## 1 Introduction  
Semi-solid formulations represent one of the most commonly prescribed compounding drug substances in Poland [1]. Similarly to all other medical products, they should fulfil some specific requirements of stability and quality, during their use by a patient. These parameters are dependent on, among others, the type and quality of the utilized raw materials, drug substances manufacturing technique, as well as appropriate storing and application of the medical product. In the compounding practice, various types of ointments can be encountered that represent multiphase formulations, in which an active substance is disintegrated, suspended or dissolved in the base. In particular, suspension-type ointments are characterized by the highest stability, compared to some other dispersive systems [2]. In such formulations, particle size cannot exceed 90 \(\upmu\)m, so the introduction of an active substance into the base often requires its proper grinding, which can be achieved using a levigation [3]. The grinding process is facilitated by the addition of small amounts of a levigating liquid (_e.g._, liquid paraffin, glycerol, or melted base), which wets the ground solid particles and thus facilitates even mixing with the base and prevents possible secondary reaggregation. It is also acceptable to use, instead of the levigating liquid, some small amounts of base, considering that it is plastic. In addition, applied excipients--and in particular, a base--have a crucial impact on the stability of the manufactured compounding drug substances. During storage, hydrophilic bases are often at risk of a gradual loss of solvents that can influence changes in the consistency of the formulation and may lead to the precipitation of crystals of the active pharmaceutical ingredient (API). Lipophilic bases are sensitive to oxidation, particularly the ones that contain fats with unsaturated carbon bonds. Pentravan(r) as a hydrophilic base is a new cream-like basis of emulsion type (oil-in-water, o/w) that has transdermal properties, due to the presence of liposomes [4, 5]. In addition, relatively new hydrophilic bases include Fitalite(tm)--based on a hydrogel structure [6], and Nourivan(tm) Antiox--which is a cream-like base, containing emulsifiers, type o/w, and emollients [7]. Lekobaza LUX is a lipophilic base, based on oleogel [1]. Eucerine is an ointment base that is most often used in compounding formulations in Poland, due to its absorptive properties. It contains an emulsifier of the water in oil (w/o) type and creates stable emulsions after hydration [8]. In Monography of Polish National Pharmacopeia (FP) XII, this base is differentiated into Eucerin Ointment I, which contains alcohols from lanoline, and Eucerin Ointment II, which is a cholesterol-cethyl ointment [9]. Benzocaine is a local anaesthetic used in the treatment of pain and belongs to the ester class of local anaesthetics [10]. Its mechanism of action is shown in Figure 1. The interactions of the nonionized and ionized forms of benzoaine are associated with blocking the permeation of sodium ions within the voltage-gated sodium channels [11]. Nerve conduction arrest is easier in nerve fibres without a myelin sheath than in fibres with a myelin sheath. First, the sensation of pain is eliminated, followed by the sensation of temperature, touch and pressure. Benzocaine is an anaesthetic, widely applied in numerous medical and surgical sub-specialities, such as ophthalmology, otorhinolaryngology, dentistry, and urology [12, 13, 14, 15, 16, 17]. It is used in spray form, liquid, creams, gels, and throat lozenges [12, 18, 19]. When applied topically, it is classified as a low-risk drug, although some patients may experience allergic reactions [20, 21, 22]. Overdose of these oxidizing agents may lead to methemoglobin [23, 24, 25, 26]. Benzocaine spray is the most commonly reported formulation to cause methemoglobin. Due to differences in absorption and metabolism, it should be used with caution, especially in children and the elderly.