Pain relief can be achieved by a diversity of methods, with drug use being the basis of analgesic treatment. Clinical use of combinations of analgesic drugs has augmented considerably in the last few years. The purpose of combining two or more drugs with different mechanisms of action is to achieve a synergistic interaction, yielding a sufficient analgesic effect with lower doses and, therefore, reduce the intensity and incidence of untoward effects. At present, many diverse classes of drugs serve as an efficient complement to nonsteroidal anti-inflammatory drugs (NSAIDs) or opioids in the management of pain. Opioids have frequently been used in combination with NSAIDs for the clinical management of both acute and chronic pain. At the end, the use of this combination limits the doses of medication that a patient can receive. However, not all the opioid-NSAID combinations are clinically successful in all cases. For example, the association of weak opioids, such as dextropropoxyphene, to acetaminophen does not significantly increase pain relief with respect to acetaminophen alone. Likewise, the combination of codeine with paracetamol results in additional pain relief but may be accompanied by an increase in drowsiness and dizziness. Therefore, several other combinations of analgesic agents must be evaluated experimentally or clinically to gain insight into their potential clinical use.

We invite investigators to contribute original research articles as well as review articles that will stimulate the continuing efforts to obtain useful evidence about the use of drug combination in the treatment of pain. We are particularly interested in articles describing novelty models for experimental or clinical characterization of drug combinations in the management of painful states, new insights into action mechanism of the drug interactions, and evaluation of adverse reactions. Potential topics include, but are not limited to:

• Development of drug interaction mathematic models
• Interaction between opioids or nonopioids with nonsteroidal anti-inflammatory drugs
• Drug interaction models in animals
• Drug combination in painful states in human
• Pharmacodinamic and/or pharmacokinetics studies about drug combination in animals or patients with pain
• Adverse reactions due to drug combination in patients with pain
• Drugs-herbal products combinations in animals or patients with pain

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