Tachyphylaxis

Tachyphylaxis : rapiud tolerance "rapidly decreasing responce to a drug may be due to variation in the absorption from one person to another

Tachyphylaxis is a medical term describing a rapidly decreasing response to a drug following administration of the initial doses. Examples of tachyphylaxis are the following    :


 * Nitroglycerine demonstrates tachyphylaxis, requiring drug-free intervals when administered transdermally
 * Repeated doses of ephedrine may display tachyphylaxis, since it is an indirectly acting sympathomimetic amine which will deplete noradrenaline from the nerve terminal. Thus repeated doses result in less noradrenaline being released than the initial dose.
 * Nicotine may also show tachyphylaxis over the course of a day, although the mechanism of this action is unclear.
 * Hydralazine displays tachyphylaxis if given as a monotherapy for antihypertensive treament. It is administered with a beta-blocker with or without a diuretic.
 * Metoclopramide is another example.
 * Dobutamine, a direct-acting beta agonist used in congestive heart failure, also demonstrate tachyphylaxis.
 * Desmopressin used in the treatment of type 1 von Willebrand disease is generally given every 12-24 hours in limited numbers due to its tachyphylactic properties.
 * Hormone replacement when used in menopausal women, oestrogen and progesterone implants can lead to tachyphylaxis