Antiviral drugs can be used for treatment and prophylaxis of influenza. In recent years, the susceptibility of circulating influenza strains has evolved rapidly and treatment recommendations have changed during the influenza season. The CDC influenza website provides frequently updated information on antiviral resistance (www.cdc.gov/flu).

Antiviral drugs can be used for treatment of patients with influenza and for prophylaxis when exposure to the disease occurs before or less than 2 weeks after vaccination. They can also be used to control institutional outbreaks of influenza. In recent years, the susceptibility of circulating influenza strains has evolved rapidly and treatment recommendations have changed during the influenza season. The CDC influenza web site provides frequently updated information on antiviral resistance (www.cdc.gov/flu)

The drugs of choice for treatment of non-HIV viral infections and their dosages are listed in Tables 1-6 on the pages that follow. Some of the indications and dosages recommended here have not been approved by the FDA. Vaccines used for the prevention of viral infections are discussed in another issue of Treatment Guidelines.

Currently circulating influenza virus is almost universally pandemic 2009 influenza A H1N1, but seasonal influenza strains could also appear soon. Antiviral drugs are an important adjunct to influenza vaccination for treatment and chemoprophylaxis of both pandemic and seasonal influenza. They may, however, interfere with the efficacy of FluMist, the live-attenuated intranasal vaccine, if they are administered within 48 hours before or <2 weeks after FluMist administration. Inactivated vaccines are not affected by antiviral drug therapy.

Since publication of our recent article on antiviral drugs for influenza, increased levels of resistance to oseltamivir (Tamiflu) have been detected in influenza A H1N1 strains.

Tetrabenazine (Xenazine - Ovation Pharmaceuticals), an old drug first synthesized 50 years ago for treatment of schizophrenia, was recently approved by the FDA for the treatment of chorea associated with Huntington's disease. It has been available in other countries for decades.

Antiviral drugs are an important adjunct to influenza vaccination and can be used for treatment of patients with influenza within 2 days of the onset of illness and for chemoprophylaxis of influenza exposures that occur before or less than 2 weeks after vaccination. Patients who are immunocompromised or immunosuppressed, have pulmonary disease, are elderly or are healthcare workers may also be appropriate candidates for chemoprophylaxis.

Many drugs can cause psychiatric symptoms, but a causal connection is often difficult to establish. Psychiatric symptoms that emerge during drug treatment could also be due to the underlying illness, previously unrecognized psychopathology, or psychosocial factors. The withdrawal of some drugs can cause symptoms such as anxiety, psychosis, delirium, agitation or depression.

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Antiviral drugs can be used for treatment of patients with influenza and for prophylaxis of influenza exposures that occur before or less than 2 weeks after vaccination. They can also be used to control institutional influenza outbreaks and for prophylaxis in years when circulating strains differ from those included in the vaccine.

ParkinsonÆs disease (PD) is caused primarily by progressive degeneration of dopamine-containing neurons in the substantia nigra. Dopamine itself cannot be used to treat PD because it does not cross the bloodbrain barrier.

The drugs of choice for treatment of non-HIV viral infections with their dosages and cost are listed in Tables 1-6. Some of the indications and dosages recommended here have not been approved by the FDA. Vaccines used in the prevention of viral infections are discussed in the "Adult Immunization" issue of Treatment Guidelines.

Antiviral drugs can be used to control institutional influenza outbreaks and for prophylaxis of influenza exposures that occur before or less than 2 weeks after vaccination with inactivated vaccine, or in years when circulating strains differ from those included in the vaccine. They can also be used for early treatment of patients with influenza.

Our article on Antiviral Drugs for Prophylaxis and Treatment of Influenza (Med Lett Drugs Ther 2005;47:93) mentioned possible use of amantadine (Symmetrel, and others) and rimantadine (Flumadine, and others), but warned that the incidence of resistance has increased substantially. The CDC recently issued a Health Alert (www.cdc.gov) saying that current evidence indicates that a high proportion of circulating influenza A viruses in the US are now resistant to amantadine and rimantadine and they should not be used for this indication, at least this year. Click here to go to this update article.

The physiologic changes that occur with aging can affect the pharmacokinetics and pharmacodynamics of many prescription and over-the-counter drugs, increasing the likelihood of adverse effects.

Antiviral prophylaxis is indicated for influenza exposures that occur before (or less than 2 weeks after) vaccination with inactivated vaccine, or in years when circulating strains differ from those included in the vaccine. Antiviral drugs can also be used for treatment of patients who develop symptoms of influenza, regardless of vaccination status.
Please see Update: Influenza Resistance to Amantadine and Rimantadine

The drugs of choice for non-HIV viral infections with their dosages and cost are listed in the tables that begin on page 24. Some of the indications and dosages recommended here have not been approved by the FDA.

Due to the unanticipated shortage in the US supply of inactivated influenza vaccine, many persons who normally would have received the vaccine will be unable to get it this year. Antiviral drugs can be used for prophylaxis of unvaccinated persons who are exposed to influenza, and for treatment of both vaccinated and unvaccinated patients who develop symptoms of the disease.

Parkinson's disease is caused by progressive degeneration of dopamine-containing neurons in the substantia nigra. Dopamine itself cannot be used to treat Parkinson's disease because it does not cross the blood-brain barrier.

Unlike the last few years there is no early-season shortage of influenza vaccine. Immunization programs for all recommended individuals can proceed. There are 2 new influenza vaccine formulations available this year, FluMist, an intranasal vaccine and Fluzone, a pediatric formulation. Timing, indications, adverse effects, dosage and cost of the vaccines is discussed. The drugs that can be used for prophylaxis of influenza are also reviewed.

The choice of drugs for treatment of pneumonia depends on the most likely pathogens causing the infection and local antimicrobial resistance patterns. Factors such as severity of illness, presence of co-morbid conditions and whether the infection is community or hospital-acquired also need to be considered.

FluMist (MedImmune), the first live-attenuated and first intranasally administered influenza vaccine, has been approved by the FDA to prevent influenza in healthy people 5-49 years old. Given as a nasal spray, it stimulates immunity by viral replication in the upper respiratory tract. This vaccine apparently will be advertised directly to the public as a "needle-free" alternative to intramuscular influenza vaccine.

Physicians and pharmacists are often asked if patients can use drugs after their expiration date. Pharmaceutical companies, because of legal restrictions and liability concerns, will not sanction such use and may not even comment on the safety or effectiveness of using their products beyond the date on the label.

Influenza vaccine for the 2002-2003 season will include last year's A strains, A/New Caledonia/20/99 (H1N1)-like and A/Moscow/10/99 (H3N2)-like, and a new B strain, B/Hong-Kong/330/01-like (MMWR Morb Mortal Wkly Rep 2002; 51:503).

Many drugs can cause psychiatric symptoms, but a causal connection is often difficult to establish. Psychiatric symptoms that emerge during drug treatment may also be due to the underlying illness, previously unrecognized psychopathology, or psychosocial factors. The withdrawal of some drugs can cause symptoms such as anxiety, psychosis, delirium, agitation or depression.

The drugs of choice for non-HIV viral infections with their dosages and cost are listed in the table that begins on the next page. Since the last Medical Letter issue on this subject, some new drugs and some new recommendations for old drugs have been added.

The centers for Disease Control and Prevention is anticipating a delay, but not a shortage, of influenza vaccine for the 2001-2002 season. Last year manufacturing problems led to a substantial delay in vaccine availability. This year's delay is being attributed, in part, to the dicontinuation of the Fluogen (King) brand of vaccine. The 2001-02 vaccine will include A/New Caledonia/20/99 (H1N1)-like, A/Moscow/10/99 (H3N2)-like, and B/Sichuan/379/99-like antigens.

The drugs of choice for non-HIV viral infections with their dosages and cost are listed in the [article's] table.

Zanamivir, a neuraminidase inhibitor taken by inhalation, has been approved by the FDA for treatment of influenza. Oseltamivir phosphate, an oral neuraminidase inhibitor, will probably be approved soon.

Bupropion hydrochloride, currently available as an antidepressant (Wellbutrin - Medical Letter, 31:97, 1989; Wellbutrin SR), is now being marketed in a sustainedrelease formulation as Zyban (Glaxo Wellcome) for use as an aid in smoking cessation.

The drugs of choice for non-HIV viral infections with their dosages and cost are listed in the table on the next page. The treatment of HIV infection will be discussed in a future issue.

Rimantadine hydrochloride (Flumadine - Forest), the alpha-methyl derivative of amantadine (Symmetrel, and others), was recently approved by the US Food and Drug Administration for prevention and treatment of influenza A virus infections in adults and for prevention of influenza in children.

The enzyme alpha-galactosidase (Beano - AkPharma), derived from a mold and classified as a food, is sold without presecription in pharmacies and food stores. The manufacturer recommends taking the anzyme to decrease intestinal gas producted by eating the high-fiber diets now widely recommended in the USA.

Since the last review of this topic (Medical Letter, 32:73, August 10, 1990) some new antiviral agents have been approved and the indications for several others expanded. The drugs of choice for viral infections are listed in the table on page 36.

A new trivalent inactivated influenza vaccine is now available for the 1989-1990 influenza season (Morbid Mortal Weekly Rep, 38:297, May 5, 1989: Can Med Assoc J, 141:425, Spet 1, 1989). Antigens in this years's Vaccine are A/Taiwan/1/86 (H1N1), A/Shanghai/11/87 (H3N2), and B/Yamagata/16/88. The A/Shanghai and B/Yamagata are new strains this year. The vaccine is available in the USA as a split-virus (subvirion) or whole virus preparation from Squibb (Fluzone), as a split-virus preparation from parke-davis (Fluogen) and Wyeth-Ayerst (Influenza Virus Vaccine, Trivalent), and as a purified-surface-antigen formulations may be less likely to cause adverse reactions, especially in children; whole-virus vaccines may be slighltly more antigenic. Vaccine from previous years should not be used.

Patients with Parkinson's disease have a deficiency of the neurotransmitter dopamine, a catecholamine. Dpamine itself cannot be used to treat the disease because it does not cross the blood-brain barrier, but its metabolic precursor, levodopa, does cross into the brain and is converted to dopamine by a decarboxylase present both in the brain and in the intestinal tract (JM Cedarbaum, Clin Pharmacokinet, 13:141, 1987).

A new trivalent inactivated influenza vaccine is now available for the 1988-1989 influenza season (Morbid Mortal Weekly Rep, 37:357, June 17, 1988). Antigens in this year's vaccine are A/Taiwan/1/86 (H1N1), A/Sichuan/2/87 (H3N2), and B/Victoria/2/87. The A/Sichuan is a new strain that caused last year's large outbreak of the disease. The vaccine is available in the USA as a split-virus (Subvirion) or whole virus preparation from Squibb (Fluzone), and as a split-virus preparation from Parke-Davis (Fluogen) and Wyeth (Influenza Virus Vaccine, Trivalent). Split-virus vaccines may be slightly more antigenic. Vaccine from previous years should not be used.