Theory 15/Palliative & Symptom Science

Opioids Work on a Drive Ratio

The claim

Opioid relief of dyspnoea is set by the ratio of mu-opioid occupancy to ventilatory drive rather than by dose, so a patient with high drive needs more drug for the same relief.

01The mechanism

Dyspnoea reflects the mismatch between drive and capacity. Opioids reduce the drive component by dampening the CO2 response, so relief depends on how much drive there is to dampen.

That makes the ratio the determinant, and predicts that high-drive patients show less relief at the same occupancy.

02What this is not

Dose-response models

Those titrate by dose. This titrates by drive, which explains variable response.

03Predictions

P1Relief should track the occupancy-to-drive ratio.
P2High-drive patients should need higher occupancy.

04Refutation

Relief tracking dose at controlled drive would favour the dose model.