the rest of the body unaffected. That is the idea behind a new class of
pH-dependent drugs that interfere with nerve signals to the brain and
spinal cord - but only where the tissue is slightly acidic due to injury.
Normal tissue has a pH of around 7.4, but this drops to around 7.0 in
injured tissue, largely because the blood supply is disrupted, resulting
in the accumulation of waste products such as carbon dioxide and a
switch to anaerobic respiration, which produces lactic acid.
The new drugs act by blocking NMDA receptors, which are found on cells
throughout the brain and central nervous system and are implicated in a
variety of nerve functions, including pain sensitisation. Earlier
generations of drugs, such as ketamine, also targeted NMDA receptors,
but these often have unwanted side effects such as impaired movement or hallucinations, because they act on undamaged nerve tissue as well.