Also referred to as anthranilic acids, these compounds are occasionally involved in overdose producing muscle twitching, and seizures, apart from gastrointestinal distress. Management is supportive, following decontamination (gastric lavage, acti-vated charcoal). Monitor renal function and acid base status in symptomatic patients. Control of convulsions can be achieved with benzodiazepines or barbiturates. Haemodialysis is not expected to be effective in treating acute intoxication, but charcoal haemoperfusion might be effective.
Mefenamic acid is used in mild to moderate pain (e.g. headache, dental pain, post-operative and postpartum pain, and dysmenorrhoea, musculoskeletal and joint disorders). Safety and effectiveness in paediatric patients under the age of 14 years have not been established. Adverse effects from therapeutic use include GI irritation or ulceration, GI bleeding, headache, dizziness, drowsiness, skin rashes, acute renal failure, elevated liver enzymes, increased bleeding time and tinnitus. Rare effects include anaphylactoid reactions, cardiovascular effects, hyper-glycaemia, hallucinations, coma, meningitis, seizures, respiratory depression, pneumonia, dermal reactions, and haematologic abnormalities (e.g. haemolytic anaemia, agranulocytosis, pancy-topenia, thrombocytopenic purpura, bone marrow aplasia).
In overdose, muscle twitching and seizures are most common. The lowest dose to cause coma and seizures in an adult was 3.5 grams. Vomiting, diarrhoea, abdominal pain, lethargy, drowsiness, and acidaemia can occur. Less frequent symptoms include respiratory depression, hypertension, coma, dyskinesias, agitation and restlessness, GI bleeding, and acute renal failure. Anaphylaxis can also occur in overdose.
It has been suggested that therapeutic serum levels must not exceed 20 mcg/ml.