Clofazimine

Absorption

Absorption varies from 45 to 62% following oral administration in leprosy patients. Co-administration of a 200mg dose of clofazimine with food resulted in a Cmax of 0.41 mg/L with a Tmax of 8 h; administered in a fasting state, the corresponding Cmax was 30% lower while the time to Cmax was 12 h.

Toxicity

The reported oral LD50 of clofazimine in rats and mice is 8400 mg/kg and >5000 mg/kg, respectively.
No specific data are available regarding the treatment of clofazimine overdosage. In cases of overdose consider gastrointestinal decontamination via gastric lavage or induced vomiting. Employ symptomatic and supportive measures as clinically indicated.

Description

Clofazimine is an antibacterial drug that was developed in the 1950s to treat tuberculosis. It failed for that use; but a few years later, it, in combination with other drugs, showed effectiveness against leprosy.
In 1954, clofazimine was synthesized by Vincent C. Barry and co-workers at Trinity College, Dublin. While it was under investigation as a tuberculosis treatment, Y. T. Chang and colleagues at the National Institutes of Health (Bethesda, MD) found that it had activity against Mycobacterium leprae, the bacterium that causes leprosy. Novartis (Basel, Switzerland) launched it as a leprosy treatment in 1969 under the brand name Lamprene. The US Food and Drug Administration approved it as an “orphan drug” in 1986, but it is no longer available in the United States.
In the age of COVID-19, clofazimine may have a new life. Ren Sun, Sumit K. Chanda, Kwok-Yung Yuen, and numerous collaborators at the University of Hong Kong and the Sanford Burnham Prebys Medical Discovery Institute (San Diego), discovered that it kills the SARS-CoV-2 virus in hamster cells. They also showed that the drug reduces the virus’ effects when given before infection.
Clofazimine can be taken as a pill and thus given in outpatient settings. It, in combination with an interferon drug, is currently in Phase 2 trials on patients hospitalized with COVID-19.

Chemical properties

Red Solid

The Uses of Clofazimine

Antibacterial (tuberculostatic, leprostatic).

The Uses of Clofazimine

antiinflammatory, glucocorticoid

Indications

Clofazimine is indicated for the treatment of lepromatous leprosy, including dapsone-resistant lepromatous leprosy and lepromatous leprosy complicated by erythema nodosum leprosum. To prevent the development of drug resistance, it should be used only in combination with other antimycobacterial leprosy treatments.

Definition

ChEBI: 3-Isopropylimino-3,5-dihydro-phenazine in which the hydrogen at position 5 is substituted substituted by a 4-chlorophenyl group, and that at position 2 is substituted by a (4-chlorophenyl)amino group. A dark red crystalline solid, clofazimine is an antimyc bacterial and is one of the main drugs used for the treatment of multi-bacillary leprosy. However, it can cause red/brown discolouration of the skin, so other treatments are often preferred in light-skinned patients.

Background

Clofazimine is a highly lipophilic antimicrobial riminophenazine dye used in combination with other agents, such as dapsone, for the treatment of leprosy. It was originally described in 1957 and was the prototypical riminophenazine dye - a bright-red dye that, in its clinical use, results in long-lasting discoloration of the skin and bodily fluids. Although it carries in vitro activity against other mycobacterium, such as Mycobacterium tuberculosis, it is generally considered an ineffective treatment in comparison to classic tuberculosis treatments such as rifampicin and isoniazid.

Indications

Clofazimine is a weakly bactericidal dye that has some activity against M. leprae. Its precise mechanism of action is unknown but may involve mycobacterial DNA binding. Its oral absorption is quite variable, with 9 to 70% of the drug eliminated in the feces. Clofazimine achieves significant concentrations in tissues, including the phagocytic cells; it has a plasma half-life of 70 days. It is primarily excreted in bile, with less than 1% excretion in urine.

brand name

Lamprene (Novartis).

Antimicrobial activity

The mode of action is not fully understood. It has bacteristatic and weak bactericidal activity against several species of mycobacteria and some species of Actinomyces and Nocardia. In-vitro minimum inhibitory concentrations (MICs) are: M. tuberculosis 0.5 mg/L and M. leprae (assayed in a mouse model) 0.1–1 mg/L, but these MICs have limited clinical relevance as clofazimine shows marked differences in accumulation in various tissues. Activity against M. leprae is demonstrable in humans only after 50 days of therapy. Clofazimine resistance, although reported, appears to be rare.

Pharmaceutical Applications

One of a number of substituted iminophenazine dyes originally synthesized as potential antituberculosis agents. It is almost insoluble in water. It stimulates various phagocyte functions including release of free oxygen radicals, but it is not clear whether this contributes to its antimicrobial activity. It also has anti-inflammatory properties, attributed to its ability to inhibit certain patterns of intracellular T-cell receptor- mediated signaling, making it a useful drug for treating leprosy reactions and possibly other autoimmune processes.

Pharmacokinetics

Clofazimine exerts a slow bactericidal effect on Mycobacterium leprae (Hansen's bacillus) due primarily to its action on the bacterial outer membrane, though there is some evidence that activity on the bacterial respiratory chain and ion transporters may play a role. It also exerts anti-inflammatory properties due to the suppression of T-lymphocyte activity. Clofazimine has a relatively long duration of action owing to its long residence time in the body, but is still administered daily.
Approximately 75-100% of patients receiving clofazimine will experience an orange-pink to brownish-black discoloration of the skin, conjunctivae, and bodily fluids. Skin discoloration may take several months or years to reverse following the cessation of therapy. Clofazimine has also been implicated in abdominal obstruction, in some cases fatal, due to the deposition of drug and formation of crystals in the intestinal mucosa - complaints of abdominal pain and nausea/vomiting should be investigated promptly, and the doses of clofazimine should be lowered or discontinued if it is found to be the culprit.
Its use should be avoided in patients with hepatic dysfunction.

Pharmacokinetics

Clofazimine is well absorbed by the intestine and is taken up by adipose tissue and cells of the macrophage/monocyte series, including those in the intestinal wall. It has a very long half-life (variously estimated as 10–70 days) and is eliminated, mostly unchanged, in the urine and feces.

Pharmacology

Clofazimine is a substituted iminophenazine that was first proposed for treating leprosy in 1962; however, it entered into medical practice toward the end of the 1980s. The mechanisms of its action is not definitively known, although there is the assumption that it can inhibit the formation of matrixes with DNA, which leads to a delay in the growth of mycobacteria. Clofazimine exhibits a bactericidal effect between that of dapsone and rifampicin. Synonym of this drug is lamprene.

Clinical Use

Clofazimine (Lamprene) is a basic red dye that exerts a slow bactericidal effect on M. leprae, the bacterium that causes leprosy. It occurs as a dark red crystalline solid that is insoluble in water. Clofazimine is used in the treatment of lepromatous leprosy, including dapsone-resistant forms of the disease. In addition to its antibacterial action, the drug appears to possess anti-inflammatory and immune-modulating effects that are of value in controlling neuritic complications and in suppressing erythema nodosum leprosum reactions associated with lepromatous leprosy. It is frequently used in combination with other drugs, such as dapsone or rifampin.The mechanisms of antibacterial and anti-inflammatory actions of clofazimine are not known. The drug is known to bind to nucleic acids and concentrate in reticuloendothelial tissue. It can also act as an electron acceptor and may interfere with electron transport processes. The oral absorption of clofazimine is estimated to be about 50%. It is a highly lipid-soluble drug that is distributed into lipoidal tissue and the reticuloendothelial system. Urinary excretion of unchanged drug and metabolites is negligible. Its half-life after repeated dosage is estimated to be about 70 days. Severe gastrointestinal intolerance to clofazimine is relatively common. Skin pigmentation, ichthyosis and dryness, rash, and pruritus also occur frequently. Clofazimine has also been used to treat skin lesions caused by Mycobacterium ulcerans.

Clinical Use

Clofazimine is given to treat sulfone-resistant leprosy or to patients who are intolerant to sulfones. It also exerts an antiinflammatory effect and prevents erythema nodosum leprosum, which can interrupt treatment with dapsone.This is a major advantage of clofazimine over other antileprosy drugs. Ulcerative lesions caused by Mycobacterium ulcerans respond well to clofazimine. It also has some activity against M. tuberculosis and can be used as last resort therapy for the treatment of MDR tuberculosis.

Clinical Use

Multibacillary leprosy (in combination with other anti-leprosy drugs)
Erythema nodosum leprosum (anti-inflammatory activity)
Clofazimine has been suggested as a drug for treatment of MDR tuberculosis, although its efficacy is unproven. It has been used to treat M. ulcerans infection (Buruli ulcer) but with limited responses. Use in disease caused by mycobacteria of the M. avium complex is no longer recommended as more effective and less toxic alternative agents are available.

Side Effects

Clofazimine is usually well tolerated, but some patients develop nausea, abdominal pain and diarrhea, relieved to some extent by taking the drug with a meal or glass of milk. Dose-related, reversible, skin discoloration is very common and is unacceptable to some patients. Discoloration of the hair, cornea, urine, sweat and tears also occurs. Infants born to mothers receiving clofazimine are reversibly pigmented at birth. Edema of the wall of the small intestine leading to subacute obstruction is a rare but serious complication of prolonged high-dose therapy for leprosy reactions. Deposition of clofazimine in lymph nodes may interfere with lymphatic drainage, occasionally manifesting as edema of the feet.

Side Effects

The most disturbing adverse reaction to clofazimine is a red-brown discoloration of the skin, especially in light-skinned persons. A rare but serious adverse reaction is acute abdominal pain significant enough to warrant exploratory laparotomy or laparoscopy. Other infrequent side effects include splenic infarction, bowel obstruction, paralytic ileus, and upper GI bleeding.

Synthesis

Clofazimine, 2-(p-chloroanilino)-5-(p-chlorophenyl)-3,5-dihydro-3-(isopropylimino)-phenazine (34.2.6), is synthesized by oxidizing 2-(p-chloroanilino)aniline using a solution of iron (III) chloride in water, which leads to the formation of 2-(p-chloroanilino)-5-(p-chlorophenyl)-3,5-dihydro-3-iminophenazine (34.2.5). Upon reacting this with a primary amine, in particular isopropylamine, the hydrogen atom in the imine region of the molecule is formally replaced with an alkyl group of the introduced amino group (in this case with an isopropyl group), forming the desired drug?aclofazimine.

Veterinary Drugs and Treatments

In small animals, clofazimine is sometimes used as part of multidrug therapy against mycobacterial diseases, primarily leprosy-like or M. avium-related disease states.
In humans, clofazimine is used primarily as part of a multi-drug regimen in the treatment of all forms of leprosy (with rifampin and dapsone), or the treatment of Mycobacterium avium complex (MAC) (with at least two of the following agents: clarithromycin or azithromycin, rifampin or rifabutin, and ethambutol). It has also been used in some treatment regimens for Crohn’s disease, pyoderma gangrenosum, etc.

Drug interactions

Potentially hazardous interactions with other drugs
Antibacterials: increased risk of ventricular arrhythmias with bedaquiline.

Metabolism

Because of its lipophilic nature, clofazimine is mainly distributed to fatty tissue and reticuloendothelial cells, including macrophages. Clofazimine accumulates in the body and is largely excreted unchanged in the faeces, both as unabsorbed drug and via biliary excretion. About 1% of the dose is excreted in 24 hours in the urine as unchanged clofazimine and metabolites. A small amount of clofazimine is also excreted through sebaceous and sweat glands, and in sputum.

Metabolism

Three metabolites have been identified in the urine following repeated oral doses of clofazimine. It is unclear whether these metabolites are pharmacologically active. Metabolite I may be the result of the hydrolytic dehalogenation of clofazimine and metabolite II presumably is formed by a hydrolytic deamination reaction followed by glucuronidation.

Purification Methods

Clofazimine recrystallises from acetone as dark red crystals. Its solubility in CHCl3 and EtOH is 7% and 0.1%, respectively,at room temperature. It is insoluble in H2O. It is antibacterial. [Barry et al. J Chem Soc 859 1958, Beilstein 25 III/IV 3033.]