Delay in onset of action may be further delayed & reduction in absorption may occur w/ food. False +ve urine screening tests for methadone, opiates & PCP. Doxylamine: Toxicity may be enhanced w/ anticholinergic agents (TCAs, MAOI, neuroleptics). Hypnotic action may be enhanced w/ sedatives (barbiturates, benzodiazepines, antipsychotic agents, opioid analgesics). Sedative effect may be enhanced w/ antihypertensive drugs w/ sedative effect on CNS (especially α-methyldopa). Enhanced toxicity w/ alcohol. Not recommended in combination w/ Na oxybate. May mask warning signs of damage caused by ototoxic drugs eg, aminoglycosides, carboplatin, cisplatin, chloroquine & erythromycin. May cause additive photosensitizing effects w/ photosensitizing medications eg, amiodarone, quinidine, imipramine, doxepin, amitriptyline, griseofulvin, chlorpheniramine, piroxicam, furosemide, captopril. Avoid concomitant use of drugs that prolong QT interval eg, antiarrhythmic drugs, certain antibiotics, drugs for malaria, antihistaminic drugs, antilipidemic drugs or neuroleptic agents; CYP450 inhibitors eg, azole derivatives, macrolides; drugs that cause electrolyte disturbances eg, hypokalemia or hypomagnesemia eg, some diuretics. False -ve in dermal hypersensitivity tests w/ antigen extr. Pyridoxine: Reduced effect of l-dopa. Reduced plasma levels of some antiepileptics eg, phenobarb & phenytoin. Hydroxyzine, INH or penicillamine may interfere w/ & increase requirements for pyridoxine.