Mefloquine is a chiral molecule with two asymmetric carbon centres, which means it has four different stereoisomers . The drug is currently manufactured and sold as a racemate of the ( R , S )- and ( S , R )-enantiomers by Hoffman-LaRoche , a Swiss pharmaceutical company. Essentially, it is two drugs in one. Plasma concentrations of the (–)-enantiomer are significantly higher than those for the (+)-enantiomer, and the pharmacokinetics between the two enantiomers are significantly different. The (+)-enantiomer has a shorter half-life than the (–)-enantiomer. 
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A dog that is potentially a candidate for long-term use of carprofen should have a complete examination by the veterinarian, a screening blood panel to establish baseline biochemical values, and ideally some kind of recheck testing two weeks after starting carprofen. This is because most adverse reactions, unusual as they may be, occur within this initial time frame and it is important that they be recognized before they get out of hand. After this initial period, complete blood panels should be screened every 6 months, an important step with any medication for long term use, not just the NSAIDs.