Renal function impairment analgesics

Analgesics. Opiates can precipitate hepatic encephalopathy in patients with decompensated liver disease. If required to control postoperative pain, doses should be reduced to 25-50% of normal. Constant intravenous infusions should be avoided if the patient is not to be insidiously overdosed. Codeine can precipitate hepatic encephalopathy by its constipating effect alone. Aspirin and other NSAIDs may exacerbate impaired renal function and fluid retention by inhibiting prostaglandin synthesis and may also precipitate gastrointestinal bleeding. 

Overdosage results in respiratory depression, skeletal muscle flaccidity, cold clammy skin, cyanosis, extreme somnolence progressing to convulsions, stupor, coma. Tolerance to analgesic effect, physical dependence may occur with repeated use. Prolonged duration of action, cumulative effect may occur in those with impaired hepatic and renal function. 

When switching to FTS, the first step is to calculate the previous 24-hour analgesic requirement and then convert it according to the dose conversion table (Table 28.1). It is important to start low and advance slowly, especially in the elderly, debilitated, cachectic, and those with impaired renal or hepatic function. The mean elimination half-life of FTS is 17 hours, and the shortest titration period is 3 days, but it takes up to 6 days to reach equilibrium on the new dose. In addition, when changing the dose, it may take 13 to 24 hours for the fentanyl to reach the new therapeutic level [1,2]. While titrating the dose, patients may require short-acting opioids for breakthrough pain. 

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