Lobucavir (previously known as BMS-180194, Cyclobut-G) is an antiviral drug that shows broad-spectrum activity against herpesviruses, hepatitis B and other hepadnaviruses, HIV/AIDS and cytomegalovirus.

[1][2][3] It initially demonstrated positive results in human clinical trials against hepatitis B with minimal adverse effects but was discontinued from further development following the discovery of increased risk of cancer associated with long-term use in mice.

[4] Although this carcinogenic risk is present in other antiviral drugs, such as zidovudine and ganciclovir that have been approved for clinical use, development was halted by Bristol-Myers Squibb, its manufacturer.

Unlike traditional chain terminators that lack a 3'-OH group to prevent further DNA replication, Lobucavir is thought to cause a conformational change that blocks optimal polymerase activity two to three nucleotides downstream of its incorporation.

[6] Lobucavir's bioavailability is 30-40% of the original oral dose and its half-life is approximately 10 hours, as demonstrated by pre-clinical testing[10][11]