solution concentrations I think I'm making this more complicated than it needs to be, but here it is:

I have 7 drug solutions, all 1 mg/mL which need to have the following concentration in urine:

A: 25,000 ng/ml

B: 25,000 ng/ml

C: 100,000 ng/ml

D: 100,000 ng/ml

E: 10,000 ng/ml

F: 1000 ng/ml

G: 1000 ng/ml

How much of each 1 mg/ml solution do I need to add to urine to get a stock with the above concentrations? My ultimate goal is to take several 75 ul aliquots of urine for testing. Any suggestions?
Since you did not tell us how much of this final solution you would like to make, let's imagine that you want to make a generic $V_f\ \ce{mL}$ of it.

Take $\text{A}$ as an example:

$$
n_A \ \text{in final solution} =  25000\ \ce{ng/mL} \times V_f\ \ce{mL}
$$

$$
V_{A}\ \text{stock to take} = \frac{n_A}{c_{A\ stock}} = \frac{25000\ \ce{ng/mL} \times V_f\ \ce{mL}}{1\ \ce{mg/mL} \times 10^6\ \ce{ng/mg}} \frac{1000\ce{\ \mu L}}{\ce{mL}}= \frac{25000}{10^3}\ V_f\ \ce{\mu L}
$$

So let's suppose that you want to make $10\ \text{mL}$ of such a solution containing $\text{A}$ at $25,000\ \text{ng/mL}$, then you need to measure out $25000 \times 10\ /\ 1000\ \ce{\mu L} = 250\ \ce{\mu L}$ of the $\text{A}$ stock and bring it up to the final volume with urine.

You will want to carry out these calculations for all your compounds, then add all the corresponding quantities to a calibrated vessel, e.g. a volumetric flask, then bring this mixture up to the final volume with your solvent, i.e. urine.