Zinc was regularly imported to Europe from the Orient in the 17th and early 18th centuries, but was at times very expensive. Isolation
Metallic zinc was isolated in India by 1300 AD, much earlier than in the West. Before it was isolated in Europe, it was imported from India in about 1600 CE. Postlewayts Universal Dictionary, a contemporary source giving technological information in Europe, did not mention zinc before 1751 but the element was studied before then.Flemish metallurgist and alchemist P. M. de Respour reported that he had extracted metallic zinc from zinc oxide in 1668. By the start of the 18th century, Étienne François Geoffroy described how zinc oxide condenses as yellow crystals on bars of iron placed above zinc ore that is being smelted. In Britain, John Lane is said to have carried out experiments to smelt zinc, probably at Landore, prior to his bankruptcy in 1726.In 1738 in Great Britain, William Champion patented a process to extract zinc from calamine in a vertical retort-style smelter. His technique resembled that used at Zawar zinc mines in Rajasthan, but no evidence suggests he visited the Orient. Champions process was used through 1851.German chemist Andreas Marggraf normally gets credit for discovering pure metallic zinc, even though Swedish chemist Anton von Swab had distilled zinc from calamine four years previously. In his 1746 experiment, Marggraf heated a mixture of calamine and charcoal in a closed vessel without copper to obtain a metal. This procedure became commercially practical by 1752.
Contraindications
Calcipotriol/betamethasone dipropionate is contraindicated in patients with hypersensitivity to either glucocorticoids or vitamin D or disorders in calcium metabolism. This drug is also contraindicated for patients with erythrodermic, exfoliative, or pustular psoriasis. Adverse effects
A number of clinical studies have been conducted to investigate possible adverse events of this fixed combination corticosteroid and vitamin D analog. Safety and tolerability of calcipotriol/betamethasone dipropionate (Cal/BD) ointment has been assessed in a combined total of 2448 patients, exposed to treatment for 4 or 8 weeks (median weekly dose of 24.5 g). The most common adverse events for patients receiving Cal/BD were pruritus (3.1%), headache (2.8%), and nasopharyngitis (2.3%). Lesional/perilesional adverse events, defined as an adverse event located ≤2 cm from the lesional border, were reported by 8.7% of patients treated with Cal/BD ointment. Median time to onset of lesional/perilesional adverse events was 7 days.Adverse events during treatment with the foam formulation have been evaluated in three 4-week randomized, multicenter, prospective vehicle- and/or active-controlled clinical trials of subjects with plaque psoriasis. The median weekly dose was 24.8 g. Application site irritation, application site pruritus (itching), folliculitis (inflammation of hair follicles), skin hypopigmentation (loss of skin color), hypercalcemia (increased blood calcium levels), urticaria, and exacerbation of psoriasis were reported in <1% of subjects. Local long-term adverse effects of continuous steroid exposure may include skin atrophy, stretch marks, telangiectasia (spider veins), dryness, local infections, and miliaria ("prickly heat").