About Pharmaceutical semi-solid composition of isotretinoin

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An oral pharmaceutical composition of isotretinoin containing at least two lipidic excipients, one of them being hydrophilic (i.e. having an HLP value superior or equal to 10), the other being an oily vehicle.

The present invention relates to an oral pharmaceutical composition of isotretinoin containing at least two excipients, one of them being hydrophilic (i.e. having an HLB value superior or equal to 10), the other being an oily vehicle.

Isotretinoin (13-cis retinoic acid or 13-cis vitamine A), its isomers and some of its analogs are widely known to have a therapeutical activity in the treatment of several severe skin disorders like cystic acne, hypertrophic lupus erythematosus, keratinization disorders. Some evidences have also been brought about the activity of isotretinoin in basal cell carcinoma and squamous cell carcinoma.

Unfortunately, isotretinoin is also a highly toxic drug. Indeed, although isotretinoin, which is a cis derivative, is known to be less toxic than all trans vitamine A derivatives, side effects resulting from its use such as headache, vomiting, irritation of mucosa and liver toxicity, occur frequently. Furthermore, isotretinoin is known to be highly teratogenic in both animals and humans.

In order to well understand the interest of this invention, it is important to briefly summarize the physico-chemical pharmacokinetic study properties.

Isotretinoin is a reddish-orange powder. It is decomposed in presence of light and atmospheric oxygen. Isotretinoin is very poorly soluble in water what mades its bioavailability quite low after an oral intake (25% in fasted conditions and 40% in fed conditions). The maximum concentration (Cmax) is reached after 2-4 hours, while the (Cmax) of the active metabolite, 4-oxo-isotretinoin is reached after 6 hours. The elimination half-life of isotretinoin is of 7 to 37 hours while the half life (t1/2) of the active metabolite is of 11 to 50 hours. The steady-state concentrations of isotretinoin are reached after 1 week of treatment.

Very few publications and/or patents about the pharmaceutical formulation of isotretinoin are available. The drug is available on most markets under the form of a soft gelatine capsule containing a fatty liquid formulation of isotretinoin.

The US patent 4,464,394 describing for the first time the therapeutical use of isotretinoin also describes briefly some possibilities of compositions including it. It involves the use of one antioxidant agent and of one carrier like lactose, starches or polyethyleneglycols.

The EP patent 0184942 describes more specific compositions of isotretinoin involving the use of one antioxidant, one chelating agent, one pharmaceutical carrier and one suspending agent. The composition obtained is stable during time.

The US patent 4,545,977 relates to improved compositions of isotretinoin wherein taurine is associated with isotretinoin to reduce the side effects thereof.

The US patent 5,716,928 describes a method for increasing bioavailability and for reducing inter and intra individual variability of an orally administered hydrophobic pharmaceutical compound, which comprises orally administering the pharmaceutical compound with an essential oil or essential oil component in an amount sufficient to provide greater bioavailability of the active ingredient.

The US patent 6,028,054 relates to a method for increasing bioavailability of an orally administered hydrophobic pharmaceutical compound to human, which comprises orally administering the pharmaceutical compound concurrently with a bioenhancer comprising an inhibitor of e-cytochrome P450 3A enzyme or an inhibitor of P-glycoprotein mediated membrane transport.

The US patent 5,993,858 describes a self microemulsifying excipient formulation for increasing the bioavailability of a drug which includes an emulsion including an oil or other lipid material, a surfactant and an hydrophilic co-surfactant.

What is not described is a composition of isotretinoin containing at least two lipid materials, one of them being hydrophilic. The said composition may be a suspension, emulsion or microemulsion.

The advent of high throughput combinatorial chemistry and efficient receptor based in vitro activity screen has resulted in molecules with poor physicochemical (ex : dissolution) properties for absorption across the gastro-intestinal tract, like isotretinoin.

It is increasingly being recognized by the pharmaceutical industry that for these molecules drug delivery systems play an important role for improving oral bioavailability.

Although the process of passive diffusion is responsible for absorption of non ionized lipophilic molecules via the transcellular pathway, specialized absorption mechanisms, first-pass metabolisms and efflux systems at the gastrointestinal wall appear to play a major role for lack of absorption and poor bioavailability for some molecules.

Isotretinoin is characterized by a low absolute bioavailability and a high inter and intra individual variability. Isotretinoin also presents a wide range of side effects among which some are severe (ocular, skin anemia, hepatic,...). It is consequently of a particular interest to dispose of a reliable, stable and highly bioavailable formulation of isotretinoin.

It has been found that a semi-solid dosage form containing isotretinoin was advantageous for obtaining a good bioavailability of the isotretinoin. A semi-solid dosage form containing isotretinoin is a form in which isotretoin is mixed with suitable melted excipients. The molten mix is then filled for example into hard gelatine capsules or other pharmaceutically acceptable capsules. At ambient temperature (temperature for example of less than 20°C), the content of the capsule is solid while at temperature higher than 20°C (for example at temperature greater or equal to 30°C, advantageously greater or equal to 35°C, preferably substantially at body temperature +/- 37°C), it is liquid or semi-solid (paste). The isotretinoin may be solubilized in the mix of excipients or partially solubilized. The active ingredient may also be formulated as a suspension, emulsion or microemulsion. Various lipidic excipients are available to the formulator to obtain a semi-solid formulation. Excipients compatible with hard gelatin capsule shells are : lipophilic liquid vehicles (refined speciality oils, medium-chain triglycerides and related esters), semi-solid lipophilic vehicles, solubilizing agents, emulsifying agents and absorption enhancers. The classification of fatty excipients is based on the hydrophilicity or lipophilicity of the excipients, characterized by the hydrophilic/lipophilic balance value (HLB). Examples of lipophilic excipients are vegetable oils (peanut oil, olive oil, soyabean oil,...), fatty acids (stearic acid, palmitic acid,...), fatty alcohols, ... Examples of hydrophilic excipients are polyethyleneglycol (PEG) with a molecular weight superior to 3,000. Examples of amphiphilic (= presenting lipophilic and hydrophilic properties) excipients are Poloxamers, Lecithin, PEG esters (Gelucire®),... .

The advantages of the semi-solid formulations of the invention are multiple for isotretinoin: protection of the active ingredient from air and humidity, possibility of increasing the dissolution rate of the molecule and hence of the bioavailability, diminution of the risk of contamination of the operator, diminution of the risk of cross contamination, no possibility of demixing under the effect of vibrational mixing during manufacturing process, facility of the production process. The choice of the nature of the formulation of course influenced the stability of the pharmaceutical form and the bioavailability of the isotretoin contained in it. Generally, a maximum bioavailability is achieved by preparing and keeping the drug in the amorphous/solubilized state in a solid dispersion or in a lipid-based formulation. For these systems, the barrier we are avoiding is the compound « washing-out » of solution to a large extent into a insoluble crystalline form during the dissolution/release step in vivo.

These systems may consist of suspension, emulsion, microemulsion, self-emulsifying drug delivery systems (SEDDS®) or self-emulsifying microemulsion drug delivery system (SMEDDS®).

Microemulsions have the added advantage over suspensions such as emulsions and dispersions since thermodynamically they are more stable, that they can be manufactured with little energy input and have generally a longer shelf-life. Nevertheless, a microemulsion formulation is not a guarantee of higher bioavailability in comparison to suspension a described hereafter.

The formation of oil-in-water (O/W) and water-in-oil (W/O) microemulsions usually involves a combination of 3-5 basic compounds i.e. oil, surfactant, cosurfactant, water and electrolytes. The challenge is to select for a particular application oil(s) and surfactant(s) that are acceptable from a toxicological perspective and that allow to obtain a high bioavailability of the drug, i.e isotretoin.

The assessment of the quality of semi-solid lipid based formulations is quite difficult since the in vitro dissolution test is of little help. Indeed, the in vitro/in vivo correlation between dissolution and bioavailability is very poor for this kind of formulations. Other analytical tools are available to the formulator to try to predict the in vivo bioavailability of isotretinoin from various formulations like CACO-2 cells model, the assessment of the percentage of drug dissolved in the formulation, differential scanning calorimetry, microscopy,...

Nevertheless, none of them present a guarantee of in vitro / in vivo correlation and ultimately only pharmacokinetic studies on human subjects are reliable to assess the bioavailabiltiy of the drug.