Monitoring of L-dopa concentrations in Parkinson's disease.

Although it is the treatment of choice in the management of idiopathic Parkinson's disease, l-DOPA (LD) shows a decline in its efficacy after years of prolonged use, with the appearance of severe motor disturbances. These complications have been interpreted on pharmacokinetic and pharmacodynamic grounds. The main pharmacokinetic reason is considered to be the decreased capacity in LD activation to dopamine along with reduction of its storage ability in the nigrostriatal terminals, as a result of disease progression. At this stage the LD action in the extrapyramidal system is thought to be closely dependent on its synaptic cleft concentrations, being directly related to those in the systemic circulation and to the events possibly perturbing them. Therapeutic drug monitoring might be useful to explain these modifications in relation to the clinical effect and even to possible problems in transport competition and so to define the LD dosage regimen. Recently LD threshold concentrations have been suggested by means of sophisticated pharmacokinetic-pharmacodynamic approaches. Unfortunately they do not correspond to real therapeutic ranges but to levels in a hypothetical effect compartment in no steady-state conditions, due to remarkable LD fluctuations. However they are considered helpful to the functional state interpretation of the nigrostriatal system.

Levodopa and 3-O-methyldopa in cerebrospinal fluid after levodopa-carbidopa association.

Since motor fluctuations in Parkinsonian patients might be, at least in part, explained by an antagonism between levodopa (LD) and its metabolite 3-O-methyldopa (3-OMD) at blood-brain-barrier (BBB), we decided to study LD and 3-OMD plasma and cerebrospinal fluid (CSF) levels in subjects undergoing lumbar puncture for diagnostic purposes. After informed consent, 70 subjects took a tablet of carbidopa-levodopa association (Sinemet or Sinemet-CR) 0.5, 1, 2, 4, 8, 12 h before blood and lumbar cerebrospinal fluid collection. LD and 3-OMD were determined by an HPLC-electrochemical method. The subjects treated with Sinemet-CR had lower LD cerebrospinal fluid concentrations along with lower LD and higher 3-OMD plasma concentrations. This pattern of LD cerebrospinal fluid concentrations may be explained by means of a transport competition between LD and 3-OMD at blood brain barrier level.

Oral gabapentin disposition in patients with epilepsy after a high-protein meal.

PURPOSE: To study the interaction between gabapentin (GBP) and high-protein meals, 12 patients with epilepsy were administered this drug both while in a fasting state and after a high-protein meal. METHODS: After having acquired their informed consent, the patients (suffering from partial complex seizures resistant to other anticonvulsants) were randomly assigned to 2 groups of 6 subjects. Each subject was treated in a fasting state with a single 400 (group A) or 800 (group B) mg GBP oral dose. After 24 h, the GBP dose regimen was repeated, but was given after a high-protein meal. Serum GBP concentrations were measured by LC-Mass at baseline and 0.5, 1, 2, 3, 5, 7, 9, 12, and 24 h. Saliva GBP concentrations were determined at baseline and 2, 4.8, and 12 h. GBP urinary excretion was determined at 0-4, 4-8, and 8-12 h intervals. The following kinetic parameters were calculated: area under the concentration time curve from zero time to 24 h after the dose, AUC 0-24 h; maximal serum concentration, Cmax; time to the maximal serum concentration, Tmax; absorption rate constant, ka; elimination rate constant, beta; elimination half-time, t1/2beta. Student's t test for paired data, with significance assigned at P < 0.05, was used. RESULTS: No statistically significant differences were seen in GBP serum or saliva concentrations or in its urinary excretion (both in A or B group) between fasting and after the high-protein meal. CONCLUSIONS: High-protein meals do not seem to interfere with oral disposition of GBP.

New antiepileptic drugs.

Notwithstanding pharmacokinetics has greatly increased the rational approach to the drug treatment of epilepsies, about 25% of the patients do not respond to the therapy. Therefore, a great effort has been made to discover new antiepileptic drugs effective in refractory seizures. On the basis of increased knowledge of seizure pathophysiology two principal groups of drugs have been developed: the first enhancing brain GABA activity (vigabatrin); the second inhibiting excitatory amino-acids (lamotrigine and felbamate). Oxcarbazepine has the same mechanism of action as carbamazepine, whereas gabapentin's mechanism is still uncertain. The major clinical indications of these new antiepileptic drugs are represented by partial complex seizures. Side effects (mostly regarding the central nervous system) appear mild, and clinical interactions have little importance. The role of therapeutic drug monitoring for these substances is at present not well established.

A case of type I Arnold-Chiari malformation of anomalous onset.

A case of type I Arnold-Chiari malformation, with onset of diplopia, without associated medullar alteration, is presented. The symptomatology remained unique and had transitory presentation for many years with negative ophthalmic examinations. Attention is drawn to the great variability of the syndrome's presenting symptoms confirming the importance of MR in the diagnostic course and of evoked potentials of the brain stem to follow progress of the illness.

Pharmacokinetic optimisation of tricyclic antidepressant therapy.

Pharmacokinetics has greatly contributed to the elucidation of the variability in clinical response to antidepressants in terms of differences in plasma concentrations due to genetic constitution, age, associated diseases and drug interactions. Despite no general agreement, therapeutic and toxic concentrations have been suggested for some tricyclic antidepressants (TCAs) [amitriptyline, nortriptyline, imipramine, desipramine]. Predictive techniques may be implemented on the basis of which starting TCA dosages may be selected to reach more rapidly those concentrations at which efficacy is more probable. Therapeutic drug monitoring may thereafter assist the clinician in refining the individualisation of the dosage regimen.

Plasma levels of levodopa and its main metabolites in parkinsonian patients after conventional and controlled-release levodopa-carbidopa associations.

The paper reports plasma levels of levodopa (LD), its main metabolites [dopamine, dihydroxyphenylacetic acid, homovanillic acid, 3-O-methyldopa (3-O-MD)] and carbidopa in 14 parkinsonian patients first treated with Sinemet and thereafter with Sinemet-CR4. A good relationship was observed between LD plasma levels and pharmacological effects. While the LD area under the curve increased after Sinemet-CR4, the same was not observed with metabolites, except with 3-O-MD. The experiments in volunteer subjects confirmed the increase in 3-O-MD in plasma after Sinemet-CR4. Higher levels were observed also in the CSF with a reduction of LD concentrations. This seems to corroborate the hypothesis of an interference with LD passage through the blood-brain barrier in humans.

Chlorpromazine disposition in relation to age in children.

The pharmacokinetics of chlorpromazine after intravenous infusion were studied in 25 children. The pharmacokinetic parameters studied are markedly different from those reported for adults. A clear relationship was demonstrated between age, serum terminal half-life (r = 0.75) and systemic clearance (r = -0.43). It appears that the pharmacokinetics of chlorpromazine are more rapid in children than in adults.

Imipramine pharmacokinetics in depressed geriatric patients.

Pharmacokinetics of single dose (25 mg i.m.) of imipramine was studied in geriatric and young adult patients with mood disorders requiring antidepressant treatment. Imipramine and its principal metabolites were determined by means of a high performance liquid chromatography method with electrochemical detection. Serum concentrations analysis was performed according to a bicompartmental open model. A relationship between age and kinetic parameters such as area under the curve, elimination phase constant, half-life and total body clearance was observed. Significant differences were demonstrated between elderly and young adult patients when comparing these parameters. It is concluded that geriatric patients treated with imipramine should receive doses of about 60% of those of young adults.

The pharmacokinetics of tricyclic antidepressant drugs in the elderly.

Antidepressants, especially tricyclic agents (TCAs), are increasingly used in geriatric patients since depression is a common mood disorder in the elderly and the size of elderly population is increasing. Notwithstanding the importance of kinetics to better use of drugs, its study in the elderly (regarding TCAs) is not sufficiently developed. The present paper briefly reviews the available data on amitriptyline, nortriptyline, protriptyline, imipramine, desipramine and clomipramine kinetics in the elderly.

Steady-state serum concentrations of imipramine, its main metabolites and clinical response in primary enuresis.

Thirty-seven children (6-13 years old), receiving a flexible dosage of imipramine (IMI) for nocturnal enuresis, were evaluated. After a mean time of 8.5 +/- 7.0 weeks of therapy, 40.5% no longer wet the bed; 32.4% had a mean benefit of 80%; 27.01% had a negligible response. The best relationship observed was between clinical effect and drug serum concentrations rather than with drug daily dose, the most satisfactory being that with IMI seric values (P = 0.019). Responders (effect higher than 50%) had higher IMI serum concentrations (P less than 0.05) than poor responders. At 3 and 6 months after stopping the drug, over 90% of the responders maintained the maximum response reached during treatment. The side-effects observed were irritability, reduction of appetite, headache, a mild increase of blood pressure.

Double-blind placebo cross-over study of long-acting (chlordesmethyldiazepam) versus short-acting (lorazepam) benzodiazepines in generalized anxiety disorders.

Chlordesmethyldiazepam a long-acting benzodiazepine was compared with lorazepam a short-acting one in a double-blind placebo cross-over study against generalized anxiety disorders. Chlordesmethyldiazepam therapy was more effective than lorazepam. Clinical efficacy, drowsiness and insomnia seem well correlated with pharmacokinetic properties of these two benzodiazepines. These results further support the use of a long-acting benzodiazepine rather than a short-acting one as an anti-anxiety agent.

Pharmacokinetics of benperidol in volunteers after oral administration.

Benperidol in a 4 mg single dose was administered orally to five healthy male volunteers. The drug was rapidly absorbed (tmax = 2.27 +/- 0.57 h) and largely distributed, the volume of distribution being 5.19 +/- 1.99 l.kg-1. Elimination half-life was 7.65 +/- 2.14 h. Urinary excretion represented only a minimal fraction of ingested dose (0.1 +/- 0.007%). Variability of the area under the curve makes a first-pass metabolism a reasonable possibility. Acute dystonias appeared in two subjects.

Electrochemical detection of benperidol in serum for drug monitoring in humans.

A high-pressure liquid chromatographic (HPLC) method for the serum assay of benperidol is described. One ml of serum is required for a single estimation. The method involves a simple and rapid extraction step (BondElut columns), HPLC separation (C8 10-mu column), and electrochemical detection (+0.65 V). Haloperidol is used as internal standard. On the basis of this procedure, recovery (93-97%) and reproducibility (intra-assay and inter-assay coefficients of variation less than 9%) are satisfactory. The detection limit is 0.2 ng/ml of serum. After therapeutic doses, trough serum levels ranged from 3.8 to 12 ng/ml in five patients.

Primidone-carbamazepine interaction: clinical consequences.

A 15-year old boy, suffering from partial complex seizures, was treated with primidone (PR) and carbamazepine (CBZ). In spite of daily doses in the usual range (PR = 12 mg/kg, CBZ = 30 mg/kg), he was not free from seizures and serum levels of CBZ were remarkably low (4.8 micrograms/ml). A good control of seizures was obtained after gradually stopping treatment with PR. This lead to a substantial increase of CBZ serum levels to a decrease of carbamazepine-10, 11-epoxide levels and a 60% reduction in total CBZ clearance.

Orphenadrine serum levels in a poisoned patient.

A patient ingested about 5 g of orphenadrine hydrochloride. He had gastric lavage and oral administration of activated charcoal. The main symptoms were neuropsychiatric in nature. Possible relation between serum levels of the drug and time course of the toxic effects are described.