Polymer incorporation method affects the physical stability of amorphous indomethacin in aqueous suspension.

This study reports the potential of different polymers and polymer incorporation methods to inhibit crystallisation and maintain supersaturation of amorphous indomethacin (IND) in aqueous suspensions during storage. Three different polymers (poly(vinyl pyrrolidone) (PVP), hydroxypropyl methylcellulose (HPMC) and Soluplus® (SP)) were used and included in the suspensions either as a solid dispersion (SD) with IND or dissolved in the suspension medium prior to the addition of amorphous IND. The total concentrations of both IND and the polymer in the suspensions were kept the same for both methods of polymer incorporation. All the polymers (with both incorporation methods) inhibited crystallisation of the amorphous IND. The SDs were better than the predissolved polymer solutions at inhibiting crystallisation. The SDs were also better at maintaining drug supersaturation. SP showed a higher IND crystallisation inhibition and supersaturation potential than the other polymers. However, this depended on the method of addition. IND in SD with SP did not crystallise, nor did the SD generate any drug supersaturation, whereas IND in the corresponding predissolved SP solution crystallised (into the recently characterised η polymorphic form of the drug) but also led to a more than 20-fold higher IND solution concentration than that observed for crystalline IND. The ranking of the polymers with respect to crystallisation inhibition potential in SDs was SP≫PVP>HPMC. Overall, this study showed that both polymer type and polymer incorporation method strongly impact amorphous form stability and drug supersaturation in aqueous suspensions.

Application of terahertz pulsed imaging to analyse film coating characteristics of sustained-release coated pellets.

Terahertz pulsed imaging (TPI) was employed to explore its suitability for detecting differences in the film coating thickness and drug layer uniformity of multilayered, sustained-release coated, standard size pellets (approximately 1mm in diameter). Pellets consisting of a sugar starter core and a metoprolol succinate layer were coated with a Kollicoat(®) SR:Kollicoat(®) IR polymer blend for different times giving three groups of pellets (batches I, II and III), each with a different coating thickness according to weight gain. Ten pellets from each batch were mapped individually to evaluate the coating thickness and drug layer thickness between batches, between pellets within each batch, and across individual pellets (uniformity). From the terahertz waveform the terahertz electric field peak strength (TEFPS) was used to define a circular area (approximately 0.13 mm(2)) in the TPI maps, where no signal distortion was found due to pellet curvature in the measurement set-up used. The average coating thicknesses were 46 µm, 71 µm and 114 µm, for batches I, II and III respectively, whilst no drug layer thickness difference between batches was observed. No statistically significant differences in the average coating thickness and drug layer thickness within batches (between pellets) but high thickness variability across individual pellets was observed. These results were confirmed by scanning electron microscopy (SEM). The coating thickness results correlated with the subsequent drug release behaviour. The fastest drug release was obtained from batch I with the lowest coating thickness and the slowest from batch III with the highest coating thickness. In conclusion, TPI is suitable for detailed, non-destructive evaluation of film coating and drug layer thicknesses in multilayered standard size pellets.

The impact of surface- and nano-crystallisation on the detected amorphous content and the dissolution behaviour of amorphous indomethacin.

The crystallinity and physical stability of amorphous drugs has previously been studied using different analytical techniques. However, the effect of the measurement method on observed crystallinity and its importance for critical quality attributes, such as dissolution, has not yet been widely investigated. The aim of this study was to (i) qualitatively analyse and understand the recrystallisation behaviour of amorphous indomethacin during storage, (ii) quantify the amorphous content during storage with complementary analytical techniques and (iii) investigate the relationship between observed recrystallisation behaviour and dissolution behaviour. Quench cooled indomethacin was stored and the samples were visualised by scanning electron microscopy to gain spatially resolved information about the recrystallisation behaviour. Crystallisation was quantified by Fourier transform attenuated total reflectance infrared (FT-ATR-IR) spectroscopy, differential scanning calorimetry and X-ray powder diffraction. These techniques resulted in different observed recrystallisation profiles. The physicochemical phenomena detected and sampling geometry for each technique together with the sample recrystallising from the surface and appearance of nano-crystals were used to explain the differences. The dissolution behaviour at the observed recrystallisation endpoints for the different analytical techniques revealed that FT-ATR-IR spectroscopy predicted the changes in dissolution behaviour due to crystallisation best.

Investigations on the effect of different cooling rates on the stability of amorphous indomethacin.

Amorphous forms of indomethacin have previously been prepared using various preparation techniques and it could be demonstrated that the way the material was prepared influenced the physicochemical properties of the amorphous form of the drug. The aim of this study was to use one preparation technique (transformation via the melt) to prepare amorphous indomethacin and to investigate the influence of the cooling rate (as a processing parameter) on the physical stability of the resulting amorphous form. The amorphous materials obtained were analysed for their structural characteristics using Raman spectroscopy in combination with multivariate data analysis. The onset of crystallisation was determined as an indicator of the physical stability of the materials using differential scanning calorimetry (DSC) and polarising light microscopy. The Johnson-Mehl-Avrami (JMA) model and Sestak-Berggren (SB) model were used in this study to describe the non-isothermal crystallisation behaviour. All differently cooled samples were completely X-ray amorphous. Principal component analysis of the Raman spectra of the various amorphous forms revealed that the samples clustered in the scores plot according to the cooling rate, suggesting structural differences between the differently cooled samples. The minimum cooling rate required to obtain amorphous indomethacin was 1.2 K min(-1), as assessed from the time-temperature-transformation (TTT) diagram. The physical stability of the samples was found to increase as a function of cooling rate in the order of 30 K min(-1) > 20 K min(-1) > 10 K min(-1) > 5 K min(-1) > 3 K min(-1) ≈ 1.2 K min(-1) and was in agreement with calculated descriptors for the glass forming ability (GFA), including the reduced glass transition temperature (T(rg)) and the reduced temperature (T(red)). The JMA model could not be applied to describe the crystallisation process for the differently cooled melts of indomethacin in this study. The kinetic exponent M from the autocatalytic SB model however, showed a positive correlation with glass stability.

Analysis of sustained-release tablet film coats using terahertz pulsed imaging.

The coating quality of a batch of lab-scale, sustained-release coated tablets was analysed by terahertz pulsed imaging (TPI). Terahertz radiation (2 to 120 cm(-1)) is particularly interesting for coating analysis as it has the capability to penetrate through most pharmaceutical excipients, and hence allows non-destructive coating analysis. Terahertz pulsed spectroscopy (TPS) was employed for the determination of the terahertz refractive indices (RI) on the respective sustained-release excipients used in this study. The whole surface of ten tablets with 10 mg/cm(2) coating was imaged using the fully-automated TPI imaga2000 system. Multidimensional coating thickness or signal intensity maps were reconstructed for the analysis of coating layer thickness, reproducibility, and uniformity. The results from the TPI measurements were validated with optical microscopy imaging and were found to be in good agreement with this destructive analytical technique. The coating thickness around the central band was generally 33% thinner than that on the tablet surfaces. Bimodal coating thickness distribution was detected in some tablets, with thicker coatings around the edges relative to the centre. Aspects of coating defects along with their site, depth and size were identified with virtual terahertz cross-sections. The inter-day precision of the TPI measurement was found to be within 0.5%.

Influence of sample characteristics on quantification of carbamazepine hydrate formation by X-ray powder diffraction and Raman spectroscopy.

This study aimed to assess the suitability of two widely utilized solid state characterization techniques namely powder X-ray diffraction (XRPD) and Raman spectroscopy, in polymorph detection and quantification for carbamazepine anhydrate and dihydrate mixtures. The influences of particle size, particle morphology, mixing, and in particular, surface bias on quantitation were investigated. Binary mixtures of carbamazepine anhydrate (form III) and dihydrate were prepared and analyzed using both XRPD and Raman spectroscopy in combination with partial least squares analysis. It was found that in principle both XRPD and Raman spectroscopy could be used to build calibration models for quantitative analysis, and a satisfactory correlation between the two techniques could be achieved. However, Raman spectroscopy appeared to be a more reliable quantification method because problems such as different particle size, morphology, and special distribution of the two solid state forms of the drug seemed to have no significant influence on Raman scattering in this study. The robust nature of Raman analysis greatly facilitates the whole quantification process from the preparation of calibration models to the quantification of in situ CBZ-DH conversion.

Visualizing the conversion of carbamazepine in aqueous suspension with and without the presence of excipients: a single crystal study using SEM and Raman microscopy.

Visual observations of the hydration process of single carbamazepine (CBZ) crystals in water and in various excipient solutions [(1% w/v) - hydroxypropyl cellulose (HPC), poly(vinyl pyrrolidone) (PVP), sodium carboxymethylcellulose (CMC) at pH 7.5 and 3.0, and polyethylene glycol (PEG)] using scanning electron microscopy (SEM) are reported in this paper. Raman microscopy was used to confirm the chemical structures of the unconverted CBZ and the CBZ dihydrate (DH) needles. It was found that defect structures were a more important driving force than the nature of crystal faces for the initiation of the hydration, but face differences became obvious after 6 h immersion. The biggest crystal face grown from methanol, (100), was the slowest one to be covered with DH needles. A comparison of the molecular arrangements along the three crystal faces [(100), (010) and (001)] was carried out using crystal structure visualization software, and fewer polar groups exposed on the (100) face than on the (001) and (010) faces were found, explaining the comparatively weak interaction of the (100) face with water during hydration. Furthermore, investigation of the influence of excipients on the hydration of CBZ showed that both HPC and PVP strongly inhibited conversion, and no conversion of CBZ to DH was found after 18 h immersion in water. PEG and CMC (pH 7.5) were less potent inhibitors than HPC and PVP, and DH needles were observed on all the faces except the (100) face after 18 h immersion. No conversion was detected for the crystal immersed in CMC solution at pH 3.0. This is likely to be caused by the decreased polarity of CMC in water at pH 3.0 (pKa,cmc = 4.3), and thus a higher surface adsorption of CMC to the CBZ crystals in dispersion. The influence of excipients on the conversion of CBZ observed in this study agreed well with our previous quantitative studies using Raman spectroscopy. In this study, visual observation using electron microscopy has been demonstrated to be a unique and powerful tool to improve our understanding of polymorphic conversions of CBZ in aqueous suspension.

Analysis of lecithin-cholesterol mixtures using Raman spectroscopy.

FT-Raman spectroscopy has been used to investigate interactions between lecithin and cholesterol. Raman spectra of lecithin show multiple peaks which can be classified into three regions: hydrophobic chain, interfacial, and headgroup regions. Binary lipid mixtures (1:1, w/w, lecithin:cholesterol) were prepared by physical mixing, granulation, coprecipitation, hydration and heating (65 degrees C), and heating (120 degrees C). Regardless of the preparation method, no changes in the spectra were observed in the hydrophobic region. A shift in the wavenumber of the choline methyl asymmetric stretching mode was observed when the samples were prepared by coprecipitation, hydration and heating (65 degrees C), and heating (120 degrees C). This may indicate a modification of phospholipids in the headgroup region in these samples. The difference in degrees of frequency shift (physical mixing approximately granulation

Characterizing the conversion kinetics of carbamazepine polymorphs to the dihydrate in aqueous suspension using Raman spectroscopy.

In an aqueous environment, polymorphic forms I-III of carbamazepine all convert to the dihydrate. This study investigated the conversion of each polymorphic form individually and of a mixture of forms III and I to the dihydrate. Two batches of form I with different crystal morphology were used. Samples were dispersed independently in water at 23+/-1 degrees C and recovered at various timepoints varying from 10 to 210 min. Scanning electron microscopy, X-ray powder diffraction and Raman spectroscopy were used to characterize the initial polymorphic forms and the recovered samples after 210 min. Raman spectroscopy combined with partial least squares analysis was used to generate quantitative models of binary and ternary mixtures of the different polymorphic forms with the dihydrate. On the basis of these models the conversion kinetics of the polymorphic forms I-III were characterized. First-order kinetics with an unconverted portion were used to model the data (R2> or =0.95). The unconverted portions ranged from 16 to 51% after dispersion for 210 min. The conversion kinetics were similar between polymorphic forms with comparable crystal morphology, but differed significantly between batches of the same polymorph (form I) with different crystal morphology. Furthermore, the conversion of forms III and I in the aqueous suspension was not influenced by the presence of the other polymorph when dispersed together.

The prevention of orthopaedic implant and vascular graft infections.

The infection rate for any surgical prosthesis insertion should be less than 1% in the first postoperative year. If infection occurs the patients will lose their new found mobility, lose their independence, be hospitalized with sepsis, both local and systemic, and perhaps die. Preoperative and intraoperative measures to prevent infection are well established in orthopaedic surgery but less scientifically applied in peripheral vascular surgery. In both specialties the problem of late infection has promoted research on the protection of the peri-prosthetic environment against both bacteria and biofilm. In orthopaedics, the incorporation of various antibiotics into bone cement is well accepted in revision surgery, but still debated for the primary operation. On-going research on bioresorbable ceramics and the incorporation of antibiotics more effective against coagulase-negative staphylococci should eventually counter late infections. As HIV-positive patients increasingly present with sepsis around implanted prostheses this need will increase. In vascular surgery as the risk factors for biomaterial infection are better understood, new generations of protein-sealed grafts are permitting ionically compatible antibiotic coatings. Large well-designed clinical trials have begun and are needed to confirm the forecast of improved long-term clinical outcomes.

Antibiotic prophylaxis in peripheral vascular and orthopaedic prosthetic surgery.

Peripheral vascular by-pass and orthopaedic joint replacement surgery have much in common. The consequences of infection are serious and occasionally fatal. The incidence of infection varies from 0.5% to 3% depending on the anatomical site; the infecting organisms and distribution of organisms are similar. In orthopaedics a clean theatre environment, high local concentrations of antibiotic in the cement and systemic antibiotic prophylaxis are well established methods of reducing infection rates and are supported by clinical trials. In contrast, scientific evidence supporting these three tenets is lacking for peripheral vascular surgery. There are wide variations in the choice of prophylaxis cover for peripheral vascular surgery and the first clinical cases of antibiotic containing graft material have only recently been described. The choice of an ideal antibiotic for the prophylaxis of infections associated with vascular surgery is debatable; wound and graft infections in those receiving antibiotic prophylaxis range from 0.9% to 5.8% and 0.0 to 0.9%, respectively. For both forms of surgery whether single dose, short course or longer periods of prophylaxis is preferred, it is agreed that the antibiotic must achieve adequate concentrations at the time of potential bacterial contamination. One of the limiting factors of single dose prophylaxis is the ability of the antibiotic to penetrate bone, soft tissue or haematoma. However, single dose prophylactic antibiotic cover in prosthetic surgery will attract increasing support whenever the criteria of spectrum and 'risk period' cover is fulfilled. This may help to contain the increase in multi-resistant bacteria, particularly staphylococci within the hospital ecosystem. Prolonged systemic administration can now be replaced by high local antibacterial activity at the site of prosthesis insertion via a bonded sealant or an impregnated cement. This permits high activity which can last for several weeks until all the lines are removed and tissue incorporation has become established.

The clinical use of an antibiotic-bonded graft.

Attempts to produce an antibiotic-bonded prosthesis have failed owing to poor binding, drug toxicity or inadequate antimicrobial activity of the antibiotic particularly against Staphylococcus epidermidis. Rifampicin, with an ideal spectrum, but untested against slime-forming S. epidermidis has recently been shown to bind with carboxyl groups on gelatin-sealed Dacron. We therefore investigated rifampicin activity against 30 slime-forming adherent S. epidermidis colonies, isolated from 40 consecutive aortic graft recipients, and compared it with their methicillin, gentamicin, cefuroxime, tetracycline and vancomycin resistance patterns. The S. epidermidis colonies were highly sensitive to very low levels of rifampicin. Rifampicin was then bonded to gelatin-sealed Dacron aortic prostheses which were inserted in four patients at high risk of developing subsequent infection.

The acquisition of antibiotic resistant coagulase-negative staphylococci by aortic graft recipients.

The staphylococcal flora of the groin and perianal area was studied in 12 patients undergoing aortic grafts and 3 patients having repair of ventral abdominal hernias. A total of 892 isolates of coagulase-negative staphylococci (CNS) were identified and their antibiotic resistance determined. The species most frequently isolated were S. epidermidis and S. haemolyticus with the latter showing the highest incidence of antibiotic resistance. Five of 15 patients had CNS resistant to methicillin and gentamicin on admission. The effect of pre-operative bathing with chlorhexidine was studied in 6 patients and appeared to reduce the acquisition of multi-resistant CNS in the week after operation.

Multiple microemboli after disintegration of clot during thrombolysis for acute myocardial infarction.

Seven of 475 consecutive patients treated with thrombolysis for acute myocardial infarction had severe embolic complications that were believed to be caused by disintegration of pre-existing clot. Three patients had symptoms that persisted for many weeks, and five died. Any potential site of pre-existing blood clot within the vascular system, notably an enlarged left atrium, ventricular aneurysm, or aortic aneurysms, should be regarded as a contraindication to treatment with thrombolytic agents.