Epilepsy is a chronic neurological disorder which affects between 0.5% and 1.0% of paediatric population1. It involves recurrent unprovoked seizures and it is the third most frequent neurological disorder, after cerebrovascular disease and dementia2. Typical pharmacological treatment includes antiepileptic drugs (AEDs) that control seizures when they are daily administered3. Unfortunately one fifth of children develop Intractable Childhood Epilepsy4 where seizures became resistant to pharmacological control. Between the AEDs administered, clobazam (CLB) is a 1,5-benzodiazepine (Figure 1) which presents anticonvulsant pharmacological properties5 widely used for adjunctive therapy on epilepsy treatment6. Actually, it is approved for clinical use as an AED in more than one hundred countries1. Also it has been recently approved by The US Food and Drug Administration as add-on therapy for seizures associated with Lennox-Gastaut syndrome7. CLB has been effective against a broad spectrum of seizure types in most patients for both shortterm and long-term treatment8. Even more, CLB resulted useful in refractory seizures control9. Due to its unique chemical structure, in comparison with the traditional 1,4-benzodiazepines, a reduction on its anxiolytic properties and collateral effects is observed1. Its major metabolite in humans is N-desmethylCLB which is pharmacologically active5. CLB is excreted unchanged and as metabolites mainly in the urine.

Figura 1.

Chemical structure of clobazam.

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CLB is a white or almost white crystalline powder which is slightly soluble in water10. It is well absorbed after oral ingestion and it presents a high oral bioavailability. Usually, oral dose recommended for children, between 1 month and 12 years, is between 0.5 and 1.0 mg/kg/day11.

It is currently available as 10 and 20 mg tablets but unfortunately, no suitable liquid formulation for paediatric administration is commercially available12.

The lack of paediatric liquid dosage forms represents a challenge for hospital and community pharmacists. Usually, children require smaller doses than adults which are adjusted by body weight. Thereby solid dosage forms must be fractionated in order to fit paediatric dosages. This practice represents a concern issue because correct dosing must be ensured13. Preparing extemporaneous liquid formulations using tablets is one of the most common practices employed to adjust doses for paediatric patients. More over, children under 7 years old are unable to swallow capsules or tablets. Liquid formulations which are flavored aqueous solutions, syrups, or suspensions, are administered directly into the child’s mouth by drop, spoon, or oral dispenser or incorporated into the child’s food14. General dose volumes are ≤ 5 ml for children under 5 years and ≤ 10 ml for those of 5 years and over15.

Among paediatric pharmacy practice, traditional compounding techniques have become a useful tool in order to develop not commercially available liquid dosage forms16,17. In this context, liquid formulations facilitate oral administration and enhance children treatment adherence. An appropriate design of a liquid dosage form requires not only a comprehensive analysis of chemical and physical considerations of drugs and pharmaceutical excipients but also evaluation of drug stability in the midlong term as well as drug effectiveness, tolerance and formulation safety16.

The purpose of this study was to prepare an optimal paediatric extemporaneous oral liquid CLB suspension from commercially available tablets and pure drug to determine the physical and chemical stability of these products for up to 56 days, stored at 4 and 25 °C. In this way, these formulations allowed to study the compounding techniques versatility on developing liquid CLB dosage forms starting from different sources. In addition to the best of our knowledge, no studies have been published describing physical and chemical stability of an oral CLB suspension.

Preliminary studies investigated the development of CLB solution with a high concentration of co-solvent such as propylene-glycol (60 %v/v) and sorbitol 70% solution (30 %v/v), in order to enhance CLB aqueous solubility. However, CLB extemporaneous solution presented low physical stability and drug remaining in solution only for 7 days. Also, formulations with lower concentration of propylene-glycol presented drug precipitation at 48 h.

Therefore, an aqueous suspension results a useful dosage form for administering a water-poorly soluble or aqueous-chemical unstable drug. This is the main reason why suspension development appears as an excellent approach for CLB liquid formulation containing a quantity of drug in an acceptable volume13,18-21. Also, suspensions could mask CLB unpleasant taste improving paediatric formulation acceptance and treatment adherence.

The figure 2 shows the chromatograms corresponding to the suspension without CLB (A), CLB standard solution (50 µg/ml) (B), CLB subjected to acid degradation (C), CLB subjected to alkaline degradation (D) and CLB subjected to oxidation (E). The CLB retention time was 3.48 min. The relative error and the CV (coefficient of variation) were lower than 10%. It was shown that the analytical method was able to separate the CLB peak of the degradations peaks and there was no interference between CLB standard, degradation products and suspension control retention times.

Figura 2.

Chromatograms showing to the suspension without CLB (A), CLB standard (B), CLB subjected to acid degradation (C). CLB subjected to alkaline degradation (D) and CLB subjected to oxidation (E).

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To assess the CLB stability in paedriatic oral formulations, extemporaneous oral liquid CLB suspensions from commercially available tablets and pure drug were assayed.

These suspensions were prepared with excipients commonly used in paediatric formulations22 and they were stored at two different temperatures (4 and 25 °C) for 56 days. In both cases, suspensions were easily re-dispersed after simple hand-shaking (30 seconds) and pH values did not show an important variation along the as-say (Table 2). However, the Vs increased between 0 and 56 days, for both storage temperatures (Table 3). Notice that formulations stored at 4 °C showed lower Vs values than their counterparts stored at 25 °C for 28 and 56 days.

Figure 3 shows the dynamic viscosity as a function of the rotational speed, for samples A and B. Both, the upward and downward curves, presented identical pathways which suggested a pseudoplastic flow without thixotropy. Also, a difference could be observed between formulation A and B viscosity values. Formulation B showed a higher viscosity values than formulation A.

Figura 3.

Viscosity of CLB suspensions prepared from pure drug (A) and commercially available tablets (B).

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Formulation A showed an increase on viscosity values after 28 and 56 days under refrigerated conditions (4 °C). However, the samples viscosity was reduced when the storage was perform at 25 °C (Table 4). A similar trend was followed by formulation B. Nevertheless, the viscosity variation at 4 °C was less marked and values remain almost unchanged.

According to the chemical characterization, CLB stability was followed by HPLC. Table 5 shows the initial CLB concentration remaining percentage up to 56 days. Encouraging results were obtained for both formulations as to CLB chemical stability. Formulations (A and B) presented a CLB remaining percentage above 98% for both storage conditions (4 and 25 °C).

The morphological characterization of the suspended CLB particles is showed on figure 4. Notice the presence of irregular CLB particles and the higher amount of suspended particles in formulation B (figure 4B).

Figura 4.

Microphotographs of CLB suspensions prepared from pure drug (A) and commercially available tablets (B). Scale bar: 17 pm.

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The aim of the present study was to develop an optimal oral liquid CLB suspension in order to enhance physical-chemical stability of the drug and paediatric patient acceptance.

As it is well known, suspensions are thermodynamic unstable systems. Therefore, suspended particles would sediment at a certain sedimentation velocity. That is the main reason why they have to be shaken before use, to ensure content uniformity19. According with the Stocks Law23, changes on viscosity values could modify sedimentation velocity of the suspended particles. Generally, suspending vehicles are used to maintain dispersed particles homogeneously distributed in the formulation by keeping an appropriate viscosity. Our formulations presented a pseudoplastic flow because the hydrocolloid used as suspending agent was CMC sodium which imparts nonNewtonian properties to the suspension. This is very important because a pseudoplastic dispersion media could support two processes: 1) retard the sedimentation of small particles, as their apparent viscosities increase under the small stresses associated with sedimentation, and 2) the medium could undergo structural breakdown under the higher stresses involved in shaking and pouring24.

Although the suspending vehicule content was reduced from 1 to 0.7 %w/v. Formulation B showed a higher viscosity values than A, probably due to the amount of pharmaceutical excipients presented on commercial tablets.

As to our results, refrigerated storage conditions (4 °C) produced a slight increase on formulation viscosity leading to a decrement on sedimentation velocity of the suspended particles. Cancela et al25 observed that the viscosity of suspensions containing CMC sodium decreases when the temperature increases. This behaviour agrees with our results. Therefore, Vs values at 4 °C resulted smaller than those for samples storage at room controlled temperature for a period of 56 days.

One of the main objectives of the present work was to investigate CLB chemical stability under different storage conditions. Both kinds of formulations (A and B) demonstrated an acceptable drug chemical stability where CLB content remain above 98% at room controlled temperature and refrigerator temperature for a period of 56 days.

As to the microscopic aspect of the samples, those prepared from commercially available tablets present a higher amount of suspended particles due to the presence of water-insoluble pharmaceutical additives in the

CLB tablets. Nevertheless, the same morphology of CLB particles was observed for both kinds of formulations (Figure 4).

In conclusion, paediatric oral liquid CLB suspensions presented an adequate physical stability in order to keep the CLB particles homogeneously distributed in the formulation. The adequate chemical CLB stability under refrigerated and room controlled temperature conditions are of real importance, since CLB suspensions could easily be distributed and storage at a paediatric hospital without any special storage conditions.

The authors acknowledge the financial support for this work provided by UBACyT 2011-2014 (Grant 20020100300088).