VIDEX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VIDEX (VIDEX).
Didanosine, a synthetic purine nucleoside analogue of deoxyadenosine, is phosphorylated to active metabolite dideoxyadenosine triphosphate (ddATP), which inhibits HIV-1 reverse transcriptase by competing with natural substrate dATP and causing chain termination after incorporation into viral DNA.
| Metabolism | Didanosine is metabolized via intracellular phosphorylation to its active triphosphate form; it is partially metabolized by purine nucleoside phosphorylase (PNP) and other enzymes. Approximately 50% of a dose is excreted unchanged in urine. |
| Excretion | Renal elimination: approximately 50-60% of dose excreted unchanged in urine via glomerular filtration and active tubular secretion. Fecal elimination: <20% as unchanged drug or metabolites. |
| Half-life | Terminal elimination half-life: 1.5-2 hours (intravenous), prolonged to 4-8 hours in renal impairment. Clinical context: Requires dose adjustment in CrCl <50 mL/min. |
| Protein binding | <5% bound to plasma proteins (mainly albumin). Low binding minimizes drug interactions. |
| Volume of Distribution | Vd: 0.8-1.0 L/kg, indicating distribution into total body water with some tissue binding. |
| Bioavailability | Oral: 30-54% (tablets), 25-43% (buffered powder). Bioavailability reduced by food and acidic pH; IV: 100%. |
| Onset of Action | Oral: Peak plasma concentration reached 0.5-1.5 hours post-dose; antiretroviral effect begins within hours to days. IV: Immediate upon administration. |
| Duration of Action | Dosing interval: 12 hours due to short half-life. Clinical note: Continuous suppression requires twice-daily dosing; missed doses lead to rapid viral rebound. |
Adults: 200 mg orally twice daily (two 100 mg chewable tablets per dose) or 250 mg orally twice daily (two 125 mg buffered powder packets per dose); administer on an empty stomach (at least 30 minutes before or 2 hours after a meal).
| Dosage form | FOR SOLUTION |
| Renal impairment | For CrCl >=60 mL/min: no adjustment. CrCl 30-59 mL/min: 150 mg twice daily (chewable tablets) or 200 mg twice daily (powder). CrCl 10-29 mL/min: 150 mg once daily (chewable tablets) or 125 mg once daily (powder). CrCl <10 mL/min: 100 mg once daily (chewable tablets) or 125 mg once daily (powder). Hemodialysis: administer after dialysis; no supplemental dose. |
| Liver impairment | Not specifically recommended; use with caution in hepatic impairment. No formal Child-Pugh based dosing adjustments established. |
| Pediatric use | Neonates (birth to 8 weeks): 50 mg/m2 orally twice daily. Infants (3 months to 8 months): 100 mg/m2 orally twice daily. Children (8 months to 16 years): 120 mg/m2 orally twice daily (max 200 mg twice daily). Administer on empty stomach. Dosing based on body surface area; use appropriate formulation (chewable tablet or oral solution). |
| Geriatric use | No specific adjustments beyond renal function; monitor renal function closely and adjust dose based on CrCl as per renal adjustment guidelines. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for VIDEX (VIDEX).
| Breastfeeding | Didanosine is excreted into human breast milk; the milk-to-plasma (M/P) ratio is approximately 0.5-1.3. Infants exposed via breast milk may develop adverse effects such as pancreatitis, peripheral neuropathy, or hepatotoxicity. Due to risk of HIV transmission and potential toxicity, breastfeeding is contraindicated in HIV-positive mothers in developed settings. The World Health Organization recommends exclusive breastfeeding for HIV-positive mothers in resource-limited settings with appropriate antiretroviral therapy, but didanosine is not preferred due to side effects. |
| Teratogenic Risk | Didanosine (VIDEX) is classified as FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic risk, but there are no adequate and well-controlled studies in pregnant women. First trimester: No increased risk of major malformations observed in prospective cohort studies. Second and third trimesters: No specific fetal risks identified, but theoretical risk of mitochondrial toxicity due to nucleoside analogue. Human data do not show increased rates of congenital anomalies compared to background. Caution is advised due to potential for lactic acidosis in pregnant women. |
■ FDA Black Box Warning
Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of nucleoside analogues alone or in combination, including didanosine. Fatal and nonfatal pancreatitis has occurred during therapy with didanosine alone or in combination with other antiretroviral agents.
| Serious Effects |
["Hypersensitivity to didanosine or any component of the formulation","Concurrent use with allopurinol (increases didanosine exposure and risk of toxicity)","Coadministration with ribavirin (increases risk of hepatic decompensation, especially in HIV/HCV co-infection)"]
| Precautions | ["Pancreatitis: Fatal and nonfatal cases reported; discontinue if clinical signs/symptoms or elevated amylase/lipase.","Lactic acidosis/severe hepatomegaly with steatosis: Monitor for symptoms; discontinue if suspected.","Peripheral neuropathy: Dose-related; monitor and consider dose reduction or discontinuation.","Retinal changes and optic neuritis: Reported; perform ophthalmologic exams in children.","Hyperuricemia: Associated with didanosine; monitor serum uric acid.","Immune reconstitution syndrome: May occur during initial combination therapy.","Fat redistribution/accumulation: Reported with antiretroviral therapy."] |
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| Fetal Monitoring | Monitor complete blood count (CBC), liver function tests (LFTs), serum amylase and lipase, and serum lactate levels in pregnant women on didanosine, especially in the 3rd trimester. Fetal monitoring with ultrasound for growth parameters and anomaly scan at 18-20 weeks. Assess for maternal peripheral neuropathy. Monitor for lactic acidosis or hepatomegaly with steatosis. Perform HIV viral load and CD4 count regularly. |
| Fertility Effects | In animal studies, didanosine did not impair fertility. Human data limited; some reports of reduced sperm count or motility in men, but reversibility after discontinuation. No significant effects on female fertility reported. Use in pregnancy has not demonstrated adverse effects on fertility for either gender. |