The justifications for formulating fixed combinations of potent, therapeutically active substances are few. All biologically active substances have a potential to induce harm as well as therapeutic benefit. The administration of two or more such substances, rather than one, increases the potential for adverse effects. Fixed-ratio combination products are consequently acceptable only when the dosage of each ingredient meets the requirements of a defined population group and when use of the combination provides a clear advantage over separate administration of the individual active compounds, in either therapeutic effect or compliance, or when it enhances safety - as in the case of multiple chemotherapy intended to reduce the emergence of resistant pathogens.