It is a thymidine analogue.

Zidovudine is a Thymidine nucleoside analogue. It undergoes phosphorylation in the presence of Kinase enzyme and form Zidovudine triphosphate. This Zidovudine triphosphate competitively inhibit HIV reverse transcriptase enzyme which is responsible for the conversion of viral RNA to pro viral DNA and is then added to host cell chromosome. Zidovudine triphosphate terminates elongation of pro viral DNA and results in inhibition of viral replication. 

Pharmacokinetics
Absorption: It is rapidly absorbed after oral administration.
Distribution: It is widely distributed in the body.
Metabolism: It undergoes rapid metabolism in the liver.
Excretion: It is excreted in urine.

On Set of Action
30 - 90 minutes

Half Life
60 minutes

Adverse Effects
1. Nausea
2. Vomiting
3. Diarrhoea
4. Anorexia
5. Headache
6. Dizziness
7. Anaemia
8. Agranulocytosis
9. Thrombocytopenia
10. Myalgia
11. Rash

ContraIndications
Hypersensitivity to Zidovudine

Special Precautions
1. Renal impairment
2. Hepatic dysfunction (Hepatitis, hepatomegaly)
3. Patient with severe bone marrow suppression
4. Pre existing anaemia
5. Granulocytopenia

Pregnancy
Use with caution

Breast Feeding
Contraindicated

Elderly
Use with caution

Children
 Use with caution

Neonates
Contraindicated

Interactions
Dapsone, Pentamidine, Amphotericin B, Flucytosine, Vincristine, Vinblastine, Adriamycin, Interferon: Concomitant use with drugs that are nephrotoxic, cytotoxic or myelosuppressive may increase toxicity risk. 
Trimethoprim: The serum levels of Zidovudine and its metabolite may be increased.
Probenecid: Toxicity of either drug may be potentiated.
Acetaminophen: Increased incidence of granulocytopenia.
Acyclovir: Concomitant use may result in neurotoxicity.
Phenytoin: Altered phenytoin levels. Zidovudine clearance decreased by phenytoin.

Indications
HIV infections

Dosage
Adult: 600 mg / day in 2 - 3 divided dose
Asymptomatic HIV infection and for preventing HIV transmission from mother to fetus: 100 mg 5 times daily; should be taken every 4 hours.
Children: 720 mg / sq.metre / day in 4 divided dose in equal interval

Storage
Store it at 15 -25 degree C in a tightly closed container . Protect away from heat and light. Keep out of the reach of Children.

Missed Dose
Take the missed dose as soon as noticed and if it is the time to take the next dose then skip the missed dose and do not double the dose.

Over Dose
Give supportive measures and treatment.