Studies on drug-milk freeze-dried formulations. I: Bioavailability of sulfamethizole and dicumarol formulations

Implications of the Digestion of Milk-Based Formulations for the Solubilization of Lopinavir/Ritonavir in a Combination Therapy

The development of formulation approaches to coadminister lopinavir and ritonavir antiretroviral drugs to children is necessary to ensure optimal treatment of human immunodeficiency virus (HIV) infection. It was previously shown that milk-based lipid formulations show promise as vehicles to deliver antimalarial drugs by enhancing their solubilization during the digestion of the milk lipids under intestinal conditions. In this study, we investigate the role of digestion of milk and infant formula on the solubilization behavior of lopinavir and ritonavir to understand the fate of drugs in the gastrointestinal (GI) tract after oral administration. Small angle X-ray scattering (SAXS) was used to probe the presence of crystalline drugs in suspension during digestion. In particular, the impact of one drug on the solubilization of the other was elucidated to reveal potential drug-drug interactions in a drug combination therapy. Our results showed that lopinavir and ritonavir affected the solubilization of each other during digestion in lipid-based formulations. While addition of ritonavir to lopinavir improved the overall solubilization of lopinavir, the impact of lopinavir was to reduce ritonavir solubilization as digestion progressed. These findings highlight the importance of assessing the solubilization of individual drugs in a combined matrix in order to dictate the state of drugs available for subsequent absorption and metabolism. Enhancement in the solubilization of lopinavir and ritonavir in a drug combination setting in vitro also supported the potential for food effects on drug exposure.

Small-volume in vitro lipid digestion measurements for assessing drug dissolution in lipid-based formulations using SAXS

Lipid-based formulations improve the absorption capacity of poorly-water-soluble drugs and digestion of the formulation is a critical step in that absorption process. A recent approach to understanding the propensity for drug to dissolve in digesting lipid-based formulations couples an in vitro pH-stat lipolysis model to small-angle X-ray scattering (SAXS) by means of a flow-through capillary. However, the conventional pH-stat apparatus used to measure the extent of lipid digestion during such experiments requires digest volumes of 15–30 mL and drug doses of 50–200 mg, which is problematic for scarce compounds and can require excessive amounts of formulation reagents. This manuscript describes an approach to reduce the amount of material required for in vitro lipolysis experiments coupled to SAXS, for use in instances where the amount of drug or formulation medium is limited. Importantly, this was achieved while maintaining the pH stat conditions, which is critical for maintaining biorelevance and driving digestion to completion. The digestibility of infant formula with the poorly-water-soluble drugs halofantrine and clofazimine dispersed into it was measured as an exemplar paediatric-friendly lipid formulation. Halofantrine was incorporated in its powdered free base form and clofazimine was incorporated both as unformulated drug powder and as drug in nanoparticulate form prepared using Flash NanoPrecipitation. The fraction of triglyceride digested was found to be independent of vessel size and the incorporation of drug. The dissolution of the two forms of clofazimine during the digestion of infant formula were then measured using synchrotron SAXS, which revealed complete and partial solubilisation over 30 min of digestion for the powdered drug and nanoparticle formulations, respectively. The main challenge in reducing the volume of the measurements was in ensuring that thorough mixing was occurring in the smaller digestion vessel to provide uniform sampling of the dispersion medium.

Opportunities for milk and milk-related systems as 'new' low-cost excipient drug delivery materials

Milk is well recognised as an amazing delivery system for essential lipids, poorly soluble nutrients, sugars, amino acids and delivery of critical biological molecules to sustain the infant and adult alike. It is also a safe and abundant resource with potential to act as a low-cost material for formulation of medicines, especially for paediatric patients and those in low economy settings. However, its use in low cost formulations has never developed beyond preclinical evaluation. Reasons for this are several-fold including variable composition and therefore regulatory challenges, as well as a lack of clear understanding around when milk or milk-related materials like infant formula could best be deployed by linking drug properties with excipient composition attributes, especially when taking digestion into account. This review collects the current understanding around these issues. It is apparent from the evolving understanding that while milk may be a bridge too far for translation as an excipient, infant formula is positioned to play a key role in the future because, as a powder-based excipient, it has the performance benefits of milk powder together with the controlled specifications during manufacture and versatility of application to function as a low cost lipid excipient to enable potential translation for the oral delivery of poorly water soluble drugs for key populations including paediatrics and low economy medicines.

Experimental and Theoretical Screening for Green Solvents Improving Sulfamethizole Solubility

Solubility enhancement of poorly soluble active pharmaceutical ingredients is of crucial importance for drug development and processing. Extensive experimental screening is limited due to the vast number of potential solvent combinations. Hence, theoretical models can offer valuable hints for guiding experiments aimed at providing solubility data. In this paper, we explore the possibility of applying quantum-chemistry-derived molecular descriptors, adequate for development of an ensemble of neural networks model (ENNM), for solubility computations of sulfamethizole (SMT) in neat and aqueous binary solvent mixtures. The machine learning procedure utilized information encoded in σ-potential profiles computed using the COSMO-RS approach. The resulting nonlinear model is accurate in backcomputing SMT solubility and allowed for extensive screening of green solvents. Since the experimental characteristics of SMT solubility are limited, the data pool was extended by new solubility measurements in water, five neat organic solvents (acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, 1,4-dioxane, and methanol), and their aqueous binary mixtures at 298.15, 303.15, 308.15, and 313.15 K. Experimentally determined order of decreasing SMT solubility in neat solvents is the following: N,N-dimethylformamide > dimethyl sulfoxide > methanol > acetonitrile > 1,4dioxane >> water, in all studied temperatures. Similar trends are observed for aqueous binary mixtures. Since N,N-dimethylformamide is not considered as a green solvent, the more acceptable replacers were searched for using the developed model. This step led to the conclusion that 4-formylmorpholine is a real alternative to N,N-dimethylformamide, fulfilling all requirements of both high dissolution potential and environmental friendliness.

Enhancement of Docetaxel Absorption Using Ritonavir in an Oral Milk-Based Formulation

OBJECTIVE

The current study aimed to develop a novel milk-based formulation of docetaxel, a sparingly soluble antineoplastic agent, administered so far exclusively by the intravenous route and evaluate its oral bioavailability.

METHODS

Pre-formulation studies included the determination of docetaxel solubility in water-alcohol mixtures as well as short-term content uniformity experiments of the final formulation. The pharmacokinetic (PK) performance of the developed milk-based formulations was further evaluated in vivo in mice using ritonavir, a potent P-glycoprotein inhibitor, as an absorption enhancer of docetaxel and the marketed intravenous docetaxel formulation, Taxotere®, as a control.

RESULTS

In vivo PK results in mice showed that all the administered oral docetaxel formulations had limited absorption in the absence of ritonavir. On the contrary, ritonavir co-administration given as pre-treatment significantly enhanced oral bioavailability of both the marketed and milk-based docetaxel formulations; an even more marked increase in drug exposure was observed when ritonavir was incorporated within the docetaxel milk-based formulation. The fixed-dose combination also showed a more prolonged absorption of the drug compared to separate administrations.

CONCLUSIONS

The current study provides insights for the discovery of a novel milk-based formulation that could potentially serve as an alternative, non-toxic and patient-friendly carrier for an acceptable docetaxel oral chemotherapy.

Formation of Self-Assembled Mesophases During Lipid Digestion

Lipids play an important role in regulating bodily functions and providing a source of energy. Lipids enter the body primarily in the form of triglycerides in our diet. The gastrointestinal digestion of certain types of lipids has been shown to promote the self-assembly of lipid digestion products into highly ordered colloidal structures. The formation of these ordered colloidal structures, which often possess well-recognized liquid crystalline morphologies (or “mesophases”), is currently understood to impact the way nutrients are transported in the gut and absorbed. The formation of these liquid crystalline structures has also been of interest within the field of drug delivery, as it enables the encapsulation or solubilization of poorly water-soluble drugs in the aqueous environment of the gut enabling a means of absorption. This review summarizes the evidence for structure formation during the digestion of different lipid systems associated with foods, the techniques used to characterize them and provides areas of focus for advancing our understanding of this emerging field.

A pharmacological review of dicoumarol: An old natural anticoagulant agent

Dicoumarol is an oral anticoagulant agent prescribed in clinical for decades. It is a natural hydroxycoumarin discovered from the spoilage of Melilotus officinalis (L.) Pall and is originally discovered as a rodenticide. Due to its structural similarity to that of vitamin K, it significantly inhibits vitamin K epoxide reductase and acts as a vitamin K antagonist. Dicoumarol is mainly used as an anticoagulant to prevent thrombogenesis and to cure vascular thrombosis. Other biological activities besides anticoagulants such as anticancer, antimicrobial, antiviral, etc., have also been documented. The side effects of dicoumarol raise safety concerns for clinical application. In this review, the physicochemical property, the pharmacological activities, the side effects, and the pharmacokinetics of dicoumarol were summarized, aiming to provide a whole picture of the "old" anticoagulant.

The Biopharmaceutics Classification System (BCS) and the Biopharmaceutics Drug Disposition Classification System (BDDCS): Beyond guidelines

The recent impact of the Biopharmaceutics Classification System (BCS) and the Biopharmaceutics Drug Disposition Classification System (BDDCS) on relevant scientific advancements is discussed. The major advances associated with the BCS concern the extensive work on dissolution of poorly absorbed BCS class II drugs in nutritional liquids (e.g. milk, peanut oil) and biorelevant media for the accurate prediction of the rate and the extent of oral absorption. The use of physiologically based pharmacokinetic (PBPK) modeling as predictive tool for bioavailability is also presented. Since recent dissolution studies demonstrate that the two mechanisms (diffusion- and reaction-limited dissolution) take place simultaneously, the neglected reaction-limited dissolution models are discussed, regarding the biopharmaceutical classification of drugs. Solubility- and dissolution-enhancing formulation strategies based on the supersaturation principle to enhance the extent of drug absorption, along with the applications of the BDDCS to the understanding of disposition phenomena are reviewed. Finally, recent classification systems relevant either to the BCS or the BDDCS are presented. These include: i) a model independent approach based on %metabolism and the fulfilment (or not) of the current regulatory dissolution criteria, ii) the so called ΑΒΓ system, a continuous version of the BCS, and iii) the so-called Extended Clearance Classification System (ECCS). ECCS uses clearance concepts (physicochemical properties and membrane permeability) to classify compounds and differentiates from BDDCS by bypassing the measure of solubility (based on the assumption that since it inter-correlates with lipophilicity, it is not directly relevant to clearance mechanisms or elimination).

Application of Low-Frequency Raman Scattering Spectroscopy to Probe in Situ Drug Solubilization in Milk during Digestion

We have recently shown that real-time monitoring of drug solubilization and changes to solid state of the drug during digestion of milk can be achieved using synchrotron small-angle X-ray scattering. A complementary laboratory-based method to explore such changes is low-frequency Raman spectroscopy, which has been increasingly used to characterize crystalline drugs and their polymorphs in powders and suspensions. This study investigates the use of this technique to monitor in situ drug solubilization in milk during the process of digestion, using a lipolysis model/flow-through configuration identical to that used previously for in situ synchrotron small-angle X-ray scattering studies. An antimalarial drug, ferroquine (SSR97193), was used as the model drug for this study. The Raman spectra were processed using multivariate analysis to extract the drug signals from the milk digestion background. The results showed disappearance of the ferroquine peaks in the low-frequency Raman region (<200 cm^-1) after approximately 15-20 min of digestion when milk fat was present in the system, which indicated drug solubilization and was in good agreement with the in situ small-angle X-ray scattering measurements. This proof-of-concept study therefore suggests that low-frequency Raman spectroscopy can be used to monitor drug solubilization in a complex digesting milk medium because of the unique vibrational modes of the drug crystal lattices.

The impact of digestion is essential to the understanding of milk as a drug delivery system for poorly water soluble drugs

Milk has previously been considered as a potential lipid-based drug delivery system for poorly water soluble drugs but it has never gained significant attention. This is in part because relying on solubility in lipid-based formulations (in this case milk) does not provide a complete picture of the behavior of such systems upon digestion. Herein, we demonstrate using time resolved X-ray scattering that the digestion of milk is actually crucial to the solubilisation of a poorly water-soluble drug, halofantrine. Halofantrine was chosen because its behaviour in lipid-based formulations has been widely investigated and because of its close structural relationship to lumefantrine, an antimalarial drug of current interest for the treatment of paediatric malaria. The transformation of the drug from a crystalline solid form in suspension in milk, to a solubilised form as a direct consequence of lipolysis highlights that consideration of digestion of the milk lipids as a critical process that influences drug solubilisation and availability for absorption is vital.

Novel milk-based oral formulations: proof of concept

The aim of this study is to develop milk-based formulations for ionized and unionized lipophilic drugs. Solubility studies of the following non-steroidal anti-inflammatory drugs (NSAIDs): mefenamic acid, tolfenamic acid, ketoprofen, meloxicam, tenoxicam and nimesulide in phosphate- and glycine-NaOH buffers at nominal pH 8-12, were performed. The solubilities of cyclosporine and danazol in water-ethanol solutions were studied. NSAIDs-, cyclosporine-, danazol-, aspirin-milk oral liquid formulations were prepared by adding the appropriate volume of (i) NSAIDs-alkaline buffer solutions, (ii) water-ethanol solutions of cyclosporine and danazol and (iii) aspirin aqueous solution to 150-200ml of milk. All the non-steroidal anti-inflammatory drugs exhibited increased solubility in the alkaline buffers. The actual pH values (range 6.7-7.7) of the final NSAIDs-milk formulations were very close to milk pH. The higher ethanol content in ethanol-water mixtures increased the solubility of danazol and cyclosporine. A 15mg meloxicam-, a 100mg cyclosporine- and a 500mg aspirin-milk formulation was administered orally to healthy volunteers. All these formulations showed a satisfactory in vivo performance. The strong buffering capacity of milk that was observed and the high solubility of unionized drugs in ethanol allow the preparation of drug-milk formulations with enhanced pharmacokinetic properties.

Improving relative bioavailability of dicumarol by reducing particle size and adding the adhesive poly(fumaric-co-sebacic) anhydride

PURPOSE

This study was carried out to show the effect of particle size reduction and bioadhesion on the dissolution and relative bioavailability of dicumarol.

METHODS

Formulations were produced by a variety of methods including a novel technique to reduce particle size as well as phase inversion with poly(fumaric-co-sebacic)anhydride p(FA:SA) to create nanospheres. Drug was administered to groups of pigs and rats via oral gavage of a suspension, and dicumarol concentration in the blood was measured using a double extraction technique.

RESULTS

In vitro results showed improved dissolution in both the micronized formulation and the encapsulated p(FA:SA) nanospheres. In vivo, relative bioavailability of a spray-dried formulation was increased by 17% in the rat and 72% in the pig by further reduction in particle size. The bioadhesive p(FA:SA) formulation also improved relative bioavailability over the spray-dried drug, increasing it by 55% in the rat and 96% in the pig. Additionally, the p(FA:SA) formulation prolonged Tmax and decreased Cmax in both species.

CONCLUSION

This work demonstrates the importance of particle size and bioadhesion to improve oral bioavailability of ducumarol.

Physical stability of redispersible dry emulsions containing amorphous sucrose

The objective of the present study was to estimate the stability of redispersible dry emulsions containing amorphous sucrose. Dry emulsions were prepared by spray drying liquid o/w-emulsions in a laboratory spray dryer. The effect of hydroxypropyl methylcellulose (HPMC) on the glass transition temperature T(g) of spray dried sucrose-HPMC mixtures, relative to the T(g) of amorphous sucrose, was investigated. For the sucrose-HPMC mixtures the values of T(g) followed the ideal Gordon-Taylor equation up to 30% HPMC. For dry emulsions containing 40% HPMC, 30% lipid and 30% sucrose, the T(g) was increased by 12 degrees C relative to the T(g) of amorphous sucrose. The stability of the dry emulsions was investigated by a conventional stability study and by an enthalpy relaxation study. The measured enthalpy recovery of amorphous sucrose below T(g) was used to calculate molecular relaxation time parameters based on the Williams-Watts equation. The molecular mobility of amorphous sucrose at temperatures 50 degrees C below T(g) was low and negligible with respect to the shelf life stability. It was concluded that the dry emulsions are physically stable with respect to the lifetime of a pharmaceutical product when stored in dry condition and at temperatures up to 28 degrees C.

Influence of physicochemical properties on dissolution of drugs in the gastrointestinal tract

The rate-limiting step to absorption of drugs from the gastrointestinal (GI) tract is often dissolution from the dosage form. Consideration of the Noyes-Whitney dissolution model shows that drug diffusivity, solubility in the gastrointestinal contents, the surface area of the solid wetted by the lumenal fluids and the GI hydrodynamics all play a role in determining the in vivo dissolution rate. Solubility in the GI contents is determined by aqueous solubility, crystalline form, drug lipophilicity, solubilization by native surfactants and co-ingested foodstuffs, and pK(a) in relation to the GI pH profile. Compounds with aqueous solubilities lower than 100 microg/ml often present dissolution limitations to absorption. The dose:solubility ratio of the drug provides an estimate of the volume of fluids required to dissolve an individual dose, and when this volume exceeds 1 l, dissolution is often problematic. The surface area of a drug available for dissolution depends on the particle size of the solid and its ability to be wetted by lumenal fluids. Other physiological factors that can play a role in dissolution include the viscosity of the lumenal contents, through its effect on the diffusivity, and mixing and flow patterns within the gut. In order to better predict in vivo dissolution of drugs, dissolution tests which more adequately simulate the physiological conditions are needed.

Preparation of redispersible dry emulsions by spray drying

Development of stable dry emulsions being able to reform the original o/w-emulsion by reconstitution in water is presented. Dry emulsions were prepared by spray drying liquid o/w-emulsions in a laboratory spray dryer. Three hydroxypropylmethylcellulose (HPMC) types were applied as solid carrier and emulsifier. The lipid phase was fractionated coconut oil. The ratio of solid carrier to lipid phase influenced the reconstitution properties. It was possible to prepare redispersible dry emulsions of a lipid content up to 40% dry powder mass. The different HPMC types had no noticeable effect on the reconstitution properties, but too viscous liquid o/w-emulsions were difficult to atomise. The type of rotary atomizer, or the rate of rotation did not affect the technical properties of the dry emulsions containing 40% lipid. It was concluded that low viscosity HPMC was a useful solid carrier. The dry emulsions remained physically stable for at least 6 months.

Technical optimisation of redispersible dry emulsions

Preparation of dry emulsions suitable for tablet processing was examined in this study. Liquid o/w-emulsions were spray dried in a laboratory spray dryer applying hydroxypropylmethylcellulose (HPMC) as a solid carrier and emulsifier. As the lipid phase, fractionated coconut oil was used. The ability of various excipients to increase the density of dry emulsions was investigated. Adding sucrose to the formulation, redispersible dry emulsions with higher density were obtained. The type of rotary atomizer did not affect the dry emulsions containing sucrose nor the rate of rotation of the atomizer applied in the spray drying process. By wet granulation, using ethanol as a binder, free-flowing and compactable dry emulsions were obtained and simultaneously the reconstitution properties were preserved. It was concluded that dry emulsions could be optimised for tablet processing by wet granulation. Tablets having a lipid content up to 20% had proper tablet properties.

Surface active drugs: self-association and interaction with membranes and surfactants. Physicochemical and biological aspects

Many pharmacologically active compounds are of amphiphilic (or hydrophobic) nature. As a result, they tend to self-associate and to interact with biological membranes. This review focuses on the self-aggregation properties of drugs, as well as on their interaction with membranes. It is seen that drug-membrane interactions are analogous to the interactions between membranes and classical detergents. Phenomena such as shape changes, vesiculation, membrane disruption, and solubilization have been observed. At the molecular level, these events seem to be modulated by lipid flip-flop and formation of non-bilayer phases. The modulation of physicochemical properties of drugs by self-association and membrane binding is discussed. Pathological consequences of drug-membrane interaction are described. The mechanisms of drug solubilization by surfactants are reviewed from the physicochemical point of view and in relation to drug carrying and absorption by the organism.

An alternative method for the estimation of the terminal slope when a few data points are available

Phase plane plots are graphical expressions for differential equations plotting the state derivative dc/dt versus the state c. Using these plots, we developed a novel method for the estimation of the terminal slope from time-concentration data. The values of the derivatives used for the construction of the phase plane plots were calculated by two different methods of numerical differentiation. The first method (D1) is based on the classical calculation of slope of the line connecting two successive data points. The alternative method (D2) relies on an initial second-order polynomial interpolation utilizing three successive data points followed by the calculation of the derivative at each one of the concentration values. A forced-through-zero linear regression of the phase plane plot data is used to derive an estimate for the slope. For comparative purposes, the standard approach based on the semilogarithmic plot was also applied. For a hypothetical drug absorbed by first-order process into a one-compartment model, simulated time-concentration data disturbed by a Gaussian zero mean random error with various coefficients of variation were generated. Various sampling schedules, with two, three, four, or five data points, were utilized for the estimation of the terminal slope. Performances of the proposed methods on simulated data were expressed by means of root-mean-squared error, bias, and standard deviation. In all cases, D2 was superior to D1. The D2 method outperforms the standard method in that it furnishes estimates closer to the real values in all cases when two data points and in most cases when three data points were used. All methods behave similarly when four or five data points were used.

Bioavailability study of a freeze-dried sodium phenytoin-milk formulation

The problematic bioavailability of phenytoin's (5,5-diphenylhydantoin) oral formulations serves as a stimulus for examining new formulations and/or administration conditions that may provide more predictable absorption. Attempts to achieve more consistent peroral phenytoin bioavailability from conventional solid dosage forms include changes of binder and crystal size, use of salt form, and inclusion of the drug in cyclodextrins. In addition, various factors which may affect the environment and/or the physiology of the upper gastrointestinal tract can profoundly affect the absorption of phenytoin. Among other approaches, the use of drug-milk freeze-dried formulations has been proposed to overcome problems associated with dissolution-limited bioavailability. The effect has been attributed to the formation of an amorphous precipitate during the drying process which facilitates the re-dissolution of the drug during the regeneration of the milk solution. In this work, we report comparative bioavailability studies utilizing a freeze-dried sodium phenytoin-milk formulation and a capsule formulation administered with either water or milk. In addition, the interaction of the drug with milk components was evaluated in vitro through binding and solubility studies.

Drug binding and solubility in milk

The binding and solubility of nitrofurantoin, piroxicam, indomethacin, prednisolone, diazepam, dicumarol, and griseofulvin in milk were determined at 15, 25, and 37 degrees C in bovine milk samples with fat contents of 0.75 and 3.50%. Drug binding to milk components was independent of drug concentration over the drug concentration studied, and the fat content of milk strongly affected binding values of most of the listed drugs. Further, drug binding increased with decreasing temperatures for most of the drugs examined. The solubility of all drugs is greatly enhanced in milk compared to their aqueous solubility (pH 6.5 phosphate buffer). The high solubility cannot be accounted for solely on the basis of drug binding to milk components. An attempt is made to correlate the binding and solubility data with physicochemical properties of the drugs (logP, pKa, aqueous solubility). The potential significance of these findings is discussed with regard to preparation and in vivo delivery of drugs from drug-milk formulations.

Effect of temperature and fat content on the solubility of hydrochlorothiazide and chlorothiazide in milk

The solubility of hydrochlorothiazide and chlorothiazide in milk has been studied. Experiments were carried out at 5, 15, 25, and 37 degrees C on a buffer solution of pH 6.5, a 2.6% solution of casein, bovine skim milk samples, and bovine milk samples with fat contents of 0.75, 1.70, and 3.50%. The "total" solubility of both drugs in the media studied was higher than the buffer solubility. The highest "total" solubility for both drugs was observed in skim milk. Based on binding data of thiazides to milk, the "total" solubility was split into "free" and "bound" solubility. The increases of solubility noted cannot be explained on the basis of drug-milk binding data. The enhancement of solubility was attributed to the increase of intrinsic solubility of drugs in milk. Results of the thermodynamic analysis of solubility data showed that a different solubilization process of hydrochlorothiazide may be responsible for the high solubility values found in skim milk for this drug. In contrast, the thermodynamic parameters of chlorothiazide in all types of milk are similar, indicating a common solubilization mechanism. The biopharmaceutical significance of the findings is discussed in light of the freeze-dried drug-milk formulations and coadministration of drugs with milk in general.

Effect of temperature and fat content on the binding of hydrochlorothiazide and chlorothiazide to milk

The binding of hydrochlorothiazide and chlorothiazide to milk has been measured. Experiments were carried out at 5, 15, 25, and 37 degrees C on bovine milk samples with fat contents of 0.75, 1.70, and 3.50%, using a wide range of drug concentrations to mimic concentrations encountered when a drug-milk freeze-dried system is utilized. Binding experiments with a 2.6% solution of casein were also carried out at the same temperature and concentration range of drugs. The binding to milk and casein was found to be not dependent on the concentration of drugs. The fat content of milk had no significant effect on the binding of both drugs. Higher binding was observed at lower temperatures than at higher temperatures for both drugs examined. The binding of both drugs to casein at 37 degrees C agrees fairly well with the corresponding binding to all types of milk at 37 degrees C. The potential significance of the findings in respect to preparation and in vivo delivery of drugs from drug-milk formulations is discussed.

Studies on freeze-dried drug-milk formulations. II: Effect of regenerated fluid volume on nitrofurantoin bioavailability

The effect of different milk volumes on the extent and consistency of nitrofurantoin (1-[(5-nitrofurfurylidene)amino]hydantoin) absorption from freeze-dried nitrofurantoin-milk formulations was studied in four male volunteers in three separate crossover designs. Each volunteer received six single-dose treatments (one 100-mg nitrofurantoin capsule with 100, 200, and 400 mL of milk and 100 mg of nitrofurantoin as a freeze-dried nitrofurantoin milk formulation regenerated with 100, 200, and 400 mL of water). Analysis of the urine data revealed superiority of the nitrofurantoin-milk formulations regenerated with 200 and 400 mL of milk over the corresponding capsule formulations in the rates and extents of nitrofurantoin excretion. The binding of nitrofurantoin to casein and bovine serum albumin and its solubility in the presence of the proteins were measured in vitro. The presence of both proteins caused increases in the solubility of nitrofurantoin. Normal protein binding is responsible for the increase of nitrofurantoin solubility in the presence of bovine serum albumin, whereas the increase of nitrofurantoin solubility in the presence of casein is attributed to the formation of aggregates in casein solution at 37 degrees C. The in vivo data were discussed in light of the in vitro data. The freeze-dried nitrofurantoin-milk formulation regenerated with 200 mL of water has a potential for use as a nitrofurantoin delivery system.