Ans. a (Entacapone) (Ref. KDT 6th/pg. 415)ADRENERGIC DRUGSSr NoStep/siteActionDrugResponse1.Synthesis of NAInhibition Utilization of same synthetic pathwaya-methyl-p-tyrosine a-methyl dopaDepletion of NAReplacement of NA by a-methyl NA(false transmitter)2.Axonal uptakeBlockadeCocaine, desipra- mine, guanethidine, antihistaminics, ephedrinePotentiation of NA (endo- and exogenous), inhibition of tyramine3.Granular uptakeBlockadeReserpineDepletion of NA (degraded by MAO)4.Nerve impulse coupled release of NAInhibitionGuanethidine, bretyliumLoss of transmission5.Granular NADisplacementGuanethidineInitially sympathomimetic, depletion later.6.Membrane NA poolExchange diffusionTyramine, ephedrineIndirect sympathomimetic7.MetabolismMAO inhibition COMT inhibitionNialamid tranylcy- promine Tolcapone, entacaponePotentiation of NA (slight),| Of tyramine (marked) Potentiation of NA (slight)8.ReceptorsMimickingPhenylephrine Clonidinea1 sympathomimetica2-inhibition of NA release, |sympathetic outflow IsoprenaiineSalbutamolb1+ b2 - sympathomimeticb2-sympathomimetic BlockadePhenoxybenzaminePrazosinYohimbinePropranololMetoprolola1 + a2 - blockadea1- blockadea2 - blockadeb1 + b2 - blockadeb1 - blockadePergolidePergolide, another ergot derivative, directly stimulates both D1 and D2 receptors.It too has been widely used for parkinsonism, and comparative studies suggest that it is more effective than bromocriptine in relieving the symptoms and signs of parkinsonism, increasing "on-time" among response fluctuators, and permitting the levodopa dose to be reduced.PramipexolePramipexole, which is not an ergot derivative, has preferential affinity for the D3 family of receptors. It is effective when used as monotherapy for mild parkinsonism.RopiniroleRopinirole, another nonergoline derivative, is a relatively pure D2 receptor agonist that is effective as monotherapy in patients with mild disease and as a means of smoothing the response to levodopa in patients with more advanced disease and response fluctuations.RasagilineRasagiline, another monoamine oxidase B inhibitor, is more potent than selegiline in preventing MPTP- induced parkinsonism and is currently under study as a neuroprotective agent.TolcaponeSelective COMT inhibitors such as tolcapone and entacapone also prolong the action of levodopa by diminishing its peripheral metabolism.