Zolpidem-induced macropsia has been reported in women with anorexia.7 The protein-binding capacity of zolpidem is approximately 92%, mainly to albumin (66%) and al-acid glycoprotein (56.6%).4 In malnourished patients with anorexia nervosa, hypoalbuminemia is common and, therefore, unbound drug
concentration is higher.
The unbound drug
may cause pharmacological activities or initiate side effects in the body [16-18].
Only the unbound drug--two per cent--can be filtered, so clearance by filtration is reduced, in comparison to an unbound drug
Higher levels of unbound drug
may exist due to hypoalbuminemia, competition for protein binding sites by uremic substances, and alterations in protein binding sites.
Because only unbound drug
is pharmacologically active, it is useful to measure the free concentration when any of the above conditions are present.
The common laboratory practice is to measure total phenytoin concentrations, which assumes that phenytoin protein binding is relatively constant, so that the concentration of the active unbound drug
can be predicted from the total drug plasma concentration (2,3).
Disopyramide Monitor unbound drug
concentrations in renal failure patients.
where r is the number of moles of bound drug per protein molecule; [[D.sub.b]] and [[D.sub.f]] are the bound and unbound drug
concentrations, respectively; [[P.sub.t]] is the total protein concentration; and [K.sub.i] and [N.sub.i] are the binding constant and the number of binding sites for the ith class of binding sites, respectively.
So, for drugs that are highly protein bound (e.g., phenytoin, which is an anti-seizure medication), there may be more unbound drugs
available in infants as compared to older patients when the same dosages are given.
1, 1990 CANCER RESEARCH that two LDL-bound injected drugs -- methotrexate and floxuridine -- successfully dodged the body's natural clearance mechanisms to circulate at least six times longer in the blood of rats than did unbound drugs
. Because the LDLs survived longer than the drugs they had been carrying, de Smidt and van Berkel say the drugs may not have been chemically bound to the LDLs firmly enough.
As unbound drugs
are removed from the plasma (either by elimination or crossing into another body compartment), bound drug molecules will be released from the plasma proteins.