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Sildenafil (Viagra®) has two actions that may be of consequence in patients with heart disease. It can lower the blood pressure, and it can interact with nitrates. It should never be used in patients who are taking nitrates.
Lower drug doses for elderly patients should be used first, with titrations of the dose as tolerated to prevent unwanted drug-related pharmacodynamic effects.
Giardia is one of the most common intestinal parasites worldwide, and infects up to 20% of the world population, mostly in poorer countries with inadequate sanitation. Infections are most common in children, though chronic Giardia is more common in adults.
Interferon was scarce and expensive until 1980, when the interferon gene was inserted into bacteria using recombinant DNA technology, allowing for mass cultivation and purification from bacterial cultures.
Disorders that may affect pharmacodynamics include genetic mutations, malnutrition, thyrotoxicosis, myasthenia gravis, Parkinson's disease, and certain forms of insulin-resistant diabetes mellitus.