I received a call recently from a surgery center looking for an intrathecal injection containing morphine, clonidine, and baclofen. Appropriately, the caller was adamant that this product contain no preservatives since it is to be delivered via the intrathecal route. However, when I asked if the center was using epidural steroid injections the caller commented that they were using Kenalog® for their epidural steroid injections (ESIs). When I explained to the caller that Kenalog contains a preservative, there was a long silence and then the question came…”is there a preservative-free steroid injection containing triamcinolone acetonide?” “Yes!” was my answer. Then we entered into a conversation about why preservatives are potentially dangerous when given via the intrathecal and/or epidural route.
Many drugs are given via the epidural or intrathecal route to induce a more direct effect on the central nervous system (CNS) by bypassing the blood-brain barrier. Pain medications, anesthesia, and even chemotherapeutic agents are given via this delivery route. However, it is important to realize that pharmaceutical agents given via the epidural or intrathecal route should be completely preservative free. There are hundreds of studies demonstrating the negative side effects of injecting preservatives into the intrathecal or epidural space. Some of the side effects include spinal leaking, bleeding and infection.
A few of the most widely used pharmaceutical preservatives include benzyl alcohol, methylparaben and propylparaben, phenol, sulfites, and polyethylene glycol. If it is unclear whether or not a drug can be given via the epidural or intrathecal space, the product package insert can be consulted. A list of active and inactive ingredients is listed in the insert. However, most injectable products clearly state whether the product contains a preservative or is preservative free. Preservative-free does not necessarily mean the product can be injected into the epidural or intrathecal space and a clear understanding of the drug and its use must be known. If there is a question whether a drug can be given via the epidural or intrathecal route, ask your consultant pharmacist or your compounding provider.