Release from or through a Wax Matrix System. VI. Analysis and Prediction of the Entire Release Process of the Wax Matrix Tablet

Modulation of release mechanisms of methylene blue (MB) monomers and dimers from silica-MB@shellac synthesized by antisolvent crystallization

Release behaviors of drugs from drug deliveries are crucial for the enhancement of therapy efficiency, reduction of toxicity and patient compliance. Herein, antisolvent crystallization is employed to coat methlyene blue (MB)-loaded silica by shellac precipitation (silica-MB@shellac), which is simultaneously induced by outward diffusion of H⁺ ions from particular silica-MB. The encapsulation of shellac shell on silica-MB modulates the aggregation state of MB, which endows silica-MB@shellac a decreased MB's thermal stability, enhanced photoluminescence intensity, improved stability against in vitro reduction by ascorbic acid and retained photodynamic therapy activity. From the absorbance of MB supernatant obtained during incubation, the concentrations of MB monomers and dimers are determined via a non-linear regression analysis to investigate the influence of shellac coating on MB's release mechanisms from silica-MB@shellac. According to the simulated models, small diffusion constants of MB are caused by limited diffusion through shellac shells with high compaction degrees. These are observed for samples synthesized under high supersaturation degree during antisolvent crystallization. High degree of supersaturation is achieved through increasing shellac concentration, additive amount and dropping rate of antisolvent, as well as decreasing pH values of aqueous buffers as antisolvent. Furthermore, a combined mechanism of Fickian diffusion and Case-IΙ relaxation is proposed to describe the release behaviors of MB monomer and dimers from silica-MB@shellac. Therefore, this work may shed light on the encapsulation method of polymer on drug-loaded powders and the control of aggregation states of photosensitizers to promote the photoluminescence intensity, photodynamic therapy efficiency and controlled release behaviors.

An update on central nervous system stimulant formulations in children and adolescents with attention-deficit/hyperactivity disorder

OBJECTIVE

To review recent literature on the different stimulant preparations regarding efficacy and safety in children and adolescents with attention-deficit/hyperactivity disorder (ADHD) and describe advantages and disadvantages of the many available dosage formulations.

DATA SOURCES

Literature retrieval was performed through PubMed/MEDLINE (2005-December 2008) using the terms methylphenidate, amphetamines, central nervous system stimulants, and attention-deficit/hyperactivity disorder. In addition, reference citations from publications identified were reviewed and drug manufacturers were contacted for any possible additional references.

STUDY SELECTION AND DATA EXTRACTION

Double-blind clinical trials found using the search criteria listed above were included for review. Open-label studies and studies prior to 2005 were included if no double-blind trials were published for that formulation within the time period reviewed.

DATA SYNTHESIS

The literature reviewed here demonstrates the efficacy and safety of stimulant medications in children and adolescents with ADHD. However, there are 19 different formulations of stimulants, leading to confusion and errors in prescribing and dispensing of these drugs. Knowing and understanding the advantages and disadvantages of the different formulations can lead to individualized treatment. Formulations like Concerta, Focalin-XR, Adderall-XR, and Vyvanse provide the convenience of once-daily dosing. Each of these provides varying amount of stimulants at different times of the day. Vyvanse has a unique delivery system that may lower the risk of patients abusing their medication. Daytrana gives patients more control over their dosing by being able to choose when the patch is removed; it is also a feasible alternative for children who cannot swallow pills. For patients who cannot swallow tablets or capsules, the capsules of Focalin-XR, Adderall-XR, Metadate-CD, and Ritalin-LA can be opened and sprinkled on applesauce.

CONCLUSIONS

Stimulants are effective medications to treat the symptoms of ADHD. The multiple available dosage forms allow for individualization of treatment.