A virus (from the Latin virus meaning toxin or poison ) is a sub-microscopic infectious agent that is unable to grow or reproduce outside a host cell .
Not all viruses cause disease, as many viruses reproduce without causing any obvious harm to the infected organism. Some viruses such as hepatitis B can cause life-long or chronic infections, and the viruses continue to replicate in the body despite the hosts' defense mechanisms.
As a class, the antivirals are not curative, and must be used either prophylactically or early in the development of an infection. Their mechanism of action is typically to inactivate the enzymes needed for viral replication.
This will reduce the rate of viral growth, but will not inactive the virus already present. Antiviral therapy must normally be initiated within 48 hours of the onset of an infection to provide any benefit.
Antiviral drugs are medicines that cure or control virus infections.
Antivirals are used to treat infections caused by viruses . Unlike antibacterial drugs, which may cover a wide range of pathogens, antiviral agents tend to be narrow in spectrum, and have limited efficacy .
Drugs used for influenza may be used throughout the influenza season in high risk patients, or within 48 hours of exposure to a known carrier.
Antiherpetic agents should be used at the first signs of an outbreak.
Anti-cytomegaloviral drugs must routinely be used as part of a program of secondary prophylaxis (maintenance therapy following an initial response) in order to prevent reinfection in immunocompromised patients.
The drugs available for treatment of viral diseases in children are:
Acyclovir (Zovirax), used for treatment of diseases caused by the erpes simplex virus and herpes zoster virus. Although it is approved only for children over the age of six months, the drug has been used for newborn infants with encephalitis . This drug is most reliable when given intravenously .
Amantidine (Symmetrel), used to prevent or treat infections of the influenza virus type A. It is recommended for patients who cannot or should not receive influenza virus vaccine . As of 2004 it has not been studied in children below the age of one year.
Foscarnet (Foscavir), is not recommended for young children but may be given to adolescents. It is used to treat cytomegalovirus infections of the eye, and for herpes simplex infections that are resistant to other drugs.
Ganciclovir (Cytovene), used to treat cytomegalovirus infections of the eye. Although the manufacturer does not recommend use of ganciclovir in patients below the age of 12 years, the drug is recommended by standard pediatric references for children as young as three months.
Oseltamivir (Tamiflu), used for treatment of influenza virus infections of children over the age of 13 years. In adults, oseltamivir has also been used for prevention if influenza , but this use has not been studied in children.
Ribavirin (Rebetol, Virazol), used for treatment of hospitalized infants and young children with severe lower respiratory tract infections caused by respiratory syncytial virus ( RSV ), but its value is controversial.
Rimantidine (Flumadine), used to protect against the influenza virus type A .
Valacyclovir (Valtrex), used for treatment of diseases caused by the herpes simplex virus and herpes zoster virus. This drug is converted to acyclovir inside the body and is more reliable for oral use. Although the manufacturer says that safety and efficacy in children have not been established, valacyclovir is recommended for use in standard pediatric resources.
An antifungal drug is a medication used to treat fungal infections such as athlete's foot , ringworm , candidiasis (thrush), serious systemic infections such as cryptococcal meningitis , and others. Such drugs are usually obtained by a doctor's prescription or purchased over-the-counter .
The drugs that can be used to treat systemic fungal infections can be toxic to the host and are not to be used indiscriminately.
Some people feel drowsy or dizzy while taking systemic antifungal drugs. Anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.
Liver problems, stomach problems and other problems may occur in people who drink alcohol while taking systemic antifungal drugs. Alcohol and prescription or nonprescription (over-the-counter) drugs that contain alcohol should be avoided while taking antifungal drugs. (Medicines that may contain alcohol include some cough syrups, tonics, and elixirs.) Alcohol should be avoided for at least a day after taking an antifungal drug.
Antiprotozoal drugs are medicines that treat infections caused by protozoa.
Antiprotozoal drugs are used to treat a variety of diseases caused by protozoa. Protozoa are animal-like, one-celled animals, such as amoebas. Some are parasites that cause infections in the body. African sleeping sickness , giardiasis , amebiasis , Pneumocystis carinii pneumonia (PCP), and malaria are examples of diseases caused by protozoa.
Antiprotozoal drugs come in liquid, tablet, and injectable forms and are available only with a doctor's prescription. Some commonly used antiprotozoal drugs are metronidazole (Flagyl), eflornithine (Ornidyl), furazolidone (Furoxone), hydroxychloroquine (Plaquenil), iodoquinol (Diquinol, Yodoquinol, Yodoxin), and pentamidine (Pentam 300).
The recommended dosage depends on the type of antiprotozoal drug, its strength, and the medical problem for which it is being used. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage. Always take antiprotozoal drugs exactly as directed.
Some people feel dizzy, confused, lightheaded, or less alert when using these drugs. The drugs may also cause blurred vision and other vision problems. For these reasons, anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.
The antiprotozoal drug furazolidone may cause very dangerous side effects when taken with certain foods or beverages. Likewise, metronidazole (Flagyl) can cause serious liver damage if taken with alcohol. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for a list of products to avoid while taking these medicines.
Anyone who has ever had unusual reactions to antiprotozoal drugs or related medicines should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.
Some antiprotozoal drugs may cause problems with the blood. This can increase the risk of infection or excessive bleeding. Patients taking these drugs shouldbe careful not to injure their gums when brushing or flossing their teeth or using a toothpick. They shouldcheck with the physician before having any dentalwork done. Care should also be taken to avoidcuts from razors, nail clippers, or kitchen knives, orhousehold tools.
Anthelmintics or antihelminthics are drugs that expel parasitic worms ( helminths ) from the body, by either stunning or killing them. They may also be called vermifuges (stunning) or vermicides (killing).
Examples of pharmaceuticals used as anthelmintics include:
Abamectin – effective against most common intestinal worms, except tapeworms, for which Praziquantel is commonly used in conjunction with abamectin