As metronidazole is excreted in relatively high concentration in human breast milk, its use should be avoided in nursing mothers. It should be avoided, if possible, during first trimester of pregnancy, for its effects on foetal development are not definitely known. Being a 'nitro-imidazole' derivative, moderate leucopenia has been reported in some patients. It is advisable to carry out total differential leucocyte count before, during and after treatment in patients requiring long term metronidazole therapy.