Injectable Formulations of Poorly Water-Soluble Drugs. In: Williams Iii RO, Watts AB, Miller DA, editors. Formulating Poorly Water Soluble Drugs. New York: Springer; 2012. pp. 209-42. [DOI: 10.1007/978-1-4614-1144-4_6]

Prodrugs as empowering tools in drug discovery and development: recent strategic applications of drug delivery solutions to mitigate challenges associated with lead compounds and drug candidates

The delivery of a drug to a specific organ or tissue at an efficacious concentration is the pharmacokinetic (PK) hallmark of promoting effective pharmacological action at a target site with an acceptable safety profile. Sub-optimal pharmaceutical or ADME profiles of drug candidates, which can often be a function of inherently poor physicochemical properties, pose significant challenges to drug discovery and development teams and may contribute to high compound attrition rates. Medicinal chemists have exploited prodrugs as an informed strategy to productively enhance the profiles of new chemical entities by optimizing the physicochemical, biopharmaceutical, and pharmacokinetic properties as well as selectively delivering a molecule to the site of action as a means of addressing a range of limitations. While discovery scientists have traditionally employed prodrugs to improve solubility and membrane permeability, the growing sophistication of prodrug technologies has enabled a significant expansion of their scope and applications as an empowering tool to mitigate a broad range of drug delivery challenges. Prodrugs have emerged as successful solutions to resolve non-linear exposure, inadequate exposure to support toxicological studies, pH-dependent absorption, high pill burden, formulation challenges, lack of feasibility of developing solid and liquid dosage forms, first-pass metabolism, high dosing frequency translating to reduced patient compliance and poor site-specific drug delivery. During the period 2012-2022, the US Food and Drug Administration (FDA) approved 50 prodrugs, which amounts to 13% of approved small molecule drugs, reflecting both the importance and success of implementing prodrug approaches in the pursuit of developing safe and effective drugs to address unmet medical needs.

Equilibria, kinetics and mechanism for the degradation of the cytotoxic compound L-NG-nitroarginine

L-N^G-nitroarginine (LNNA), an analog of L-arginine, is a competitive inhibitor of nitric oxide synthase which causes the selective reduction of blood flow to tumor cells. Despite the potential of LNNA to function as an adjuvant in cancer therapies, its poor solubility and stability have hindered the development of an injectable formulation of LNNA that is suitable for human administration. This work, for the first time, details a systematic study on the determination of equilibrium K_a constants and the rate law of LNNA degradation. The four K_a values of LNNA were determined to be 1.03, 1.10 × 10^-2, 2.51 × 10^-10, and 1.33 × 10^-13 M. From the kinetic and equilibrium studies, we have shown that the deprotonated form of LNNA is the main form of LNNA that undergoes degradation in aqueous media at room temperature. The rate law of LNNA degradation was found to be first order with respect to OH^- concentration and first order with respect to LNNA^- concentration. The rate constant at 25 °C and 1 atm was determined to be 0.04453 M^-1min^-1. A base catalyzed mechanism of LNNA degradation was proposed based on the kinetic study. The mechanism was found to be very useful in explaining the discrepancies and changes of the rate law at different pH values. It is thus recommended that LNNA should be formulated as a concentrated solution in acidic conditions for maximum chemical stability during storage and be diluted with a basic solution to near physiological pH just before administration.

Stability of latanoprost in generic formulations using controlled degradation and patient usage simulation studies

PURPOSE

To evaluate the stability of latanoprost in generic formulations by using controlled degradation and patient usage simulation studies

METHODS

Standard latanoprost was subjected to controlled degradation studies. Latanoprost content was assessed by using MRM, and generated Degradation Products (DP) were analysed by using the Information Dependent Acquisition (IDA) protocol of positive ESI-LC-MS/MS. Latanoprost content and formation of DP were assessed in generic formulations and were compared with Xalatan(®) in a controlled patient usage simulation studies. The last few drops of latanoprost, present in containers used by patients were also evaluated.

RESULTS

Extreme pH conditions, oxidation, light and heat were found to be the significant factors for high degree of latanoprost degradation. Systematic analysis of 7 selected generics revealed that the latanoprost content varied from 90-330%. Concentration of the latanoprost in Xalatan was found to be 97% of the label claim. Degradation studies showed the formation of 3 novel and 3 already known impurities. Upon simulated patient usage, 2 of the generic formulations showed significant degradation of latanoprost. Generic formulations having thermally sealed gas tight packing showed good stability during patient usage. Overage of latanoprost was observed in generics with other than thermal sealing. Latanoprost bottles used by patients showed concentrations ranging from 20 to 250% of label claim (144% median).

CONCLUSION

This study revealed the presence of overage of latanoprost in some generic formulations and formation of degradation products. Packaging with gas tight containers may be one of the important factors for latanoprost stability, along with its storage at low temperature during patient usage.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.