| Subarachnoid space | |
|---|---|
 Diagrammatic representation of a section across the top of the skull, showing the membranes of the brain, etc. ("Subarachnoid cavity" visible at left.) | |
 Diagrammatic transverse section of the medulla spinalis and its membranes. (Subarachnoid cavity colored blue.) | |
| Details | |
| Identifiers | |
| Latin | Spatium subarachnoideum, cavum subarachnoideale |
| Anatomical terminology | |
Intrathecal administration is aroute of administration for drugs via aninjection into thespinal canal, or into thesubarachnoid space so that it reaches thecerebrospinal fluid (CSF). It is useful in several applications, such as forspinal anesthesia,chemotherapy, orpain management. This route is also used to introduce drugs that fight certain infections, particularly post-neurosurgical. Typically, the drug is given this way to avoid being stopped by theblood–brain barrier, as it may not be able to pass into the brain when given orally. Drugs given by the intrathecal route often have to be compounded 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 pseudodelivery is a technique where the drug is encapsulated in a porous capsule that is placed in communication with the cerebrospinal CSF. In this method, the drug is not released into the CSF. Instead, the CSF is in communication with the capsule through its porous walls, allowing the drug to interact with its target within the capsule itself. This allows for localized treatment while avoiding systemic distribution of the drug, potentially reducing side effects and enhancing the therapeutic efficacy for conditions affecting the central nervous system.
The route of administration is sometimes simply referred to as "intrathecal"; however, the term is also an adjective that refers to something occurring in or introduced into theanatomic space orpotential space inside a sheath, most commonly thearachnoid membrane of thebrain orspinal cord[1] (under which is thesubarachnoid space). For example, intrathecal immunoglobulin production is production of antibodies in the spinal cord.[2] The abbreviation "IT" is best not used; instead, "intrathecal" is spelled out to avoid medical mistakes.[citation needed]
Intrathecal administration of drugs foranaesthesia or analgesia can be utilized in the form of single-dose or continuous viacatheter with external or internal pump depending on indication and duration needed. Usually a combination of alocal anesthetic and one or moreadjuvant drugs are used.
Intrathecalclonidine ordexmedetomidine can be used to prolong duration of anaesthesia and analgesia but comes with increased risk of hypotension.[3][4]
Lipophilic opioids such asfentanyl andsufentanil can be administered intrathecally for short duration of anaesthesia and analgesia.
Hydrophilic opioids such asmorphine, diamorphine andhydromorphone can be administered intrathecally for longer duration of analgesia, up to 24 hours.
Pethidine has the unusual property of being both a local anaesthetic and opioidanalgesic, which occasionally permits its use as the sole intrathecal anaesthetic agent.
Caution should be exercised with intrathecal opioids due to the risk ofhypoventilation. Hydrophilic opioids comes with a dose-dependent risk of late onset hypoventilation, however, low-dose intrathecal hydrophilic opioids have similar risk for hypoventilation as systemic opioids.[5] Other adverse effects of intrathecal opioids include nausea and vomiting,pruritus andurinary retention.[6]
Amphotericin B is administered intrathecally to treat fungal infections involving the central nervous system infections.[7]
Currently, only four agents are licensed for intrathecal cancer chemotherapy:methotrexate,cytarabine,hydrocortisone, andthiotepa.[8]
Administration of anyvinca alkaloids, especiallyvincristine, via the intrathecal route is nearly always fatal.[9][10][11]
Often reserved forspastic cerebral palsy,baclofen can be administered through anintrathecal pump implanted just below the skin of the abdomen or behind the chest wall, with a catheter connected directly to the base of the spine. Intrathecal baclofen pumps sometimes carry serious clinical risks, such as infection or a possibly fatal sudden malfunction.[citation needed]
Treatment of chronic spinal injuries via the administration ofmesenchymal stem cells,[12] either from adipose tissue or bone marrow, is experimental, with better results from the former method. Introduction of mesenchymal stem cells promote the microenvironment needed for axonal regrowth and reduction of inflammation caused by astrocytes proliferation and glial scar tissue.[13]
Animal models have shown improved motor control under the site of injury. A clinical trial also showed statistically significant improved sensitivity under the site of injury in patients.[14]
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