Tetanus immunoglobulin is a blood product derived from human blood and is a bit more expensive than tetanus antitoxin. Depending on the size, the manufacturer, and the time of year, the price can vary a bit. However, the tetanus immunoglobulin that is known to cost around$300 for a 250-unit size for one. Tetanus immunoglobulin is applied when a person is injured and bears the risk of contracting tetanus, and its immunization is more effective for a longer period of time, usually lasting 4-5 weeks. One injection, or 250 units, is usually sufficient after an injury, and some may choose to have 500 units injected as well. The injection lasts for such a long period of time that any Clostridium tetani infection and secretion of tetanus toxin can be neutralized by tetanus immunoglobulin so that the symptoms of tetanus do not appear.