Didanosine is an oral medication that is used for the treatment of infections with the human immunodeficiency virus HIV. It is in a class of drugs called reverse transcriptase inhibitors which also includes zalcitabine Hivid zidovudine Retrovir stavudine Zerit and lamivudine Epivir. During infection with HIV the HIV virus multiplies within the bodys cells. The newly-formed viruses then are released from the cells and spread throughout the body where they infect other cells. In this manner the infection spreads to new uninfected cells that the body is continually producing and HIV infection is perpetuated. When producing new viruses the HIV virus must manufacture new DNA for each virus. Reverse transcriptase is the enzyme that the virus uses to form this new DNA. Specifically didanosine is converted within the body to its active form dideoxyadenosine triphosphate. This active form is similar to a compound deoxyadenosine triphosphate a chemical that is required by the HIV virus to make new DNA. The reverse transcriptase uses dideoxyadenosine triphosphate instead of deoxyadenosine triphosphate for making DNA and it is the dideoxyadenosine triphosphate that interferes with the reverse transcriptase. Didanosine does not kill existing HIV virus and it is not a cure for HIV. The FDA approved didanosine in October 1991.

Adults weighing 60 kg or more should receive 200 mg twice daily of the tablets or 250 mg twice daily of the powder. Adults weighing less than 60 kg require 125 mg twice daily of the tablets or 167 mg twice daily of the powder.

Didanosine is broken down by stomach acid. To prevent breakdown each formulation contains a buffer antacid. In order to achieve adequate buffering each adult or pediatric dose should contain two tablets of didanosine. Children less than one year of age can achieve adequate buffering with one tablet.

Pediatric doses are based on body surface area according to the following schedule. If body surface area is 1.1-1.4 m2 100 mg as tablets twice daily or 12.5 ml twice daily of the pediatric solution should be administered. Children with a body surface area 0.8-1 m2 should receive 75 mg of the tablets twice daily or 9.5 ml twice daily of the pediatric solution. A body surface area of 0.5-0.7 m2 corresponds to 50 mg as tablets twice daily or 6 ml of the pediatric solution twice daily. If the body surface area is less than 0.4 m2 the recommended dose is 25 mg as tablets twice daily or 3 ml of the pediatric solution twice daily.

Didanosine should be administered on an empty stomach because food reduces the absorption of didanosine by as much as 50. Videx ED is a long-acting formulation of didanosine. Adults should receive 250-400 mg once daily on an empty stomach. Capsule should be swallowed intact. Videx EC causes less stomach irritation than regular didanosine Videx.

The most severe side effects are inflammation of the pancreas pancreatitis liver failure and nerve damage in the arms and legs peripheral neuropathy. Symptoms of peripheral neuropathy are tingling numbness and pain in the feet or hands. Other side effects include diarrhea chills fever rash stomach pain headache nausea and vomiting.

Didanosine formulations contain an antacid which reduces the absorption of tetracycline e.g. Vibramycin Minocin and fluoroquinolone antibiotics e.g. Cipro Floxin. Therefore tetracyclines and fluoroquinolones should be administered at least two hours before or after administration of didanosine.

The antacid in didanosine formulations reduces stomach acid. Therefore didanosine may decrease the absorption of ketoconazole Nizoral and other drugs that need stomach acid for absorption.

Didanosine is used for the treatment of HIV infection in adults and children.

Store tablets and unmixed powder at room temperature 15-30°C 59-86°F.

If the tablets are dissolved in water or apple juice the mixture should be used within one hour and the powder for solution should be used within four hours after dissolving it in water. The pediatric powder may be stored in the refrigerator at 2-8°C 36-46°F for up to 30 days after mixing in water.