Drug Interactions between caffeine / pheniramine / phenylephrine / sodium citrate / sodium salicylate and clobazam

MONITOR: Coadministration of two or more sympathomimetic agents may increase the risk of adverse effects such as nervousness, irritability, and increased heart rate. Central nervous system (CNS) stimulants, particularly amphetamines, can potentiate the adrenergic response to vasopressors and other sympathomimetic agents. Additive increases in blood pressure and heart rate may occur due to enhanced peripheral sympathetic activity.

MANAGEMENT: Caution is advised if two or more sympathomimetic agents are coadministered. Pulse and blood pressure should be closely monitored.

MONITOR: Agents that cause urinary alkalinization can reduce serum salicylate concentrations in patients receiving anti-inflammatory dosages of aspirin or other salicylates. The mechanism involves reduction in salicylate renal tubular reabsorption due to increased urinary pH, resulting in increased renal salicylate clearance especially above urine pH of 7. This interaction is sometimes exploited in the treatment of salicylate toxicity.

MANAGEMENT: Patients treated chronically with urinary alkalinizers and large doses of salicylates (i.e. 3 g/day or more) should be monitored for potentially diminished or inadequate analgesic and anti-inflammatory effects, and the salicylate dosage adjusted if necessary.

MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients. Sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Cautious dosage titration may be required, particularly at treatment initiation. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

A number of studies have reported that antacids can delay the gastrointestinal absorption and reduce the peak plasma concentration (Cmax) of some benzodiazepines, including clorazepate, chlordiazepoxide and diazepam, although the overall extent of absorption is generally not affected. The exact mechanism of interaction is unknown, but may involve delayed gastric emptying or cation binding of the benzodiazepine. As a result, benzodiazepine onset of action may be delayed and clinical effects diminished. However, one study reported a significant increase in diazepam absorption during coadministration with aluminum hydroxide, and there was a marginal increase in the onset of sedative effect. Aluminum hydroxide also increased triazolam Cmax and systemic exposure (AUC) in 11 dialysis patients such that their drug levels reached into the range observed for the matched controls. In contrast, another study by the same group of investigators found no significant effect of aluminum hydroxide on temazepam absorption or Cmax in 11 patients with end-stage renal disease. A multi-dose study also failed to find an effect of antacids on the steady-state levels of N-desmethyldiazepam, the active metabolite of clorazepate, although an acidic environment is thought to be necessary for the rapid conversion. Based on available data, the clinical significance of this interaction appears to be minor. As a precaution, patients may consider separating the administration times of benzodiazepines and antacids or other oral medications that contain antacids (e.g., didanosine buffered tablets or pediatric oral solution) by 2 to 3 hours.