Influenza A and syncytial virus drugs
Amantadine and its derivative, rimantadine hydrochloride, areused to prevent or treat influenza A
infections. Ribavirin is used to
treat respiratory syncytial virus (RSV) infections in children.
To treat RSV, ribavirin is administered by aerosol
inhalation, using a small-particle aerosol generator.
After oral administration, amantadine and
rimantadine are well absorbed in the GI tract and widely distributed throughout
the body. Ribavirin is administered by nasal or oral inhalation and is well
absorbed. It has a limited, specific distribution, with the high-est
concentration found in the respiratory tract and in red blood cells (RBCs).
Ribavirin capsules are rapidly absorbed after admin-istration and are
distributed in plasma.
Amantadine is eliminated primarily in urine;
rimantadine is exten-sively metabolized and then excreted in urine.
Ribavirin is metabolized in the liver and by RBCs.
It’s excreted primarily by the kidneys, with some excreted in stool.
Although its exact mechanism of action is unknown,
amantadine appears to inhibit an early stage of viral replication. Rimantadine
inhibits viral RNA and protein synthesis.
The mechanism of action of ribavirin isn’t known
completely, but the drug’s metabolites inhibit viral DNA and RNA synthesis,
subsequently halting viral replication.
Amantadine and rimantadine are used to prevent and
treat respi-ratory tract infections caused by strains of the influenza A virus.
They can reduce the severity and duration of fever and other symptoms in
patients already infected with influenza A.
Ribavirin, used to treat severe RSV infection in
children, is also used in adults in combination with interferon alfa-2B for
treat-ment of chronic hepatitic C.
These drugs also protect the patient who has
received the influen-za vaccine during the 2 weeks needed for immunity to
develop as well as the patient who can’t take the influenza vaccine because of
Amantadine is also used to treat parkinsonism and
drug-induced extrapyramidal reactions (abnormal involuntary movements).
Amantadine may interact with some drugs. (See Adverse
reac-tions to amantadine and rimantadine)
with amantadine increases adverse anti-cholinergic effects.
Amantadine given with
the combination drug hydrochloroth-iazide and triamterene results in decreased
urine excretion of amantadine, causing increased amantadine levels.
Amantadine and co-trimoxazole
levels are increased when used together.
No clinically significant drug interactions have
been documented with rimantadine.
§ Ribavirin has few interactions with other
§ Ribavirin reduces the antiviral activity of
zidovudine, and con-comitant use of these drugs may cause blood toxicity.
§ Taking ribavirin and digoxin can cause
digoxin toxicity, produc-ing such effects as GI distress, CNS abnormalities,
and cardiac ar-rhythmias. (See Adverse
reactions to ribavirin.)