Primidone, a medication used to treat epilepsy and essential tremor, has been associated with hexagonal crystals in the urine, typically when levels are very high such as following an overdose. Primidone crystalluria is depicted in the video below:
What is primidone?
Used rarely for the treatment of essential tremors or seizure disorders
Decreases central nervous system excitation
Metabolized to 2 active metabolites: phenobarbital and phenylethylmalonamide (PEMA) 
Phenobarbital results in decreased CNS excitation by GABA receptor agonism
PEMA enhances phenobarbital activity at the receptor
Common symptoms after exposure include crystalluria, sedation, ataxia, nystagmus, decreased deep tendon reflexes, hypotension, and coma [1,3,4,5]
Has been described as white, shimmering, chalky urine or as “white paint” urine [1,4,6]
Crystals are hexagonal in structure [1,3,7]
Crystalluria is reported at serum concentrations of primidone >80 mg/L [3,4,7]; therapeutic concentration is typically 5-12 mg/L
Primidone crystalluria is generally not associated with kidney injury [2,6] although there is a single case report 
What other substances can produce crystalluria?
Crystals associated with ethylene glycol toxicity are a result of the metabolite, oxalate 
Calcium oxalate monohydrate crystals are most often seen, however different morphologies including calcium oxalate dihydrate crystals have been reported 
Oxalate crystalluria has been reported with other disease states or ingestions as well 
Urine has been described as opaque, cloudy, or milky in color [9,10]
Crystals have been described as long and needle-shaped that are water soluble; however, crystals may not have a distinctly unique morphology [9,10]
N-acetyl sulfamethoxazole, a metabolite of sulfamethoxazole, has been reported to produce crystals with various shapes including rectangular, spheroids, truncated lozenges, flowers, and more [11-13]
Crystals have been identified as a metabolite of sulfamethoxazole using infrared spectroscopy in multiple cases [11-13]
Indinavir crystals are generally needles, flat rectangular plates, fan-shaped, or starburst-shaped in morphology 
Crystals should dissolve in an acidic environment 
Other drugs that have been associated with crystalluria include: 
Crystalluria can be seen with many different substances.
Crystal morphology may help determine the etiology. Contacting the laboratory to assist with the identification of physical characteristics of the crystals may be beneficial.
History is the most important determinant in diagnosing the etiology of crystalluria.
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The Crystalline Nephropathies. Kidney Int Rep. 2021 Sep 17;6(12):2942-57. PMID: 34901567.