Comparison of intravenous and intramuscular routes of administering cosyntropin for corticotropin stimulation testing in cats

Mark E. Peterson From the Department of Medicine, The Animal Medical Center, New York, NY 10021 (Peterson), and the Department of Pharmacology and Physiology, College of Veterinary Medicine, Auburn University, AL 36830 (Kemppainen).

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Robert J. Kemppainen From the Department of Medicine, The Animal Medical Center, New York, NY 10021 (Peterson), and the Department of Pharmacology and Physiology, College of Veterinary Medicine, Auburn University, AL 36830 (Kemppainen).

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Summary

Plasma cortisol and immunoreactive (ir)-acth responses to 125 μg of synthetic acth (cosyntropin) administered iv or im were compared in 10 clinically normal cats. After im administration of cosyntropin, mean plasma cortisol concentration increased signficantly (P < 0.05) within 15 minutes, reached maximal concentration at 45 minutes, and decreased to values not significantly different from baseline concentration by 2 hours. After iv administration of cosyntropin, mean plasma cortisol concentration also increased significantly (P < 0.05) at 15 minutes, but in contrast to im administration, the maximal cortisol response took longer (75 minutes) and cortisol concentration remained significantly (P < 0.05) higher than baseline cortisol concentration for 4 hours. Mean peak cortisol concentration (298 nmol/L) after iv administration of cosyntropin was significantly (P < 0.05) higher than the peak value (248 nmol/L) after im administration. All individual peak plasma cortisol concentrations and areas under the plasma cortisol response curve were significantly (P < 0.05) higher after iv administration of cosyntropin than after im administration. Mean plasma ir-acth concentration returned to values not statistically different from baseline by 60 minutes after im administration of cosyntropin, whereas ir-acth concentration still was higher than baseline concentration 6 hours after iv administration. Peak plasma ir-acth concentration and area under the plasma ir-acth response curve also were significantly (P < 0.05) higher after iv administration of cosyntropin. Results of the study confirmed that iv adminstration of cosyntropin induces significantly (P < 0.05) greater and more prolonged adrenocortical stimulation than does im administration. The reason for this greater degree of stimulation of the adrenal cortex is presumably the result of the higher circulating acth concentration attained by iv, compared with im, administration.

Summary

Plasma cortisol and immunoreactive (ir)-acth responses to 125 μg of synthetic acth (cosyntropin) administered iv or im were compared in 10 clinically normal cats. After im administration of cosyntropin, mean plasma cortisol concentration increased signficantly (P < 0.05) within 15 minutes, reached maximal concentration at 45 minutes, and decreased to values not significantly different from baseline concentration by 2 hours. After iv administration of cosyntropin, mean plasma cortisol concentration also increased significantly (P < 0.05) at 15 minutes, but in contrast to im administration, the maximal cortisol response took longer (75 minutes) and cortisol concentration remained significantly (P < 0.05) higher than baseline cortisol concentration for 4 hours. Mean peak cortisol concentration (298 nmol/L) after iv administration of cosyntropin was significantly (P < 0.05) higher than the peak value (248 nmol/L) after im administration. All individual peak plasma cortisol concentrations and areas under the plasma cortisol response curve were significantly (P < 0.05) higher after iv administration of cosyntropin than after im administration. Mean plasma ir-acth concentration returned to values not statistically different from baseline by 60 minutes after im administration of cosyntropin, whereas ir-acth concentration still was higher than baseline concentration 6 hours after iv administration. Peak plasma ir-acth concentration and area under the plasma ir-acth response curve also were significantly (P < 0.05) higher after iv administration of cosyntropin. Results of the study confirmed that iv adminstration of cosyntropin induces significantly (P < 0.05) greater and more prolonged adrenocortical stimulation than does im administration. The reason for this greater degree of stimulation of the adrenal cortex is presumably the result of the higher circulating acth concentration attained by iv, compared with im, administration.

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