Canagliflozin (Invokana): uses, foot care and cautions

Canagliflozin is an SGLT2 inhibitor licensed for adults, and children aged ten and over, with type 2 diabetes whose blood sugar is not controlled by diet and exercise. The emc SmPC says it can be used alone when metformin is unsuitable or with other diabetes medicines. It stops the kidney transporter SGLT2 from reabsorbing glucose, so glucose is lost in the urine, with a mild increase in urine volume and modest weight loss. A dedicated NHS patient page was not available when checked.

The usual starting dose in the SmPC is 100 mg once daily, preferably before the first meal of the day, with a possible increase to 300 mg if kidney function allows and tighter control is needed. With moderate kidney impairment only the lower dose is used, and it is not started when filtration is very low. Kidney function is checked before treatment and yearly, and blood pressure and fluid status are reviewed, especially in the first months.

An increased number of lower-limb amputations, mostly of the toe or mid-foot, was seen in people with established cardiovascular disease taking canagliflozin. The SmPC asks clinicians to watch higher-risk people carefully and counsel on routine preventive foot care and hydration. In practice this means checking feet daily, wearing well-fitting shoes, and reporting any ulcer, infection, new pain or tenderness promptly.

• Look at both feet every day or ask someone to help.

• Report blisters, sores, discolouration or pain without delay.

• Keep your annual diabetic foot check.

Vulvovaginal thrush is very common in women and balanitis in men. Most cases respond to topical antifungal treatment, though tight foreskin may occasionally need surgical management. Complicated urinary infections, including kidney infection, have been reported, and treatment may be interrupted temporarily. Rare necrotising fasciitis of the perineum (Fournier's gangrene) calls for urgent care when genital pain, redness and swelling come with fever.

The SmPC describes a routine of kidney checks, blood pressure and fluid-status review, and attention to electrolytes and creatinine. Small early falls in kidney filtration within the first weeks are expected and usually reverse, but larger drops are more likely if you are dehydrated. Cholesterol (LDL) and haematocrit can rise slightly. Tell the clinic about any diarrhoea, vomiting or poor intake, because these change how safe it is to carry on with the tablets.

Diabetic ketoacidosis is rare but can be life threatening and can show up with only moderately raised glucose. Treatment stops if it is suspected and is paused before surgery. Dehydration and low blood pressure are likelier in people aged 65 and over, those taking diuretics, and those with reduced kidney function, producing dizziness, fainting and kidney impairment that normally reverses.

Diuretics add to dehydration; insulin and sulfonylureas increase hypoglycaemia risk, so their doses may be lowered. Enzyme inducers such as rifampicin, phenytoin and St John's wort reduce canagliflozin exposure. Cholestyramine may reduce absorption, so doses are separated by hours. Digoxin levels can rise, lithium levels should be monitored, and dabigatran exposure may increase. The 1,5-anhydroglucitol test is unreliable during treatment.

Canagliflozin is contraindicated in pregnancy and breastfeeding. Dizziness and hypoglycaemia (with insulin or sulfonylureas) could affect driving. It is prescription only. Report suspected side effects to the Yellow Card scheme.