VIDEX EC
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VIDEX EC (VIDEX EC).
Nucleoside reverse transcriptase inhibitor (NRTI); intracellularly phosphorylated to active metabolite didanosine triphosphate, which inhibits HIV reverse transcriptase by competing with natural deoxynucleotides and causing DNA chain termination.
| Metabolism | Partially metabolized by xanthine oxidase to hypoxanthine; also undergoes purine nucleoside phosphorylase conversion to uric acid. Not significantly metabolized by CYP450 isoenzymes. |
| Excretion | Renal: >50% unchanged via glomerular filtration and tubular secretion; minimal biliary/fecal excretion (<2%) |
| Half-life | 0.6–1.5 hours (short terminal half-life due to rapid intracellular phosphorylation and cellular retention of active triphosphate; clinical dosing accounts for intracellular half-life of ~12–15 hours) |
| Protein binding | <5% bound to plasma proteins (negligible binding) |
| Volume of Distribution | 0.8–1.4 L/kg (indicates extensive distribution into total body water; clinical significance: good penetration into tissues including CNS and genital tract) |
| Bioavailability | Oral: 40% (delayed-release capsules; food reduces absorption by 50%, must be taken on empty stomach) |
| Onset of Action | Oral: peak plasma concentration at 1.5–2 hours; antiviral effect begins within hours of first dose based on intracellular active metabolite accumulation |
| Duration of Action | Plasma: 4–6 hours; intracellular active triphosphate persists for 12–24 hours supporting twice-daily dosing |
400 mg orally once daily on an empty stomach.
| Dosage form | CAPSULE, DELAYED REL PELLETS |
| Renal impairment | CrCl ≥60 mL/min: 400 mg once daily. CrCl 30-59 mL/min: 250 mg once daily. CrCl 10-29 mL/min: 125 mg once daily. CrCl <10 mL/min: 125 mg once daily (dosing interval not established; consider extended interval). Hemodialysis: 125 mg once daily, administer after dialysis. |
| Liver impairment | Child-Pugh Class A and B: No adjustment necessary. Child-Pugh Class C: Not recommended due to lack of data. |
| Pediatric use | Weight ≥60 kg: 400 mg orally once daily. Weight 25-59 kg: 250 mg orally once daily. Weight 20-24 kg: 200 mg orally once daily. Weight 15-19 kg: 167 mg orally once daily. Weight 10-14 kg: 125 mg orally once daily. Weight 8-9 kg: 100 mg orally once daily. Administer on an empty stomach. |
| Geriatric use | No specific adjustments recommended other than monitoring renal function and adjusting dose based on creatinine clearance as per adult renal adjustment guidelines. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for VIDEX EC (VIDEX EC).
| Breastfeeding | Didanosine is excreted into human breast milk to a limited extent. Studies report a milk-to-plasma (M/P) ratio of approximately 0.5-0.8. The concentration in breast milk is lower than therapeutic plasma levels. However, the WHO recommends that HIV-infected women avoid breastfeeding to prevent HIV-1 transmission. Therefore, breast-feeding is contraindicated in this population. If used in other contexts, caution is advised. |
| Teratogenic Risk | Didanosine (VIDEX EC) is classified as FDA Pregnancy Category B. Animal studies have not demonstrated fetal harm, but there are no adequate and well-controlled studies in pregnant women. However, didanosine has been associated with lactic acidosis and hepatic steatosis in pregnant women, which can be fatal. Placental transfer occurs. The risk of teratogenicity is considered low overall but must be balanced against the risk of untreated HIV transmission to the fetus. Use during first trimester: no increased risk of major malformations observed in human data; use in second and third trimesters: no specific teratogenic effects noted, but mitochondrial toxicity risk may exist. Fetal monitoring for growth and development is recommended. |
■ FDA Black Box Warning
Fatal and nonfatal pancreatitis has occurred, especially in patients with advanced HIV disease or prior pancreatitis. Lactic acidosis and severe hepatomegaly with steatosis have been reported, including fatal cases.
| Serious Effects |
Hypersensitivity to didanosine or any component; concurrent use with allopurinol or ribavirin (increased didanosine exposure); coadministration with certain drugs (e.g., stavudine, hydroxyurea) increases toxicity risk.
| Precautions | Pancreatitis risk (discontinue if signs/symptoms); lactic acidosis/hepatic steatosis; retinal changes/optic neuritis; peripheral neuropathy; immune reconstitution syndrome; fat redistribution; monitor serum amylase, liver enzymes, and blood glucose. |
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| Fetal Monitoring | Maternal: Monitor liver function tests, serum lactate, amylase, lipase, and complete blood counts periodically due to risks of pancreatitis, lactic acidosis, and hepatotoxicity. Assess for signs of neuropathy (e.g., numbness, tingling). Renal function should be evaluated as dose adjustments may be needed. Fetal: Ultrasonography to monitor fetal growth and development; consider fetal echocardiography if maternal exposure is prolonged due to mitochondrial toxicity concerns. |
| Fertility Effects | There are no well-controlled human studies on the effect of didanosine on fertility. Animal studies have shown no significant impairment of fertility. In HIV-positive patients, didanosine does not appear to have major adverse effects on male or female fertility, but underlying HIV disease and other medications may impact fertility. Use of didanosine is not known to cause infertility. |