Didanosine and Ritonavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ritonavir
Didanosine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Inactivation of both drugs
Interaction Deep Dive
Coadministration of didanosine 200 mg twice daily and ritonavir 600 mg twice daily for four days in 12 patients resulted in no changes in the pharmacokinetics of ritonavir. Didanosine may be administered without dosage adjustments in patients taking ritonavir. However, administration of these two medications should be separated by 2.5 hours because of formulation incompatibilities1.
Why it happens (mechanism)
Formulation incompatibility
Literature reports
2 reports — tap to read
a) Eighteen HIV-positive asymptomatic males were assigned to six different sequences of the following regimens during a multiple-dose, open-label, three-period crossover study. The regimens were didanosine 200 mg every 12 hours for four days, ritonavir 600 mg every 12 hours for four days, and didanosine and ritonavir for four days. The administration of the two agents was staggered by 2.5 hours. Ritonavir concentrations were slightly higher during didanosine administration (17.62 mcg/mL vs 18.65 mcg/mL), although this was not statistically significant. Didanosine maximum concentrations were reduced from 1.06 mcg/mL to 0.9 mcg/mL in the presence of ritonavir. While this is statistically significant, it fails to reach clinical significance. Therefore, dosage adjustments of either drug do not appear necessary when concurrent administration is required 2.
b) When didanosine 200 mg was administered twice-daily concomitantly with ritonavir 500 mg twice daily to subjects for four days, the AUC and Cmax for didanosine was decreased by 13% and 16% respectively1.
Common questions
Can I take Didanosine and Ritonavir together?
Inactivation of both drugs Always confirm with your pharmacist or prescriber before making any change.
How serious is the Didanosine and Ritonavir interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Didanosine or Ritonavir need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (2)
- Product Information: Norvir(R) oral capsule, oral solution, ritonavir oral capsule, oral solution. Abbott Laboratories, North Chicago, IL, 2008. DailyMed
- Cato A, Qian J, Vomvouras S, et al: Pharmacokinetic interaction between ritonavir and didanosine when administered concurrently to HIV-infection patients. J Acquir Immune Defic Syndr Hum Retrovirol 1998; 18:466-472.
Keep reading about Ritonavir
Keep reading about Didanosine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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