Half Life | Tools To Influence Sympathetic Transmission | Expectorants, Antitussives

Question 1

Drug half life concept and elimination

Answer 1

T1/2 = [0,693 * Vd]/CL

Zero order kinetics elimination [T1/2 not constant, constant amount of drug is eliminated | Ethanol, Phenytoin, Salicylates at high doses, Cisplatin, Omeprazole, Floxetine SSRI]

First order kinetics elimination [most drugs | T1/2 constant, constant fraction of drug is eliminated]

Question 2

Pharmacology tools to influence sympathetic neurotransmission

Answer 2

Sympathetic neurotransmission involves Norepinephrine and Epi synthesis, storage, release, reuptake and receptor interactions

Drugs used to influence and/or block NE/E synthesis:
- Methyl-p-tyrosine [blocks rate limiting step Tyrosine to Dopa]
- MAO-A inhibitor [blocks NE metabolism but increases NE avaibility]
- Alpha2 agonists [alpha 2 receptors on presynaptic neuron, blocks NE mobilisation, thus agonist allows higher function] and antagonists
- COMT inhibitors [reduces metabolism of NE in synaptic cleft]
- Reserpine [destroys storage vessicle]
- Guanethidine [inhibits NE release from synaptic terminal, prevents exocytosis]
- Reuptake blockers Na/KATPase [Cocaine, TCA depressants]

Question 3

Expectorants and Antitussives

Answer 3

NH4CL [Secretolytics - increases respiratory tract secretions]
Salbutamol, Terbutaline [Secretomotorics - increases cilia movements]
Bromhexine [Mucolytics - induces hydrolysis of mucus, lowers viscosity]

Codeine, Dextromethorphan [Centrally acting antitussives, decreases coughing reflex; Codeine is narcotic while Dextromethorphan is nonnarcotic and found in all cough syrups]
Lidocaine, Prenoxdiazine, Levodropropizine [Peripherally acting antitussives, rarely used]