HAPTO Study: Haemoglobin And Vancomycin Pharmacokinetics in the Cerebrospinal Fluid Following Subarachnoid Haemorrhage: Therapeutic Optimisation of Haptoglobin

The HAPTO study aims to improve the treatment of a specific type of stroke known as aneurysmal subarachnoid haemorrhage (aSAH). This stroke can occur when a weak point in a blood vessel in the brain called an aneurysm bursts. This causes bleeding into the surrounding area. aSAH is not only life-threatening, but also leaves many survivors with long-term disabilities and health issues that affect the quality of their life.

After aSAH, haemoglobin - a protein normally found inside red blood cells - leaks out into the brain and its surrounding fluid. While inside red blood cells, haemoglobin is safe, but when it leaks out it is toxic and causes more damage to the brain. Our bodies have a natural defence, which is a substance called haptoglobin. Haptoglobin can grab onto haemoglobin and potentially stop its harmful effects. Although there is lots of haptoglobin in the rest of the body, there is virtually none in the brain to protect against haemoglobin. Therefore, haptoglobin is being developed as a drug that can be delivered directly to the brain to treat patients with aSAH.

The HAPTO study measures the amount of haemoglobin that different areas of the brain and spine are exposed to after aSAH. These areas are the ventricles (cavities in the brain), the lumbar spine (lower back), and the basal cisterns (near the brain's base where aneurysms are normally found). By collecting fluid samples from these places, we can measure how much haemoglobin there is, and from this, we can work out how much haptoglobin will be needed.

Apart from knowing how much to give, we need to know where to give it. The main options are to insert it either through a tube in the cavities of the brain (external ventricular drain) or a tube inserted into the spine (lumbar drain). Little is known about how drugs distribute around the nervous system in general, and even less in patients who have had an aSAH in whom the flow of fluid around the brain is disturbed. This study will try to find out more by using a common antibiotic, vancomycin, as a tracer to understand how drugs move within different regions of the brain and spine following aSAH. This approach will provide valuable insights into the possible ways to give haptoglobin (and any other future treatments requiring injection into the brain or spine).

The HAPTO study will recruit adult patients with aSAH due to a burst aneurysm. These patients must be scheduled to have their aneurysm treated surgically to prevent further bleeds, and need an external ventricular drain for clinical reasons (to drain fluid and relieve pressure on the brain). At the end of their surgery for their aneurysm, a further drain will be left at the site of the surgery (which is in the basal cisterns) and they will additionally have a drain sited in their lumbar spine. Vancomycin will be given through these drains. Additionally, these drains will allow the fluid in the brain to be collected to measure how haemoglobin levels and vancomycin levels differ between compartments and change over time. Patients will participate in the study over a period from recruitment at three days after aSAH to a maximum of ten days after aSAH. The data will be analysed to determine the relationship in haemoglobin concentrations between different areas of the brain and spine after aSAH, and how vancomycin distribution is related to its route of administration.