Occupational exposure limits for therapeutic substances.

Few therapeutic substances have occupational exposure limits (OELs) set by regulatory bodies and reliance is often placed on in-house OELs derived from a formula based on the therapeutic dose. This mode of derivation relies on assumptions about pharmacokinetics, pharmacodynamics and risk acceptability which might not be soundly based for occupational health purposes. Pharmacodynamic evidence shows that occupational exposure to airborne therapeutic substances can be associated with a much higher risk of an adverse health effect especially on the lungs or skin than by their therapeutic administration. Pharmacokinetic studies indicate that for certain therapeutic substances occupational exposure by inhalation results in a more rapid and complete systemic absorption than a similar dose administered (usually orally) for therapeutic purposes. These and other considerations are used to develop a systematic strategy for deriving OELs for therapeutic substances. The first stage of this consists of a qualitative assessment and ranking of likely occupational health effects. This is based on pharmacological studies, analogy and specific workplace studies. Subsequently assessment of the relevant pharmacological data together with environmental monitoring and exposure-linked health surveillance provides the quantitative data for the setting of appropriate OELs.