Acetylcholinesterase inhibitors inhibit the enzyme acetylcholinesterase (AChE) and allow ACh to remain active at the synapse and alter timing of synaptic transmission. This can result in prolonged contraction of muscles and resultant paralysis as well as overactivity of the parasympathetic nervous system. 

Acetylcholinesterase inhibitors

Drugs altering transmitter clearance can work by inhibiting degradation, the chemical process of breaking down neurotransmitter into inactive metabolites, allowing the transmitter to accumulate and have a greater effect on the postsynaptic cell. 

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Immediately after release, transmitter is rapidly cleared from the synapse. Getting rid of the used transmitter is normally an important step because unit it is gone, new release of transmitter from the presynaptic side won't be able to have much extra effect. 
 This can occur through: 
- The inactivation of transmitter reuptake
- The blockade of transmitter degradation

Drugs effects on transmitter clearance from the synapse

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Drugs interfere with transmitter reuptake by blocking the specialized proteins called transporters that normally remove neurotransmitter from the cleft for reuse. 

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