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.

Pyrimethamine pharmacokinetics were studied in 11 HIV-infected subjected receiving pyrimethamine (50 mg daily for three weeks) and zidovudine. Population pharmacokinetic analysis yielded parameter estimates for pyrimethamine that were similar to those seen in subjects without HIV infection. Data on zidovudine pharmacokinetics were available from 10 subjects and showed no significant differences when administered alone or with pyrimethamine.
Pyrimethamine pharmacokinetics in human immunodeficiency virus-positive patients seropositive for Toxoplasma gondii. Jacobson JM, et al. Antimicrob Agents Chemother, 1996, 40: 1360-1365.