Influenza A and syncytial virus drugs

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.

Breathe in

To treat RSV, ribavirin is administered by aerosol inhalation, using a small-particle aerosol generator.

Pharmacokinetics

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.

Metabolism and excretion

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.

Pharmacodynamics

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.

Pharmacotherapeutics

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.

In the meantime

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 hypersensitivity.

Calming the shakes

Amantadine is also used to treat parkinsonism and drug-induced extrapyramidal reactions (abnormal involuntary movements).

Drug interactions

Amantadine may interact with some drugs. (See Adverse reac-tions to amantadine and rimantadine)

§    Taking anticholinergics 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.

All quiet on the rimantadine front

No clinically significant drug interactions have been documented with rimantadine.

§    Ribavirin has few interactions with other drugs.

§    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.)