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. |
| Molecular Weight | 236.2 |
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 | Use only if clearly needed; no adequate studies in pregnant women. May cause lactic acidosis and hepatotoxicity, especially when used with other antiretrovirals. Known to cross placenta; risk of mitochondrial toxicity in fetus. |
| 2nd trimester | Use only if clearly needed; limited data. Monitor for lactic acidosis and hepatic steatosis. Consider alternative agents if possible. |
| 3rd trimester | Use only if clearly needed; limited data. Monitor maternal liver function and lactic acid levels. Risk of lactic acidosis/hepatotoxicity persists. |
Clinical note
Comprehensive clinical and safety monograph for VIDEX (VIDEX).
| Placental transfer | Evidence suggests didanosine crosses the human placenta. In vitro studies show transfer; human data limited but detectable in cord blood. |
| Breastfeeding | Breastfeeding is not recommended due to potential for HIV transmission and because didanosine is excreted in human milk. Infants may be exposed to the drug and experience adverse effects. |
■ 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 formulationConcomitant use with allopurinolPatients with history of pancreatitisLactic acidosis or hepatic toxicity (severe)Concomitant use with ribavirin in HIV/HCV coinfection (increased risk of hepatic decompensation)
| 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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| Lactation Rating | L5 - Contraindicated |
| 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. |
| 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. |
| Food/Dietary |
| Food significantly reduces didanosine absorption (AUC decreased by up to 55%). Must be taken on an empty stomach. Avoid high-fat meals, as they further impair absorption. Acidic beverages (e.g., fruit juices) may degrade the drug; take with plain water only. |
| Clinical Pearls | Didanosine (VIDEX) requires administration on an empty stomach (at least 30 minutes before or 2 hours after a meal) due to reduced absorption with food. Monitor for pancreatitis (discontinue if suspected) and peripheral neuropathy. Dose adjustment is needed in renal impairment (CrCl <60 mL/min). Avoid concurrent use with ribavirin or stavudine due to increased toxicity risk. Chewable tablets must be thoroughly chewed or crushed before swallowing. |
| Patient Advice | Take VIDEX on an empty stomach, at least 30 minutes before or 2 hours after a meal. · Chew or crush the chewable tablets completely before swallowing; do not swallow whole. · Report immediately any signs of pancreatitis: severe upper stomach pain, nausea, vomiting, or back pain. · Watch for symptoms of peripheral neuropathy: numbness, tingling, or pain in hands or feet. · Do not take VIDEX with alcohol or other medications that can damage the pancreas. · Store tablets in a dry place at room temperature; keep bottle tightly closed. |