The use of amantadine in children for prophylaxis and treatment of influenza A infections

Clinical use of approved influenza antivirals: therapy and prophylaxis

Currently, there are two commonly used classes of antiviral agents approved for the prevention of and treatment for influenza: the M2 Inhibitors (amantadine and rimantadine) and the neuraminidase inhibitors (oseltamivir, laninamivir, peramivir and zanamivir). These agents have been proven to be safe and effective alone or in combination for the treatment of uncomplicated influenza in otherwise healthy individuals. Although there are few prospective, randomized studies of these antivirals for the treatment of pregnant women, hospitalized patients, and immunocompromised patients infected with seasonal, pandemic, or avian H5N1 influenza, these agents are widely used for these indications. This article reviews the pharmacokinetics and clinical data available relative to the use of commercially available antiviral agents for the prevention of and treatment for influenza.

Effect of influenza treatment with oseltamivir on health outcome and costs in otherwise healthy children

OBJECTIVE

To evaluate the effect of treating children with influenza with oseltamivir on health outcomes and costs to healthcare payers.

PATIENTS AND DESIGN

Health outcome data from the oseltamivir paediatric clinical development programme plus data from the literature were used in an economic model developed to predict morbidity and mortality due to influenza and its specified complications. Published data on the cost of care in the UK were used to compare oseltamivir with usual care in children aged 1-12 and 1-5 years by estimating cost-effectiveness and cost-utility ratios.

RESULTS

Oseltamivir reduced median time to return to normal health and activity by almost 2 days (40% reduction, 67.1 vs 111.7 hours; p < 0.0001) versus placebo. In children aged 1-5 years, a 48% reduction (63.5 vs 121.3 hours; p = 0.0003) was observed. Oseltamivir-treated children who developed otitis media returned to normal health and activity 30% faster (99.6 vs 141.5 hours; p = 0.0517) than the placebo group. In the economic model, oseltamivir in the base-case analysis (assuming 60% diagnostic accuracy, full compliance, and 100% receive and start treatment within 48 hours, standard discounting according to the UK National Institute of Clinical Excellence guidelines) resulted in favourable cost-utility ratios in children aged both 1-12 and 1-5 years, with incremental cost-utility rates of £11 173/quality-adjusted life year (QALY) and oseltamivir being dominant compared with usual care, respectively (year of costing, 2002). Even in conservative scenarios, most cost-utility ratios remained <£30 000/QALY.

CONCLUSIONS

Oseltamivir is an effective treatment for children with influenza, allowing faster return to normal health and activity compared with usual care. From the healthcare payer perspective, oseltamivir is a potentially cost-effective strategy for otherwise healthy children.

Chapter 12. Antiviral Agents

This chapter discusses the agents with activity primarily against RNA viruses. The communicable diseases of the respiratory tract are probably the most common cause of symptomatic human infections. The viruses that are causative agents for human respiratory disease comprise the five taxonomically distinct families: orthomyxoviridae, paramyxoviridae, picornaviridae, coronaviridae, and adenoviridae. The influenza viruses, which consist of types A, B, and C, belong to the family orthomyxoviridae. Types A and B have been associated with significant increases in mortality during epidemics. The disease may be asymptomatic or cause symptoms ranging from the common cold to fatal pneumonia. Immunization against influenza has been recommended for high-risk groups and antiviral chemotherapy (amantadine) is available for the treatment and prophylaxis of all influenza A infections. There is both a great need for and interest in developing a chemotherapeutic agent for the treatment of these two viral, respiratory tract pathogens. The family picornaviridae contains the genus Rhinovirus that is composed of over a hundred distinct serotypes. Amantadine and rimantadine are specifically active against influenza A virus infections. The amantadine recipients reported a higher incidence of side effects largely attributed to the central nervous system (CNS) symptoms. This difference in side effects may be a pharmacokinetic phenomenon that results in higher plasma concentrations of amantadine. Significant progress continues to be made in the clinical use and development of agents active against DNA viruses. Acyclovir (9-(2-h droxyethoxymethyl)guanine) has been the subject of several reviews and of a syrnposium. Considerable progress has been made in evaluating the clinical promise of acyclovir; however, there remains much to be learned concerning the best use of this drug in clinical practice. Significant strides have been made in the development of clinically useful antiviral agents, especially against the DNA viruses of the herpes family. Most of these agents are directed against viral nucleic acid synthesis and require activation by a virus-induced thymidine kinase. Researchers have begun to focus on other strategies that may produce broader spectrum anti-viral agents with different mechanisms of action.

Simultaneous liquid chromatographic assay of amantadine and its four related compounds in phosphate-buffered saline using 4-fluoro-7-nitro-2,1,3-benzoxadiazole as a fluorescent derivatization reagent

Simultaneous HPLC assay of 1-adamantanamine hydrochloride (amantadine) and its four related compounds [2-adamantanamine hydrochloride (2-ADA), 1-adamantanmethylamine (ADAMA), 1-(1-adamantyl)ethylamine hydrochloride (rimantadine) and 3,5-dimethyl-1-adamantanamine hydrochloride (memantine)] in phosphate-buffered saline (pH 7.4) after pre-column derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was developed. Phosphate-buffered saline samples were mixed with borate buffer and NBD-F solution in acetonitrile at 60 degrees C for 5 min and injected into HPLC. Five derivatives were well separated from each other. The lower limits of detection of amantadine, 2-ADA, ADAMA, rimantadine and memantine were 0.008, 0.001, 0.0008, 0.0015 and 0.01 microg/mL, respectively. The coefficients of variation for intra- and inter-day assay were less than 6.4 and 8.2%, respectively. The method presented was applied to a binding study of these compounds to human alpha(1)-acid glycoprotein. While affinity constants and capacities for ADAMA, rimantadine and memantine were calculated by means of Scatchard plots, those for the others were not determined. ADAMA, rimantadine and memantine were bound with different affinities and capacities. These results indicate that NBD-F is a good candidate as a fluorescent reagent to simultaneously determine amantadine and its four related compounds by HPLC after pre-column derivatization. Our method can be applied to binding studies for protein.

Simultaneous determination of amantadine and rimantadine by HPLC in rat plasma with pre-column derivatization and fluorescence detection for pharmacokinetic studies

We investigated simultaneous high-performance liquid chromatographic (HPLC) determination of amantadine hydrochloride (AMA) and rimantadine hydrochloride (RIM) levels in rat plasma after fluorescent derivatization with o-phthalaldehyde and 2-mercaptoethanol. Afterwards, the method was applied to determine their pharmacokinetics. The retention times of AMA and RIM derivatives were 12.6 and 22.2 min and the lower limits of detection were 0.025 and 0.016 microg/mL, respectively. The coefficients of variation for intra- and inter-day assay of AMA and RIM were less than 5.1 and 7.6%, respectively. After i.v. administration of AMA or RIM to rats, the total body clearance and distribution volume at the steady-state of RIM were higher than those of AMA. Bioavailability of AMA and RIM was 34.9 and 37.2%, respectively. When AMA and RIM were p.o. co-administered, the area under the plasma concentration--time curve of RIM was significantly lower than that after RIM alone. On the other hand, pharmacokinetic parameters of AMA did not significantly change. These results indicate that our HPLC assay is simple, rapid, sensitive and reproducible for simultaneously determining AMA and RIM concentrations in rat plasma and is applicable to their pharmacokinetic studies. Also, co-administration of AMA and RIM may result in the lack of pharmacological effects of RIM.

Liquid chromatographic determination of 1-adamantanamine and 2-adamantanamine in human plasma after pre-column derivatization with o-phthalaldehyde and 1-thio-β-d-glucose

We investigated high-performance liquid chromatographic (HPLC) determination of 1-adamantanamine hydrochloride (1-ADA) and 2-adamantanamine hydrochloride (2-ADA) in human plasma after the derivatization with o-phthalaldehyde (OPA) and 1-thio-beta-D-glucose (TG). Extracted human plasma samples were mixed with OPA and TG at room temperature for 6 min and injected onto HPLC. Retention times of 1-ADA and 2-ADA derivatives were 12.6 and 14.1 min, respectively. The lower limits of detection of 1-ADA and 2-ADA were 0.02 and 0.008 microg/ml, and the lower limits of quantitation of 1-ADA and 2-ADA were 0.025 and 0.01 microg/ml, respectively. The coefficients of variation for intra-day and inter-day assay of 1-ADA and 2-ADA were less than 4.4 and 6.0%, respectively. L-Dopa and dopamine were not found to interfere with the peaks of 1-ADA and 2-ADA derivatives. Human plasma unbound fraction (f(p)) values of 1-ADA varied between 0.32 and 0.48, while those of 2-ADA varied between 0.38 and 0.68. These results indicate that HPLC assay of 1-ADA and 2-ADA by derivatization with OPA and TG is simple, rapid, sensitive and reproducible for determining 1-ADA and 2-ADA in human plasma.

Clinical use of antiviral drugs

Remarkable progress has been made in antiviral chemotherapy. Six approved antiviral drugs are now available for the treatment of various viral infections. Trifluridine, idoxuridine and vidarabine are all effective in patients with herpes keratitis; trifluridine is preferred due to its low toxicity. Acyclovir is the drug of choice in patients with infections due to herpes simplex viruses, including genital herpes, herpes encephalitis, and neonatal herpes, and infections due to varicella-zoster virus. Amantadine is the only drug currently available for prophylaxis and treatment of influenza A, but an investigational drug, rimantadine, appears to be equally effective and less toxic than amantadine. Ribavirin is the most recently approved antiviral agent for the treatment of respiratory syncytial virus infections. Numerous antiviral drugs are being studied in patients with acquired immunodeficiency syndrome. Although currently available drugs have improved our ability to manage a variety of viral illnesses, much needs to be learned about specific dosage guidelines based on the studies of pharmacokinetics, pharmacodynamics, potential adverse effects and viral resistance, and the role of combination therapy to optimize therapy.

Monoclonal antibodies for the rapid diagnosis of influenza A and B virus infections by immunofluorescence

Mouse monoclonal antibodies, directed against antigenic sites on influenza A and B viruses and found to be type-specific in an immunoassay, were assessed for use as diagnostic reagents in an indirect immunofluorescence assay on nasopharyngeal secretions. The influenza A antibodies were directed against nucleoprotein or matrix protein antigens and the influenza B antibodies against nucleoprotein and haemagglutinin antigens. The influenza A anti-matrix monoclonal antibody was found to give a strong intranuclear particulate fluorescence in normal baboon kidney cells and cells from nasopharyngeal secretions negative for influenza A virus, including those from a patient infected with respiratory syncytial virus. Pools of the remaining monoclonal antibodies gave satisfactory results on 25 specimens from patients with influenza A H1N1 and H3N2 subtypes and 12 from patients with influenza B.