Professional Information

Didanosine

Pronouncation: (die-DAN-oh-SEEN)
Class: Nucleoside reverse transcriptase inhibitor

Trade Names:
Videx
- Tablets, buffered, chewable/dispersible 25 mg
- Tablets, buffered, chewable/dispersible 50 mg
- Tablets, buffered, chewable/dispersible 100 mg
- Tablets, buffered, chewable/dispersible 200 mg
- Powder for Oral Solution, buffered 100 mg
- Powder for Oral Solution, buffered 250 mg
- Powder for Oral Solution, pediatric 2 g
- Powder for Oral Solution, pediatric 4 g

Trade Names:
Videx EC
- Capsules, delayed-release (with enteric-coated beadlets) 125 mg
- Capsules, delayed-release (with enteric-coated beadlets) 200 mg
- Capsules, delayed-release (with enteric-coated beadlets) 250 mg
- Capsules, delayed-release (with enteric-coated beadlets) 400 mg

Pharmacology

Feedback for Didanosine

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Inhibits replication of HIV by interfering with DNA synthesis.

Pharmacokinetics

Absorption

T _max is 0.25 to 1.5 h (buffered formulation), 2 h (delayed-release). Bioavailability approximately 42% (buffered formulation). Food decreases the C _max and AUC approximately 55% of the buffered formulation and decreases the C _max and AUC of the delayed-release capsules approximately 46% and 19%, respectively. Take on an empty stomach.

Distribution

Less than 5% protein bound. Vd approximately 1.08 L/kg.

Metabolism

Intracellularly converted by enzymes to dideoxyadenosine 5′-triphosphate (active).

Elimination

t _½ approximately 1.5 h (buffered formulation). Approximately 18% recovered in the urine (buffered formulation). Renal Cl approximately 5.5 mL/min/kg (buffered formulation).

Special Populations

Renal Function Impairment

t _½ is increased and Cl is decreased. Dosage reduction recommended in those with Ccr less than 60ߙmL/min.

Indications and Usage

Didanosine ( Videx )

Treatment of HIV-1 infection in combination with other antiretrovirals.

Didanosine EC ( Videx EC )

In combination with other antiretroviral agents for the treatment of HIV-1 infection in adults who require once-daily administration of didanosine or an alternative didanosine formulation.

Contraindications

Standard considerations.

Dosage and Administration

Didanosine EC ( Videx EC ) has not been studied in children. Children's dosage recommendations are for didanosine ( Videx ).

Adults less than 60ߙkg

PO 125 mg (as 2 tablets) or 167 mg (powder for suspension) everyߙ12ߙh or 250 mg every day (capsules).

Adults more than 60 kg

PO 200 mg (as 2 tablets) or 250 mg (powder for suspension) every 12 h or 400 mg every day (capsules).

Children

PO 120 mg/m ² twice daily.

General Advice

Give on an empty stomach.
Have patients chew or manually crush tablets or disperse tablets in water (2 tablets per 1 oz water).
When dispersing tablets in water, stir until uniform dispersion occurs, then have patient drink entire amount immediately.
When preparing buffered powder for oral suspension, do not use fruit juice or other acid-containing liquid. Stir until completely dissolved in 4 oz liquid, then have patient drink entire amount immediately.
Pediatric powder for oral suspension is first mixed with purified water to obtain concentration of 20 mg/mL, then mixed with antacid to obtain final concentration of 10 mg/mL.

Storage/Stability

Pediatric oral solution admixture may be stored for up to 30 days if refrigerated. Shake well before use.

Drug Interactions

Allopurinol

Because allopurinol may cause increased didanosine plasma levels, do not coadminister.

Antacids

Aluminum or magnesium containing antacids may potentiate adverse reactions associated with the antacid component of didanosine chewable or dispersible tablets and pediatric powder.

Antiretroviral agents

Antiretroviral agents have caused fatal lactic acidosis in women when coadministered with didanosine.

Delavirdine, indinavir

Administer 1 h prior to didanosine to avoid decreasing plasma levels of delavirdine or indinavir.

Drugs that cause peripheral neuropathy or pancreatitis

Increased risk of these toxicities.

Food

Reduces absorption of didanosine by as much as 50%.

Fluoroquinolones, tetracyclines

Do not administer within 2 h of didanosine.

Ganciclovir

When coadministered with didanosine, an increase in didanosine plasma levels and a decrease in ganciclovir concentrations may occur.

Itraconazole, ketoconazole, dapsone, and other drugs whose absorption can be affected by gastric acidity

Administer at least 2 h before didanosine.

Methadone

May decrease didanosine plasma levels.

Laboratory Test Interactions

None well documented.

Adverse Reactions

CNS

Peripheral neuropathy; asthenia; headache; pain; seizure.

Dermatologic

Rash; pruritus; alopecia.

EENT

Retinal depigmentation.

GI

Pancreatitis; diarrhea; abdominal pain; nausea; vomiting; anorexia; dry mouth.

Hematologic

Leukopenia, thrombocytopenia, granulocytopenia.

Hepatic

Hepatic failure; elevated LFTs.

Miscellaneous

Myopathy; chills, fever.

Precautions

Monitor

Monitor for diarrhea in patient receiving oral solution. Switching to tablets may alleviate symptoms. Monitor uric acid levels closely for possible asymptomatic hyperuricemia.

Pregnancy

Category B .

Lactation

Undetermined. HIV-infected mothers should not breast-feed their infants.

Children

Safety and efficacy of didanosine EC ( Videx EC ) not established.

Renal Function

Dosage reduction is recommended with Ccr less than 60 mL/min.

Hepatic Function

Dosage may need to be reduced. Hepatic failure has occurred in children.

Mutagenesis

May be genotoxic.

Hepatomegaly with steatosis

Fatal cases of severe hepatomegaly with steatosis have been reported.

Lactic acidosis

Fatal cases of lactic acidosis have been reported. Use with caution in pregnancy.

Pancreatitis

Major toxicity; has been fatal. Should be considered if patient develops abdominal pain, nausea, vomiting, or lab test abnormalities.

Peripheral neuropathy

Occurs frequently; may be dose-related.

Retinal changes and optic neuritis

Retinal changes and optic neuritis have been reported in adults and children.

Special diets

Each tablet contains 36.5 mg phenylalanine; single-dose powder packet contains 1380 mg sodium.

Patient Information

Advise patient to take drug on empty stomach and to chew or crush tablets.
Inform patient that drug does not completely eliminate HIV virus and, therefore, does not reduce risk of transmitting HIV. Appropriate precautions must be continued.
Emphasize that drug does not cure AIDS or AIDS-related complex (ARC) and to report significant changes in health to health care provider.
Instruct patient to report these symptoms to health care provider: abdominal pain, diarrhea, nausea, vomiting, tingling pain or numbness in hands or feet, fever, sore throat, flu-like symptoms.
Advise patient to avoid alcoholic beverages or taking OTC medications without first notifying health care provider.