Oseltamivir

Mechanism of action:

• Selectively inhibit neuraminidase activity due to sialic acid analog characteristic. Neuraminidase is deployed by viruses to enable the release of virions. As neuraminidase is inhibited, newly formed virions accumulate at the internal cell surface
• Keep in mind that oseltamivir needs to be metabolized by hepatic metabolism to oseltamivir carboxylate  first as it is administered as a prodrug

Adverse effects:

Adults:

• Nausea and vomiting
• Abdominal pain
• Bronchitis
• Insomnia
• Vertigo
• Diarrhea
• Dizziness
• Headache
• Cough
• Fatigue
• Unstable angina ( Crescendo angina )
• Anemia
• Pseudomembranous colitis
• Pneumonia
• Pyrexia
• Peritonsillar abscess
• Elevated liver enzymes
• Hepatitis
• Aches and pains
• Dyspepsia
• Rhinorrhea
• Upper respiratory tract infections

Children:

• Vomiting
• Gastrointestinal disturbances
• Asthma 
• Bronchitis
• Conjunctivitis
• Dermatitis
• Epistaxis
• Ear-disorders
• Otitis media
• Lymphadenopathy
• Pneumonia
• Sinusitis

Fatal adverse effects ( may occur to both adults and children ):

• Anaphylaxis
• Severe dermatologic reactions

Therapeutic uses:

• Treatment of Influenza A and B infections
• Prophylaxis of Influenza A and B

Pharmacokinetics:

• Readily absorbed in the gastrintestinal tract after oral administration
• 3% protein binding (carboxylate) and 42% parent drug
• Extensive hepatic metabolism to oseltamivir carboxylate
• Renal excretion via urine

Drug interactions:

• With probenecid, probenate and probenecidum. All three increase toxicity levels of oseltamivir

Special precautions:

• Moderate renal impairment
• Hepatic impairment
• Pregnancy and lactation
• Chronic cardiac disorders
• Respiratory disorders
• Immunocompromised patients

Contraindications:

• Severe renal impairment
• Hypersensitivity

Administration:

• Oral administration, preferably with food to avoid gastrointestinal discomfort

Pregnancy class:

• C

Key Facts Comparing Amantadine With Rimantadine

Rimantadine

Mechanism of action:

• Inhibit the viral membrane M2 matrix proteins that function ashydrogen ion channels. These channels are required for thefusion of viral membrane to host cell membrane to form endosomes via endocytosis. These channels are also required to provide acidic environment necessary for viral uncoating.
• Interferes with the release of new virions.

Adverse effects:

• Nausea and vomiting
• Diarrhea
• Dyspepsia
• Abdominal pain
• Xerostamia
• Anorexia
• Headache
• Insomnia
• Taste alterations
• Impaired concentrations
• Nervousness
• Dizziness
• Asthenia
• Ataxia
• Bronchospasms
• Depression
• Skin rash
• Tinnitus
• Cardiac failure
• Heart block

Therapeutic uses:

• Prophylaxis and treatment of influenza A

Pharmacokinetics:

• Rapid gastrointestinal absorption after oral administration, with 6 hours duration to achieve peak blood concentration
• Does not readily penetrate CNS through blood-brain barrier compared to amantadine, thus less CNS adverse effects
• 40% bounded to plasma proteins, mainly albumin
• Extensive hepatic metabolism
• Renal excretion 

Drug interactions:

• Live influenza virus vaccines

Special precautions:

• Renal impairment
• Hepatic impairment
• Epileptic or other seizure disorders patients
• Psychosis
• Pregnancy
• Elderly

Contraindications:

• Hypersensitivity

Adminidstration:

• Oral

Pregnancy class:

• C

Amantadine

Mechanism of action:

• Inhibit the viral membrane M2 matrix proteins that function as hydrogen ion channels. These channels are required for the fusion of viral membrane to host cell membrane to form endosomes via endocytosis. These channels are also required to provide acidic environment necessary for viral uncoating.
• Interferes with the release of new virions.

Adverse effects:

• Seizures
• Psychosis
• Ataxia
• Hallucinations
• Heart failure
• Depression
• Orthostatic / Postural hypotension
• Blood dyscrasias
• Urinary retention
• Irritability
• Gastrointestinal disturbances
• Anorexia
• Livedo reticularis
• Ankle edema
• Congestive heart failure
• Convulsions
• Cardiac arrest (overdosage)

Therapeutic uses:

• Influenza A treatment and prophylaxis
• Herpes zoster infections in immunocompromised patients
• Parkinson's 

Pharmacokinetics:

• Rapid GIT absorption after oral administration
• Cross placenta and breast milk
• 67% bounded to plasma protein
• Cross blood-brain barrier and readily penetrate CNS
• Lower hepatic metabolism
• Excreted via urine by glomerular filtration and tubular secretion, mostly as unchanged metabolite and less acetylated forms

Drug interactions:

• Enhances the adverse effects of antimuscarinics, levodopa, CNS stimulants and drugs that increase urinary pH

Special precautions:

• Renal impairment
• Patients with cardiovascular or liver diseases
• Recurrent eczema
• Withdrawal of amantadine from the elderly (should be gradual)

Contraindications:

• Gastric ulcerations
• Hypersensitivity
• Pregnancy and lactating
• Epileptic or other seizure disorders
• Severe renal impairment

Administration:

• Oral, should be taken with food

Pregnancy class:

• C

Summary Of Antivirals

Treatment of respiratory virus infections:

• Amantadine (Inhibitors of viral uncoating)
• Oseltamivir (Neuraminidase inhibitors)
• Ribavirin 
• Rimantadine (Inhibitors of viral uncoating)
• Zanamivir (Neuraminidase inhibitors)

Treatment of hepatic viral infections:

• Adefovir
• Entecavir
• Interferon
• Lamivudine
• Telbivudine

Treatment of herpes and cytomegalovirus infections:

• Acyclovir
• Cidofovir
• Famiciclovir
• Fomivirsen
• Foscarnet
• Ganiciclovir
• Peniciclovir
• Valacyclovir
• Valganciclovir
• Vidarabine

Treatment of HIV:

• Abacavir
• Atazanavir
• Darunavir
• Delavirdine
• Didanosine
• Emtricitabine
• Enfuvirtide
• Efavirenz
• Etravirine
• Fosamprenavir
• Indinavir
• Lamivudine
• Lopinavir
• Maraviroc
• Nelfinavir
• Nevirapine
• Raltegravir
• Ritonavir
• Saquinavir
• Stavudine
• Tenofovir
• Tipranavir
• Zidovudine