9-deoxy-9-methylene-16,16-dimethyl Prostaglandin E2 (metenprost) is a potent analog of PGE2 with an extended half-life in vivo. In combination with various other prostaglandin derivatives, metenprost results in the termination of first trimester pregnancy in monkeys. A single intramuscular injection containing 0.5 mg of metenprost and 7.5 mg of 17-phenyl trinor PGF1α is very effective in terminating early pregnancy.{4692} This prostaglandin mixture is ineffective on monkeys in their third trimester of pregnancy.{4692} Metenprost, when compared to PGE2 and PGF1α, in monkey and rat, does not result in unwanted side effects such as fever or gastrointestinal problems.{4692,464}