Intrathecal administration is the administration of drugs into the central nervous system (CNS) via the cerebrospinal fluid. This is usually achieved using a lumbar puncture (Polovich et al. [287], Stanley [340], Wilkes [372]).

Medications can be administered intrathecally if they have poor lipid solubility and therefore do not pass the blood–brain barrier (Downie et al. [82]). Only medication specially prepared for the intrathecal route should be used; doses should be carefully calculated and are usually much smaller than would be given by intramuscular or intravenous injection. Water‐soluble antibiotics are administered by the intrathecal route to achieve adequate concentrations in the cerebrospinal fluid in the treatment of meningitis. Other medicines administered via this route include antifungal agents, opioids, cytotoxic therapy and radio‐opaque substances (used in the diagnosis of spinal lesions) (Downie et al. [82]).

The advantage of this route is that it allows direct access to the CNS by drugs that do not normally cross the blood–brain barrier in sufficient amounts; it thus ensures constant levels of the drug in this area. The main disadvantage is that it requires a standard lumbar puncture before the drug can be injected, and this may need to be performed on a daily to weekly basis (Wilkes and Barton‐Burke [373]). Although this can be quick and easy to perform, it can be distressing for the patient, and can even result in CNS trauma and infection. It may also only reach the epidural or subdural spaces and therefore the concentrations in the ventricles may not be therapeutic (Wilkes and Barton‐Burke [373]). However, central instillation of the drug into the ventricle can be achieved via an Ommaya reservoir (Figure 15.27), which is surgically implanted through the cranium (Weinstein and Hagle [363], Wilkes and Barton‐Burke [373]). It carries more risk but provides permanent access and can be inserted under local or general anaesthetic (Wilkes and Barton‐Burke [373]). Doses of intraventricular drugs tend to be lower than those given intrathecally.

Chemotherapy administered using this route has the potential to cause great harm and it was associated with the deaths of at least 13 patients between 1985 and 2002 (Sewell et al. [330]). The risks of intrathecal chemotherapy were well documented in An Organisation with a Memory (DH [58]) and the government set a target to eliminate the incidents of patients dying or being paralysed by maladministered intrathecal injections by the end of 2001 (DH [58]). Two reports on injection errors (see Toft [350]) gave rise to the publication of national guidance on the safe administration of intrathecal chemotherapy.

Following the publication of the guidance, all UK trusts that undertake to administer intrathecal cytotoxic chemotherapy must ensure safe practice guidelines have been introduced and that they are fully compliant with the Updated National Guidance on the Safe Administration of Intrathecal Chemotherapy (DH [65]). The key requirements of the guidance are noted in Box 15.10.

The hospital's chief executive must identify a ‘designated lead’, who in turn must ensure the appropriate induction, training and continuing professional development of designated personnel authorized to administer intrathecal chemotherapy. A register of these personnel must be kept along with details of certain competency‐based tasks such as prescribing, dispensing, issuing, checking and administration. It is important to keep up to date with relevant safety alerts concerning intrathecal therapy; these may be issued by Department of Health agencies such as the Medicines and Healthcare products Regulatory Agency (MHRA), previously known as the National Patient Safety Agency (NPSA), whose function was taken over by the NHS Commissioning Board in 2012. Such reports have highlighted concerns over the risk of neurological injury due to implantable drug pumps for intrathecal therapy (MHRA [206]) and the storage of vinca alkaloid minibags (NPSA [272]). More recently, the NPSA published two alerts to ensure that all needles, syringes and other devices used for intrathecal administration of medication cannot be attached to any intravenous equipment to prevent maladministered injections (NPSA [276]). Injection of a drug intended for intravenous use into the intrathecal space is considered a ‘Never Event’ (NHSI [237]).