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The crystallization of active pharmaceutical ingredients (APIs) in matrix-type transdermal patches has implications for the rate of drug absorption through the skin and patch adhesion strength. Therefore, the presence or absence and the degree of API crystallinity must be controlled to guarantee the quality of patches. In this study, the utility of laboratory-level X-ray diffractometers for the detection and analysis of crystalline APIs in transdermal patches was investigated using medical patches of tulobuterol and isosorbide dinitrate. Several matrix-type patches employ a controlled drug delivery system containing intentionally crystallized API. Both benchtop and high-resolution laboratory X-ray diffractometers can detect several characteristic peaks of the APIs in these patches even if the patches are wrapped in an outer bag, although a benchtop model provides peak heights one-seventh to one-fifth that of a high-resolution instrument. An isosorbide dinitrate patch containing an unintentionally crystallized spot was wrapped in an outer bag, followed by measurements using both X-ray diffractometers. For both instruments, several isosorbide dinitrate-derived peaks were detected only at the crystallized spot, although the signal-to-noise ratio was poorer for the benchtop model. These results show that a high-resolution X-ray diffractometer is advantageous for high-detection sensitivity and offers a high degree of freedom of the measurement position on the sample. It was concluded that a laboratory-level high-resolution X-ray diffractometer can be used to examine the crystalline state of APIs in patches inside an unopened outer bag.

Forty-four brands of transdermal patches for twelve kinds of active pharmaceutical ingredients (APIs) are available in Japan as of April 30, 2018. Although approximately one-third of the corresponding pharmaceutical interview forms lack information on how to evaluate the adhesive properties of the patches, the peel test, probe tack test, or inclined ball tack test have generally been adopted. This means that it might be difficult to simply compare the adhesive properties among the patches because the testing methods are not unified in some cases. In this study, measurements of the adhesive properties of 38 transdermal patches of ten different APIs were performed using several unified testing methods (180° peel test, 90° peel test, self-adhesion test, and probe tack test) under unified experimental conditions. The adhesive properties were found to be quite different among the patches, even for the same API, dose, and size. For example, the ratios of the maximum to minimum measured values of tack and 180° peel strength for tulobuterol patches were 5 and 29, respectively. In the case of generic products for which the bioequivalence to a brand-name product is assured, the variation in adhesive properties can extend the range of choices for patients, which is advantageous. Providing information to medical experts on adhesive properties through, for example, pharmaceutical interview forms and package inserts, is considered to be useful for helping patients to make better choices.

The purpose of the present study was to clarify the feasibility of 19F-NMR for assessing the molecular mobility of flufenamic acid (FLF) in solid dispersions. Amorphous solid dispersions of FLF containing poly(vinylpyrrolidone) (PVP) or hydroxypropylmethylcellulose (HPMC) were prepared by melting and rapid cooling. Spin-lattice relaxation times (T1 and T(1rho)) of FLF fluorine atoms in the solid dispersions were determined at various temperatures (-20 to 150 degrees C). Correlation time (tauc), which is a measure of rotational molecular mobility, was calculated from the observed T1 or T1rho value and that of the T1 or T1rho minimum, assuming that the relaxation mechanism of spin-lattice relaxation of FLF fluorine atoms does not change with temperature. The tauc value for solid dispersions containing 20% PVP was 2-3 times longer than that for solid dispersions containing 20% HPMC at 50 degrees C, indicating that the molecular mobility of FLF in solid dispersions containing 20% PVP was lower than that in solid dispersions containing 20% HPMC. The amount of amorphous FLF remaining in the solid dispersions stored at 60 degrees C was successfully estimated by analyzing the solid echo signals of FLF fluorine atoms, and it was possible to follow the overall crystallization of amorphous FLF in the solid dispersions. The solid dispersion containing 20% PVP was more stable than that containing 20% HPMC. The difference in stability between solid dispersions containing PVP and HPMC is considered due to the difference in molecular mobility as determined by tauc. The molecular mobility determined by 19F-NMR seems to be a useful measure for assessing the stability of drugs containing fluorine atoms in amorphous solid dispersions.

The miscibility of a drug with excipients in solid dispersions is considered to be one of the most important factors for preparation of stable amorphous solid dispersions. The purpose of the present study was to elucidate the feasibility of (1)H-NMR spin-lattice relaxation measurements to assess the miscibility of a drug with excipients. Solid dispersions of nifedipine with the hydrophilic polymers poly(vinylpyrrolidone) (PVP), hydroxypropylmethylcellulose (HPMC) and alpha,beta-poly(N-5-hydroxypentyl)-L-aspartamide (PHPA) with various weight ratios were prepared by spray drying, and the spin-lattice relaxation decay of the solid dispersions in a laboratory frame (T(1) decay) and in a rotating frame (T(1rho) decay) were measured. T(1rho) decay of nifedipine-PVP solid dispersions (3 : 7, 5 : 5 and 7 : 3) was describable with a mono-exponential equation, whereas T(1rho) decay of nifedipine-PHPA solid dispersions (3 : 7, 4 : 6 and 5 : 5) was describable with a bi-exponential equation. Because a mono-exponential T(1rho) decay indicates that the domain sizes of nifedipine and polymer in solid dispersion are less than several nm, it is speculated that nifedipine is miscible with PVP but not miscible with PHPA. All the nifedipine-PVP solid dispersions studied showed a single glass transition temperature (T(g)), whereas two glass transitions were observed for the nifedipine-PHPA solid dispersion (3 : 7), thus supporting the above speculation. For nifedipine-HPMC solid dispersions (3 : 7 and 5 : 5), the miscibility of nifedipine and HPMC could not be determined by DSC measurements due to the lack of obviously evident T(g). In contrast, (1)H-NMR spin-lattice relaxation measurements showed that nifedipine and HPMC are miscible, since T(1rho) decay of the solid dispersions (3 : 7, 5 : 5 and 7 : 3) was describable with a mono-exponential equation. These results indicate that (1)H-NMR spin-lattice relaxation measurements are useful for assessing the miscibility of a drug and an excipient in solid dispersions.

Crystallization rates of drug-polymer solid dispersions prepared with acetaminophen (ACA) and p-aminoacetanilide (AAA) as model drugs, and polyvinylpyrrolidone and polyacrylic acid (PAA) as model polymers were measured in order to further examine the significance of drug-polymer interactions. The crystallization of AAA and ACA was inhibited by mixing those polymers. The most effective inhibition was observed with solid dispersions of AAA and PAA. The combination of AAA and PAA showed a markedly longer enthalpy relaxation time relative to drug alone as well as a higher T(g) than predicted by the Gordon-Taylor equation, indicating the existence of a strong interaction between the two components. These observations suggest that crystallization is effectively inhibited by combinations of drug and polymer that show a strong intermolecular interaction due to proton transfer between acidic and basic functional groups.

The partition behavior of tropane alkaloids (TrA) between organic solvent and water was studied under various conditions. The apparent partition coefficient, log P', increases with pH with a slope of +1 in the acidic to neutral pH range, then tends to approach to a constant value in the alkaline region. Thus the partition of TrA to the organic phase is based on the neutral form of TrA. From the pH dependency of the partition and pH titration of TrA, the intrinsic partition coefficients log P0 and pKa values for each TrA were estimated. Values of pKa and log P0 for scopolamine were smaller than those for atropine or homatropine. It was considered that the presence of the epoxide ring in scopolamine molecule reduces the log P0 and pKa because of its polar and electro-inductive effect. It was also expected from the results of pH-dependent partition behavior that in the low pH region some portion of TrA cations is transferred to the organic phase by forming an ion-pair complex with an anion, in the aqueous phase. The log P' of TrA was measured in the presence of various kinds of anions (halides and alkyl sulfonates, C5-C8) at about pH 2, where almost all TrA are present as a protonated form. The relations between the log P' and the logarithmic concentration of anions is linear at low concentrations of anions as expected from the ion-pair partition equation.(ABSTRACT TRUNCATED AT 250 WORDS)