Concomitant treatment, especially acute therapy, with potentially nephrotoxic or myelosuppressive drugs (e.g. systemic pentamidine, dapsone, pyrimethamine, co-trimoxazole, amphotericin, flucytosine, ganciclovir, interferon, vincristine, vinblastine and doxorubicin) may also increase the risk of adverse reactions to zidovudine. If concomitant therapy with any of these drugs is necessary then extra care should be taken in monitoring renal function and haematological parameters and, if required, the dosage of one or more agents should be reduced. Limited data from clinical trials do not indicate a significantly increased risk of adverse reactions to zidovudine with cotrimoxazole, aerosolised pentamidine, pyrimethamine and aciclovir at doses used in prophylaxis.
Retrovir Summary of Product Characteristics, ViiV Healthcare UK, Ltd, December 2018.

The effect of trimethoprim/sulfamethoxazole (160/800 mg, twice daily, three times weekly) on the pharmacokinetics of zidovudine (250 mg twice daily) was studied in 16 HIV-infected subjects. There were no significant differences in the pharmacokinetics of zidovudine or zidovudine glucuronide when administered alone or with trimethoprim/sulfamethoxazole.
Absence of effect of trimethoprim/sulfamethoxazole on pharmacokinetics of zidovudine in patients infected with human immunodeficiency virus. Canas E, et al. Antimicrob Agents Chemother, 1996, 40: 230-233.

The effects of dapsone (100 mg once daily) and/or trimethoprim (200 mg twice daily) on single doses of zidovudine (200 mg ) were investigated in 8 HIV-infected subjects. Zidovudine did not influence the pharmacokinetics of dapsone or trimethoprim. Dapsone had no effect on the pharmacokinetics of zidovudine. Trimethoprim significantly decreased renal clearance of zidovudine by 58%, with a concurrent 54% decrease in the mean urinary recovery of zidovudine. The combination effect of trimethoprim plus dapsone on the pharmacokinetics of zidovudine was similar to effect of trimethoprim alone.
Zidovudine, trimethoprim and dapsone pharmacokinetic interactions in patients with human immunodeficiency virus infection. Lee BL, et al. Antimicrob Agents Chemother, 1996, 40: 1231-1236.

The pharmacokinetics of zidovudine (3 mg/kg iv infusion over 1 h) were evaluated in 9 HIV-infected subjects alone, with trimethoprim (150 mg) or with trimethoprim/sulfamethoxazole (160/800 mg). Metabolic clearance of zidovudine was not affected by TMP or TMP/SMX. However, zidovudine renal clearance decreased in the presence of TMP (48%) and TMP/SMX (58%) and that of zidovudine glucuronide by 20% and 27% respectively.
Trimethoprim, alone or in combination with sulphamethoxazole, decreases the renal excretion of zidovudine and its glucuronide. Chatton JY, et al. Br J Clin Pharmacol, 1992, 34: 551-554.