Lopinavir/ritonavir, a new galenic oral formulation from commercial solid form, fine-tuned by nuclear magnetic resonance spectroscopy

Objectives: The lopinavir/ritonavir combination is one of the first antiretroviral drugs to be used in the treatment of COVID-19. In incapacitated patients, such as those in intensive care, an oral liquid formulation is needed. In Italy a marketed formulation is available, but only by importing it from other European countries. A galenic oral formulation prepared in the hospital pharmacy from lopinavir/ritonavir tablets was fine-tuned, evaluating the content of the active pharmaceutical ingredient (API) and stability of the formulation by using nuclear magnetic resonance (NMR) spectroscopy.

Methods: To overcome the insolubility of lopinavir/ritonavir in water, ethanol and glycerol have been used as additional excipients. To define the best excipient proportion and best preparation method, three different formulations (ethanol 7.1-7.5%, glycerol 6-15%, and water) and two different preparation procedures (two step vs one step) have been studied. Each formulation has been compared with Kaletra oral solution (lopinavir 80 mg/mL, ritonavir 20 mg/mL) by NMR spectroscopy. API content and stability were measured.

Results: The presence of ethanol and glycerol as co-solvents is crucial both to improve solubilisation and promote the stability of the oral form. In the two-step preparation method, when crushed tablets were first dispersed in the ethanol/glycerol mixture and then in water, the content of solubilised active ingredients was equal or only slightly lower than the standard Kaletra (range 89-100%). The one-step method provided a comparable API content (65%) to that obtained by using water as the sole dispersing medium.

Conclusions: The two-step setup method with final 7.1% ethanol and 11% glycerol concentration is an efficient procedure for extemporaneous preparation of lopinavir/ritonavir liquid formulations from crushed tablets. The method combines simplicity of preparation and reconstitution in the hospital ward with good solubilisation, comparable to the commercial solution, and stability of active ingredients over time.