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NRTI (antiretroviral) Pregnancy: §4.6, verbatim: 'the use in pregnant women of zidovudine, with subsequent treatment of the newborn infants, has been shown to reduce the rate of maternal-foetal transmission of HIV. A large amount of data on pregnant women (more than 3000 outcomes from first trimester and more than 3000 outcomes from second and third trimester exposure) indicate no malformative toxicity. Zidovudine can be used during pregnancy if clinically needed. The malformative risk is unlikely in humans based on the mentioned large amount of data.' The SPC also notes reproductive toxicity findings in animals, that zidovudine 'has been shown to be a transplacental carcinogen in one animal study' whose clinical relevance is unknown, that placental transfer occurs in humans, and that mitochondrial dysfunction has been reported in HIV-negative infants exposed in utero and/or post-natally to nucleoside analogues. Breast-feeding: 'After administration of a single dose of 200 mg zidovudine to HIV-infected women, the mean concentration of zidovudine was similar in human milk and serum. It is recommended that women living with HIV do not breast-feed their infants in order to avoid transmission of HIV.' Fertility: no impairment of male or female fertility in rats; no human female fertility data; in men, no effect shown on sperm count, morphology or motility. The SPC's dosing regimen for prevention of maternal-foetal transmission is a separate indication and is not reproduced on this page (see adultDose.notes).

Zidovudine

Brand names: Retrovir

A nucleoside reverse transcriptase inhibitor (NRTI) antiretroviral used as part of combination therapy for HIV infection and for prevention of mother-to-child transmission.

Adult dose

Dose: 250 mg or 300 mg twice daily, in combination with other antiretroviral agents (adults and adolescents weighing at least 30 kg)
Route: Oral — Zidovudine 100 mg capsules; §4.2: 'Method of administration: Oral use.'
Frequency: Twice daily
VERBATIM (§4.2, 'Dosage in adults and adolecents weighing at least 30 kg' — the source's own spelling): 'The usual recommended dose of Zidovudine in combination with other anti-retroviral agents is 250 or 300 mg twice daily.' SCOPE: this is the page's primary indication and route (oral HIV treatment as part of combination antiretroviral therapy). The fetched SPC is an oral capsule product and contains NO intravenous regimen for HIV treatment — any IV zidovudine dose belongs to a different presentation with its own SPC, which is not in this bundle, so none is published here. The SPC does contain a separate regimen for PREVENTION OF MATERNAL-FOETAL TRANSMISSION covering pregnant women, labour and delivery (intravenous) and newborn infants; that is a different indication, its intravenous components have no product, diluent or concentration behind them in this capsule SPC, and its figures are deliberately not reproduced on this page — consult the SPC and specialist HIV/obstetric guidance. PRESCRIBER RESTRICTION (verbatim): 'Zidovudine should be prescribed by physicians who are experienced in the treatment of HIV infection.' HAEMATOLOGICAL DOSE ADJUSTMENT (verbatim): 'Substitution of zidovudine should be considered in patients whose haemoglobin level or neutrophil count fall to clinically significant levels. Other potential causes of anaemia or neutropenia should be excluded. Dose reduction or interruption of Zidovudine should be considered in the absence of alternative treatments.' §4.4 adds that if haemoglobin falls to between 7.5 g/dl and 9 g/dl, or the neutrophil count to between 0.75 x 10^9/l and 1.0 x 10^9/l, 'the daily dosage may be reduced until there is evidence of marrow recovery; alternatively, recovery may be enhanced by brief (2-4 weeks) interruption of Zidovudine therapy.' ELDERLY (verbatim): pharmacokinetics have not been studied over 65 years; 'special care is advised in this age group due to age-associated changes such as the decrease in renal function and alterations in haematological parameters, appropriate monitoring of patients before and during use of Zidovudine is advised.' NO MAXIMUM DOSE IS STATED — §4.4 and §4.8 mention that haematological reactions 'occurred more frequently at higher dosages (1200-1500 mg/day)', which is an observation, not a ceiling, so maxDose is left empty. Some sections of the product information we used were incomplete — check the full SPC.

Paediatric dose

Route: Oral — 100 mg capsules (a 250 mg capsule is offered as an alternative at 28-30 kg)
Frequency: Twice daily, except the 14-21 kg band, which is split as one capsule in the morning and two in the evening
CHILDREN, ORAL CAPSULE WEIGHT BANDS (§4.2, verbatim table; all doses in combination with other antiretroviral agents): 8-13 kg — one 100 mg capsule in the morning and one 100 mg capsule in the evening (daily dose 200 mg); 14-21 kg — one 100 mg capsule in the morning and two 100 mg capsules in the evening (daily dose 300 mg); 22-30 kg — two 100 mg capsules in the morning and two in the evening (daily dose 400 mg); alternatively, children weighing at least 28 kg to 30 kg inclusive may take one 250 mg capsule in the morning and one in the evening (daily dose 500 mg). Adolescents weighing at least 30 kg take the adult dose. LOWER LIMITS (verbatim): 'Available data are insufficient to propose specific dosage recommendations for children weighing less than 4 kg.' 'Other pharmaceutical formulations containing zidovudine is available for dosing children less than 8kg and for those children above 8kg unable to swallow capsules.' dosePerKg IS DELIBERATELY NULL: this is a fixed weight-BAND capsule regimen, not a per-kg calculation. The only per-kg figures in the SPC belong to the separate prevention-of-maternal-foetal-transmission regimen (pregnant women, labour and delivery, and newborn infants), which is a different indication — partly intravenous, with no product in this capsule SPC — and is not reproduced here; using any of those figures as a general paediatric per-kg dose would be wrong. concentration IS NULL: the fetched product is capsules; the oral solution referred to for children under 8 kg or unable to swallow capsules has its own SPC, which is not in this bundle, so no mg/mL figure is asserted. Confirm every under-18 dose against a children's formulary and specialist paediatric HIV advice.

Dose adjustments

Renal

§4.2, verbatim: 'The recommended dose for patients with severe renal impairment (creatinine clearance 10ml/min) and patients with end-stage renal disease maintained on haemodialysis or peritoneal dialysis is 100 mg every 6 to 8 hrs (300-400 mg daily). Haematological parameters and clinical response may influence the need for subsequent dosage adjustment.' CAUTION: the comparator in front of '10ml/min' is missing from the fetched text (it reads 'creatinine clearance 10ml/min' with no '<'), so the creatinine-clearance threshold is not asserted here — verify it against the full SPC before applying this reduction.

Hepatic

§4.2, verbatim: 'Data in patients with cirrhosis suggest that accumulation of zidovudine may occur in patients with hepatic impairment because of decreased glucuronidation. Dosage reductions may be necessary but, due to the large variability in zidovudine exposures in patients with moderate to severe liver disease, precise recommendations cannot be made. If monitoring of plasma zidovudine levels is not feasible, physicians will need to monitor for signs of intolerance, such as the development of haematological adverse reactions (anaemia, leucopenia, neutropenia) and reduce the dose and/or increase the interval between doses as appropriate.'

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Known hypersensitivity to zidovudine or to any of the excipients listed in section 6.1 (§4.3)
  • Abnormally low neutrophil counts — less than 0.75 x 10^9/litre (§4.3)
  • Abnormally low haemoglobin levels — less than 7.5 g/decilitre or 4.65 mmol/litre (§4.3)
  • Newborn infants with hyperbilirubinaemia requiring treatment other than phototherapy, or with increased transaminase levels of over five times the upper limit of normal (§4.3)
  • Not a contraindication but a §4.4 avoidance: 'The concomitant use of rifampicin or stavudine with zidovudine should be avoided.'

Side effects

  • Most serious (§4.8): anaemia (which may require transfusions), neutropenia and leucopenia — more frequent at higher dosages (1200-1500 mg/day), in advanced HIV disease with poor marrow reserve, and particularly with CD4 counts less than 100/mm3
  • Very common (§4.8): headache; nausea
  • Common (§4.8): anaemia, neutropenia and leucopenia; dizziness; vomiting, diarrhoea and abdominal pain; raised blood levels of liver enzymes and bilirubin; myalgia; malaise
  • Uncommon (§4.8): pancytopenia with bone marrow hypoplasia, thrombocytopenia; dyspnoea; flatulence; rash and pruritus; myopathy; asthenia, fever and generalised pain
  • Rare (§4.8): pure red cell aplasia; lactic acidosis in the absence of hypoxaemia, anorexia; anxiety and depression; convulsions, loss of mental acuity, insomnia, paraesthesia, somnolence; cardiomyopathy; cough; pancreatitis, oral mucosa pigmentation, taste disturbance and dyspepsia; liver disorders such as severe hepatomegaly with steatosis; urticaria, nail and skin pigmentation and sweating; urinary frequency; gynaecomastia; chest pain, influenza-like syndrome, chills. Very rare: aplastic anaemia
  • Lactic acidosis with hepatomegaly and hepatic steatosis (§4.4) — 'has a high mortality and may be associated with pancreatitis, liver failure, or renal failure'; treatment should be discontinued in symptomatic hyperlactataemia, metabolic/lactic acidosis, progressive hepatomegaly or rapidly rising aminotransferases
  • This side-effect list may be incomplete — check the full SPC.

Monitoring

  • Full blood count (§4.4, verbatim): 'Haematological parameters should be carefully monitored. For patients with advanced symptomatic HIV disease it is generally recommended that blood tests are performed at least every two weeks for the first three months of therapy and at least monthly thereafter. Depending on the overall condition of the patient, blood tests may be performed less often, for example every 1 to 3 months.'
  • Haemoglobin and neutrophil thresholds (§4.4): if haemoglobin falls to between 7.5 g/dl (4.65 mmol/l) and 9 g/dl (5.59 mmol/l), or the neutrophil count to between 0.75 x 10^9/l and 1.0 x 10^9/l, reduce the daily dosage until there is evidence of marrow recovery, or interrupt therapy briefly (2-4 weeks); marrow recovery is usually seen within 2 weeks
  • Signs of lactic acidosis (§4.4): nausea, vomiting, abdominal pain, non-specific malaise, loss of appetite, weight loss, rapid and/or deep breathing, or motor weakness — discontinue in symptomatic hyperlactataemia or metabolic/lactic acidosis
  • Liver function and hepatomegaly (§4.4): caution in any patient (particularly obese women) with hepatomegaly, hepatitis or other risk factors for liver disease and hepatic steatosis; discontinue for progressive hepatomegaly or rapidly elevating aminotransferase levels
  • Older patients (§4.2): 'appropriate monitoring of patients before and during use of Zidovudine is advised' because of age-associated decline in renal function and altered haematological parameters
  • Plasma zidovudine levels in hepatic impairment where feasible; otherwise monitor for signs of intolerance such as anaemia, leucopenia and neutropenia (§4.2)

Clinical monograph

How it works

As a thymidine analogue it is phosphorylated intracellularly and incorporated into viral DNA, inhibiting HIV reverse transcriptase and terminating the growing DNA chain.

Prescribing in practice

  • It can cause serious bone-marrow suppression with anaemia and neutropenia, and rarely lactic acidosis with hepatic steatosis, so the full blood count and clinical status must be monitored.
  • It must always be used within a combination antiretroviral regimen and never as monotherapy outside specific perinatal prophylaxis contexts.
  • Concurrent use with other myelosuppressive or marrow-toxic drugs increases haematological risk and should be reviewed against current prescribing references.

Monitoring

Monitor the full blood count regularly, along with HIV viral load and CD4 count and liver function, as guided by specialist HIV care.

Counselling the patient

  • Take every dose exactly as prescribed to keep the virus suppressed and reduce resistance.
  • Report unusual tiredness, breathlessness, or signs of infection promptly.
  • Do not stop or change your other HIV medicines without specialist advice.

Evidence & guidelines

Its role is established by historical landmark antiretroviral trials and current British HIV Association treatment guidance.

Reference: BHIVA guidelines; NICE CG185 (legacy); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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