1 research outputs found
The Role of Glass Transition Temperatures in Coamorphous Drug–Amino Acid Formulations
The improved physical stability associated
with coamorphous drug–amino
acid (AA) formulations may indicate a decrease in mobility of the
amorphous drug molecules, compared to the neat amorphous form of the
drug. Since the characteristic glass transition temperatures (<i>T</i><sub>gα</sub> and <i>T</i><sub>gβ</sub>) represent molecular mobility in amorphous systems, we aimed to
characterize <i>T</i><sub>gα</sub> and <i>T</i><sub>gβ</sub> and to determine their role in physical stability
as well as their potential usefulness to determine the presence of
an excess component (either drug or AA) in coamorphous systems. Indomethacin
(IND)–tryptophan (TRP) and carvedilol (CAR)–TRP were
used as model coamorphous systems. The analytical techniques used
were X-ray powder diffractometry (XRPD) to determine the solid-state
form, dynamic mechanical analysis (DMA) to probe <i>T</i><sub>gα</sub> and <i>T</i><sub>gβ</sub>, and
differential scanning calorimetry (DSC) to probe thermal behavior
of the coamorphous systems. <i>T</i><sub>gα</sub> analysis
showed a gradual monotonous increase in <i>T</i><sub>gα</sub> values with increasing AA concentration, and this increase in the <i>T</i><sub>gα</sub> value is not the cause of the improved
physical stability. The <i>T</i><sub>gβ</sub> analysis
for the IND–TRP sample with 10% drug had a <i>T</i><sub>gβ</sub> of 226.8 K, and samples with 20–90% drug
had similar <i>T</i><sub>gβ</sub> values around 212.5
K. For CAR–TRP, samples with 10–40% drug had similar <i>T</i><sub>gβ</sub> values around 230.5 K, and samples
with 50–90% drug had similar <i>T</i><sub>gβ</sub> values around 223.3 K. The similar <i>T</i><sub>gβ</sub> values in coamorphous systems at different drug ratios indicate
that they in fact are the <i>T</i><sub>gβ</sub> of
the component that is in excess to an ideal drug–AA coamorphous
mixture. DSC and XRPD analysis showed that for IND–TRP, IND
is in excess if the drug concentration is 30% or above and will eventually
recrystallize. For CAR–TRP, CAR is in excess and recrystallizes
when the drug concentration is 50% or above. We have proposed a means
of estimating, on the basis of <i>T</i><sub>gβ</sub>, which drug to AA ratios will lead to optimally physically stable
coamorphous systems that can be considered for further development