British journal of anaesthesia
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Direct or indirect acting cholinergic muscarinic agonists such as neostigmine, are potent antinociceptives when administered intrathecally (i.t.). This study examines whether spinal neostigmine tolerance and cross-tolerance to spinal morphine occurs. ⋯ Thus, unidirectional cross-tolerance from morphine to neostigmine was evident. Previous studies suggest morphine has a cholinergic mechanism of action partially accounting for its antinociceptive effect, which may explain this observed unidirectional cross-tolerance.