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PNS Drugs
Peripheral neurotransmission drugs
| Term | Definition |
|---|---|
| Verapamil | Aminoglycoside Abx -> inhibit Cav channels -> affect transmitter release |
| Tetracycline | Chelate Ca2+ -> less Ca2+ available for vesicle fusion |
| Hemicholinium | Inhibits ChT1 (choline transporter 1) -> ACh pre-synaptic reuptake inhibited |
| Vesamicol | Non-competitive/reversible blocker of vAChT (vesicular ACh transporter) |
| Trimetaphan | Neuronal nAChR competitive antagonist |
| Hexamethonium | Neuronal nAChR inhibitor -> blocks channel pores -> use dependent |
| Nicotine | Neuronal nACh agonist, low [ ] -> stimulates neuronal nAChR, high [ ] -> desensitises neuronal nAChR |
| Varenicline | High affinity partial agonist for α4β2 neuronal nAChR, full agonist for α7 neuronal nAChR |
| Neostigmine | AChE reversible inhibitor -> increase NMJ [ACh] -> anaesthesiologists shorten neuromuscular blockade |
| Aminosteroids | -uronium -> non-depolarising neuronal mAChR competitive antagonist |
| Rocuronium | Non-depolarising neuronal mAChR competitive antagonist, IM acting (30-40 mins) |
| Pancuronium | Non-depolarising neuronal mAChR competitive antagonist, long-acting (60-120 mins) |
| Benzylisoquinolinium | -urium -> non-depolarising neuronal mAChR competitive antagonist |
| Atracurium | Non-depolarising neuronal mAChR competitive antagonist, IM acting (30-40 mins) |
| Streptomycin/neomycin | Aminoglycoside Abx, high dose -> inhibit Cav channels -> myasthenia gravis NM blockade, low dose -> prolong muscle paralysis w/ NM blocking agents (general anaesthesia adjunct) |
| Carbachol/bethanechol | Choline synthetic esters |
| Bethanechol mechanism | Hybrid of methacoline/carbachol -> lacks nicotinic actions but non-selectively activates mAChR subtypes -> M3 -> stimulates detrusor bladder muscle, trigone/sphincter muscles relaxed -> voiding |
| Pilocarpine | Naturally occuring cholinomimetic alkaloid -> stable to AChE hydrolysis -> M3 agonist |
| Pilocarpine superior mechanism | Eye drops -> readily absorbed across conjunctival membrane -> treat glaucoma -> contract ciliary muscle -> increased aqueous humour drainage -> drop in intraocular Pa |
| Pilocarpine inferior mechanism | Promote salivary secretion in xerostomia -> dry mouth from head/neck cancer radiotherapy -> treat Sjogren's syndrome - autoimmune fluid-secreting gland disease |
| Atropine/scopolamine | Naturally occuring alkaloids -> mAChR antagonist |
| Homotropine, methscopolamine, ipratropium | Semi-synthetic derivatives -> mAChR antagonist |
| Pirenzepine, darifenacin, solifenacin | Synthetic agents -> mAChR antagonist -> p - M1 selective -> inhibit gastric acid secretion, d/s - M3 selective -> inhibit detrusor muscle relaxation -> treat urinary incontinence |
| Tropicamide clinical use | Synthetic mAChR antagonist -> used in ophthalmic fundoscopy -> 4-6 hrs -> mydriasis - pupil dilation, cycloplegia - ciliary muscle paralysis |
| Atropine uses/effects | Naturally occuring alkaloid -> mAChR antagonist -> irreversible, long-acting AChEi -> large dose - progressive tachycardia -> blocks SA node M2 receptors -> block vagal stimulation |
| BuChE | Broader substrate specificity than AChE -> pseudocholinesterase -> breaks down local anaesthetic procaine/suxamethonium (NMJ depolarising blocker) -> synthesised in liver, works in plasma |
| Isoprenaline | Non-selective beta agonist, synthetic N-isopropyl NA derivative -> experimentally used as synthetic catecholamine -> bronchial dilation (asthma treatment) -> problematic +ve chronotropic effect (beta1) |
| Alpha-methylTyr | TOH competitive inhibitor (less L-Tyr -> DOPA -> DA - NA) -> preoperative treatment of phaeochromocytoma |
| Disulfiram | Experimentally inhibits DBH - DA beta-hydroxylase (less DA -> NA) |
| Alpha-methyldopa | Taken in by NA nerve terminals -> converted into alpha-methylDA/NA -> released as NA false transmitter -> less active at alpha1 receptors, more selective for alpha2 receptors |
| Clonidine | Inhibit C/PNS NA release via presynaptic alpha2 receptor/I1 imidazoline receptor -> reduce vasoconstriction -> fall in blood Pa |
| Reserpine | Naturally ocurring alkaloid -> high affinity for VMAT2 amine site -> irreversibly blocks monoamine (DA/NA/5-HT) uptake into vesicles |
| Tetrabenazine/valbenazine | VMAT2 inhibitors -> manage abnormal involuntary mvmt (Huntington's, tardive dyskinesia) |
| Alpha-dihydrotetrabenazine (DTBZ) | Reversibly inhibits VMAT2 -> larger DA inhibition than other monoamines |
| Guanethidine | Selectively accumulates into NA nerves via Uptake1/NET -> low doses - block nerve impulse conduction -> accumulate into vesicles via VMAT2 -> long-lasting NA depletion, high doses - irreversible nerve damage |
| Tyramine | Ca2+ independent NA nerve ending transmitter release -> taken into NA nerves via Uptake1/NET -> loaded into presynaptic vesicles via VMAT2 -> displace NA -> expelled into synapse by NET reverse transport |
| Ephedrine | Mixed-acting sympathomimetic amine -> indirectly releases NA (tyramine/dexamfetamine), directly activates ARs -> NA-mediated vasoconstriction in nasal blood vessels, direct action on bronchial beta2 ARs -> bronchodilation |
| Presynaptic alpha2 R | Gi/o coupled -> activation decreases cAMP production -> deactivate PKA -> decrease Ca2+ channel PO43- -> decrease NA release, beta-gamma activation -> opens GIRK -> K+ efflux -> hyperpolarisation -> reduce excitability |
| Presynaptic alpha2 R blockers | Increase NA released -> remove AC inhibition, close GIRK |
| Presynaptic beta2 R | Gs coupled -> increase cAMP -> activate PKA -> increase Ca2+ channel PO43- -> increase NA release |
| Entacapone | COMT inhibitor -> less L-DOPA metabolised -> more reaches CNS -> produce DA |
| Xylometazoline | Selective alpha > beta agonist -> relieve nasal congestion by dilating nasal mucosal blood vessels -> previously constricted due to inflammation/swelling |
| Phenylephrine/oxymetazoline | Selective alpha1 R agonist -> nasal decongestants, mydriasis -> dilate pupils for ophthalmic fundoscopy -> anti-hypotensive (vasoconstriction) |
| Triethylcholine | Competes w/ choline as CAT (choline acetyl transferase) substrate -> converted into acetyltriethylcholine -> false transmitter -> less potent at cholinergic receptors |
| Suxamethonium | Neuronal mAChR agonist, increasing [ ] -> NM block converts to non-depolarising block (phase 2) -> membrane repolarises as neuronal mAChR desnsitised, fast onset/brief action -> tracheal intubation, plasma hydrolysis by BuChE |
| Curare | Non-depolarising neuronal mAChR competitive antagonist, natural alkaloids -> poor selectivity btwn ganglionic/NMJ AChR |
| Tiotropium | Long-acting muscarinic antagonist -> slow M3 dissociation, fast M2 dissociation, additional bronchodilation |
| Glycopyrronium | Long-acting M3 antagonist -> doesn't cross BBB -> treat drug induced salivation/heavy-metal poisoning/Parkinson's -> bronchodilation for COPD patients |
| Dexamfetamine | Indirectly-acting sympathomimetic amine -> taken up into NA nerve endings via Uptake1/NET -> loaded into presynaptic vesicles via VMAT2 -> displace NA -> expelled into synapse by NET reverse transport -> narcolepsy |
| 6-OHDA (hydroxydopamine) | Synthetic neurotoxic organic compound -> uptake into NA nerves via NET -> readily oxidised into reactive metabolites (6-OHDA quinone, H2O2) -> nerve damage -> selectively destroys DA/NA neurons -> Parkinson's |
| Mirabegron | Beta3 R selective agonist -> relax detrusor smooth muscle -> increase bladder capacity |
| Phentolamine/phenoxybenzamine | Alpha-AR selective antagonists -> xcs blood Pa reduction -> reflex tachycardia |
| Prazosin | Selective competitive alpha1-AR antagonist -> antihypertensive but postural hypotension/incontinence (detrusor smooth muscle contraction) |
| Atenolol | Selective beta1-AR antagonist -> antihypertensive w/out postural hypertension (alpha unaffected) -> inhibit endogenous catecholamine +ve chrono/ionotropy (beta1) |
| Suramin | ATP antagonist for peripheral NANC transmitter corelease -> abolishes early peak -> treat trypanosomes (selective uptake and inhibit cellular metabolism) |
| Regadenoson | Adenosine derivative -> selective A2A receptor agonist -> coronary vasodilating -> radionuclide myocardial perfusion imaging -> stress agent (similar effect to exercise) |
| Dobutamine | Beta1 R selective agonist -> increase CO in cardiogenic shock -> can cause cardiac dysrhythmias |
| Salbutamol/terbutaline | Short-acting beta2 R selective agonists -> bronchodilation in asthma -> max effect w/in 30 mins lasting 5 hours |
| Salmeterol/formoterol | Long-acting beta2 R agonists -> prophylactic against chronic asthma |
| Indacaterol | Long-acting beta2 R selective agonist -> treat COPD |
| Phenoxybenzamine | Alpha-AR selective antagonist -> covalently binds -> long-term inhibition |
| Tamsulosin | Selective competitive alpha1B-AR antagonist -> prostate capsule relaxation -> inhibit prostrate hypertrophy, better voiding -> reduce urinary retention from BPH, less postural hypertension |
| Yohimbine | Selective alpha2-AR antagonist -> naturally occuring alkaloid -> no human clinical use |
| Propranolol | Non-selective beta1/2 AR blockers -> antihypertensive but inhibits bronchodilation |
| Nebivolol | Selective beta1-AR antagonist -> antihypertensive -> inhibit endogenous catecholamine +ve chrono/ionotropy -> cardioprotective (promote endothelium/myocardium NO release) |
| Carvedilol | Mixed alpha1/beta-AR antagonist -> antioxidant/inflammatory |
| Dipyridamole | Blocks adenosine cell uptake via NsT (nucleoside transporter) -> indirectly increases [adenosine]e |
| Methotrexate | Purine metabolism inhibitor -> increase [adenosine]e -> anticancer/immunosuppressant drug |
| Methylxanthines | Caffeine -> competitive presynaptic A1 R antagonist -> increase C/PNS excitatory neurotransmitter release |
| Imipramine/cocaine | Uptake 1 inhibitors (NET - norepinephrine transport protein) -> prevent NA reuptake from synaptic cleft -> enhance/prolong NA actions |
| Normetanephrine | Uptake 2 inhibitors (ENT - extraneuronal amine transporter) -> prevent NA reuptake in non-neuronal cells -> no effect on released NA response |
| NMJ depolarising blockers | Bind to nAChR -> not hydrolysed -> longer depolarisation -> transient repetitive muscle excitation (fasciculation) -> flaccid paralysis (phase 1 block) as open nAChR maintain depolarisation but Nav channels inactivated -> can cause hyperkalaemia |
| NMJ non-depolarising blockers | Prevent sarcolemma depolarisation (no fasciculations) but inhibit muscular contraction -> flaccid paralysis -> overcome w/ anticholinesterases |
| Carbidopa | Inhibits peripheral DOPA decarboxylase -> prevents peripheral L-DOPA from deCO2 and producing unwanted DA/NA |
| L-DOPA | Natural precursor for DOPA (bypass TOH rate limiting step) -> cross BBB -> boost Parkinsonian brain DA synthesis |
| Pargyline | Non-specific MAO inhibitor -> prevent catecholamine metabolism |
| Clorgyline/moclobemide | Selective MAO-A inhibitor -> mito outer membrane in NA neurons, liver, GI tract -> degrades 5-HT, DA, NA |
| Selegiline | Selective MAO-B inhibitor -> mito outer membrane in NA neurons, platelets -> degrades DA |
Created by:
vykleung
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