Salicylic acid

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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Synonym(s)

salicylic acid; Salicylic acid; Spiric acid

Definition
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Medium strength acid which produces a pH of 2-3 in aqueous vehicle systems. Only in its acid form can it be absorbed by the skin. Salicylic acid is used as antiseptic and keratolytic agent. It is one of the active agents most frequently prescribed in individual formulations. It very often occurs in suspended semisolid formulations but also in dissolved form in hydrophilic and lipophilic vehicles.

Pharmacodynamics (Effect)
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Salicylic acid has keratoplastic and keratolytic effects; also antibacterial and antimycotic.

Indication
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Standard concentration
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  • 1-10% in peeling ointments and peeling collodies
  • 40-60% in keratolytic patches (only small area application)
  • 3-5% in anti-hydrotic powders
  • 2-10% in oils (also in head oils)
  • 0.5-1% in antiseptic brushes and ointments

Remember! In infants and toddlers, the use of salicylic acid-containing topicals should be limited to a maximum of 5-10% of the body surface and - depending on age - to a concentration of 1-3% (Mehlhorn p. 2017).

Undesirable effects
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Allergic reactions, dermatitis, salicylism (kidney damage, confusion), especially by resorption with large-area application. In this respect it should not be used in ointment applications where there is a risk of large-area application, not higher than 2.5% (recommendation of Commission 7 of the former BGA). In the case of small-area application, up to 60% concentrations can be used (e.g. in plasters).

Salicylic acid can hydrolytically split fats and oils (chemically speaking: triglyceride ester of unsaturated fatty acids) without the presence of water. This produces free fatty acids which have an unpleasant (rancid) odor and may also be irritating to the skin. For this reason, NRF 11.400. contains another lipid, namely octyldodecanol (Euntanol® G) which does not show an ester structure.

Salicylic acid reacts with zinc. The resulting salts have no effect and are considered inert (Wolf G 2014). Salicylic acid should therefore not be formulated in zinc-containing bases.

Recipe(s)
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Other (reviewed) formulations containing salicylic acid:

Rp.1) Washable salicylic acid head oil (with eutanol G)

  • salicylic acid 2,0
  • Macrogol-4-lauryl ether 10,0
  • octyldodecanol 80,0
  • S: Usage period: 6 months above 8°C (glass bottle)

Rp.2) Salicylic acid head oil (with eutanol G and castor oil - n. G. Wolf)

  • Salicylic acid 5,0
  • Macrogol-4-lauryl ether 10,0
  • Refined castor oil 40,0
  • Octyldodecanol ad 100,0
  • S: Usage period: 6 months above 8°C (glass bottle)

Rp.3) Salicylic acid head oil (with triamcinolone acetonide/chlororamphenicol/ clotrimazole- n. G. Wolf)

  • Salicylic acid 5,0
  • triamcinolone acetonide 0,1
  • chloramphenicol 1,0
  • clotrimazole 2,0
  • Macrogol-4-lauryl ether 10,0
  • Refined castor oil 40,0
  • Octyldodecanol ad 100,0
  • S: Usage period: 6 months above 8°C (glass bottle)

Preparations
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Contrheuma® bath L, Criniton® solution, Guttaplast, Humpin®, Kytta® balm, Lygal head ointment N, Menthoneurin® full bath N, Moorbar-Saar, Pernionin® partial bath N, Psorimed Lsg., Pyralvex® gel, Salhumin® rheumatism bath, Salhumin® partial bath N, Squamasol gel/Lsg., Verrucid, Collomack; Salicylvaseline Lichtenstein

Note(s)
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Salicylic acid is poorly soluble in olive oil! In the cold, a maximum of 2.2% dissolves in this fatty base. In terms of application technology this means that pure salicylic acid crystals would be rubbed onto the skin at higher concentrations! For castor oil the solubility is considerably higher and amounts to 16%. The NRF 11.44 recommends up to a 5% salicylic acid concentration octyldodecanol (eutanol G = alcohol with lipid regulating properties); at > 5% a mixture of castor oil and octyldodecanol.

The standardized washable salicylic acid oil is recommended, among others, the formulation given in NRF 11.85.(salicylic acid oil, washable 2/5 or 10% ).

Salicylic acid is often combined with glucocorticoids and clotrimazole less frequently with antibiotics. This leads to turbidity and precipitation of undissolved components. This means that the solution should always be shaken before application to avoid dosage inaccuracies.

Literature
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  1. Flour horn S (2017) Salicylic acid oils for use on the scalp. dermatologist 68: 248-249
  2. Wolf G (2013) Polypragmasia in formulations. dermatologist 64: 478-47
  3. Wolf G (2014) Complex interactions between active ingredient and base. Dermatologist 65: 486-487
  4. Wolf G (2008) Individual recipe - but correct. derm 14: 49-50

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Last updated on: 29.10.2020