Testosterone Suspension~longer "half life" than once thought?

[heavyiron]

J Vet Pharmacol Ther. 2011 Mar 2. doi: 10.1111/j.1365-2885.2011.01277.x. [Epub ahead of print]

An interlaboratory study of the pharmacokinetics of testosterone following intramuscular administration to Thoroughbred horses.

Moeller BC, Sams RA, Guinjab J, Szabo N, Colahan P, Stanley SD.

Source

K.L. Maddy Equine Analytical Chemistry Laboratory, California Animal Health and Food Safety Laboratory, School of Veterinary Medicine, University of California at Davis, Davis, CA, USA Florida Racing Laboratory, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Gainesville, FL, USA.

Abstract

Moeller, B. C., Sams, R. A., Guinjab, J., Szabo, N., Colahan, P., Stanley, S. D.

An interlaboratory study of the pharmacokinetics of testosterone following intramuscular administration to Thoroughbred horses. J. vet. Pharmacol. Therap. doi: 10.1111/j.1365-2885.2011.01277.x.

Testosterone is an anabolic androgenic steroid (AAS) that is endogenously produced by both male and female horses that also has the potential for abuse when administered exogenously to race horses. To recommend appropriate withdrawal guidelines so that veterinarians can discontinue therapeutic use prior to competition, the pharmacokinetics and elimination of testosterone were investigated. An aqueous testosterone suspension was administered intramuscularly in the neck of Thoroughbred horses (n?=?20). The disposition of testosterone from this formulation was characterized by an initial, rapid absorption phase followed by a much more variable secondary absorption phase. The median terminal half-life was 39?h. A second focus of this study was to compare the testosterone concentrations determined by two different laboratories using a percentage similarity model with a coefficient of variation of 16.5% showing good agreement between the two laboratories results. Based on the results of this study, a withdrawal period of 30?days for aqueous testosterone administered IM is recommended.

© 2011 Blackwell Publishing Ltd.

 

[Michael Scally MD]

Moeller BC, Sams RA, Guinjab J, Szabo N, Colahan P, Stanley SD. An interlaboratory study of the pharmacokinetics of testosterone following intramuscular administration to Thoroughbred horses. Journal of Veterinary Pharmacology and Therapeutics. http://www.rmtcnet.com/resources/An_interlaboratory_study_of_the_pharmacokinetics_of_testosterone_following_intramuscular_administration_to_Thoroughbred_horses.pdf

 

[Bill Roberts]

It seems that they are calculating, or attempting to calculate, half-life from three data points which do not themselves fit any exponential decay curve.

Of course, that is because suspensions do not follow the kinetics associated with half-lives at all.

Interesting certainly however that the duration of action was so long for the horses.

 

[heavyiron]

Very interesting to see the two plasma testosterone concentration peaks. The first peak is almost immediate and the second peak is a whopping 7 days later on average according to the chart in the full study. The study indicates that the initial peak is from the Testosterone formulation solution and the following peak(s) from the solid material in the suspension.

Looks like eod injects should be fine with this particular Testosterone Suspension.

 

[Bill Roberts]

For any test suspension, I think.

 

[MR10X]

When i did suspension 100mg ED my test level was crazy high ED.

 

[Bill Roberts]

100 mg/day (700 mg/week) of testosterone suspension delivers as much testosterone as 1000 mg/week of enanthate.It's one of those cases where ester length, or lack of an ester, does make a substantial difference in how much active drug one gets per mg of a product.

 

[MR10X]

I think it would take more than 1000mg a week of test e to get the same level as 100mg a day of test suspension.

 

[Joedoe]

Had to bump this. Short thread but good read!!