Cancer Chemotherapy Prescribing Principles

Cytotoxic chemotherapy has a narrow margin between benefit and harm, so every order is checked as a complete package: the right regimen for the intent of treatment, the right dose for this patient’s size and organ function, the right route, and the right supportive care. Intent decides how much toxicity is acceptable: curative and adjuvant treatment justifies full doses and tight schedules, while palliative treatment justifies dose reduction to keep quality of life.

Before the first cycle.

• Confirm tissue diagnosis, stage and a documented treatment intent.
• Record performance status, weight, height, full blood count, creatinine and eGFR, liver tests, and baseline tests for the planned drugs (echocardiogram before anthracyclines, audiometry and magnesium before cisplatin, lung function before bleomycin).
• Screen for hepatitis B and C and HIV; start entecavir or tenofovir for hepatitis B surface antigen positive or core antibody positive patients before chemotherapy and continue 6 to 12 months after.
• Pregnancy test, contraception advice and fertility discussion.
• Informed consent that names the main short-term and long-term risks.

Safety rules for every order.

• Prescribe by generic name, dose in mg/m2 or mg/kg and the calculated total in mg, route, cycle number, day of cycle and the date of the next cycle.
• Use a written regimen sheet with day-by-day drugs, doses, premedication and supportive care; do not prescribe from memory.
• Two independent clinicians check the dose calculation; a pharmacist verifies before preparation.
• Vinca alkaloids (vincristine, vinorelbine) are fatal if given intrathecally: label them “for intravenous use only” and dispense in a minibag, never a syringe.
• Intrathecal drugs are given only by trained staff, and never on the same trolley as vinca alkaloids.
• Give vesicants (doxorubicin, vincristine, vinorelbine) through a free-flowing vein or a central line with a documented extravasation plan.

Common single agents (adult, usual doses; the regimen sheet decides the schedule).

Combination regimens. Chosen by tumour type from the regimen sheet. Doses of each drug in a combination are often lower than the single-agent dose.

Supportive care to prescribe with the first order. Antiemetics by emetic risk, growth factor where febrile neutropenia risk is 20% or more, mouth care, and a written emergency plan with a 24 hour contact number.

Kidney impairment. Avoid cisplatin at eGFR under 60 mL/min and use carboplatin by Calvert formula; reduce methotrexate, pemetrexed (avoid under 45 mL/min) and capecitabine (reduce at 30 to 50 mL/min, avoid under 30 mL/min).

Liver impairment. Reduce or delay doxorubicin, vincristine, paclitaxel, docetaxel and irinotecan for raised bilirubin. A common practice is to halve doxorubicin when bilirubin is 26 to 51 micromol/L and avoid it when over 51 micromol/L.

Older adults. Assess fitness before choosing intensity, start with less toxic schedules or reduced first-cycle doses, and give growth factor early.

Children. Doses are given by body surface area (by weight in infants under 10 kg) in specialist paediatric units only.

HIV. Antiretroviral interactions: ritonavir or cobicistat boosting raises vinca alkaloid, etoposide and taxane toxicity; prefer a dolutegravir or raltegravir based regimen where possible and review each cycle.

Pregnancy and breastfeeding. Avoid in the first trimester; some regimens are used in the second and third trimesters under specialist care. Do not breastfeed during treatment.

Regional. Cancer presents late in East Africa, drug supply and monitoring are limited, and traditional medicines are widely used and may interact. Ask about herbal products, test for hepatitis B and HIV before the first cycle, and confirm laboratory access for each cycle’s counts before giving the drug.

Before every cycle. Review symptoms and performance status; check full blood count, creatinine and liver tests within 48 hours; proceed only if neutrophils are 1.0 x 10⁹/L or more (1.5 x 10⁹/L for many curative regimens) and platelets 100 x 10⁹/L or more, or as the regimen sheet states.

During treatment. Cumulative dose tracking for anthracyclines and bleomycin; echocardiogram at defined doses; audiology and neuropathy checks for platinum.

Emergencies. Fever of 38 degrees C or more, rigors, bleeding, severe vomiting or diarrhoea, new breathlessness or confusion: same-day assessment. Febrile neutropenia is an emergency, with cultures and broad-spectrum IV antibiotics within 1 hour.

Response and stopping. Assess response after 2 to 3 cycles; stop for progression, unacceptable toxicity, patient choice, or cumulative dose limits. Refer to oncology for any unplanned delay over 2 weeks.