Intrathecal is an adjective that refers to something introduced into or occurring in the space under the arachnoid membrane of the brain or spinal cord. For example, intrathecal immunoglobulin production means production of this substance in the spinal cord.
Another way the word is used is to refer to an intrathecal injection (often simply called "an intrathecal"). This is an injection into the spinal canal, more specifically into the sub-arachnoid space so that it reaches the CSF and is useful in spinal anaesthesia, chemotherapy, or pain management applications. This route is also used to introduce drugs that fight certain infections, particularly post-neurosurgical. The drug needs to be given this way to avoid the blood brain barrier. The same drug given orally must enter the blood stream and may not be able to pass out and into the brain. Drugs given intrathecally often have to be made up specially by a pharmacist or technician because they cannot contain any preservative or other potentially harmful inactive ingredients that are sometimes found in standard injectable drug preparations.
Intrathecal administration of analgesic agents 
- Very popular for a single 24-hour dose of analgesia (opioid with Local anesthetic)
- Caution because of late onset respiratory depression
- Severe pruritus and urinary retention may limit the use of intrathecal morphine
- Meperidine has the unusual property of being both a local anaesthetic and opioid analgesic which occasionally permits its use as the sole intrathecal anaesthetic agent
- Ziconotide is a conotoxin-derived peptide used for chronic pain therapy
Intrathecal chemotherapy 
- Currently, only three agents are licensed for intrathecal chemotherapy
- Administration of other chemotherapeutic agents such as vincristine via the intrathecal route can lead to fatal outcomes.
Intrathecal baclofen 
Often reserved for spastic cerebral palsy, intrathecally-administered baclofen is done through an intrathecal pump implanted just below the skin of the stomach with a tube connected directly to the base of the spine, where it bathes the appropriate nerves using a dose about one thousand times smaller than that required by orally-administered baclofen. Intrathecal baclofen also carries none of the side effects, such as sleepiness, that typically occur with oral baclofen. However, intrathecal baclofen pumps carry serious clinical risks, such as infection or a possibly fatal sudden malfunction, that oral baclofen does not.
- ^ "Route of Administration". Data Standards Manual. Food and Drug Administration. Retrieved 11 March 2011.
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See also