Domperidone is supplied as 10mg tablets. The suggested regime is to take two tablets (20mg) an hour before taking the lethal drug. Although a dopamine-antagonist, the drug does not easily cross into the brain (the blood brain barrier). As a consequence, Domperidone has a significantly lower risk of neurologic (extra-pyramidal) movement-related side effects. Note - This drug is not available in the US.
Prochlorperzine is another dopamine-antagonist with significant anti-emetic properties. Common brand names are Stemetil and Promat. Marketed as 5mg tablets, a useful end of life regime is 2 tablets (10mg) taken an hour before the lethal drug. This medication crosses readily into the brain and has a propensity for sedation and extrapyramidal movement-related symptoms. These side effects can limit the drug’s usefulness and a test- dose should be taken before considering this as your chosen anti-emetic.