Free PTCE flashcards

Why does combining clarithromycin with simvastatin increase the risk of muscle injury?

Simvastatin is cleared by CYP3A4, and clarithromycin is a strong CYP3A4 inhibitor. Blocking that enzyme sharply raises plasma simvastatin levels, and the elevated exposure drives dose-dependent muscle toxicity including myopathy and rhabdomyolysis.

St John's wort inhibits hepatic enzymes, raising warfarin levels and increasing major bleeding risk.

Enzyme inhibition would indeed raise warfarin levels, which tempts candidates who confuse inducers with inhibitors. But St John's wort induces rather than inhibits CYP enzymes, so it lowers warfarin levels and raises clot risk, not bleeding.

How should a dose less than one (for example a half milligram) be written to prevent a tenfold dosing error?

Write it with a leading zero before the decimal point, as 0.5 mg, and never add a trailing zero. The leading zero flags that a fraction follows, so a faint or missed decimal point cannot turn 0.5 into 5. A trailing zero would do the opposite and risk inflating the value.

A dose written by the prescriber as ".5 mg" should be entered exactly as written so the record matches the order character for character.

Faithful transcription feels safe, which is the trap. A naked decimal with no leading zero reads as "5" if the point is missed, causing a tenfold overdose. Adding the leading zero (0.5 mg) is the safer record, not a deviation from intent.

How do you calculate the days supply for an ophthalmic solution dosed in both eyes once daily, given the bottle volume and a drops-per-mL estimate?

Convert the bottle volume to total drops (volume in mL times about 20 drops/mL), then divide by the total daily drops across all dosed eyes. One drop into each of two eyes once daily uses 2 drops/day, so a 2.5 mL bottle (about 50 drops) lasts roughly 25 days. The key is counting every dosed eye in the daily total.

A drop bottle dosed in both eyes once daily lasts about 50 days because each bottle delivers one drop per day.

Tempting because it treats the once-daily sig as one drop per day, but a sig that doses each eye means 2 drops daily, not 1. Counting only one drop halves the daily use and doubles the apparent supply, so the real figure is about 25 days.

When a Schedule II prescription is partially filled at the patient's request, within what period may the remaining quantity be supplied?

Federal law permits partial filling of a Schedule II prescription at the patient's request, and the pharmacy may supply the balance within 30 days of the date the prescription was written. No refills are ever allowed on Schedule II, so the remainder is collected against the same original order, not a refill. A separate 72-hour limit applies only to partials caused by insufficient stock.

A patient-requested partial fill of a Schedule II prescription must be completed within 72 hours or the remainder is void.

This is tempting because a genuine 72-hour limit does exist for Schedule II partial fills. However, that 72-hour rule governs partials caused by the pharmacy lacking stock. When the patient requests a partial fill, the balance may be supplied within 30 days of the written date, so the 72-hour deadline is not the operative rule here.