Tachyphylaxis Subject

Indirect sympathomimetics (B) are agents that elevate the concentration of NE at neuroeffector junctions, because they either inhibit re-uptake (cocaine), facilitate release, or slow breakdown by MAO, or exert all three of these effects amphetamine, metham-phetamine). The effectiveness of such indirect sympathomimetics diminishes or disappears (tachyphylaxis) when ve-Ltillmann, Color Atlas of Pharmacology 2000 Thieme All rights reserved. Usage subject to terms and conditions of license. 

Tolerance Following 12 days of dronabinol, tolerance to the cardiovascular and subjective effects developed at doses 210 mg/day or less. An initial tachycardia induced by dronabinol was replaced successively by normal sinus rhythm and then bradycardia. A fall in supine blood pressure, made worse by standing, was also observed initially. Within days, these effects disappeared, indicating development of tolerance. Tachyphylaxis and tolerance did not, however, appear to develop to the appetite stimulant effect. 

Pretreatment with octreotide enhanced the gastric prokinetic effects of erythromycin in eight healthy subjects, suggesting that octreotide may be clinically useful in patients with tachyphylaxis to this effect of erythromycin (55). 

The blood pressure of guinea pigs shows a biphasic response after injection of AT. Initially, it falls and then it rises above normal. The latter effect but not the former is subject to tachyphylaxis and can be blocked by sympatholytics. It is probably due to catecholamine liberation. 

Some effects of AT (see above) are not subject to tachyphylaxis (Bodammer and Vogt, 1967). 

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