Polymorphism in nimodipine raw materials: Development and validation of a quantitative method through differential scanning calorimetry

Identification and quantification techniques of polymorphic forms - A review

In the pharmaceutical industry, the unexpected appearance of crystalline forms could impact the therapeutic efficacy of an Active Pharmaceutical Ingredient (API). For quality control, a thorough qualitative and quantitative monitoring of pharmaceutical solid forms is essential to ensure the detection and the quantification of crystalline forms, wither different or with the same chemical composition (polymorphs) at a low detection level. The purpose of this paper was to review and highlight the importance of choosing adequate solid-state techniques for detection and quantification APIs that present polymorphism - based on limits of detection (LOD) and quantification (LOQ), pharmacopeias specifications, international guidelines and studies reported in the literature. To this study, the powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), Infrared and Raman spectroscopies and solid-state nuclear magnetic resonance (NMR) were the solid-state techniques analyzed. Additionally, the Argentine, Brazilian, British, European, International, Japanese, Mexican and the United States of America pharmacopeias were reviewed. Based on the analysis performed, the advantages and disadvantages of these techniques, as well as the LOD and LOQ values of APIs were reported. In comparison to these solid-state techniques, reference material used for identification analyses should be previously identified with the corresponding polymorph. Without this previous procedure, the patterns, the spectra, and DSC curves of the reference material can only be used to confirm the mixture of solid forms, not being able to specify which polymorphs are contained in the sample. A major advantage of PXRD is the use of the calculated diffraction patterns obtained from the Crystallographic Information Frameworks (CIFs) files which could be used as a reference pattern without any other information, assistance technique, or physical standards. Regarding the quantification aspect, different pharmacopeias suggest various methods such as the PXRD combining with Rietveld method, which can be used to obtain lower LOD values for minority phases in the mixture of different substances without the need for a calibration curve. Raman spectroscopy can detect polymorphs in small particles and solid-state NMR spectroscopy is a powerful technique for quantification not only crystalline but also crystalline-amorphous mixtures. Finally, this review intends to be a useful tool to control, with efficiency and accuracy, the polymorphism of APIs in pharmaceutical compounds.

Characterization of Controlled Release Starch-Nimodipine Implant for Antispasmodic and Neuroprotective Therapies in the Brain

Parenteral depot systems can provide a constant release of drugs over a few days to months. Most of the parenteral depot products on the market are based on poly(lactic acid) and poly(lactide-co-glycolide) (PLGA). Studies have shown that acidic monomers of these polymers can lead to nonlinear release profiles or even drug inactivation before release. Therefore, finding alternatives for these polymers is of great importance. Our previous study showed the potential of starch as a natural and biodegradable polymer to form a controlled release system. Subarachnoid hemorrhage (SAH) is a life-threatening type of stroke and a major cause of death and disability in patients. Nimotop® (nimodipine (NMD)) is an FDA-approved drug for treating SAH-induced vasospasms. In addition, NMD has, in contrast to other Ca antagonists, unique neuroprotective effects. The oral administration of NMD is linked to variable absorption and systemic side effects. Therefore, the development of a local parenteral depot formulation is desirable. To avoid the formation of an acidic microenvironment and autocatalytic polymer degradation, we avoided PLGA as a matrix and investigated starch as an alternative. Implants with drug loads of 20 and 40% NMD were prepared by hot melt extrusion (HME) and sterilized with an electron beam. The effects of HME and electron beam on NMD and starch were evaluated with NMR, IR, and Raman spectroscopy. The release profile of NMD from the systems was assessed by high-performance liquid chromatography. Different spectroscopy methods confirmed the stability of NMD during the sterilization process. The homogeneity of the produced system was proven by Raman spectroscopy and scanning electron microscopy images. In vitro release studies demonstrated the sustained release of NMD over more than 3 months from both NMD systems. In summary, homogeneous nimodipine-starch implants were produced and characterized, which can be used for therapeutic purposes in the brain.

Optical Properties of Meloxicam in the Far-Infrared Spectral Region

One of the most commonly used nonsteroidal anti-inflammatory active pharmaceutical ingredient called Meloxicam has been characterized spectroscopically both by Terahertz (THz) time domain spectroscopy (THz-TDS) and by Fourier Transform Infrared (FTIR) spectroscopy in far-IR regions of electromagnetic spectrum; 0.2 THz to 20 THz. While many relatively sharp features are observed in the far-IR range between 2 THz to 20 THz as expected for being an organic substance, very distinct and relatively strong absorption bands are also observed at 1.00, 1.66, 2.07 and 2.57 THz in the THz range. These well separated, defined, and fairly strong spectral features can be used for discrimination and quantification of Meloxicam in drug analysis. Frequency dependent refractive index of the drug was determined in a range of 0.2 THz and 2.7 THz, where an almost constant index was observed with an average index of 1.75. Powder XRD, and solid-state Density Functional Theory (SS-DFT) calculations were utilized to determine the crystalline form of the Meloxicam sample in its enolic crystalline form. Single molecule DFT calculations were also performed in all four possible structures of Meloxicam. In addition, the capability of THz waves transmission through common packaging materials is demonstrated for possibility of future on-site analysis. The results suggest that drug analysis will be possible to perform not only at every stage of manufacturing without destruction but also directly at the shelf of a market after development of portable THz technologies.

Effect of age on the pharmacokinetics of polymorphic nimodipine in rats after oral administration

The previous investigation has proved that their existed pharmacokinetic difference between the different crystal forms of the polymorphic drugs after oral administration. However, no systemic investigations have been made on the change of this pharmacokinetic difference, resulted either from the physiological or from the pathological factors. In this paper, we used polymorphic nimodipine (Nim) as a model drug and investigated the effect of age difference (2- and 9-month old) on the pharmacokinetics after oral delivery in rats. As the results shown, for L-form of Nim (L-Nim), the AUC_0-24 h in 2-month-old rats was 343.68±47.15 ng·h/mL, which is 23.36% higher than that in 9-month-old rats. For H-form of Nim (H-Nim), the AUC_0-24 h in 2-month-old rats was 140.91±19.47 ng·h/mL, which is 54.64% higher than that in 9-month-old rats. The AUC_0-24 h ratio between H-Nim and L-Nim was 2.44 in 2-month-old rats and 3.06 in 9-month-old rats. Since age difference could result in unparallelled change of the absorption and bioavailability of the polymorphic drugs, the results in this experiment are of value for further investigation of crystal form selection in clinical trials and rational clinical application of the polymorphic drugs.

Insight into the conformational polymorph transformation of a block-buster multiple sclerosis drug fingolimod hydrochloride (FTY 720)

Single-crystal structures of fingolimod hydrochloride (FTY 720), a block-buster multiple sclerosis drug, were revealed for the first time in this study. Three different conformational polymorphs (designated as forms I-III) were characterized using a variety of analytical techniques, including single-crystal XRD, VT-PXRD, DSC, HSM, and VT-confocal Raman spectroscopy. A temperature-dependent solid-solid transformation between different conformational polymorphs was observed to be reversible, and the transition process was studied using both VT-PXRD and VT-Raman techniques. Structural analysis revealed that the FTY 720 molecules adopt distinctive conformations in different polymorphs. Single-crystal to single-crystal transformation from form I to II was observed and was closely monitored by X-ray diffraction.

The in situ monitoring of the transformation of moxidectin ethanol solvate to form I in an ethanol–water mixture

Moxidectin is a single-component and semisynthetic macrocyclic lactone antibiotic, which has been widely used in the prevention and treatment of parasites in farm animals.

Development and validation of an intrinsic dissolution method for nimodipine polymorphs

The polymorphs of nimodipine, Modification I (Mod I), the metastable racemate, and Modification II (Mod II), the stable conglomerate, were evaluated by means of the intrinsic dissolution procedure. For this purpose, a hydro alcoholic solution (ethanol:water, 50:50, v/v) was selected as the dissolution medium, maintained at 37±0.5°C. Different rotation speeds were tested (50, 75 and 100 rpm) and the lower one was chosen for the test validation. Although the sample initially characterized as polymorph Mod I presented higher intrinsic dissolution rates in all the conditions tested, no statistical differences were noticed between the two polymorphs. This result can be attributed to the partial solution-mediated phase transformation from Mod I to Mod II, detected through X-ray powder diffraction and differential scanning calorimetry. Also, reliable intrinsic dissolution rate data were acquired for the polymorph Mod II. The dissolution method was validated, being considered stable, specific, linear, sensible, accurate and precise.

A two-step strategy to design high bioavailable controlled-release nimodipine tablets: the push-pull osmotic pump in combination with the micronization/solid dispersion techniques

In order to decrease the fluctuation of blood concentration and to increase the oral bioavailability of nimodipine (NMD), a two-step strategy including the push-pull osmotic pump (PPOP) method in combination with micronization and solid dispersion techniques, was used to prepare the controlled-release high-bioavailability solid dosages. The optimization of formulation and process was conducted by comparing effects of different solubilization methods on release behavior of NMD. The in vitro dissolution studies indicated that both the two strategies were able to deliver NMD in the predetermined zero-order manner from 2 to 12h, regardless of effects of release media and agitation rates. Although the Cmax values of two PPOP tablets were lower than that of the reference formulation, both the Tmax values were prolonged, demonstrating the prominent controlled release performance. In comparison with the commercial reference tables, the relative bioavailability of the two formulations was 67.0% and 121.1%, respectively, indicating the solid dispersion technique was more efficient than the micronization technique in terms of solubilization capability and absorption enhancement. In summary, the two-step strategy, combining the push-pull osmotic pump method with the solid dispersion technique, is a very effective method to prepare high bioavailable controlled-release formulations of the poorly soluble drugs, i.e. NMD, taking into account the therapeutical efficiency and safety.

Assessing the impact of nimodipine devitrification in the ternary cosolvent system through quality by design approach

Nimodipine (NM) commercial formulation has been recalled due to drug crystallization in the product. Aim of present investigation was to systematically evaluate NM ternary cosolvents systems, characterize the crystallized drug and develop discriminating dissolution method that could detect the drug crystallization in the product. Mixture design was constructed using independent components namely water (X1), glycerin (X2) and polyethylene glycol 400 (X3, PEG-400). Nineteen formulations were developed using various level of cosolvents mixture while drug concentration was kept constant. The response selected was the drug crystallized in the formulations kept at four storage conditions 5 °C, 15 °C, 25 °C and 25 °C/60% RH for four weeks. The crystallized drug was characterized by Fourier transformed infrared (FTIR), near infrared (NIR), NIR-chemical imaging and Raman spectroscopies, powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and scanning electron microscopy. Dissolution of formulation and modification was tested by USP method 2 in 0.25 and 0.50% sodium lauryl sulphate (SLS) aqueous media and run at 50 and 75 rpm. X1 promoted drug crystallization at all conditions of storage and reverse was true for X3. Characterization data indicated that the crystallized drug in most of the formulations were modification II, but a few formulations contained significant proportion of the modification I. Dissolution in 0.25% (w/v) SLS at 75 rpm was more discriminating in detecting the crystallization in the product compared to dissolution in 0.5% (w/v) SLS media. In summary, cosolvents system of NM was prone to crystallization depending upon the cosolvents composition and storage conditions. A more rational approach to develop NM formulation would entail a then through understanding of the causes of crystallization and their characterization in a variety of storage conditions.