Chloroquine reduces bioavailability of praziquantel, whichwould be expected to reduce its efficacy in systemic worm infections such as schistosomiasis.
Clinical evidence,mechanism, importance and management
A single 40-mg/kg oral dose of praziquantel was given to 8 healthy subjects alone,and 2 hrs after chloroquine 600 mg. The chloroquine reduced praziquantel AUC by 65 % and maximum serum levels by 59%. The reasons for this effect are not understood. There were large individual variations in levels,and one subject was not affected. The effect of this interaction could be that some patients will not achieve high enough serum praziquantel levels to treat systemic worm infections such as schistosomiasis. After taking chloroquine, praziquantel serum levels of 4 out of 8 subjects (50%) did not reach threshold of
0.3 micrograms/mL for about 6 hrs (which is required to effectively kill schistosomes), compared with only 2 of 8 (25%) during control period. The authors conclude that an increased dosage of praziquantel should be considered if chloroquine is given (they do not suggest how much),particularly in anyone who does not respond to initial treatment with praziquantel (See reference number 1). More study of this interaction is needed.
The interaction is of no importance when praziquantel is used for intestinal worm infections (where its action is a local effect on worms in gut)
1. Masimirembwa CM,Naik YS, Hasler JA. The effect of chloroquine on the pharmacokineticsand metabolism of praziquantel in rats and in humans. Biopharm Drug Dispos (1994) 15, 33–
43.