Kaletra is a prescription medication that is used in the treatment of HIV (Human Immunodeficiency Virus), which is the virus responsible for causing AIDS (Acquired Immunodeficiency Syndrome). It is a combination drug that contains two active ingredients, lopinavir and ritonavir. Lopinavir belongs to a class of medications known as protease inhibitors, which work by inhibiting the protease enzyme that HIV uses to replicate within the body. Ritonavir is included primarily to boost the levels of lopinavir, making it more effective at a lower dose. Kaletra can be used in adults and children over the age of 14 days. It is usually taken in conjunction with other antiretroviral medications as part of an antiretroviral therapy (ART) regimen to help reduce the amount of HIV in the blood, maintain the immune system function, and slow the progression of the disease.