14 research outputs found
Quantitative Analysis of Drug Supersaturation Region by Temperature-Variable Nuclear Magnetic Resonance Measurements, Part 1: Effects of Polymer and Drug Chiralities
We examined the effects of the polymer-additive
and drug chiralities
on the ketoprofen (KTP) supersaturation region using temperature-variable
nuclear magnetic resonance (NMR). Quantitative NMR analysis revealed
that the racemic KTP and corresponding S-enantiomer
(rac- and s-KTP) exhibited similar amorphous solubilities in a buffer,
while the crystalline solubility of s-KTP was higher than that of
rac-KTP. Therefore, rac-KTP exhibited a larger supersaturation region
than s-KTP. In contrast, polyvinylpyrrolidone (PVP) reduced the amorphous
solubility of both rac- and s-KTP, whereas the crystalline solubility
of KTP remained unchanged. Partitioning PVP into the KTP-rich phase
reduced the chemical potential of KTP in the KTP-rich phase and the
amorphous solubility of KTP. At higher temperatures, the distribution
of PVP into the KTP-rich phase became more significant, which considerably
reduced the amorphous solubility. Because the upper limit of the KTP
supersaturation decreased, PVP narrowed the KTP supersaturation region.
The maximum KTP supersaturation ratio decreased with increasing temperature,
and the supersaturated dissolvable area of KTP finally disappeared.
The maximum temperature at which KTP can form the supersaturation
was lowered by replacing rac- with s-KTP and the addition of PVP.
The maximum supersaturation temperature was dominated by the melting
behavior of crystalline KTP in an aqueous solution. The present study
highlighted that a quantitative understanding of the supersaturation
region is essential to determine whether supersaturated formulations
are beneficial for improving the oral absorption of poorly water-soluble
drugs
Quantitative Analysis of Drug Supersaturation Region by Temperature-Variable Nuclear Magnetic Resonance Measurements, Part 2: Effects of Solubilizer
This
study utilized temperature-variable nuclear magnetic resonance
(NMR) spectroscopy to investigate the effects of a solubilizing agent
on the ketoprofen (KTP) supersaturation region. Quantitative NMR analysis
showed that the solubilizing agent cetyltrimethylammonium bromide
(CTAB) increased both the crystalline and amorphous solubilities of
KTP, shifting the KTP supersaturation region to a higher KTP concentration
range. The amorphous solubility of KTP was found to be independent
of the enantiomeric composition of KTP, even in the presence of CTAB.
However, the supersaturation region of the S-enantiomer
of KTP (s-KTP) in CTAB solutions was smaller than that of the racemic
form of KTP (rac-KTP), likely because of the higher crystalline solubility
of s-KTP. When KTP formed a KTP-rich phase via liquid–liquid
phase separation from KTP-supersaturated solutions, CTAB was observed
to be distributed into the KTP-rich phase, decreasing the chemical
potential of KTP and the maximum thermodynamic activity of KTP in
the aqueous phase. Additionally, the incorporation of CTAB into the
KTP-rich phase diminished the solubilization effect of CTAB micelles
in the aqueous phase, narrowing the KTP supersaturation region to
a greater extent at higher KTP dose concentrations. Furthermore, the
upper-temperature limit of the supersaturated dissolvable region of
KTP was lowered in the presence of CTAB, which was rationalized by
the melting point depression of the KTP crystal upon mixing with CTAB.
The findings of this study highlight the importance of considering
the molecular-level impact of solubilizing agents on the drug supersaturation
region to fully exploit the potential benefits of supersaturated formulations
Direct NMR Monitoring of Phase Separation Behavior of Highly Supersaturated Nifedipine Solution Stabilized with Hypromellose Derivatives
We
investigated the phase separation behavior and maintenance mechanism
of the supersaturated state of poorly water-soluble nifedipine (NIF)
in hypromellose (HPMC) derivative solutions. Highly supersaturated
NIF formed NIF-rich nanodroplets through phase separation from aqueous
solution containing HPMC derivative. Dissolvable NIF concentration
in the bulk water phase was limited by the phase separation of NIF
from the aqueous solution. HPMC derivatives stabilized the NIF-rich
nanodroplets and maintained the NIF supersaturation with phase-separated
NIF for several hours. The size of the NIF-rich phase was different
depending on the HPMC derivatives dissolved in aqueous solution, although
the droplet size had no correlation with the time for which NIF supersaturation
was maintained without NIF crystallization. HPMC acetate and HPMC
acetate succinate (HPMC-AS) effectively maintained the NIF supersaturation
containing phase-separated NIF compared with HPMC. Furthermore, HPMC-AS
stabilized NIF supersaturation more effectively in acidic conditions.
Solution <sup>1</sup>H NMR measurements of NIF-supersaturated solution
revealed that HPMC derivatives distributed into the NIF-rich phase
during the phase separation of NIF from the aqueous solution. The
hydrophobicity of HPMC derivative strongly affected its distribution
into the NIF-rich phase. Moreover, the distribution of HPMC-AS into
the NIF-rich phase was promoted at lower pH due to the lower aqueous
solubility of HPMC-AS. The distribution of a large amount of HPMC
derivatives into NIF-rich phase induced the strong inhibition of NIF
crystallization from the NIF-rich phase. Polymer distribution into
the drug-rich phase directly monitored by solution NMR technique can
be a useful index for the stabilization efficiency of drug-supersaturated
solution containing a drug-rich phase
Crystallization of Probucol in Nanoparticles Revealed by AFM Analysis in Aqueous Solution
The
crystallization behavior of a pharmaceutical drug in nanoparticles
was directly evaluated by atomic force microscopy (AFM) force curve
measurements in aqueous solution. A ternary spray-dried sample (SPD)
was prepared by spray drying the organic solvent containing probucol
(PBC), hypromellose (HPMC), and sodium dodecyl sulfate (SDS). The
amorphization of PBC in the ternary SPD was confirmed by powder X-ray
diffraction (PXRD) and solid-state <sup>13</sup>C NMR measurements.
A nanosuspension containing quite small particles of 25 nm in size
was successfully prepared immediately after dispersion of the ternary
SPD into water. Furthermore, solution-state <sup>1</sup>H NMR measurements
revealed that a portion of HPMC coexisted with PBC as a mixed state
in the freshly prepared nanosuspension particles. After storing the
nanosuspension at 25 °C, a gradual increase in the size of the
nanoparticles was observed, and the particle size changed to 93.9
nm after 7 days. AFM enabled the direct observation of the morphology
and agglomeration behavior of the nanoparticles in water. Moreover,
AFM force–distance curves were changed from (I) to (IV), depending
on the storage period, as follows: (I) complete indentation within
an applied force of 1 nN, (II) complete indentation with an applied
force of 1–5 nN, (III) partial indentation with an applied
force of 5 nN, and (IV) nearly no indentation with an applied force
of 5 nN. This stiffness increase of the nanoparticles was attributed
to gradual changes in the molecular state of PBC from the amorphous
to the crystal state. Solid-state <sup>13</sup>C NMR measurements
of the freeze-dried samples demonstrated the presence of metastable
PBC Form II crystals in the stored nanosuspension, strongly supporting
the AFM results
Direct Evaluation of Molecular States of Piroxicam/Poloxamer Nanosuspension by Suspended-State NMR and Raman Spectroscopies
A nanosuspension of piroxicam (PXC)
and poloxamer 407 (poloxamer)
prepared by the wet milling method was directly evaluated at the molecular
level from the viewpoint of both solution and solid phases. <sup>13</sup>C solution-state NMR measurements revealed a reduction in the concentration
of dissolved poloxamer in the nanosuspension. Furthermore, the fraction
of dissolved polyÂ(ethylene oxide) (PEO) chain, which is the hydrophilic
part of poloxamer, was higher than that of dissolved polyÂ(propylene
oxide) (PPO) chain, the hydrophobic part. <sup>13</sup>C suspended-state
NMR and Raman spectroscopies detected both solid-state PXC and poloxamer
involved in the nanoparticles. Interestingly, the coexistence of crystalline
and amorphous PXC in the nanoparticle was demonstrated. The yellow
color of the nanosuspension strongly supported the existence of amorphous
PXC. Changes in the peak intensity depending on the contact time in
the suspended-state NMR spectrum revealed that the PEO chain of poloxamer
in the nanoparticle had higher mobility compared with the PPO chain.
The PEO chain should project into the water phase and form the outer
layer of the nanoparticles, whereas the PPO chain should face the
inner side of the nanoparticles. Amorphous PXC could be stabilized
by intermolecular interaction with the PPO chain near the surface
of the nanoparticles, whereas crystalline PXC could form the inner
core
Inhibitory Effect of Hydroxypropyl Methylcellulose Acetate Succinate on Drug Recrystallization from a Supersaturated Solution Assessed Using Nuclear Magnetic Resonance Measurements
We
examined the inhibitory effect of hydroxypropyl methylcellulose
acetate succinate (HPMC-AS) on drug recrystallization from a supersaturated
solution using carbamazepine (CBZ) and phenytoin (PHT) as model drugs.
HPMC-AS HF grade (HF) inhibited the recrystallization of CBZ more
strongly than that by HPMC-AS LF grade (LF). 1D-<sup>1</sup>H NMR
measurements showed that the molecular mobility of CBZ was clearly
suppressed in the HF solution compared to that in the LF solution.
Interaction between CBZ and HF in a supersaturated solution was directly
detected using nuclear Overhauser effect spectroscopy (NOESY). The
cross-peak intensity obtained using NOESY of HF protons with CBZ aromatic
protons was greater than that with the amide proton, which indicated
that CBZ had hydrophobic interactions with HF in a supersaturated
solution. In contrast, no interaction was observed between CBZ and
LF in the LF solution. Saturation transfer difference NMR measurement
was used to determine the interaction sites between CBZ and HF. Strong
interaction with CBZ was observed with the acetyl substituent of HPMC-AS
although the interaction with the succinoyl substituent was quite
small. The acetyl groups played an important role in the hydrophobic
interaction between HF and CBZ. In addition, HF appeared to be more
hydrophobic than LF because of the smaller ratio of the succinoyl
substituent. This might be responsible for the strong hydrophobic
interaction between HF and CBZ. The intermolecular interactions between
CBZ and HPMC-AS shown by using NMR spectroscopy clearly explained
the strength of inhibition of HPMC-AS on drug recrystallization
Equilibrium State at Supersaturated Drug Concentration Achieved by Hydroxypropyl Methylcellulose Acetate Succinate: Molecular Characterization Using <sup>1</sup>H NMR Technique
The
maintenance mechanism of the supersaturated state of poorly
water-soluble drugs, glibenclamide (GLB) and chlorthalidone (CLT),
in hydroxypropyl methylcellulose acetate succinate (HPMC-AS) solution
was investigated at a molecular level. HPMC-AS suppressed drug crystallization
from supersaturated drug solution and maintained high supersaturated
level of drugs with small amount of HPMC-AS for 24 h. However, the
dissolution of crystalline GLB into HPMC-AS solution failed to produce
supersaturated concentrations, although supersaturated concentrations
were achieved by adding amorphous GLB to HPMC-AS solution. HPMC-AS
did not improve drug dissolution and/or solubility but efficiently
inhibited drug crystallization from supersaturated drug solutions.
Such an inhibiting effect led to the long-term maintenance of the
amorphous state of GLB in HPMC-AS solution. NMR measurements showed
that HPMC-AS suppressed the molecular mobility of CLT depending on
their supersaturation level. Highly supersaturated CLT in HPMC-AS
solution formed a gel-like structure with HPMC-AS in which the molecular
mobility of the CLT was strongly suppressed. The gel-like structure
of HPMC-AS could inhibit the reorganization from drug prenuclear aggregates
to the crystal nuclei and delay the formation of drug crystals. The
prolongation subsequently led to the redissolution of the aggregated
drugs in aqueous solution and formed the equilibrium state at the
supersaturated drug concentration in HPMC-AS solution. The equilibrium
state formation of supersaturated drugs by HPMC-AS should be an essential
mechanism underlying the marked drug concentration improvement
Vapor-Phase-Mediated Encapsulation of Guest Drug Molecules in the Hexagonal Columnar Form Structure of Polyethylene Glycol/γ-Cyclodextrin-Polypseudorotaxane
The drug/(PEG/γ-CD-PPRX) complex is a unique multicomponent
supramolecular structure where the drug molecules are incorporated
in the intermolecular spaces of the polypseudorotaxane (PPRX) prepared
from polyethylene glycol (PEG) and γ-cyclodextrin (γ-CD).
Herein, we report a sealed-heating preparation method to obtain an
unanticipated polymorphic form of the drug/(PEG/γ-CD-PPRX) complex,
which is the hexagonal-columnar (HC) form. The encapsulation efficiency
of the six guest drugs was evaluated. The crystalline structural changes
and the guest encapsulation monitored by powder X-ray diffraction
revealed that a low sealed-heating temperature with a small amount
of water was the optimal preparation condition for obtaining the HC
form complex. The solution-state 1H nuclear magnetic resonance
measurement demonstrated that stoichiometric complexation was dependent
on the cross-sectional area of the guest drug molecule. However, stoichiometric
complexation could not be achieved with all guest drugs, and the encapsulation
efficiency was found to be governed by the guest drug properties,
such as vapor pressure and molecular size. The findings of this study
would contribute to understanding the complexation behavior of guest
molecules in multicomponent supramolecular complexes and offer new
insights into the fabrication of novel ordered supramolecular structures
Structural Determination of a Novel Polymorph of Sulfathiazole–Oxalic Acid Complex in Powder Form by Solid-State NMR Spectroscopy on the Basis of Crystallographic Structure of Another Polymorph
Two
polymorphic forms of a sulfathiazole (STZ):oxalic acid (OXA)
1:1 complex were successfully prepared by different cogrinding methods
and characterized by multiple analytical techniques. Rod-milled and
ball-milled ground mixtures had different powder X-ray diffraction
patterns, showing polymorph formation of the STZ-OXA complex (complex
A and complex B). The heat of fusion from differential scanning calorimetry
curves and terahertz time-domain spectra helped differentiating the
polymorphs. According to infrared spectra, <sup>13</sup>C NMR chemical
shifts, and the relative intensities of <sup>15</sup>N NMR peaks,
both polymorphs were salts where the proton of a −COOH group
in OXA was transferred to a −NH<sub>2</sub> group in STZ. High-resolution <sup>1</sup>H NMR and <sup>1</sup>H–<sup>13</sup>C heteronuclear
correlation NMR spectra indicated that complex B in powder form had
a <i>cocrystal</i> type structure compared to complex A
having a <i>clathrate-</i>type structure. Complex B structure
suggested by solid-state NMR coincided well with the experimentally
determined one, which was formed from three layers of thiazole rings,
benzene rings, and OXAs, by using single-crystal X-ray diffraction
(SC-XRD) measurement. Advanced solid-state NMR spectroscopy measurements
was useful to elucidate the structure of a polymorph, for which SC-XRD
data are not available, by referring to the SC-XRD data of another
polymorph
Mechanistic Differences in Permeation Behavior of Supersaturated and Solubilized Solutions of Carbamazepine Revealed by Nuclear Magnetic Resonance Measurements
A solid dispersion (SPD) of carbamazepine (CBZ) with
hydroxypropyl
methylcellulose acetate succinate (HPMC-AS) was prepared by the spray
drying method. The apparent solubility (37 °C, pH 7.4) of CBZ
observed with the SPD was over 3 times higher than the solubility
of unprocessed CBZ. The supersaturated solution was stable for 7 days.
A higher concentration of CBZ in aqueous medium was also achieved
by mixing with Poloxamer 407 (P407), a solubilizing agent. From permeation
studies of CBZ using Caco-2 monolayers and dialysis membranes, we
observed improved CBZ permeation across the membrane in the supersaturated
solution of CBZ/HPMC-AS SPD. On the contrary, the CBZ-solubilized
P407 solution exhibited poor permeation by CBZ. The chemical shifts
of CBZ on the <sup>1</sup>H NMR spectrum from CBZ/HPMC-AS SPD solution
were not altered significantly by coexistence with HPMC-AS. In contrast,
an upfield shift of CBZ was observed in the CBZ/P407 solution. The
spin–lattice relaxation time (<i>T</i><sub>1</sub>) over spin–spin relaxation time (<i>T</i><sub>2</sub>) indicated that the mobility of CBZ in the HPMC-AS solution was
much lower than that in water. Meanwhile, the mobility of CBZ in P407
solution was significantly higher than that in water. NMR data indicate
that CBZ does not strongly interact with HPMC-AS. CBZ mobility was
suppressed due to self-association and microviscosity around CBZ,
which do not affect permeation behavior. Most of the CBZ molecules
in the CBZ/P407 solution were solubilized in the hydrophobic core
of P407, and a few were free to permeate the membrane. The molecular
state of CBZ, as evaluated by NMR measurements, directly correlated
with permeation behavior