Following cocaine use metabolites of cocaine may be found in the urine long after the parent compound has disappeared. The excretion of benzoylecgonine is affected by the size of the dose taken as well as the time interval since use. The author was at Northwestern University in Chicago.
A nomogram for excretion of benzoylecgonine versus time based on dose taken is shown on page 245 of Ambre (1985). The peak excretion is reached about 5-6 hours after use. Extrapolating the elimination line back to time = 0, the following equations can be used to approximate excretion.
LOG10(benzoylecgonine level in urine after 10 mg dose in µg/mL) =
= (-0.04033 * (hours since taken)) + 0.9275
LOG10(benzoylecgonine level in urine after 50 mg dose in µg/mL) =
= (-0.041059 * (hours since taken)) + 1.6522
LOG10(benzoylecgonine level in urine after 100 mg dose in µg/mL)=
= (-0.040934 * (hours since taken)) + 1.9493
LOG10(benzoylecgonine level in urine after 500 mg dose in µg/mL) =
= (-0.04 * (hours since taken)) + 2.628
LOG10(benzoylecgonine level in urine after 1000 mg dose in µg/mL) =
= (-0.04015 * (hours since taken)) + 2.935
The average slope of the lines is –0.0405.
Cocaine Dose in mg |
Y-Intercept (t = 0) |
10 |
0.9275 |
50 |
1.6522 |
100 |
1.9493 |
500 |
2.628 |
1,000 |
2.935 |
Y intercept in µg/mL =
= (0.9986 * LOG10(dose in mg)) – 0.05819
Cocaine Dose in mg |
X-Intercept (0 µg/mL) |
10 |
23 hours |
50 |
40.24 hours |
100 |
47.62 hours |
500 |
65.7 hours |
1,000 |
73.1 hours |
Using JMP, the X-intercept can be predicted based on dose in mg:
X intercept in hours =
= (25.165 * LOG10 (dose in mg)) – 2.3
If a dose of D mg cocaine is ingested at one sitting, then the level of benzoylecgonine in the urine can be predicted over time, including the time when no more will be detected in the urine.
LOG10(urine excretion in µg/mL of benzoylecgonine) =
= (-0.0405 * (hours since use)) + (Y-intercept for dose) =
= (-0.0405 * (hours since use)) + (0.9986 * LOG10(dose in mg)) – 0.05819
urine excretion in µg/mL of benzoylecgonine =
= 10 ^ ((-0.0405 * (hours since use)) + (0.9986 * LOG10(dose in mg)) – 0.05819)
time when benzoylecgonine no longer detected in hours from dose =
= X intercept =
= (25.165 * LOG10 (dose in mg)) – 2.3
If A amount of benzoylecgonine is present in the urine H hours after use, then the amount taken can be estimated.
LOG10(A) =
= (-0.0405 * (H hours)) + (Y-intercept for dose) =
= (-0.0405 * (H hours)) + (0.9986 * LOG10(dose in mg)) – 0.05819
LOG10(dose in mg)) =
= (LOG10(A) + (0.0405 * (H hours)) + 0.05819) / 0.9986
dose in mg =
= 10 ^ ((LOG10(A) + (0.0405 * (H hours)) + 0.05819) / 0.9986)
Specialty: Toxicology, Emergency Medicine, Critical Care
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