Slow release compositions

Details Slow release compositions Slow release compositions

1993-04-21

1995-05-16

Robinson, Allen J.

Drug, bio-affecting and body treating compositions

Inorganic active ingredient containing

Alkali metal or alkaline earth containing

424617, 424482, 424682, A61K 3300, A61K 3324, A61K 3306, A61K 932

Patent

active

054158788

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to slow (or extended) release compositions which release metal ions into their surrounding environment over an extended period of time. A preferred embodiment of the invention relates to slow release orally administered pharmaceutical or veterinary compositions for releasing monovalent metal ions to a human or animal, especially compositions containing lithium ions.
Controlled release drug delivery systems are designed to achieve a prolonged therapeutic effect by releasing active ingredient into their surroundings over an extended period of time. The use of sustained release compositions allows optimisation of delivery of the active ingredient to the site of absorption and to achieve availability of the active ingredient at its site of action. Controlled release systems are of particular value where the active ingredient is to be supplied over an extended period, for instance during long term, continuous treatment, such as for treatment of nervous disorders such as mania and depression.
Most controlled release systems release active ingredient at a rate which is not zero-order, that is the rate of release changes over time. Usually the rate of release gradually decreases as the time from administration increases. This tends to provide a level of circulating active ingredient in the body which is not constant, which is undesirable. Attempts have been made to provide sustained release compositions with zero order release characteristics. Osmotic pump devices are intended to give zero order rate characteristics but in practice the rate of release of active ingredient reduces as time goes on. Tablets have been provided with complicated shapes, for instance of hollow cylindrical shape, in order that their surface area remains substantially constant throughout their dissolution, but in practice such compositions do not give the desired zero-order release characteristics.
Lithium ions have long been used in the prophylaxis and treatment of manic depressive illness. Lithium has also been used to augment the anti-depressant effect of other anti-depressants and to treat particularly types of headaches. It is generally used in oral dosage forms, for instance comprising lithium carbonate in capsule or tablet form, or more rarely in syrup form. A lithium carbonate extended release tablet is available commercially. It is important that the concentration of lithium in the serum is maintained below toxic levels, which can be very close to therapeutic levels. Equally, particularly during manic episodes, the serum concentration should be maintained at levels sufficiently high for it to be of therapeutic value. An improved form of lithium-containing composition which satisfies these requirements is desirable.


Brief Description of the Drawings

FIG. 1 shows the cumulative amount of lithium released from tablets;
FIG. 2 shows the release of lithium at different heating temperatures; and
FIG. 3 shows the release of lithium at different heating periods.
According to the present invention there is provided an extended release composition comprising a compound of the formula I and 1 when M is di-valent and X is a group IVa element.
M is generally a mono-valent metal ion, as such ions are releasable at a satisfactory rate from the composition. Under some circumstances, for instance where a slow rate of release is desired and where the composition releases the ion over a very long period, di-valent metal ions may be suitable, for instance of zinc, magnesium, copper (11) or manganese. Mono-valent metal ions are for instance copper (1), or more usually alkali metal ions, for instance lithium, sodium or potassium. The invention is of particular value for compounds where M is lithium.
Although X may be any group IVa element, it is most usually the most common of these, namely titanium. The invention may, however, also be of value for compounds where X is hafnium or zirconium.
The compositions allow sustained release of M.sup.(2
)+ ions into surrounding, aqueous environments. The inventors have found that

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