Abstract
PurposeIn situ-forming gels (semi-solid state) (ISFGs) are widely used as sustained drug delivery, but they show a high burst release as well. The purpose of the current study is to make triblock that can make a quick gel on injection with a minimum burst release.MethodsIn this study, to control the release of levothyroxine from ISFG, PLGA-PEG-PLGA (triblock) polymer was used. The melting method was employed to synthesize the triblock via ring-opening polymerization (ROP). Different weight percentages of triblock in the formulation were investigated to reach the minimum initial burst release of levothyroxine from ISFGs. Furthermore, the results of the in-situ forming implant (solid-state) (ISFI) of levothyroxine prepared from PLGA 504 H polymers were compared with ISFG.ResultsThe melting method employed in this study showed a successful ROP of the triblock. As the % triblock concentration was increased from 30 to 50%, the initial burst release decreased significantly. The initial burst release levothyroxine from ISFG (6.52 ± 0.30%) was much lower than the amount of levothyroxine released from ISFI (14.15 ± 0.79%). No cytotoxicity was observed for the sustained-release formulation containing ISFG 50% according to the MTT assay.ConclusionThe results indicated that this formulation was safe to be administered subcutaneously. As the synthesized triblock has thermosensitive properties, and also has the hydrogen bonding between the N-methyl pyrrolidone molecules and PEG, therefore, these properties make ISFG formulation to have a smaller initial burst release compared to ISFI formulation.
Highlights
In hypothyroidism disease, the primary function of the human thyroid, endogenous production of thyroxine (T4), and triiodothyronine (T3) is below normal
PLGA RG 504H (50:50, molecular weight (Mw) 38,000–54,000 Da) and levothyroxine were purchased from Sigma (USA) as the standard materials. 3-(4,5-dimethylthiazol-2-yl)-2, diphenyltetrazolium bromide (MTT) and Nmethyl pyrrolidone (NMP) were provided by Merck, Germany
Roswell Park Memorial Institute (RPMI) 1640 culture medium, fetal bovine sera (FBS), penicillin-streptomycin, and trypsin were purchased from Gibco, Germany
Summary
The primary function of the human thyroid, endogenous production of thyroxine (T4), and triiodothyronine (T3) is below normal. Enough secretion of these thyroid hormones is essential to maintain cardiovascular, physical, and mental health, as well as the growth and development of children which is done via the regulation of gene transcription [1, 2]. Levothyroxine sodium is administered orally as a thyroid hormone [3, 4]. The oral bioavailability of levothyroxine is 65%, which is achieved if consumed 30 min to 1 h before breakfast on an empty stomach with a full glass of water [5, 6] because of complex formation of levothyroxine with soybean products, sodium, calcium, and other minerals [7].
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