Eflornithine, sold under the brand name Vaniqa among others, is a medication used to treat African trypanosomiasis (sleeping sickness) and excessive hair growth on the face in women.

[10] Eflornithine is not effective in the treatment of Trypanosoma brucei rhodesiense due to the parasite's low sensitivity to the drug.

[14][15] After its introduction to the market in the 1980s, eflornithine has replaced melarsoprol as the first line medication against Human African trypanosomiasis (HAT) due to its reduced toxicity to the host.

[13] The gene TbAAT6, conserved in the genome of Trypanosomes, is believed to be responsible for the transmembrane transporter that brings eflornithine into the cell.

However, since African trypanosomiasis has a high mortality rate if left untreated, treatment with eflornithine may justify any potential risk to the fetus.

Most side effects related to systemic use through injection are transient and reversible by discontinuing the drug or decreasing the dose.

Because of its additional difluoromethyl group in comparison to ornithine, eflornithine is able to bind to a neighboring Cys-360 residue, permanently remaining fixated within the active site.

[citation needed] The remaining fluoride atom that resides attached to the additional methyl group creates an electrophilic carbon that is attacked by the nearby thiol group of Cys-360, allowing eflornithine to remain permanently attached to the enzyme following the release of the second fluoride atom and transimination.

[30] Utilizing fast-atom bombardment mass spectrometry (FAB-MS), the structural conformation of eflornithine following its interaction with ODC was determined to be (S)-((2-(1-pyrroline-methyl) cysteine, a cyclic imine adduct.

[30] Eflornithine's suicide inhibition of ODC physically blocks the natural substrate ornithine from accessing the active site of the enzyme (Figure 3).

Eflornithine was initially developed for cancer treatment at Merrell Dow Research Institute in the late 1970s, but was found to be ineffective in treating malignancies.

In the 1980s, Gillette was awarded a patent for the discovery that topical application of eflornithine HCl cream inhibits hair growth.

In the 1990s, Gillette conducted dose-ranging studies with eflornithine in hirsute women that demonstrated that the drug slows the rate of facial hair growth.

[11] However, in 1995 Aventis (now Sanofi-Aventis) stopped producing the drug, whose main market was African countries, because it did not make a profit.

According to Médecins sans Frontières, this only happened after "years of international pressure," and coinciding with the period when media attention was generated because of the launch of another eflornithine-based product (Vaniqa, for the prevention of facial-hair in women),[34] while its life-saving formulation (for sleeping sickness) was not being produced.

[citation needed] Ornidyl, intended for injection, was supplied in the strength of 200 mg eflornithine hydrochloride per ml.

[37] Vaniqa, granted marketing approval by the US FDA, as well as by the European Commission[38] among others, is currently the only topical prescription treatment that slows the growth of facial hair.

[19] Besides being a non-mechanical and non-cosmetic treatment, it is the only non-hormonal and non-systemic prescription option available for women with facial hirsutism.

[18] Vaniqa is marketed by Almirall in Europe, SkinMedica in the US, Triton in Canada, Medison in Israel, and Menarini in Australia.

[39] It has been noted that ornithine decarboxylase (ODC) exhibits high activity in tumor cells, promoting cell growth and division, while absence of ODC activity leads to depletion of putrescine, causing impairment of RNA and DNA synthesis.

Typically, drugs that inhibit cell growth are considered candidates for cancer therapy, so eflornithine was naturally believed to have potential utility as an anti-cancer agent.

Several additional studies have found that eflornithine in combination with other compounds decreases the carcinogen concentrations of ethylnitrosourea, dimethylhydrazine, azoxymethane, methylnitrosourea, and hydroxybutylnitrosamine in the brain, spinal cord, intestine, mammary gland, and urinary bladder.

However although Jansson et al. 2008 also effectively treated mice with it they found the pharmacokinetics of oral administration in rats very negative.