In anti retroviral therapy, Zidovudine should not be combined with:

Nucleoside reverse transcriptase inhibitors (Nis): Zidovudine: It is a thymidine analogue (azidothymidine, AZT), the prototype NI. After phosphorylation in the host cell-zidovudine triphosphate selectively inhibits viral reverse transcriptase (RNA-dependent DNA polymerase) in preference to cellular DNA polymerase Stavudine (d4T): It is also a thymidine analogue which acts in the same way as AZT. By utilizing the same thymidine kinase for activation, AZT antagonises the effect of stavudine. Stavudine and zidovudine exhibit mutual antagonism by competing for the same activation pathway. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:770,771