tracer-tracee kinetics

Dear NONMEM Users Group I have been asked to help with modelling saliva concentration data from a tracer-tracee study of an endogenous substance. Human volunteers were given an oral dose of the labelled tracer substance and a series of saliva samples were collected over the following 24 hours. * The dependent variable is in the form of a ratio (unitless) of the tracer to tracee (endogenous) saliva concentrations. * The dose amount (micromoles) and time of dose are known. The dose is given as the oxidised form of the measured compound. Modelling it as a 2-compartment mammillary model with a depot compartment produces reasonable plots but of course, the output data is not useful. My questions are: 1) How does one work with a ratio as a DV and make sense of the output data? 2) Would a metabolite model be a suitable way of dealing with the dose being in a different chemical form to that measured? Is there a better way? 3) Can anyone guide me towards similar published work? Grateful for any advice. With thanks and all best wishes Ann Dr Ann Rigby-Jones Lecturer in Pharmacology, Anaesthesia Research Group Plymouth University Peninsula Schools of Medicine & Dentistry Website: http://www.plymouth.ac.uk/peninsula [Facebook] http://www.facebook.com/pupsmd [Twitter] http://www.twitter.com/pupsmd [PUPSMD logo] ________________________________ http://www.plymouth.ac.uk/worldclass This email and any files with it are confidential and intended solely for the use of the recipient to whom it is addressed. If you are not the intended recipient then copying, distribution or other use of the information contained is strictly prohibited and you should not rely on it. If you have received this email in error please let the sender know immediately and delete it from your system(s). Internet emails are not necessarily secure. While we take every care, Plymouth University accepts no responsibility for viruses and it is your responsibility to scan emails and their attachments. Plymouth University does not accept responsibility for any changes made after it was sent. Nothing in this email or its attachments constitutes an order for goods or services unless accompanied by an official order form.