Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Pharmaceutical Sciences

Research Advisor

James R. Johnson


Isaac O. Donkor, Ph.D. Timothy D. Mandrell, DVM, DACLAM Arthur D. Straughn, Pharm.D. George C. Wood, Ph.D.


Accelerated study, Dissolution model, Formulation, IVIVC, Mechanism, Sustained release


Laboratory animals are often subjected to various painful surgical procedures such as laparotomy, thoracotomy or orthopedic procedures as well as non-surgical procedures such as the induction of arthritis. Any procedure that causes pain in humans is assumed to cause pain in animals too. It is the ethical obligation of all research personnel to reduce or preferably eliminate pain and distress by using analgesics. Furthermore, the Institutional Animal Care and Use Committee (IACUC) requires that appropriate anesthetics and/or analgesics must be used to minimize or eliminate pain and distress for animals undergoing painful procedures.

The oral administration route is the most convenient delivery method for humans. However, using the oral administration route for rodents, such as putting an analgesic in the water, runs the risk of inaccurate dosing and that of degradation due to hydrolysis. Therefore methods for analgesic delivery to rodents are primarily limited to parenteral rather than oral delivery.

Rodents are the most universally used laboratory animals and are often subjected to research involving painful procedures. A survey of current literature indicates that buprenorphine is the most widely used narcotic analgesic for rodents because of its excellent analgesic activity and long duration of action. The Formulary for Laboratory Animals lists the buprenorphine dose for rats as 0.05 mg/kg (SC, tid, qid). Other referenced buprenorphine doses for rats vary widely (0.01-0.05 mg/kg, SC/IV, tid, bid) and require multiple administrations. The recommended dose of buprenorphine for mice following laparotomy is 0.05 to 0.1 mg/kg, subcutaneously (SC) twice a day. Referenced buprenorphine doses for maintaining analgesia in mice vary widely (0.05-2.5 mg/kg, SC, IV) and repeated administration is required. However, no sustained-release analgesic product for rodents was available when we started the project in 2008. Therefore, in order to reduce the stress of frequent handling and injection as well as improve the well-being of research animals, the first objective of this project was to develop a long-acting sustained release formulation of buprenorphine which is capable of maintaining analgesia in rats and mice for 3 to 5 days following a single subcutaneous administration.

Current United States Pharmacopeia (USP) apparatus for in vitro drug release testing was designed mainly for oral and transdermal products. In contrast, there are no standard regulatory methods for parenteral sustained release products at present. As regards to quality control as well as formulation development purposes, it is still highly desirable to develop a suitable in vitro release model for parenteral products with the characters of Level A In Vitro-In Vivo Correlation (IVIVC) and elaborate drug release mechanism. So far there is no successful in vitro dissolution method with the character of Level A IVIVC exists at present for parenteral oily formations. Only a few publications stated in vitro in vivo correction for parenteral product, but they were developed from only one particular formulation. In addition, for most examples in which IVIVC was stated for parenterals, the mathematical models that described the drug release had not been provided. Therefore, the second objective of this study was to (1) design and develop a new dissolution model with the character of Level A IVIVC for oily formulations, and (2) develop a mathematical equation to describe the drug release mechanism from the in vitro model. In general, it is accepted that the process of development and validation of IVVIC for parenterals could follow the same principles as modified release (MR) oral products. The principles of FDA IVIVC MR guidance for oral products were used to develop and validate level A IVIVC for parenterals in this study.

In order to develop sustained release analgesic formulations, nine hydrophobic vehicles, which have been used in the pharmaceutical products, were selected based on clogP values. Solubility and short-term stability studies were performed and six vehicles were selected as candidates according to the results. Since there is no validated in vitro dissolution model for sustained release parenterals at present, a new in vitro dissolution model were designed based on the in vivo drug absorption mechanism after subcutaneous injection. In addition, a mathematical equation was proposed and validated to describe the drug release from this dissolution system. In order to apply this dissolution model to screen the parenteral formulations in vitro, Level A IVIVC study were performed. In-vivo release of buprenorphine from two different oily solutions was performed with subcutaneous administration in rats. Loo-Reigelman method was used to deconvolute plasma data. The mathematical equation, proposed to describe the in vitro drug release profiles, was also corresponded well with the in-vivo deconvolution data for the tested formulations (R2 >0.99). Good linear correlations (R2 > 0.99) were also obtained between the mean percentage of drug absorbed and the mean percentage of drug dissolved. Internal predictability showed that absolute predictive error (%PE) of Cmax and AUC were 4.9% and 0.9%, 12.6% and 3.4% for the tested formulations, respectively. External predictability showed that absolute predictive error (%PE) of Cmax and AUC were 11.9% and 1.1%. This new designed in vitro dissolution apparatus was used to screen six oily vehicles and TBC was selected. After subcutaneous injection of TBC formulation at the dose of 1.5 mg/Kg in rats, 55% of maximum possible effect (MPE) analgesia can be maintained for 3 days and 20% MPE for 5 days in conventional tail flick model. The same formulation was tested in mice at the dose of 2.2 mg/Kg which can maintain more than 30% MPE analgesia for 3 days and at the dose of 8.9 mg/Kg which can keep at least 47% MPE analgesia for 4 days.