Perhaps I would state it stronger. I think if one were to use different units for dose and concentration, the units (or parameter name) of clearance and volume would need to be modified to acknowledge this fact. I actually cannot recall ever having seem such modification.... anyone? Using different input units (such as salt form for dose and free base for concentration) without further annotation would be a bad practice if you ask me.
With a pharmacological and even pharmacokinetic perspective in mind I personally would prefer to use molar concentrations over mass concentrations. Molecules bind targets or enzymes, not mass. Unfortunately other forces are driving towards the use of mass concentrations obviously. It cannot - or at least should not - hurt to push back once in a while. Best regards, Jeroen J. Elassaiss-Schaap Senior Principal Scientist Phone: + 31 412 66 9320 MSD | PK, PD and Drug Metabolism | Clinical PK-PD Mail stop KR 4406 | PO Box 20, 5340 BH Oss, NL -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Capparelli, Edmund Sent: Wednesday, March 26, 2014 17:46 To: Fisher Dennis; [email protected] Subject: Re: [NMusers] Correcting for salt vs. base I prefer converting dose to the base. The advantages I see is that the resulting PK parameter values can be more correctly interpreted in the context of physiologic processes (hepatic blood flow, GFR, absolute bioavailability etc). Edmund At 05:57 AM 3/26/2014, Fisher Dennis wrote: >Colleagues > >I have been troubled by a minor issue for some time. Consider the >following situation: > Dose is reported in mg salt > Cp is reported in ng/ml base > >Since CL is dose / AUC and AUC is merely the integral of Cp vs. >time, in theory, dose should be converted to mg base (or >concentration to ng/ml salt). >However, I am not sure if everyone does that. >In fact, an argument against it is that not doing the conversion >permits one to relate the administered dose (which is usually based >on salt) to a Cp value (usually based on base). > >I am interested to hear what approach people use. > >Dennis > >Dennis Fisher MD >P < (The "P Less Than" Company) >Phone: 1-866-PLessThan (1-866-753-7784) >Fax: 1-866-PLessThan (1-866-753-7784) ><http://www.plessthan.com/>www.PLessThan.com > > Edmund V. Capparelli, Pharm.D. Professor of Clinical Pediatrics and Clinical Pharmacy Director, Center for Research in Pediatric and Developmental Pharmacology (RPDP) Pediatric Pharmacology and Drug Discovery University of California, San Diego 858-246-0009 (telephone) 858-534-5611 (fax) Notice: This e-mail message, together with any attachments, contains information of Merck & Co., Inc. (One Merck Drive, Whitehouse Station, New Jersey, USA 08889), and/or its affiliates Direct contact information for affiliates is available at http://www.merck.com/contact/contacts.html) that may be confidential, proprietary copyrighted and/or legally privileged. It is intended solely for the use of the individual or entity named on this message. If you are not the intended recipient, and have received this message in error, please notify us immediately by reply e-mail and then delete it from your system.
