Causes have not been specifically identified but the most likely are viral opportunists and autoimmune responses. Viruses linked to this can include; hepatitis C, cytomegalovirus, paramyxovirus, influenza A, and adenovirus. Treatment is anti-retroviral therapy.Disseminated histoplasmosis: During a large urban disseminated histoplasmosis outbreak (est. 100,000 victims) in Indianapolis from 1978 to 1979, manifestations included parotitis. Autoimmune causes
These are also collectively known as chronic punctate parotitis or chronic autoimmune parotitis.Sjögrens syndrome:
Chronic inflammation of the salivary glands may also be an autoimmune disease known as Sjögrens syndrome. The disease most commonly appears in people aged 40–60 years, but it may affect small children. In Sjögren syndrome, the prevalence of parotitis in women versus men is approximately 9:1. The involved parotid gland is enlarged and tender at times. The cause is unknown. The syndrome is often characterized by excessive dryness in the eyes, mouth, nose, vagina, and skin.Lymphoepithelial lesion of Godwin:
Most frequently associated with a circumscribed tumor with the histologic features of Sjögren syndrome. This designation has also fallen out of favour. Blockage
Blockage of the main parotid duct, or one of its branches, is often a primary cause of acute parotitis, with further inflammation secondary to bacterial superinfection. The blockage may be from a salivary stone, a mucous plug, or, more rarely, by a tumor, usually benign. Salivary stones (also called sialolithiasis, or salivary duct calculus) are mainly made of calcium, but do not indicate any kind of calcium disorder. Other causes can be duct stricture (narrowing of the duct), infection or injury.
As it is so heavily bound to plasma proteins haemodialysis is unlikely to be helpful in cases of overdose.Early symptoms of overdose can include:

It is worth noting, however, that may of these symptoms are also indicative of kidney failure and hence may be masked by the patients condition.Late symptoms of overdose include:

Mechanism of action
Like 1,25-dihydroxyergocalciferol, paricalcitol acts as an agonist at the vitamin D receptor and thereby lowers parathyroid hormone levels in the blood. Pharmacokinetics
The plasma concentration of paricalcitol decreases rapidly and log-linearly within two hours after initial intravenous administration. Therefore, it is not expected to accumulate with multiple dosing, since paricalcitol is usually given no more frequently than every other day (3 times per week). == References ==