High-performance liquid chromatographic assay for cinnarizine in human plasma

The high performance liquid chromatography for the determination of cinnarizine in human plasma is described. The procedure involves liquid-liquid extraction followed by reversed phase high-performance chromatographic analysis with fluorometric detection. The method was validated for accuracy, precision, specificity, linearity, sensitivity, recovery, and stability. No endogenous compounds were found to interfere. The absolute extraction recovery of cinnarizine and clocinizine (internal standard) from plasma samples were 97% and 89%, respectively. The linearity was assessed in the range 1-100 ng/mL. The intra-day and inter-day relative standard deviations were less than 10%, and the accuracy of the assay expressed by bias was in the range 0.14-2.37%. The method was proved to be suitable for human pharmacokinetic studies following single oral dose.

A lipid-based liquid crystalline matrix that provides sustained release and enhanced oral bioavailability for a model poorly water soluble drug in rats

Liquid crystalline phases that are stable in excess water, formed using lipids such as glyceryl monooleate (GMO) and oleyl glycerate (OG), are known to provide a sustained release matrix for poorly water soluble drugs in vitro, yet there has been no report of the use of these materials to impart oral sustained release behaviour in vivo. In the first part of this study, in vitro lipolysis experiments were used to compare the digestibility of GMO with a second structurally related lipid, oleyl glycerate, which was found to be less susceptible to hydrolysis by pancreatic lipase than GMO. Subsequent oral bioavailability studies were conducted in rats, in which a model poorly water soluble drug, cinnarizine (CIN), was administered orally as an aqueous suspension, or as a solution in GMO or OG. In the first bioavailability study, plasma samples were taken over a 30 h period and CIN concentrations determined by HPLC. Plasma CIN concentrations after administration in the GMO formulation were only sustained for a few hours after administration while for the OG formulation, the plasma concentration of cinnarizine was at its highest level 30 h after dosing, and appeared to be increasing. A second study in which CIN was again administered in OG, and plasma samples taken for 120 h, revealed a Tmax for CIN in rats of 36 h and a relative oral bioavailability of 344% when compared to the GMO formulation (117%) and the aqueous suspension formulation (assigned a nominal bioavailability of 100%). The results indicate that lipids that form liquid crystalline structures in excess water, may have application as an oral sustained release delivery system, providing they are not digested rapidly on administration.

Influence of the intermediate digestion phases of common formulation lipids on the absorption of a poorly water‐soluble drug

The influence of different model intestinal phases (modelled on those likely to be produced in vivo after the digestion of commonly used formulation lipids) on the absorption profile of cinnarizine has been studied. Combinations of C8, C12, or C18:1 fatty acid and monoglyceride and simulated endogenous intestinal fluid were formulated to provide examples of liquid (L1), lamellar (L(alpha)), and cubic (C) liquid crystalline phases. Phases containing cinnarizine were dosed intraduodenally and absorption was assessed in an anesthetized rat model. Bile duct ligation was performed to inhibit the effects of digestion/dilution on the phase structure. Absorption from the L(alpha) phases (C8 and C12 lipids) was statistically higher (p < 0.05) than a cinnarizine suspension: however, a statistically significant difference was not observed from the L1 and C phases. The rigid C18:1 C phase showed evidence of providing for sustained drug absorption. Experiments in bile intact rats with the C8 L(alpha) and C18:1 C phase highlighted that the absorption-modifying properties of these phases were influenced by dilution in the endogenous bile milieu, with absorption from L(alpha) phase reducing (possibly through precipitation of solubilized drug) and increasing in the case of the C18:1 C phase, possibly through the coexistence of L1 and C upon dilution permitting more efficient transfer of solubilized drug.

A novel cubic phase of medium chain lipid origin for the delivery of poorly water soluble drugs

The existence of a novel cubic liquid crystalline phase is described within the pseudo-ternary system comprising lauric acid, monolaurin, and simulated endogenous intestinal fluid (SEIF). This phase behaviour has been characterized using cross-polarizing light microscopy (CPLM), and the structure of the cubic phase identified by small angle X-ray scattering (SAXS). The presence of the cubic phase was found to be temperature sensitive within the 20-37 degrees C range making it putative material for in situ gelation purposes. The cubic phase was shown to have a high capacity to solubilise a model poorly water-soluble drug, cinnarizine, and initial in vitro release data highlight the potential of this phase to provide sustained release. Absorption of cinnarizine from the cubic phase was studied in an unconscious rat model via duodenal administration and blood sampling via the carotid artery. The rate of absorption was significantly reduced when compared to a simple suspension formulation, a likely combination of retarded erosion of the cubic phase together with hindered drug release from the cubic matrix. The results of this study suggest that this cubic phase may potentially be of benefit in the delivery of poorly water-soluble compounds due to its high loading capacity and potential for sustained release. The ability to manipulate this system using temperature may warrant further interest in delivery applications via other routes of administration.

LC and TLC determination of cinnarizine in pharmaceutical preparations and serum

New high performance liquid chromatography (HPLC) and thin layer densitometry (TLC) methods are developed for quantification of cinnarizine in dosage forms in the presence of its photo-degradation products and related substances and in the presence of its metabolites in serum. Mobile phases consisting of benzene-methanol-formic acid (80:17:3) and methanol-acetate buffer of pH 4 (70:30) are satisfactorily used for resolution of cinnarizine from associated substances by TLC and HPLC techniques, respectively. The lower detection limits are 16 and 10 ng microl(-1) of cinnarizine with standard deviations of 1.3 and 1.1% with TLC and HPLC, respectively. The methods are used for assessment of drug purity, stability, bioavailability, bioequivalency and tablet dissolution rate. Four cinnarizine related substances and six drug degradation products are isolated and identified by infrared and mass spectrometry. The results obtained by both techniques are in good agreement and offer the advantages of reproducibility and accuracy.

Pharmacokinetics of cinnarizine after single and multiple dosing in healthy volunteers

Cinnarizine (CAS 298-57-7) pharmacokinetics were studied after single and repetitive dosing in healthy volunteers. Six young male healthy subjects received a 75 mg tablet and blood samples were drawn for 72 h after medication. Cinnarizine plasma levels were determined by gas chromatography. Cmax was 275 +/- 36 ng/ml, tmax 3.0 +/- 0.5 h, AUC extrapolated to infinity 4437 +/- 948 ng.h/ml and terminal half-life 23.6 +/- 3.2 h. After a 2-week washout period, 5 of these subjects received 75 mg tablets b.i.d. for 15 days. After the administration of doses 1 and 29, blood samples were drawn for 12 h and cinnarizine plasma levels were measured. Cinnarizine accumulated under these conditions. At steady state (dose 29), the observed accumulation factor was 2.79 +/- 0.23, being not significantly different from that predicted with the terminal half-life obtained from single dose data, which was 3.37 +/- 0.37. AUC0-12 for dose 29 was 5074 +/- 1021 ng.h/ml, being not significantly different from the AUC extrapolated to infinity obtained with the single dose. Results indicate that cinnarizine accumulates with repetitive dosing due to its pharmacokinetic properties.

Effect of betahistine dihydrochloride compared with cinnarizine on induced vestibular nystagmus

The effect of betahistine compared with cinnarizine on induced vestibular nystagmus was evaluated using a rotating chair, in 6 healthy volunteers. The subjects underwent a slow acceleration followed by a sudden stop. Electronystagmograph tracings were taken initially as pretreatment control values, and after betahistine 8 mg t.i.d. and cinnarizine 15 mg t.i.d. had been taken. The duration of nystagmus and average eye speed were measured. No difference was recorded in either parameter between the pretreatment rotation and that following betahistine (P greater than 0.05). A significant difference (P less than 0.05) was seen in the duration of nystagmus during initial acceleration, and in average eye speed following the sudden stop after treatment with cinnarizine.

The value of flunarizine in the treatment of tinnitus

The suppressive effect of flunarizine on tinnitus was assessed in a double-blind trial in 50 patients with tinnitus due to various causes. The duration of the study was 6 weeks. Serum levels of the drug were determined. The patient's subjective assessment of the effect was taken as criterion for the evaluation; objective tests were found to be unsuitable for this purpose. Ten of the patients suffered from dizziness as a secondary complaint. For the group as a whole, there was no difference between flunarizine and the placebo with respect to the effect on tinnitus, but in the 10 patients with dizziness as well there was a significant difference in favor of the drug. Conclusions cannot be drawn as to the reason for this divergence, because the number of patients was too small.

[Flunarizine in drug-resistant epilepsies of childhood and adolescence]

Therapeutic effects of flunarizine have been studied on 26 patients, aged from 9 months to 17 years, suffering for epilepsies resistant to common anticonvulsant treatment, despite proper plasmatic levels of drugs. All the cases were monitored with monthly clinical and EEG controls, neuropsychological evaluations and monitoring antiepileptic drugs plasmatic levels. At first, a study was performed on an intra-patient basis: after a basal observation during two months, an open clinical trial was started, using for three months flunarizine 5 mg a day in patients weighing over 10 kg, and 5 mg every two days in children weighing less than 10 kg. Later on, a simple blind clinical trial has been performed on 16 patients, using flunarizine or placebo for three months. The results, obtained in resistant epilepsy of children and adolescent, showed that flunarizine induced in 47.6% of cases a significant reduction of critical (stroke) frequency and intensity, together with normalization of sleeping-waking rhythm, and amelioration of attention performances (vigilance, reactivity, environmental participation). The only side-effect, noticed in 23.8% of cases, was a light diurnal sleepiness, spontaneously regressing after a few days of treatment.

Open dose-ranging trial of flunarizine as add-on therapy in epilepsy

A double-blind placebo-controlled crossover trial of flunarizine as add-on treatment in therapy-resistant epilepsy offered significant evidence of efficacy, but the plasma levels of flunarizine were lower than anticipated, probably due to induction of liver enzymes by comedication. An open dose-ranging trial was therefore undertaken to investigate the relationships among dose, efficacy, side effects, and blood level. With basal medication held constant, flunarizine was added at 3-month intervals in increasing doses of 0, 10, 15, 20, and 25 mg daily, or until side effects occurred or marked seizure reduction was obtained. Forty-seven patients completed the trial; all were adults with therapy-resistant epilepsy who had at least 3 seizures per month. All had complex partial seizures, with additional types in 20. Sixteen patients showed a 50% and 24 a 25% reduction of seizure incidence on flunarizine; 6 and 7, respectively, showed a corresponding increase. The greatest seizure reduction, when observed, occurred generally at a daily dose of 15-20 mg. Side effects, chiefly drowsiness and weight gain, increased markedly between 15 and 20 mg daily. Flunarizine administration produced no change in serum levels of comedication, but flunarizine levels were lower in patients taking more than one other drug. Seizure reduction was obtained most consistently in patients with secondary generalized epilepsy or neurologic deficits. The findings confirm the antiepileptic action of flunarizine in humans and justify further trials.

Hormonal and metabolic changes induced by flunarizine therapy: preliminary results

The effect of 30-days of flunarizine (5 mg/day) therapy on pituitary, B-pancreatic, gonadic and adrenal function was studied in five adolescents with common migraine. Baseline concentration of growth hormone was significantly reduced after flunarizine therapy. The response of prolactin to thyrotrophin-releasing hormone was significantly increased after flunarizine therapy. The percentages of HbA1 and HbA1c were significantly higher after flunarizine therapy. The drug had no apparent effect on gonadic and adrenal function. Further studies are needed to confirm the effect of flunarizine on the hypothalamus-pituitary axis and glucose tolerance.

Determination of the calcium antagonist flunarizine in biological fluids by gas-liquid chromatography

A method is described for the quantitation of flunarizine in biological fluids including plasma, urine, milk, fecal and tissue homogenates using the analogue cinnarizine as the internal standard. As little as 1.5 ng of flunarizine per ml of plasma can be accurately quantitated, this being achieved by the combination of a selective extraction procedure and a nitrogen detector. The method has been used to determine the concentration of flunarizine in biological fluids in support of human and animal pharmacokinetic studies.

Sensitive gas chromatographic method for the determination of cinnarizine and flunarizine in biological samples

A sensitive method has been developed for the determination of the vasoactive compounds cinnarizine and flunarizine in plasma, urine and milk samples from man and animals. The procedure involves the extraction of the drugs and their internal standard from the biological samples at alkaline pH, back-extraction into sulphuric acid and re-extraction into the organic phase (heptane-isoamyl alcohol). The analyses were carried out by gas chromatography using a nitrogen-selective thermionic specific detector. The detection limit was 0.5 ng/ml of biological fluid and extraction recoveries were sufficiently high (87-94%). The method was applied to plasma samples from bioavailability studies of both cinnarizine and flunarizine in healthy volunteers, and to plasma, urine and milk samples from flunarizine-treated dogs.

Plasma cinnarizine levels resulting from oral administration as capsule or tablet formulation investigated by gas-liquid chromatography

1 A gas chromatographic assay for the estimation of therapeutic concentrations of cinnarizine in plasma is described. 2 Cinnarizine (75 mg) was administered orally to twelve healthy subjects in the form of capsules and tablets on two separate occasions. No difference was found in the plasma levels or absorption of cinnarizine from these formulations. 3 The mean plasma elimination half-life of cinnarizine was 3.24 h.