caustic

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caustic

 [kaws´tik]
1. burning or corrosive; destructive to tissue.
2. having a burning taste.
3. a corrosive or escharotic agent.

caus·tic

(kaws'tik),
1. Chemically exerting an effect resembling a burn.
2. An agent producing this effect.
3. Denoting a solution of a strong alkali; for example, caustic soda, NaOH.
Synonym(s): pyrotic (2)
[G. kaustikos, fr. kaiō, to burn]

caustic

/caus·tic/ (kaws´tik)
1. burning or corrosive; destructive to living tissues.
2. having a burning taste.
3. an escharotic or corrosive agent.

caustic

[kôs′tik]
Etymology: Gk, kaustikos, burning
1 n, any substance that is destructive to living tissue, such as silver nitrate, nitric acid, or sulfuric acid.
2 adj, exerting a burning or corrosive effect.

caus·tic

(kaws'tik)
1. Exerting an effect resembling a burn.
2. An agent producing this effect.
3. Denoting a solution of a strong alkali (e.g., caustic soda, NaOH).
[G. kaustikos, fr. kaiō, to burn]

caustic

Any chemical substance which corrodes and destroys bodily tissue.

caustic

strong inorganic acid or alkali, or organic acid (e.g. phenol) applied to soft tissue, e.g. verruca or nail matrix, to cause controlled destruction of that area of tissue; different caustics exert different actions on tissues: silver nitrate forms insoluble chlorides (i.e. creating a barrier to further tissue penetration), nitric acid precipitates albumen (i.e. forming a barrier to further tissue penetration), pyrogallol acts as a reducing agent (i.e. penetrating deep into tissues, and continuing to act for some weeks after the initial application), mono and trichloroacetic acids hydrolyse tissues (soften and penetrate proteins); Table 1 and see Table 2
Table 1: Caustic agents used in podiatric practice to achieve local tissue destruction
AgentActionSpecial precautionsContraindications
Monochloroacetic acid (crystals or saturated solution) e.g. single VPKeratolytic; hydrolysing agent
Non-self-limiting
Deep penetration
Painful
Do not use mask if applying solution
Use a mask if applying crystals
Review in 5-7 days
Neutralize with foot bath ± NaHCO3 or NaCl
Soft-tissue atrophy
Peripheral vascular disease
Sensory neuropathy
Salicylic acid paste (40-70%) e.g. single VP; plantar hard cornKeratolytic; hydrolysing agentMacerates tissues
Review in 7-14 days
May be used in conjunction with monochloroacetic acid crystals
Neutralize with foot bath ± NaHCO3 or NaCl
Soft-tissue atrophy
Peripheral vascular disease
Sensory neuropathy
Pyrogallic acid e.g. single VPKeratolytic; oxidizing agentDeep penetration
Review in 3-5 days
Prolonged caustic action
Do not apply more than 3 times sequentially
Stains skin black/brown
Use with great care: may cause deep tissue breakdown
Soft-tissue atrophy
Peripheral vascular disease
Sensory neuropathy
Trichloroacetic acid (saturated solution; 10% solution) e.g. mosaic VPMild keratolytic
Protein precipitant
Shallow penetration
Neutralize with foot bath ± NaHCO3 or NaCl
Review in 3 weeks
Peripheral vascular disease
Sensory neuropathy
Silver nitrate (70% solution; 75-95% stick) e.g. mosaic VP; as a protective skin application below a maskProtein precipitant
Self-limiting
Stains skin black/brown
Maximum effect occurs within 24 hours
Some patients show hypersensitivity to silver nitrate (or experience acute pain)
Neutralize with NaCl foot bath
May be applied in alternate layers with trichloroacetic acid
Peripheral vascular disease
Known sensitivity
Potassium hydroxide (KOH; 85% pellets)Strong keratolyticPotentially deep penetration
Action of KOH stopped by application of 5% acetic acid after macerated coagulum has been removed
Single treatment
Soft-tissue atrophy
Peripheral vascular disease
Sensory neuropathy
Phenol (80% solution or 100% crystal)Protein precipitateAction retarded by flooding with industrial methylated spirit
Skin overspill flooded with glycerine
Review as per postoperative protocol
Peripheral vascular disease (phenol suppresses inflammatory response)

VP, verruca pedis.

Table 2: Keratolytic and caustic agents
Keratolytic/caustic agentIndicated use
Whitfield's ointment (3% salicylic acid and 6% benzoic acid in white soft paraffin)Treatment of mild tinea pedis
5% salicylic acid ointmentApplied daily for 7 days to soften hyperkeratosis and facilitate its removal
12% salicylic acid in collodionMacerating agent; painted over callosity and left in situ for 7 days, to assist removal of heavy callosity
20-40% salicylic acid plasterApplied topically and left in situ for 1-2 days to aid removal of corns
40-70% salicylic acid ointmentApplied topically in a cavitied pad and left in situ for 7 days for verruca treatment; the lesion should be masked
Calmurid cream (10% urea)To hydrate anhidrotic skin; applied daily to treat dyskeratosis
40% urea creamA strongly keratolytic agent, applied under an occlusive dressing and left in situ for 7 days, to soften, macerate and aid the reduction and removal of hypertrophied nails in patients who are unsuitable for nail avulsion
Monochloroacetic acidA deeply penetrating caustic that is painful in use Applied, retained in situ and reviewed within 3-7 days, for the treatment of verrucae:
1. as a saturated solution to the lesion
2. as a tiny crystal strapped over a masked lesion
3. as a tiny crystal embedded in 40-70% salicylic acid retained by a cavitied pad
Trichloroacetic acidA self-limiting caustic with a superficial action
Applied directly to the verruca, after initial scalpel debridement of the lesion
May be used in conjunction with 75-95% silver nitrate (see below) as a diagnostic or a final treatment of verrucae
75-95% Silver nitrateA self-limiting caustic with a superficial action, causing a dark brown discoloration of the skin to which it is applied; it is used for the treatment of shallow or mosaic verrucae.
Note: Some patients show an idiosyncratic local sensitivity or inflammatory reaction to applied silver nitrate
1. Applied directly to the lesion, after overlying callosity has been debrided off
2. Applied directly to the lesion in alternating layers with trichloroacetic acid
3. As a diagnostic aid to identify verrucous tissue; viral-infected skin cells show up as bright white dots within a few moments of the application of the layers of silver nitrate and trichloroacetic acid
Potassium hydroxide (KOH)A powerful keratolytic caustic with a great affinity for water that penetrates deeply dissolving precipitated protein; used to destroy soft tissues
1. Overlying hyperkeratosis is debrided off the verruca and the foot is immersed in water for 5 minutes to hydrate the skin, then dried; a KOH pellet is rubbed into the lesion; the foot is reimmersed in water and the jelly-like material formed by the KOH on the lesion surface is debrided off. The process is repeated once or twice until the lesion appears to have gone, then glacial acetic acid is applied to neutralize the KOH
2. A similar protocol may be used to ablate nail matrix after removal of the overlying section of nail plate
3. KOH 5% liquid applied to heavy callosity and left in situ for 5 minutes softens heavy callosity to ease its removal
Pyrogallol (pyrogallic acid)A powerful analgesic, non-self-limiting, caustic reducing agent. It may be used in the treatment of recalcitrant verrucae or neurovascular corns in areas of skin overlying a healthy layer of fibrofatty padding. It should only be used with great caution as its action continues after application has ceased and can lead to severe tissue breakdown that is slow to heal. It is incompatible with alkalis, iron salts, oxidizing agents and ammonium salts
1. 20% pyrogallol ointment for the treatment of neurovascular corns
2. 40% pyrogallol ointment for the treatment of VP
3. WP ointment (20% pyrogallol, 20% wheat germ oil) for the treatment of tough, fibrous, hyperkeratotic plantar lesions
PhenolAn analgesic, corrosive caustic. It is used as an 80% solution (liquefied phenol) to destroy soft-tissue lesions such as VP, or nail matrices (three applications, each of 1 minute duration). Its action is quenched by dilution with IMS or isopropyl alcohol. Healing is delayed for several weeks after its application
Glacial acetic acidA weakly acidic mild caustic that is crystalline at 14°C
1. As a paint to hard or vascular corns, or VP (return period 14-21 days)
2. As a paint to VP, alternating with silver nitrate 75% (in a similar manner to trichloroacetic acid)
3. To neutralize KOH (see above: KOH, point 1)
Nitric acidA powerful analgesic oxidizing caustic agent with a superficial action that offers a 'one-off' VP treatment
1. Applied to VP with a glass rod and left in situ for 5 minutes, followed by phenol solution 10%; the skin stains bright yellow
2. The lesion is saturated with phenol solution 5% for 5 minutes, then with nitric acid for 20-30 seconds, then once again with phenol solution 5%
Strong iodine solution (iodine solution 10%; iodine fortis)A strong astringent and vesicant agent. It is incompatible with many topical medicaments, and can cause sensitivity reactions in some patients
1. to shrink nail tufts
2. to shrink hypergranulation tissue
FormaldehydeA strongly astringent and antiseptic agent used in the treatment of VPs (the skin surrounding the lesion should be protected with petroleum jelly; sensitivity is likely)
1. 10% formaldehyde in collodion, painted on daily
2. 36% formaldehyde solution, painted on daily
Thermal caustics
CryosurgeryThe topical application of liquid nitrogen (at -196°C) or nitrous oxide (at -88.5°C) to destroy small soft-tissue lesions; the cell cytoplasm must be reduced to and maintained at -24°C or lower for at least 1 minute, and repeated for two further freezing episodes between which the area has been allowed to thaw. Cryosurgery is more effective when any overlying hyperkeratosis is removed before freezing
HyfrecationTissue destruction by initial fulguration (outlining and superficial charring) of the lesion by the application of high-frequency electrical energy), then electrodesiccation (electrocautery) of the lesion by the release of electrical energy whilst the probe is inserted into the lesion
ElectrosurgeryTissue removal using high-frequency energy waves to incise through tissue

Note: Please also refer to the text entries for each listed agent.

IMS, industrial methylated spirit; VP, verrucae pedis.

caustic 

The concentration of light in the caustic surface of a bundle of converging light rays which represents the focal image in an optical system uncorrected for spherical aberration. It appears as a hollow luminous cusp with its apex at the paraxial focus.

caus·tic

(kaws'tik)
1. Chemically exerting an effect resembling a burn.
2. An agent producing this effect.
[G. kaustikos, fr. kaiō, to burn]

caustic,

adj destroying living tissue by chemical burning action.

caustic

1. burning or corrosive; destructive to tissue.
2. having a burning taste.
3. a corrosive or escharotic agent.

caustic bush
sarcostemmaaustrale, S. viminale.
bottle tree caustic
caustic creeper
euphorbiadrummondii, sarcostemmaviminale.
lunar caustic
toughened silver nitrate.
caustic pencil
see silver nitrate (toughened).
caustic plant
sarcostemmaaustrale.
caustic potash
potassium hydroxide.
caustic soda
sodium hydroxide.
caustic treated grain
grain treated with caustic to improve its digestibility; can cause abomasal ulcer and interstitial nephritis in cattle.
caustic treated roughage
roughage treated with caustic to improve its digestibility; can cause interstitial nephritis when fed to cows over long periods.
caustic vine
sarcostemmaaustrale, S. viminale. Called also caustic bush.
caustic weed
euphorbiadrummondii.