The distribution of approximately equipotent doses of 14C-labelled clodronate (0.1 mmol/kg), etidronate (0.1 mmol/kg), and amidronate (0.015 mmol/kg), and also an equimolar dose of amidronate (0.1 mmol/kg), was studied in mice by measuring the 14C-activities in various tissues up to 360 days after a single intravenous injection. With the higher dose of amidronate the distribution could be, however, monitored only for 7 days because of the toxicity of the drug. The results indicate that there are major differences in the deposition of the bisphosphonates into soft tissues, while the disappearance from plasma and incorporation into bone are quite similar in terms of percentage of dose per g of tissue. However, the binding capacity of bone for clodronate and etidronate is many times greater than that for amidronate expressed as nmol of the drug per g of tissue. Amidronate deposits in the spleen and liver of mice, when injected in saline, whereas clodronate and etidronate do not. This agrees with the suggestion that amidronate, but not the other two, can interfere with the mononuclear phagocyte system of spleen and liver.

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