin
 Sparfloxacin
 Trovafloxacin

Tetracycline Derivatives
 Doxycycline
 Minocycline
 Tetracycline

Anticonvulsant Medications
 Hydantoin Derivatives
 Phenytoin

RELATED INFORMATION
Vitamin H (Biotin)
  Uses of this Supplement

Candidiasis
Diabetes Mellitus
Hair Disorders
Hypercholesterolemia