Iontophoretic application of adenine arabinoside monophosphate to herpes simplex virus type 1-infected hairless mouse skin

Iontophoretic drug delivery

The composition and architecture of the stratum corneum render it a formidable barrier to the topical and transdermal administration of therapeutic agents. The physicochemical constraints severely limit the number of molecules that can be considered as realistic candidates for transdermal delivery. Iontophoresis provides a mechanism to enhance the penetration of hydrophilic and charged molecules across the skin. The principal distinguishing feature is the control afforded by iontophoresis and the ability to individualize therapies. This may become significant as the impact of interindividual variations in protein expression and the effect on drug metabolism and drug efficacy is better understood. In this review we describe the underlying mechanisms that drive iontophoresis and we discuss the impact of key experimental parameters-namely, drug concentration, applied current and pH-on iontophoretic delivery efficiency. We present a comprehensive and critical review of the different therapeutic classes and molecules that have been investigated as potential candidates for iontophoretic delivery. The iontophoretic delivery of peptides and proteins is also discussed. In the final section, we describe the development of the first pre-filled, pre-programmed iontophoretic device, which is scheduled to be commercialized during the course of 2004.

Iontophoresis for enhancing penetration of dermatologic and antiviral drugs

Iontophoresis is the process of introducing ionic drugs into the body for therapeutic purposes. Although iontophoresis has the potential for systemic therapy, it has mainly been used for local therapy at body surfaces. Many ionic drugs are available including lidocaine, epinephrine, methylprednisolone succinate, dexamethasone phosphate, several antivirals, various antibiotics, and other specific drugs. The use of an indicated ionic drug by iontophoresis offers a broad potential for promoting the development of more effective therapies in dermatology. Iontophoresis of ionized drugs provided a 20-60 fold increase in penetration over topical application. Iontophoresis for dermatological use requires that: a) a charged drug be placed at an electrode having a polarity the same charge as the drug, b) the condition or disease under treatment be at or near the body surface, and c) a modern, sophisticated source of direct current, with appropriate accessories, be used. The current source must have features that make it not only effective, but also safe for application to the patient. Modern systems for application of drugs by iontophoresis have features that make the process simple and efficient for use in practice. Iontophoresis has a long history of use, having been suggested for various therapies for many years in medicine, physical therapy and dentistry. Pilocarpine iontophoresis is a preferred method for cystic fibrosis detection. Also, lidocaine iontophoresis has been advocated to anesthetize the tympanic membrane before myringotomy. Anesthesia of the skin to a depth of 1.0 cm or more has been reported in double-blind studies of human volunteers. Local anesthesia by iontophoresis was reported to be effective for: 1) cutaneous cutdowns in patients requiring kidney dialysis, 2) delicate eyelid surgery, as the sole anesthetic, 3) preinjection topical anesthesia, and 4) shave biopsies of skin lesions. The use of iontophoresis for treating difficult cases of hyperhydrosis is quite popular among dermatologists. The present report emphasizes uses of iontophoresis in dermatology and is divided into discussion of studies using iontophoresis for postherpetic neuralgia, local anesthesia, antiviral therapy, and for corticosteroid therapy of nonspecific inflammatory lesions. Over 1250 patients have been treated for postherpetic neuralgia by corticosteroid iontophoresis at 6 medical centers with 60-80% of patients showing a major therapeutic response with return to a tolerable pain level. Double-blind studies of varicella zoster (active and postherpetic) and herpes simplex have proven that iontophoresis is a valuable modality for treating viral diseases of the skin. Many other uses for iontophoresis have been proposed in the literature that involve several hundred research papers, several textbooks and many book chapters. Review of the literature supports the concept that iontophoresis provides an optimal method for drug application in therapy of surface tissues.

Topical treatment of cutaneous herpes simplex virus infections

Topical antiviral chemotherapy has a number of potential advantages over systemic drug delivery for the treatment of cutaneous herpes simplex virus infections, including convenience; higher target tissue drug levels and greater efficacy; and specific targeting of the drug to the site of infection, with reduced cost and reduced exposure of the remainder of the body to drug side effects. Realization of these possibilities has been slow in part because of the paucity of 'active' topical drug formulations with effective penetration-enhancing agents and a technical barrier-our failure as yet to measure drug levels in the epidermis, which could guide formulation development. Recent success with a topical treatment for herpes simplex labialis should stimulate continued laboratory and clinical research in this field.

Hydrolysis and solvent-dependent 2'----5'and 3'----5' acyl migration in prodrugs of 9-beta-D-arabinofuranosyladenine

As a prerequisite to quantitative in vivo studies to further explore the promising topical activity of the 2',3'-di-O-acetyl derivative of 9-beta-D-arabinofuranosyladenine (ara-A) against herpes virus infections, the kinetics of solution degradation of the 2',3'-di-O-acetyl derivative and the 2'-,3'-, and 5'-monoacetates were investigated. The rates of aqueous solution hydrolysis were found to be consistent with rank order predictions based on a consideration of substituent effects. Preliminary in vivo hydrolysis data, however, do not correlate with such predictions, indicating a need for more systemic studies of the effect of molecular structure on enzyme-catalyzed hydrolysis. An important reaction of the 2'-3'-diester and the 3'-monoester in aqueous solution, in addition to ester hydrolysis, is 3'----5' acyl migration. 2'----5' Acyl migration does not occur in water but is the predominant migration pathway in organic solvents, as verified by studies in acetonitrile. 1H NMR spectroscopy was employed to study the dependence of the conformation of the sugar ring on the solvent environment. Although a change in the equilibrium between the C(2')endo and C(3')endo conformational states does occur, it is not a dramatic change and cannot explain the solvent selectivity observed in the acyl migration kinetics.

Iontophoretic treatment of oral herpes

Recent development of pharmaceutical agents that interfere with reproduction and metabolism of the herpes virus appear to have clinical applications in the treatment of orocutaneous herpetic lesions. Use of topical medications has always been limited by skin penetration. Combining these new pharmaceutical agents with iontotransport techniques has been shown to be effective for treatment of herpetic lesions. Instrumentation and a specially designed applicator electrode are described. Use of this instrumentation and its clinical application is described in the treatment of 32 patients and the results are summarized. Combining the use of the new pharmaceuticals with the iontotransport instrumentation is described as an effective treatment of localized herpetic lesions. Similar technique offers fascinating possibilities in other areas of skin pathology.

Arabinosyladenine monophosphate in genital herpes: a double-blind, placebo-controlled study

A double-blind, placebo-controlled study was performed in 55 male patients with recurrent herpes simplex genitalis. The 29 patients who received topical arabinosyladenine monophosphate (ara-AMP) showed no significant difference in viral shedding, duration of pain, healing time or development of new lesions as compared to 26 placebo-treated patients. Ara-AMP was well-tolerated when topically applied. Serum neutralizing antibody titers did not change significantly during the acute and convalescent periods of the patient's recurrent HSG attacks. We conclude that ara-AMP, when applied topically as a 10% gel five times a day within 24 h of onset of recurrent HSG, does not influence the virologic and clinical evolution of the recurrent episode.

Acyclovir and vidarabine monophosphate: comparison of iontophoretic and intravenous administration for the treatment of HSV-1 stromal keratitis

We determined the therapeutic efficacy of iontophoretic application of acyclovir and vidarabine monophosphate (ara-AMP) for the treatment of herpes simplex virus (HSV) type 1-induced stromal keratitis in rabbits. The therapeutic efficacy of intravenous administration of acyclovir was assessed in the same model. Stromal keratitis was produced by intrastromal injection of 10 microliters purified HSV-1, McKrae strain. Treatment began the first day after intrastromal injection. Iontophoresis (0.5 mAmp for four minutes) of 3.4 percent (0.1 M) ara-AMP and 5.0 percent (0.22 M) acyclovir was performed once daily for five consecutive days in two treatment groups. Intravenous administration of 50 mg acyclovir/kg was performed twice daily for eight consecutive days. Intravenous administration of NaCl (0.14 M) and ocular iontophoresis of NaCl (0.14 M) were performed as controls in the two treatment groups. At least two scorers performed a single masked evaluation of the disease severity (lesion scoring) of the conjunctiva, corneal epithelium, stroma, and iris by still lamp examination. The eyes were scored daily for 12 consecutive days, and then every other day up to day 22. Iontophoresis of acyclovir or ara-AMP significantly reduced the course of the disease compared with iontophoresis of NaCl. Intravenous administration of acyclovir significantly reduced the disease compared with intravenous NaCl. This suggests that iontophoresis of acyclovir or ara-AMP either alone or in combination with intravenous administration of acyclovir may be of value in the treatment of HSV-1 stromal keratitis.

Anti-herpesvirus activity of adenine arabinoside analogues in tissue culture and a genital infection of mice and guinea pigs

Four analogues of adenine arabinoside (ara-A) were compared for activity against herpes simplex virus (HSV) in tissue culture and in a genital infection of mice and guinea pigs. These analogues, 5'-monophosphate (ara-AMP), 5'-valerate ester (ara-AV), 2'3'-diacetate ester (ara-ADA), and 2',3',5'- triacetate ester (ara-ATA) have greater water and lipid solubility and resistance to deamination than ara-A. In mouse embryo fibroblast cells, similar viral inhibitory levels were noted with ara-A, AMP, and ara-Av, while ara-ADA and ara-ATA were 6-10 time less active. In mice infected intravaginally with HSV type 2 (HSV-2), intravaginal treatment with 10% concentrations of each of the compounds beginning 3 h after viral challenge, had no effect on infection rates, titers of virus in vaginal secretions, mortality rates or the mean day of death as compared with placebo-treated controls. In the HSV-2 genital infection of guinea pigs, treatment with 10% vaginal creams or placebo vehicle was initiated 6 or 24 h after viral inoculation. In animals treated at 6 h with ara-A, ara-AMP and ara-AV, there was complete inhibition of viral replication in the vaginal tract and development of external genital lesions. When treatment with these three drugs was delayed 24 h after infection, there was no effect on vaginal virus titers, but lesions severity was reduced by ara-A or ara-AMP therapy. Ara-ATA was ineffective whether begun at 6 or 24 h. The greater solubility in water and lipid as well as the resistance to deamination of ara-AMP and ara-AV did not appear to enhance their antiviral activity over that of ara-A. Additionally, ara-ADA and ara-ATA exhibited less activity both in tissue culture and in the experimental genital infections.

Ineffectiveness of topical adenine arabinoside 5'-monophosphate in the treatment of recurrent herpes simplex labialis

The ability of topical 10 per cent adenine arabinoside 5'-monophosphate to decrease the severity and frequency of recurrent herpes simplex labialis was evaluated in a double-blind, randomized study of 233 patients at three collaborating institutions. Nine clinical and four virologic measurements were used to evaluate drug efficacy during a single episode. No statistically significant improvement in any measurement was seen in the drug-treated patients. Analyses according to institution and age, stage and size of lesion before therapy also indicated no benefit attributable to the drug. There was no effect of the drug on the rate of recurrence of herpes simplex labialis. We conclude that, despite activity against herpes simplex virus infection in tissue culture and in some laboratory animal models, topical use of the drug is ineffective against recurrent herpes simplex labialis. This may be due to failure of the drug to penetrate the skin.