RABITO ICHTHAMMOL OINTMENT

Indications

• Eczema
• Psoriasis
• Chronic lichenified eczema
• Mild inflammatory skin disorders associated with infection

Dosage

Children: Consult product literature for specific dosing recommendations.

Adults: Apply 1–3 times a day to the affected area.

Mechanism of action

Ichthammol works by reducing inflammation and irritation in the skin. It may act by promoting the normalization of skin function and by exerting an anti-inflammatory effect, although the precise mechanism of action is not fully understood. Its keratolytic properties help in the softening and removal of scales and crusts associated with various skin conditions.

Pharmacodynamics

Ichthammol exhibits anti-inflammatory and antiseptic properties, which help in reducing redness, swelling, and discomfort associated with skin conditions. The keratolytic effect promotes the shedding of dry, scaly skin, facilitating the healing process.

Pharmacokinetics

Ichthammol is applied topically, leading to localized effects. Systemic absorption is minimal, and therefore, it is primarily confined to the site of application. The pharmacokinetic profile in humans has not been extensively studied, but the local effects are significant in managing skin conditions.

Pregnancy

Tetracyclines should not be given to pregnant women. Effects on skeletal development have been documented when tetracyclines have been used in the first trimester in animal studies. Administration during the second or third trimester may cause discoloration of the child's teeth.

Breast-feeding

Tetracyclines should not be given to women who are breast-feeding, although absorption and therefore discoloration of teeth in the infant is probably prevented by chelation with calcium in milk.

Storage

Store in a cool, dry place away from direct sunlight.

Formulations

• Cream
• Ointment

Mechanism of action

The precise mechanism by which hydroxyurea produces its antineoplastic effects cannot, at present, be described. However, the reports of various studies in rat and human tissue cultures lend support to the hypothesis that hydroxyurea causes an immediate inhibition of DNA synthesis, by acting as a ribonucleotide reductase inhibitor, without interfering with the synthesis of ribonucleic acid or of protein. Hydroxyurea probably acts by decreasing the rate of conversion of ribonucleotides and deoxyribonucleotides. This effect is particularly apparent in cells with a high rate of proliferation. Particularly, hydroxyurea reduces the tyrosyl free radical at the active site of the M2 via a one-electron transfer reaction through the –NH2-OH moiety. Three mechanisms have been postulated for the potentiation of the therapeutic effects of irradiation by hydroxyurea on squamous cell (epidermoid) carcinomas of the head and neck. In vitro studies utilizing Chinese hamster cells suggest that hydroxyurea is lethal to normally radioresistant S-stage cells and holds other cells of the cell cycle in the G1 or pre-DNA synthesis stage where they are most susceptible to the effects of irradiation. The third mechanism of action has been theorized on the basis of in vitro studies of HeLa cells: it appears that hydroxyurea, by inhibition of DNA synthesis, hinders the normal repair process of cells damaged but not killed by irradiation, thereby decreasing their survival rate; there is no alteration of RNA and protein syntheses. Another proposed mechanism of action of hydroxyurea is the elevation of HbF concentrations in Sickle Cell Disease patients. HbF interferes with the polymerization of HbS (sickle haemoglobin) and thus impedes the sickling of red blood cell. Recently, hydroxyurea has shown to be associated with the generation of nitric oxide, suggesting that nitric oxide stimulates cyclic guanosine monophosphates (cGMP) production, which then activates a protein kinase and increases the production of HbF. Other known pharmacological effects of hydroxycarbamide which may contribute to its beneficial effects in Sickle Cell Disease include decrease of neutrophils, improved deformability of sickled cells, and altered adhesion of red blood cells to the endothelium. The exact mechanism of antineoplastic activity of hydroxyurea has not been fully determined. Some studies indicate that hydroxyurea interferes with the synthesis of DNA without interfering with the synthesis of RNA or protein. Although hydroxyurea may have multiple sites of action, it appears likely that the drug inhibits the incorporation of thymidine into DNA; in addition, it may directly damage DNA. Hydroxyurea can destroy the tyrosyl free radical that is formed as the catalytic center of ribonucleoside diphosphate reductase, the enzyme that catalyzes the reductive conversion of ribonucleotides to deoxyribonucleotides; this conversion is a critical and probably rate-limiting step in the synthesis of DNA. The drug is an S-phase inhibitor and may cause cells to arrest at the G1-S border, decrease the rate of cell progression into the S phase, and/or cause cells to accumulate in the S phase as a result of inhibiting DNA synthesis. Animal studies indicate that the cytotoxic effects of hydroxyurea are limited to those tissues with high rates of cellular proliferation and the effects are evident only in those cells that are actively synthesizing DNA. Hydroxyurea, a drug widely used in therapy of several human diseases, inhibits deoxynucleotide synthesis and, consequently, DNA synthesis by blocking the cellular enzyme ribonucleotide reductase. Hydroxyurea inhibits human immunodeficiency virus type 1 (HIV-1) DNA synthesis in activated peripheral blood lymphocytes by decreasing the amount of intracellular deoxynucleotides, thus suggesting that this drug has an antiviral effect. Hydroxyurea has now been shown to block HIV-1 replication in acutely infected primary human lymphocytes (quiescent and a

Pharmacodynamics

The correlation between hydroxyurea concentrations, reduction of crisis rate, and increase in HbF, is not known.