Patients  with very severe acne  often  have cysts.  In addition  to oral therapy these can be treated by the use of intralesional triamcinolone or liquid nitrogen. In patients with the most severe acne, or in those whose moderate acne is getting worse despite 3-6 months  of therapy and adequate  compliance  then, whatever the patient's  sex,  isotretinoin should  be seriously considered.  In the UK this is a hospital-only, dermatologist-only  prescribable therapy but, used in the correct situation,  it is unquestionably a most valuable drug. 

Other  indications  for  isotretinoin  are in patients with moderate acne who have responded well on three occasions  to conventional  treatment but have quickly  relapsed on  stopping oral therapy.  Another group  meriting isotretinoin are those  patients with severe  acne who have responded well but, despite all other attempts, show an improvement  of only  50  per cent or less 6-9 months after starting therapy. Patients with Gram-negative  folliculitis also  respond well to isotretinoin.

 

  Resistant bacteria (P. acnes) are uncommon although both in the USA and in this author's department there is  evidence to  indicate  an increase in resistance  to commonly used antibiotics.  This  either involved a  resistant P. acnes or Gram-negative folliculitis. In up to 65 per cent the resistance  was, in  some instances, transferred to other antibiotics. It was found that 66 per cent of these nonresponding patients had a significantly elevated sebum excretion rate; this may produce a lower and  ineffective  concentration  of the  antibiotic  in  the duct.

 

  Gram-negative folliculitis is an uncommon complication of oral antibiotics.89 This term is not necessarily the best,  though in some patients the description fits  the title  in  that  suddenly crops of multiple  pustules  develop. The sudden  deterioration of the patient's acne associated with many small superficial pustules should make the physician aware of possible Gram-negative folliculitis. However,  another type of 'Gram-negative folliculitis' is that associated with many  nodules and cysts. The organisms  involved are  usually Escherichia coli, Proteus, Pseudomonas and Klebsiella.  This diagnosis can  be confirmed  by taking swabs both from  the lesions  and the  nose,  which  commonly  harbour  the organisms.

 

  Pityrosporum folliculitis has been suggested as a further explanation for the nonresponsive patient. Such lesions  present  as  ill-defined  superficial  papules and pustules.  The  diagnosis  is  usually reached by excluding other possibilities. P. ovale can often be found in normal follicles so their presence does not confirm the diagnosis. A  therapeutic trial for 6-8 weeks (in addition to acne therapy) with topical imidazole alone (or combined with benzoyl peroxide) or oral ketoconazole may help.

 

  The most likely explanation  for most patients who fail to respond lies in the way in which the skin handles the drug. Ongoing research shows that 66 per cent of the so-called failures  have a high  sebum  excretion rate (SER) compared with responding subjects. This could reflect a reduced level of the antimicrobial substance in the pilosebaceous  duct caused by the washout effect of the higher SER.