A drug injected around the dura or into the central nervous system can elicit unwanted reactions if it contains preservatives or particulate matter.


Chemical preservatives may include:

(1) phenol

(2) formaldehyde

(3) benzyl alcohol

(4) parabens

(5) polyethylene glycol

(6) sodium sulfite


Consequences of injecting a drug that contains a preservative or particulate matter:

(1) inflammation (arachnoiditis, ventriculitis, aseptic meningitis)

(2) neurotoxicity

(3) neuropathy


It may be hard to be sure that the preservative is the cause of a patient's problems, so usually it is easier to avoid the preservative all together. A preservative can be implicated with some certainty if:

(1) The patient has a problem after use of a formulation that contains a preservative, but not after use of formulation without the preservative (requires multiple injections).

(2) The preservative is a known toxin (like formaldehyde.

(3) The concentration of the preservative is high, above levels known to be safe.



(1) Use a preservative-free formulation if possible.

(2) If a preservative-free formulation is not available, then select a formulation with a level of a preservative unlikely to cause harm.

(3) Filter out any particulate matter.


Differential diagnosis:

(1) true meningitis caused by injecting a contaminated solution or lack of sterile technique

(2) toxicity due to the drug being injected

(3) toxicity due to chemical solutions used to clean the skin prior to the injection


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