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An oral press-coated tablet was developed by means of direct compression to achieve the time-controlled disintegrating or rupturing function with a distinct predetermined lag time. This press-coated tablet containing sodium diclofenac in the inner core was formulated with an outer shell by different weight ratios of hydrophobic polymer of micronized ethylcellulose (EC) powder and hydrophilic excipients such as spray-dried lactose (SDL) or hydroxypropyl methylcellulose (HPMC). The effect of the formulation of an outer shell comprising both hydrophobic polymer and hydrophilic excipients on the time lag of drug release was investigated. The release profile of the press-coated tablet exhibited a time period without drug release (time lag) followed by a rapid and complete release phase, in which the outer shell ruptured or broke into 2 halves. The lag phase was markedly dependent on the weight ratios of EC/SDL or EC/HPMC in the outer shell. Different time lags of the press-coated tablets from 1.0 to 16.3 hours could be modulated by changing the type and amount of the excipients. A semilogarithmic plot of the time lag of the tablet against the weight ratios of EC/SDL or EC/HPMC in the outer shell demonstrated a good linear relationship, with r = 0.976 and r = 0.982, respectively. The predetermined time lag prior to the drug release from a presscoated tablet prepared by using a micronized EC as a retarding coating shell can be adequately scheduled with the addition of hydrophilic excipients according to the time or site requirements.

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The dry-coated tablet with optimal lag time was designed to simulate the dosing time of drug administration according to the physiological needs. Different compositions of ethylcellulose (EC) powder with a coarse particle (167.5 µm) and several fine particles (<6 µm), respectively, were mixed to formulate the whole layer of the outer shell of dry-coated tablets. The formulations containing different weight ratios of coarse/fine particles of EC powders or 167.5 µm EC powder/excipient in the upper layer of the outer shell to influence the release behavior of sodium diclofenac from dry-coated tablet were also explored. The results indicate that sodium diclofenac released from all the dry-coated tablets exhibited an initial lag period, followed by a stage of rapid drug release. When the mixture of the coarse/fine particles of EC powders was incorporated into the whole layer, the lag time was almost the same. The outer shell broke into 2 halves to make a rapid drug release after the lag time, which belonged to the time-controlled disruption of release mechanism. When the lower layer in the outer shell was composed of 167.5 µm EC powder and the upper layer was formulated by mixing different weight ratios of 167.5 µm and 6 µm of EC powders, the drug release also exhibited a time-controlled disruption behavior. Its lag time might be freely modulated, depending on the amount of 6 µm EC powder added. Once different excipients were respectively incorporated into the upper layer of the outer shell, different release mechanisms were observed as follows: time-controlled explosion for Explotab, disruption for Avicel and spray-dried lactose, erosion for dibasic calcium phosphate anhydrate, and sigmoidal profile for hydroxypropyl methylcellulose.