VPT 321: Veterinary Neuropharmacology (2+1) copy 1

Non - Catecholamine - Ephedrine

EPHEDRINE

• It is a naturally occurring alkaloid obtained from the Chinese shrub Ephedra vulgaris.
• It is now synthesized chemically and the clinically used ephedrine is levo form of ephedrine.
• Mechanism of action
  • It is mixed acting sympathomimmetic which can directly stimulate both α and β receptors and cause release of endogenous nor adrenaline.
• Pharmacological effects
  • Similar to epinephrine, but is many times less potent than adrenaline.
  • However it is 7-10 times long acting and produces the effects even after oral administration.
  • Ephedrine produced mild CNS stimulation that is evident as increased alertness, decreased fatigue and insomnia.
  • Unlike adrenaline and or adrenaline repeated injetions of ephedrine produces progressively diminishing response and this phenomenon is called “tachyphylaxis”.
  • Tachyphylaxis is attributes to the following:
    • Repeated administration, gradually diminish the available stores of endogenous noradrenaline.
    • When cardiovascular system is stimulated, reflex mechanisms are pressed into action to return the heamodynamics towards normally.
    • As adrenergic receptors are already occupied by previously administered long acting ephedrine, less and less number of adrenergic receptors are available for subsequent doses of ephedrine.
• Pharmacokinetics
  • Rapidly absorbed after oral or parenteral administration. Also absorbed from topical instillation in the eye to produce mydriasis.
  • It is a poor substrate for both MAO or COMT and is largely excreted unchanged.
• Clinical uses
  • Ephedrine lacks selectively and its efficacy is low. Mainly used in urinary incontinence and bronchoconstriction.
  • Advantages over other sympathomimetics are long duration of action (hence no need of infusion) and oral administration