Factors affecting iontophoretic delivery

8.4.1.1 Molecular weight As discussed in Section 8.2.1, the pathways of iontophoretic delivery are different from those for passive transdermal delivery. Because a pore path way is most likely involved, the flux is expected to be size dependent with a cutoff at some point. Using eight tripeptides of the general structure (ala-nine-X-alanine), Green et al.89 investigated their delivery across hairless mouse skin in vitro. The normalized iontophoretic flux was independent of lipophilicity but...

Rectal delivery

The human rectum is the terminal 15- to 20-cm long region of the large intestine. The rectal epithelium does not contain villi and has a surface area of only 200 to 400 cm2. It is abundant in blood, lymphatic vessels, and microflora. The mucous membrane is permeated by three types of hemor-rhoidal veins the superior, middle, and inferior hemorrhoidal veins. The inferior and middle rectal veins are directly connected to the systemic circulation, and the superior rectal vein is connected to the...

Formulation components for lyophilization

A typical lyophilized protein formulation may contain a bulking agent, buffer, tonicity modifier, and other excipients that may be classified as cry-oprotectants and lyoprotectants.44 Nonionic surfactants can be used to reduce protein aggregation. Because phosphate buffer often causes problems during lyophilization, alternate buffers such as Tris, histidine, or citrate may be used. Trehalose or sucrose are often used to stabilize the protein as both are non-reducing sugars that can act as both...

Carrier systems

Carrier systems such as nanoparticles, microspheres, liposomes, or erythro-cytes can also be used to improve the oral absorption of peptides and proteins. Emisphere Technologies, Incorporated (Tarrytown, NY) initiated clinical trials for oral delivery of insulin using its carrier eligen technology. The company has also initiated oral delivery of recombinant human growth hormone in collaboration with Novartis and is currently in phase II clinical trials for oral delivery of calcitonin (http...

Buccal delivery

The buccal mucosa covers the inside of the cheek and is a part of the oral mucosa. The oral mucosa lines the oral cavity, which is situated within the dental arches framed on the top by the hard and soft palates and in the bottom by the tongue and floor of the mouth. The oral mucosa is keratinized in the gingiva, hard palate, and dorsum of the tongue regions it is nonkera-tinized for the soft palate, ventral surface of the tongue, buccal cavity, and lips. The buccal epithelium is about 500 to...

Transcutaneous immunization

The skin is the largest organ of the human body, with a surface area of about 2 m2. It is composed of an outer epidermis, an inner dermis, and the underlying subdermal tissue. For more details on skin structure, refer to Chapter 8. The physiologically active epidermis contains keratinocyte antigen-expressing cells as the predominant cell type. These cells can only express antigens for a few days before sloughing off with the normal sloughing of the epidermal layers of the skin. However, this...

Structurebased drug design

The first structure-based search in 1975 discovered the antihypertensive agent captopril. Over the next 15 years, millions of dollars were spent in this area with few results. This has begun to change now because of advances in nuclear magnetic resonance, x-ray crystallography, and computer model-ing.124-127 Traditionally, pharmaceutical companies have discovered new drugs by screening an extensive collection of chemical compounds. This screening stage of drug discovery is followed by toxicity...

Selection of excipient

It is evident from the discussion in this chapter that although several excipients can be used, each has its advantages and disadvantages. If an excipient can provide the desired buffering capacity while enhancing protein solubility and stabilizing the formulation, that would be close to an ideal excipient. However, usually more than one excipient may be required in the formulation to provide all these desirable attributes. The best excipients must be found for each individual protein, and it...

Oral immunization

Though oral polio vaccine has been used for several decades, the oral route offers a formidable challenge to vaccine delivery, especially for the protein-based vaccines. These challenges include the proteolytic and permeability barrier imposed by the intestine. Repeated large doses of vaccine antigens could be effective for oral immunization, but the approach is not of practical importance because of the cost and availability issues for antigens. Another approach has been to identify molecules...

Introduction

The focus of this chapter is on protein or recombinant protein-based subunit vaccines as these fit better with the overall scope of this book, especially because many of the products in development will have a therapeutic focus. Recombinant vaccines in development are listed in Table 10.1. Peptides and peptidomimetics are also in development as vaccines. Peptidomimetic vaccines contain antigenic fragments that mimic the antibody-binding site.1 However, an introduction to vaccines in general is...

Pulsatile drug delivery systems

Many physiological peptides and proteins are released in the body in a pulsatile fashion as opposed to continuous release. Examples of peptides and proteins that are released in a pulsatile pattern include vasopressin,154 LHRH,118 insulin,155 and GH,156 among others. GH is secreted in discrete pulses by the anterior pituitary gland in response to a complex collection of external and internal stimuli.156 As discussed in Section 6.4.4, a different pharmacological response may result depending on...

Penetration enhancers

Penetration enhancers can enhance oral absorption by their action on the transcellular or paracellular pathway. For effects on the transcellular pathway, surfactants and fatty acids may alter membrane lipid organization and may thus increase oral transport. Surfactants can be incorporated into lipid bilayers, thus changing the physical properties of the cell membranes. For effects on the paracellular pathway, chelating agents can disrupt the integrity of occluding junctional complexes by...

Approaches to enhance transdermal peptide delivery 831 Skin microporation

A very promising technology is under development for transdermal delivery of macromolecules such as proteins and vaccines. It involves a minimally invasive technique in which micron-size transport pathways are created in the skin. These micron-size holes are huge compared to drug dimensions but still much smaller than the holes made by hypodermic needles. These micron-size holes can be created in the skin using mechanical microneedles2425 or by using a thermal microporation process.26 The holes...

Aggregation

Protein molecules can often undergo self-association by physical or chemical forces to form dimers, trimers, tetramers, or higher oligomers. This self-association or aggregation is a common problem during formulation development and pharmaceutical processing. Although aggregation is physical instability, it can lead to loss of biological activity. However, some proteins may exert their biological effects as a dimer, trimer, or higher oligomeric forms and may lose biological activity on...

Chemical modification

Nobex Corporation (North Carolina) has used an approach to attach low molecular weight polymers at specific sites on proteins to create a conjugated molecule with improved oral absorption. The carrier molecules used revers-ibly destabilize the native protein, favoring a partially unfolded conformation. This noncovalent interaction between the carrier and partially unfolded protein conformation increases solvent exposure of hydrophobic side chains, thereby increasing lipid solubility and oral...

References

A. C., and Oussoren, C. Release and absorption rates of intramuscularly and subcutaneously injected pharmaceuticals (II). Int. J. Pharm., 105 189-207, 1994. 2. Porter, C. J. Drug delivery to the lymphatic system. Crit. Rev. Ther. Drug Carrier Syst., 14 333-393, 1997. 3. McLennan, D. N., Porter, C. J., Edwards, G. A., Brumm, M., Martin, S. W., and Charman, S. A. Pharmacokinetic model to describe the lymphatic absorption of r-metHu-leptin after subcutaneous...

Preformulation studies

Product development of a peptide or protein drug starts with preformulation studies on the bulk material. These studies include physicochemical characterization of the bulk material and evaluation of its solubility and stability.5 The primary sequence and carbohydrate profile of the protein will be established, and its extinction coefficient will be determined. The solubility profile of the protein, its stability, and its isoelectric point (pi) will determine which pH should be used for...

Immunoassays and bioassays

Radioimmunoassay (RIA) was first developed in the mid-1950s for assay of insulin but gained widespread acceptance only in the 1970s.130136 The assay exploits the specific and tight association of antibody with a peptide or protein drug as the antigen to determine very low concentrations of the drug. In carrying out the assay, the unlabeled protein is exposed to its antibody in the presence of a known amount of radiolabeled protein. The concentration of protein is determined by measuring the...

Immunogenicity of proteins

The body generates an immune response if it considers the administered protein to be foreign. Thus, proteins derived from animal sources such as bovine or porcine insulin are expected to be immunogenic. However, in reality, even recombinant human proteins are generally immunogenic, although to a lesser extent. This could be caused by various reasons. The protein may have product-related impurities such as oxidized forms or aggregates. Another major source of immunogenicity is the presence of...

Microsphere formulations of luteinizing hormonereleasing hormone and analogues

Luteinizing hormone-releasing hormone (LHRH), also known as gonado-tropin-releasing hormone (GnRH), is a naturally occurring decapeptide that stimulates the release of the pituitary gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LHRH is secreted in a pulsatile manner, and its replacement for treatment of primary infertility of hypotha-lamic origin requires pulsatile administration every 60 to 90 min through programmable pumps.118 LHRH is readily degraded in the...

Protease inhibitors

Protease inhibitors may also promote oral absorption of therapeutic peptides and proteins by reducing their proteolytic breakdown in the GI tract. Generally, inhibitory agents may be classified as (1) polypeptide protease inhibitors (e.g., aprotinin) (2) peptides and modified peptides (e.g., bacitracin, chymostatin, and amastatin) (3) amino acids and modified amino acids (e.g., a-aminoboronic acid derivatives), and (4) others (e.g., p-aminobenzamidine and camostat mesilate).87 An aminopeptidase...

Measurement of lyophilizationinduced thermal changes

The changes in transition states induced by lyophilization may be measured by DSC. For a discussion of DSC as an analytical tool and the use of micro-calorimeter and modulated DSC for characterization of proteins, please see Chapter 2. A freeze-drying microscope can also be utilized to visualize the ice crystals directly because it uses a low-temperature stage that can be evacuated.29 As complete solidification of a formulation takes place during freezing, the resistance increases thus,...

Formulation of peptidesproteins for pulmonary delivery

The choice of a drug delivery device and control of MMAD are important formulation parameters discussed thus far. In addition, other formulation components that may have a significant influence on pulmonary delivery or adverse reactions in the lung include the proper choice of osmolality, pH, and buffering agents and the use of protease inhibitors and penetration enhancers. Many of these aerosols have an objectionable taste, and the use of taste-masking excipients has been investigated. It was...

Approaches to overcome barriers to nasal absorption

In general, the nasal route is suitable for delivery of molecules with a molecular weight of less than about 1000. For these molecules, the nasal bioavailability may be sufficient to achieve therapeutic levels without the use of any adjuvants. For small peptides, the intranasal bioavailability may approach that of an intravenous injection. Serum levels of metkephamid, a pentapep-tide, following intranasal administration in the rat have been reported to be similar to those resulting after...

Examples of iontophoretic delivery of therapeutic peptides

8.4.2.1 Amino acids and small peptides Iontophoresis of the building blocks of peptides (i.e., amino acids) may yield some information that may be useful to predict the delivery of small peptides. Amino acids may also have a direct benefit of moisturizing the skin.97 Wearley et al.98 showed that the binding of a series of amino acids in excised abdominal skin of hairless rat decreased with an increase in the alkyl side chain. This suggests that binding is likely to be polar or electrostatic in...

Oxidation

Oxidation is one of the major degradation pathways of peptides, both in solution and lyophilized formulations. Amino acids that may undergo oxidation include methionine, cysteine, histidine, tryptophan, and tyrosine. Most oxidation reactions commonly encountered in therapeutic proteins under normal storage conditions involve methionine or cysteine residues. Methionine is easily oxidized, even by atmospheric oxygen, to methionine sulfoxide. Under extreme oxidative conditions, it forms methionine...

Aggregation behavior of insulin

Insulin is an example of a protein that has a quaternary structure (i.e., it normally exists in a self-associated form rather than as a monomer). Insulin exists as a monomer only at a very low concentration (< 0.1 M, 0.6 mg ml). At higher concentrations, insulin exists as a dimer. The dimers are believed to result from the hydrophobic association of the B23 to B28 regions on insulin monomers. In the presence of zinc ions and in the pH range 4.0 to 8.0, three dimers come together to form a...