On their limited antiviral efficacy in severe cases of influenza. Available anti-influenza drugs target two different steps of the viral life cycle, the uncoating and the release of virus particles from infected cells. Uncoating of influenza A viruses is induced by the viral M2 ion channel protein and can be blocked by the adamantane-based compounds amantadine and rimantadine. Although clinically effective, these drugs caused considerable gastrointestinal and neurological side-effects in patients. Moreover, emerging resistant influenza A viruses during seasonal influenza epidemics have been observed. Today, the resistance level to amantadine has reached nearly 100% for H3N2-type influenza A virus strains, but resistant mutants are also frequently found among seasonal H1N1 isolates. Therefore, adamantanes are not considered anymore for routine use, but might be an option when all other measures fail. The more recently approved antiviral agents to treat influenza infections are the neuraminidase inhibitors zanamivir and oseltamivir, both developed by rational drug design. Influenza virus neuraminidaseis anchored in the viral membrane and cleaves sialic CHIR-99021 acid-containing receptors on the surface of infected cells and on progeny virions. This enzymatic activity facilitates the movement of virus particles through the upper respiratory tract as well as the releaseof newly synthesized virions from infected cells. Although highly efficacious in vitroand in animal models, in clinical trials neuraminidase inhibitors showed lower than expected efficacy against influenza symptoms in otherwise healthy adults. However, in children with laboratory confirmed influenza, neuraminidase inhibitors were effective in reducing illness duration if given within 48 hours post exposure, but their efficacy in reducing severe Nutlin-3 complications in ��at risk�� children, e.g. with asthma, awaits further investigation. Nonetheless, neuraminidase inhibitors have been used successfully as antiviral chemoprophylaxis for preventing and reducing the symptoms of seasonal influenza. Accordingly, in many countries neuraminidase inhibitors are stockpiled as means to prevent a worldwide pandemic. However, alternative treatment options are urgently needed as the current choice of drugs is limited and resistance is a constant threat. One alternative approach to prevention and treatment of influenza is the creation of a protective physical barrier in the nasal cavity with carrageenans, high molecular weight sulphated polysaccharides derived from red seaweed. Three main forms of carrageenans have been identified: kappa, iota, and lambda. They differ from each other in sulphation degree, solubility and gelling properties. Carrageenan is in widespread commercial use as an additive contributing to the texture and stability of various processed foods and cosmetic products, including some brands of 
sexual lubricant. Since highquality carrageenan preparationsappear to have a good safety profile for long-term useand can inhibit HIV infections in model systems, clinical studies were conducted to validate the usefulness of carrageenanas a vaginal microbicide for the prevention of HIV-1 transmission. Reasons for the failure of these studies are manifold and approaches to improve the efficacy of such topical formulations are in the focus of current research. The antiviral potential of carrageenan and other sulphated polysaccharides in vitro against infections by several enveloped viruses such as herpes simplex virus, human cytomegalovirus, vesicular stomatitis virus, Sindbis virus, and human immunodeficiency virus has been described more than 20 years ago, and has been reviewed recently.