Methaqualone in human serum and cerebrospinal fluid after oral intake

Clinical pharmacokinetics of cerebrospinal fluid

The distribution of drugs into the cerebrospinal fluid has long been considered a challenging field of investigation in 2 major respects: (a) understanding how the physicochemical properties (molecular weight, pKa, plasma protein binding) of various molecules influence their movements across such a specific structure as the blood-brain barrier; and (b) defining the relationship between cerebrospinal fluid concentrations of various drugs and their central (side) effects. An attempt has been made to review the very dispersed information presently available to offer a clinically orientated picture of this area of pharmacokinetics. Drugs acting on the central nervous system (benzodiazepines, tricyclic antidepressants, anticonvulsants, opioids), antibacterial agents, cardiovascular drugs (beta-adrenoceptor blockers and digoxin), antineoplastic drugs (mainly methotrexate), and other miscellaneous agents (corticosteroids, cimetidine, methylxanthines) are reviewed. The available evidence seems to support the conclusion that only for methotrexate and antibacterial agents does knowledge of cerebrospinal fluid pharmacokinetics have direct therapeutic implications, while the mosaic of information available for other drugs does little more than provide a partially satisfactory picture.

Entry of quinidine into cerebrospinal fluid

Some of the unwanted effects of quinidine commonly occurring in clinical practice involve the central nervous system. We therefore assessed the rate and extent of quinidine passage into cerebrospinal fluid (CSF) in humans and dogs. In eight human subjects receiving oral quinidine therapy, lumbar CSF quinidine concentrations averaged 16% of unbound serum concentrations (range: 4% to 37%). The findings were confirmed when simultaneous serum (total and unbound) and CSF quinidine concentrations were followed for up to 8 hours after a single intravenous dose of quinidine in anesthetized dogs. Quinidine appeared promptly in CSF of all animals, but CSF concentrations averaged only 37% to 46% of unbound serum levels. The in vitro octanol:water partition coefficient for quinidine at physiologic pH was greater than 100, indicating that unbound quinidine should readily traverse the blood-brain barrier. Thus, passage of quinidine into CSF appears not to be governed by passive diffusion alone. Quinidine may participate in an active transport system such as that which removes certain other basic substances from CSF.

Cerebrospinal-fluid concentrations of nitrazepam in man

The concentrations of nitrazepam in the plasma and cerebrospinal-fluid (CSF) of 38 neurological patients were determined by gas chromatography 2-36 hours after a single 5 mg oral dose. The percentage ratio between the mean CSF and the plasma concentrations increased from 8.0% at 2 hours to 15.6% at 36 hours. This percentage rise was significant (P less than 0.001). The maximum concentration of nitrazepam in the plasma was 36.7 +/- 5.7 ng/ml (at 2 hours) and CSF 3.0 +/- 0.3 ng/ml (at 4 hours). During the beta-phase the half-life of nitrazepam in plasma was about 27 hours and in the CSF markedly longer about 68 hours, indicating a very slow elimination of nitrazepam from the CSF.