alpha-Chymotrypsin-catalyzed degradation of desmopressin (dDAVP): influence of pH, concentration and various cyclodextrins

Comparative study of extension area based methods for spectrophotometric determination of desmopressin acetate in the presence of its acid-induced degradation products

Desmopressin acetate (DPA) is a synthetic analogue of vasopressin used in the treatment of diabetes insipidus, bedwetting, hemophilia A, and elevated levels of urea in the blood. Sensitive and selective stability-indicating methods are needed to be developed and validated for its assay pure and pharmaceutical dosage forms in the presence of its degradation products as no method has been reported for its determination in the presence of its degradants. This work describes a comparative study of five simple stability-indicating spectrophotometric techniques for determination of DPA in presence of its acid-degradation products (acid-degradants) without prior separation. The proposed spectrophotometric techniques (First derivative, Derivative ratio, Ratio difference, Mean centering and Dual wavelength) were developed and validated according to ICH guidelines. Acid degradation was carried out with 0.1 N HCl; the acid-degradants were separated on TLC plates and the acidic degradation pathway was established by IR, H-NMR and MS techniques. The TLC method was based on the separation of DPA and its acid-induced degradation products on silica gel plates using methanol: water (80:20, v/v) as a developing system and UV detection at 254 nm. All assay suggested methods were successfully applied for quantitation of DPA in pure and tablet forms. They are specific, sensitive, precise and accurate. They showed good linearity in the concentration range of 1-14 µg/mL with good correlation coefficients, and limit of detection (LOD) of 0.304, 0.274, 0.167, 0.248 and 0.199 and limit of quantitation (LOQ) of 0.920, 0.829, 0.506, 0.751 and 0.604) for each method, respectively. These methods were successfully applied for the simultaneous determination of DPA in its pure and tablet dosage form in the presence of its acid-degradants. The results obtained were statistically comparable with those of reported HPLC assay method; no significant differences were observed with relevance to accuracy and precision. All the methods are sensitive, selective and can be used for the routine analysis of DPA in its pure and dosage forms.

Effects of medicines used to treat gastrointestinal diseases on the pharmacokinetics of coadministered drugs: a PEARRL Review

Objectives

Drugs used to treat gastrointestinal diseases (GI drugs) are widely used either as prescription or over-the-counter (OTC) medications and belong to both the 10 most prescribed and 10 most sold OTC medications worldwide. The objective of this review article is to discuss the most frequent interactions between GI and other drugs, including identification of the mechanisms behind these interactions, where possible.

Key findings

Current clinical practice shows that in many cases, these drugs are administered concomitantly with other drug products. Due to their metabolic properties and mechanisms of action, the drugs used to treat gastrointestinal diseases can change the pharmacokinetics of some coadministered drugs. In certain cases, these interactions can lead to failure of treatment or to the occurrence of serious adverse events. The mechanism of interaction depends highly on drug properties and differs among therapeutic categories. Understanding these interactions is essential to providing recommendations for optimal drug therapy.

Summary

Interactions with GI drugs are numerous and can be highly significant clinically in some cases. While alterations in bioavailability due to changes in solubility, dissolution rate, GI transit and metabolic interactions can be (for the most part) easily identified, interactions that are mediated through other mechanisms, such as permeability or microbiota, are less well-understood. Future work should focus on characterising these aspects.

Solid lipid particles for oral delivery of peptide and protein drugs III - the effect of fed state conditions on the in vitro release and degradation of desmopressin

The effect of food intake on the release and degradation of peptide drugs from solid lipid particles is unknown and was therefore investigated in vitro using different fed state media in a lipolysis model. Desmopressin was used as a model peptide and incorporated into solid lipid particles consisting of trimyristin (TG14), tripalmitin (TG16), and tristearin (TG18), respectively. Fasted state and fed state media with varying phospholipid and bile salt concentrations, as well as fed state media with milk and oleic acid glycerides, respectively, were used as the release media. The presence of oleic acid glycerides accelerated the release of desmopressin significantly from all solid lipid particles both in the presence and absence of lipase. The presence of oleic acid glycerides also reduced the degradation rate of desmopressin, probably due to the interactions between the lipids and the protease or desmopressin. Addition of a medium chain triglyceride, trilaurin, in combination with drug-loaded lipid particles diminished the food effect on the TG18 particles, and trilaurin is therefore proposed to be a suitable excipient for reduction of the food effect. Overall, the present study shows that strategies to reduce food effect, such as adding trilaurin, for lipid particle formulations should be considered as drug release from such formulations might be influenced by the presence of food in the gastrointestinal tract.

Solid lipid particles for oral delivery of peptide and protein drugs II--the digestion of trilaurin protects desmopressin from proteolytic degradation

PURPOSE

To investigate the in vitro release and degradation of desmopressin from saturated triglyceride microparticles under both lipolytic and proteolytic conditions.

METHODS

The release of desmopressin from different solid lipid microparticles in the absence and presence of a microbial lipase and protease was determined. Trilaurin (TG12), trimyristin (TG14), tripalmitin (TG16), and tristearin (TG18) were used as lipid excipients to produce solid lipid microparticles.

RESULTS

In the presence of lipase, the rate of drug release from different lipid particles was in the order of TG14 > TG16 > TG18, which is the same rank order as the lipid degradation rate. A reverse rank order was found for the protection of desmopressin from enzymatic degradation due to spatial separation of desmopressin from the protease. TG12 accelerated the release of desmopressin from all lipid particles when added as either drug-free microparticles to the lipolysis medium or incorporated in TG16 particles. Additionally, TG12 particles protected desmopressin from degradation when present in the lipolysis medium with the other lipid microparticles.

CONCLUSIONS

TG12 is a very interesting lipid for oral lipid formulations containing peptides and proteins as it alters release and degradation of the incorporated desmopressin. The present study demonstrates the possibility of bio-relevant in vitro evaluation of lipid-based solid particles.

Trypsin-catalyzed deltamethrin degradation

To explore if trypsin could catalyze the degradation of non-protein molecule deltamethrin, we compared in vitro hydrolytic reactions of deltamethrin in the presence and absence of trypsin with ultraviolet-visible (UV/Vis) spectrophotometry and gas chromatography-mass spectrometry (GC/MS). In addition, acute oral toxicity of the degradation products was determined in Wistar rats. The results show that the absorption peak of deltamethrin is around 264 nm, while the absorption peaks of deltamethrin degradation products are around 250 nm and 296 nm. In our GC setting, the retention time of undegraded deltamethrin was 37.968 min, while those of deltamethrin degradation products were 15.289 min and 18.730 min. The LD₅₀ of deltamethrin in Wistar rats is 55 mg/kg, while that of deltamethrin degradation products is 3358 mg/kg in female rats and 1045 mg/kg in male rates (61-fold and 19-fold reductions in toxicity), suggesting that trypsin could directly degrade deltamethrin, which significantly reduces the toxicity of deltamethrin. These results expand people's understanding of the functions of proteases and point to potential applications of trypsin as an attractive agent to control residual pesticides in the environment and on agricultural products.

Effect of 2-hydroxypropyl-β-cyclodextrin on thermal stability and aggregation of glycogen phosphorylase b from rabbit skeletal muscle

The study of the kinetics of thermal aggregation of glycogen phosphorylase b (Phb) from rabbit skeletal muscles by dynamic light scattering at 48°C showed that 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) accelerated the aggregation process and induced the formation of the larger protein aggregates. The reason of the accelerating effect of HP-β-CD is destabilization of the protein molecule under action of HP-β-CD. This conclusion was supported by the data on differential scanning calorimetry and the kinetic data on thermal inactivation of Phb. It is assumed that destabilization of the Phb molecule is due to preferential binding of HP-β-CD to intermediates of protein unfolding in comparison with the original native state. The conclusion regarding the ability of the native Phb for binding of HP-β-CD was substantiated by the data on the enzyme inhibition by HP-β-CD. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 986-993, 2010.

Effects of various cyclodextrins on the stability of freeze‐dried lactate dehydrogenase

The effects of eight cyclodextrins (CDs) on the stability of freeze-dried lactate dehydrogenase (LDH) were investigated. Five low-molecular weight saccharides were used as a reference. In the samples without saccharides, LDH activity was decreased by freeze-drying. The LDH activities of the samples with 2-hydroxypropylated CDs (HP-CDs) such as 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) showed only a small decrease and were more effective protein stabilizers than low-molecular weight saccharides. HP-beta-CD more effectively stabilized LDH than trehalose, at a sugar concentration of less than 1.0 w/w% and furthermore, a close relationship existed between the highly stabilizing effect and the degree of substitution of polar substituents.

In vitro evaluation of the effect of cyclodextrin complexation on pulmonary deposition of a peptide, cyclosporin A

The effect of hydroxypropyl-alpha-cyclodextrin (HP-alpha-CD) complexation on in vitro pulmonary deposition of a cyclic peptide cyclosporin A (CsA) was studied. In addition, the effect of storage (32 days, 40 degrees C, 75% RH) on CsA/HP-alpha-CD complexes was studied. The complexation of CsA with CDs was evaluated by a phase-solubility method. Solid CsA/HP-alpha-CD complexes were prepared by freeze drying. Three inhalation formulations were prepared: CsA/lactose reference formulation (LF) (drug:carrier 1:364, w/w), CsA/HP-alpha-CD complex formulation (CDF) (drug:CD 1:269, w/w) and CsA/HP-alpha-CD complex/lactose formulation (CDLF) (complex:carrier 100:114, w/w). The inhalation studies were performed in vitro using Andersen Sampler (Ph. Eur.) and Taifun multi-dose dry powder inhalers (DPIs). Before the storage, the respirable fraction value (RF%) of CsA was 19.8+/-0.7%, 33.0+/-7.0% and 34.6+/-1.1% (mean+/-S.D., n=4 x 20) with LF, CDF and CDLF, respectively. When exposed to moisture (storage in a permeable polystyrene tube), the RF% values of CsA from formulations containing CsA/HP-alpha-CD complexes were lower than before the storage. However, when stored in the Taifun DPI, the RF% value of CsA from any of the formulations did not decrease. In conclusion, an acceptable RF% value of a peptide CsA from freeze-dried, simply micronized CsA/HP-alpha-CD complex powder was achieved before and after storage in the DPI.

Stability of desmopressin loaded in liposomes

Desmopressin-containing liposome formulations have been developed for intranasal administration previously. Positively charged liposomes were found to be an efficient delivery system for desmopressin. In this study, stability of the loaded desmopressin in positively charged liposomes was further investigated. Comparison of the stability of desmopressin in solution and liposomes was made. Degradation of desmopressin was shown to follow a pseudo-first-order reaction. Degradation of desmopressin in both solution and liposomes demonstrated the same kinetic behavior and exhibited no significant difference in half-lives. Similar v-shape pH-rate profile was found for desmopressin degradation in solution and liposomes. At pH 4.0, the inflection point of the v-shape pH-rate curve, the reaction rate of desmopressin was lowest and the stability was greatest. The stability of lipid ingredients of dioleoylphosphatidylcholine (DOPC), cholesterol (C), and stearylamine (S) in the liposome dispersion at pH 4.0 was studied. Results demonstrated that DOPC, C, and S were relatively stable in the liposome structure when formulated with desmopressin. The degradation of desmopressin in solution and liposomes in the presence of alpha-chymotrypsin was investigated. A longer half-life for desmopressin in liposomes than in solution was observed. It was suggested that desmopressin was protected by the liposomes against alpha-chymotrypsin digestion.

Enzymatic hydrolysis of diloxanide furoate in the presence of β-cyclodextrin and its methylated derivatives

In this study, we investigated the susceptibility to enzymatic and alkaline hydrolysis of diloxanide furoate (DF) and its cyclodextrin inclusion complexes, in aqueous solution. The cyclodextrins (CDs) utilized were beta-cyclodextrin (beta-CD), (2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD) and (2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD). All cyclodextrins studied provided a stabilizing effect to diloxanide furoate hydrolysis. In alkaline hydrolysis (pH 10.75), without the enzyme, beta-CD and TM-beta-CD provided similar effect on the stability of DF, with an inhibition factor in the order of 2.0. The DM-beta-CD, on the other hand, provided more pronounced stabilization effect than the other two CDs, with an inhibition factor around of 8. The maximum activity of the enzyme occured around pH 7.0. In the presence of enzyme, all cyclodextrins produced similar effect, with a DF hydrolysis inhibition factor in the order of 10. However, the plot of rate of hydrolysis versus [CD] fit with a equation based in a model that considers the association of the enzyme with the CDs. Therefore, it is concluded that the stabilization of DF is not only due to its cyclodextrin complex but also due to enzyme inhibition by cyclodextrin complexation.