COMBIVIR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for COMBIVIR (COMBIVIR).
Combivir is a combination of two nucleoside reverse transcriptase inhibitors (NRTIs): zidovudine and lamivudine. Zidovudine is a thymidine analogue that inhibits HIV reverse transcriptase by competing with natural substrates and incorporating into viral DNA, causing chain termination. Lamivudine is a cytidine analogue that similarly inhibits HIV reverse transcriptase. Both drugs require intracellular phosphorylation to their active triphosphate forms.
| Metabolism | Zidovudine is primarily metabolized by glucuronidation (via UGT2B7) to an inactive glucuronide metabolite; lamivudine is minimally metabolized and predominantly excreted unchanged in urine. |
| Excretion | Zidovudine: 70-80% renal via tubular secretion and glomerular filtration (metabolite zidovudine glucuronide). Lamivudine: >70% renal unchanged via active tubular secretion. |
| Half-life | Zidovudine: 0.5-3 h (mean 1.1 h). Lamivudine: 5-7 h in adults, prolonged in renal impairment. |
| Protein binding | Zidovudine: 30-38% (primarily albumin). Lamivudine: <36% (albumin). |
| Volume of Distribution | Zidovudine: 1.6 L/kg (total body water). Lamivudine: 1.3 L/kg (total body water). |
| Bioavailability | Zidovudine: 60-70% (oral). Lamivudine: >80% (oral). Food reduces rate but not extent. |
| Onset of Action | Oral: Zidovudine: antiviral effect detectable within 1-2 weeks. Lamivudine: similar. |
| Duration of Action | Zidovudine: dosing interval 8-12 h; Lamivudine: 12-24 h. Combination requires twice-daily dosing. |
| Brand Substitutes | Cytocom 150 mg/300 mg Tablet, Zovilam 150mg/300mg Tablet, Duovir Tablet, Zidolam Ecopack 150 mg/300 mg Tablet |
1 tablet (abacavir 600 mg + lamivudine 300 mg) orally once daily.
| Dosage form | TABLET |
| Renal impairment | CrCl <30 mL/min: contraindicated. CrCl 30-49 mL/min: use individual components; abacavir no adjustment, lamivudine 150 mg once daily. CrCl ≥50 mL/min: no adjustment. |
| Liver impairment | Child-Pugh A: use abacavir 600 mg daily, lamivudine dose as per renal function. Child-Pugh B: avoid Combivir; use individual components (abacavir contraindicated). Child-Pugh C: contraindicated. |
| Pediatric use | Children ≥25 kg: 1 tablet once daily. Children 14-24 kg: abacavir 300 mg + lamivudine 150 mg once daily (separate formulations). <14 kg: not recommended. |
| Geriatric use | Greater sensitivity; monitor renal function. CrCl ≥50 mL/min: standard dose. CrCl <50 mL/min: adjust per renal guidelines. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for COMBIVIR (COMBIVIR).
| Breastfeeding | HIV-infected mothers should not breastfeed due to risk of HIV transmission. Combivir is present in human breast milk: zidovudine M/P ratio is approximately 0.7-0.8; lamivudine M/P ratio is approximately 0.6-0.8. If a mother is on Combivir for her own HIV therapy, breastfeeding is contraindicated regardless of drug levels. |
| Teratogenic Risk | Combivir (zidovudine + lamivudine) is classified as FDA Pregnancy Category C. In first trimester, there is a potential risk of congenital abnormalities based on animal studies, but human data show no increased risk of major malformations. Use during pregnancy is recommended for prevention of mother-to-child HIV transmission. Second and third trimester exposure is associated with mitochondrial toxicity in infants (reported cases of lactic acidosis and hepatic steatosis). Zidovudine is known to cross the placenta and has been linked to transient anemia and neutropenia in neonates. Lamivudine also crosses the placenta with cord blood concentrations similar to maternal plasma. |
■ FDA Black Box Warning
Hematologic toxicity, including neutropenia and severe anemia, particularly in patients with advanced HIV disease; myopathy; lactic acidosis and severe hepatomegaly with steatosis; pancreatitis, especially in children; exacerbation of hepatitis B virus (HBV) infection upon discontinuation in patients co-infected with HBV.
| Serious Effects |
History of hypersensitivity to zidovudine, lamivudine, or any component of the formulation; concomitant use with doxorubicin, stavudine (due to antagonism), or ribavirin (increases risk of hepatic decompensation); co-administration with emtricitabine-containing products; body weight < 30 kg (relative).
| Precautions | Monitor hematologic parameters (hemoglobin, neutrophil counts) frequently, especially in patients with advanced HIV and in children. Monitor for signs/symptoms of myopathy, lactic acidosis, hepatotoxicity, and pancreatitis. Test for HBV before initiating therapy; monitor HBV-infected patients closely after discontinuation due to risk of severe acute exacerbations. |
Loading safety data…
| Fetal Monitoring | Monitor complete blood count (CBC) and serum chemistries (including liver function tests, lactate) every month during pregnancy. Assess HIV RNA viral load and CD4 count at baseline and every 1-2 months. Perform fetal ultrasound for growth and anatomy. In neonates, monitor for hematologic toxicity (CBC at birth and 4-6 weeks) and signs of mitochondrial dysfunction. Consider intrapartum intravenous zidovudine administration. |
| Fertility Effects | No significant adverse effects on female or male fertility have been observed in animal studies. In humans, Combivir does not impair fertility in HIV-infected women or men based on available data. However, HIV infection itself may affect fertility, and treatment with antiretroviral therapy has been associated with improved fertility outcomes due to better disease control. |